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Protocols for Multislice CT: 4- and 16-row Applications in Radiology
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Protocols for Multislice CT 4- and 16-row Applications Roland Bruening Thomas Flohr R. Bruening · T. Flohr Protocols for Multislice CT 4- and 16-row Applications Springer-Verlag Berlin Heidelberg GmbH R. Bruening · T. Flohr Protocols for Multislice CT 4- and 16-row Applications With 195 Figures 123 Roland Bruening Neuroradiology Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Thomas Flohr Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany ISBN 978-3-540-40584-9 ISBN 978-3-662-05142-9 (eBook) DOI 10.1007/978-3-662-05142-9 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. Springer-Verlag Berlin Heidelberg NewYork a member of BertelsmannSpringer Science+Business Media GmbH http://www.springer.de/medizin © Springer-Verlag Berlin Heidelberg 2003 Originally published by Springer-Verlag Berlin Heidelberg in 2003 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. Product management and layout: B. Wieland, Heidelberg Typesetting: B. Wieland, Heidelberg Printing: Saladruck, Berlin 21/3150 – 5 4 3 2 1 0 Printed on acid-free paper Preface The radiology community has seen a substantial technical innovation with the development of multislice computed tomography (CT). The introduction of multiple parallel detectors is undoubtedly one of the most important technical improvements in the field of CT. Moreover, the new advantages of CT may also have an impact on the general use of CT and magnetic resonance imaging (MRI). Multislice CT is becoming increasingly available in industrialized countries. Consequently, interest in practical aspects of the method is also growing. Common questions include when and how to use the systems. While the initial scanners were equipped with two or four detector rows, current advances have led to scanners with up to 16 rows becoming available for clinical use. And there is still more to come. As these multislice CT systems maintain the general advantages of CT, i.e. reliability and short examination times, their ability to investigate large areas of the body in a very short time with improved transverse resolution has broadened the potential medical applications of CT. Thus, new medical indications for CT, such as cardiac CT, have emerged. Some questions in diagnostic imaging, e.g. a non-invasive neck study for suspected carotid stenosis, may in future be solved more frequently with multislice CT than with MRI. Other indications such as the staging of rectal or laryngeal cancer may see a higher sensitivity and specificity with multislice CT than with single-slice systems. There is also a substantial change in the way the examination is planned and carried out. Instead of individual axial slices, there is a thin-collimation acquisition of a volume. Subsequent reconstructions are becoming more and more important. In some protocols, such as the cranial sinuses, only the coronal reconstructions are read at our institution, while the axial data are not used. Thin-collimation acquisition is also useful for minimizing artefacts. It is here that reconstructions are made in thicker slices to minimize image noise. Care must be taken so as not to increase the patient radiation dose unnecessarily. Therefore, whenever possible, the mAs must be adapted and reduced, the scanned volume must be restricted and last but not least the indication for the examination must be established. The increased speed of multislice CT suggests a change in the use of intravenous contrast agents. While the different injection doses, velocities and concentrations are currently under investigation, the protocols in this book include a subjective recommendation for use. This book includes a personal selection of protocols for application with four-row or 16-row scanners. These protocols have been optimized for Siemens scanners; however, the protocol layout and the data presented can also be employed with different bands. While we made substantial effort to adjust the protocols to the current knowledge, preferences on the use of protocols change quickly and also vary from site to site. Therefore, if the reader has any comments or suggestions for variations of these protocols, they should not hesitate to contact us. Please note that despite careful proofreading, there can be no liability on the part of the authors for the use of any of the protocols. VI Preface We would like to express our sincere thanks to all the contributors and to the local CT technicians. We gratefully acknowledge Prof. Maximilian Reiser, who enabled and encouraged this early clinical experience with multislice CT in Großhadern by his personal patronage and vision. Springer kindly supported the idea of publishing this volume and provided us with invaluable assistance. We hope that everyone interested in the technique of multislice CT finds this book useful. R. Bruening T. Flohr Munich Forchheim Contributors Becker, C Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Flohr, T. Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany Bruening, R. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Glaser, C. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Eibel, R. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Haw, Loke Gie Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany Ertl-Wagner, B. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Hofmann, R. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Flatz, W. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Hong, C. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany VIII Contributors Jaeger, L. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Rust, G.F. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Kohl, G. Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany Schaller, S. Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany Kulinna, C. Abteilung für Radiologie AKH Wien Universität Wien Währinger Gürtel 18–20 1090 Wien Austria Schoepf, U.J. Dept. of Radiology Brighams Woman Hospital Boston, MA 02115 USA Mueller-Lisse, U. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Ohnesorge, B. Siemens Medical Solutions CT Division Siemensstr. 1 91301 Forchheim Germany Wieser, A. Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Wintersperger, B Department of Clinical Radiology University of Munich – Grosshadern Marchioninistr. 15 81377 Munich Germany Contents Technical Principles and Applications of Multislice Spiral CT . . . . . . . . . . . . . . . 1 4-row Scanning Head Routine CCT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Contrast-Enhanced CCT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Temporal Bone and Inner Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 CTA Intracranial Aneurysm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Venous Sinus CTA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Cerebral Perfusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Neck Routine Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Routine Sinuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Sinus Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Nasopharynx and Oropharynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Larynx and Hypopharynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 CTA Carotids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Chest Routine Chest and HR-Chest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Pulmonary Embolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Combi Thorax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 CTA Aortic Arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 X Contents Heart Coronary Artery Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 CTA Bypasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 CTA Coronary Arteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Abdomen Routine Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Venous Upper Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Biphasic Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Biphasic Liver (Including CTAP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 CT Enteroclysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Biphasic Pancreas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Routine Kidney . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Renal Differential Diagnosis and Tumors. . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Rectal Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 CTA Abdomen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Spine Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Thoracic Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Lumbar Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Peripherals Wrist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Shoulder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Ankle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Knee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Trauma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Peripheral CTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Contents Interventions Drainages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Biopsies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 Sympaticolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 16-row Scanning Head Routine CCT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Temporal Bone and Inner Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 CTA Intracranial Aneurysm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Neck Routine Neck. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Larynx and Hypopharynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 CTA Carotids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Chest Routine Chest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Pulmonary Embolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 CTA Aortic Arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 Heart Coronary Artery Screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 CTA Coronary Arteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Abdomen Routine Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 CTA Abdomen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 XI XII Contents Spine Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Peripherals Peripheral CTA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Abbreviations CCT CT CTA FOV HR MDCT MIP MPR MRI MSCT SSD STS US VRT cranial CT computed tomography CT angiography field of view high resolution multidetector CT maximum intensity projections multiplanar reformats magnetic resonance imaging multislice CT shaded surface display sliding thin slices ultrasound volume rendering techniques 1 Technical Principles and Applications of Multislice Spiral CT T. Flohr · B. Ohnesorge · G. Kohl · S. Schaller Introduction With the introduction of multislice computed tomography (CT) into clinical practice a new era began, leading to the possibility of nearly isotropic voxel imaging and highquality reconstructions. The main drawbacks of single-slice spiral CT are insufficient volume coverage of the patient within the time of one breathhold and missing spatial resolution in the z-axis due to wide collimation. Larger volume coverage and improved axial resolution may be achieved by simultaneous acquisition of more than one slice and by a shorter rotation time. In 1998, all major CT manufacturers introduced multislice CT systems offering increased scan speed, improved axial resolution, and better utilization of the tube output. These new devices typically offer simultaneous acquisition of four slices at 0.5 s rotation time, thus increasing the performance of a single-slice CT scanner at 1 s rotation time by a factor of 8. This increased performance allows for the optimization of different clinical parameters: for example, the examination time for a standard protocol may be reduced by a factor of 8, which is clinically important in a variety of instances, such as in dealing with trauma or uncooperative patients. Alternatively, the scan range may be extended correspondingly, as for oncological screening or for CT angiographies (CTAs) of the extremities. Most important, however, is the capacity to scan a given volume in a given time with considerably smaller slice width, thus to approach the ideal of isotropic resolution. Chest and abdomen examinations may be routinely performed with 1.25-mm slice width on a 4-slice CT system, obtaining high-quality image data for volumetric visualization, evaluation, and quantification. As a consequence, volumetric viewing and diagnosis in a volumetric mode have become integrated elements of the routine workflow. Still, true isotropic resolution cannot be reached with 4-slice CT systems. In a typical abdomen examination the in-plane resolution is about 0.5 mm using a standard body kernel. This is not fully matched by the axial resolution of about 1 mm. For long-range studies, such as peripheral CTAs, even thicker slices (2.5 mm collimated slice width) have to be chosen for acceptable scan times. Consequently, an increased number of simultaneously acquired slices and sub-millimeter collimation for routine clinical applications were seen to be the next steps on the way towards true isotropic scanning with multislice CT, and 16-slice CT systems were introduced in 2001. This technical introduction concentrates on the principles of multislice scanning with established 4-slice CT systems and ends with an outlook to state-of-the-art 16-slice technology. Technical Principles of 4-Slice Scanning In the following subsections we will discuss the relevant design features for volumetric scanning with established 4-slice CT systems. 2 Technical Principles and Applications of Multislice Spiral CT Detector Design The simplest model of a 4-slice CT detector consists of four detector rows: with this, however, only one fixed-beam collimation may be realized. For clinical purposes a variety of different beam collimations is absolutely necessary.A useful 4-slice detector has to have more than four detector rows, which are combined differently according to the selected beam collimation. The adaptive array detector (Schaller 2000; Ohnesorge 2000a) consists of eight detector rows with different widths and allows for the following beam collimations: 2×0.5 mm, 4×1 mm, 4× 2.5 mm, 4 ×5 mm, 2× 8 mm, and 2 × 10 mm (see Fig. 1). The selection determines the intrinsic axial resolution of a scan; for a spiral mode, the slice width can be adjusted independently (see “Multislice Spiral Concept”). The adaptive array detector is designed for optimum dose efficiency, as the width of the detector rows is tailored to the available beam collimations and unnecessary cuts and dead zones are avoided. Fig. 1. Adaptive array detector for a 4-slice CTsystem.The detector consists of eight rows of different size, which define slices between 1 mm and 5 mm in the center of rotation. Due to geometrical magnification, the detector itself is about 40 mm wide Multislice Spiral Concept Basic Parameters: Definition of Pitch and Dose A very important parameter to characterize a spiral scan is the pitch. A historical, now obsolete definition for a multislice spiral scanner is the volume pitch (Pvol). For a multislice spiral CT scanner, we define the volume pitch Pvol: Pvol =tablefeed per rotation/ width of one subbeam (1) For a beam collimation of 4 ×1 mm, the beam consists of four subbeams, each 1 mm wide at the center of rotation. With 7 mm table feed per rotation, the volume pitch is Pvol =7. The usable pitch range of a 4-slice scanner is between 1 and 8. Within this range, the pitch can be freely selected, ac- cording to the needs of the clinical examination. For a better comparison with single-slice CT systems, an alternative definition, the normalized pitch factor P, also called normalized pitch, must be used. According to IEC this is the official definition of the pitch. This definition uses the total width of the Xray beam in the denominator, giving: P=tablefeed per rotation/ total width of X-ray beam (2) In the above example, P=7/4. The usable pitch range of a 4-slice scanner then is 0.25 to 2. In this volume, the normalized pitch factor is used throughout. Technical Principles and Applications of Multislice Spiral CT Fig. 2. Full width at half maximum (FWHM) of the slice sensitivity profile as a function of the pitch for the two most commonly used single-slice spiral interpolation approaches, 180LI and 360LI. For both, the slice significantly broadens with increasing pitch.As a consequence,multiplanar reformats (MPRs) of a spiral z-resolution phantom scanned with 2-mm collimation (180LI) show increased blurring of the 1.5-mm and 2-mm cylinders with increasing pitch Clinically appropriate measures for dose are the local dose as given by the weighted computerized tomographic dose index (CTDI) or, more appropriate to volume scanning, the dose-length product (McCollough 2000).With the above definition of the pitch factor P (see Eq. 2), the dose of a spiral scanner with rotation time trot is given by: Dose=mA¥trot ¥1/P¥CDTI, (3) with CTDI in mGy/mAs. This fundamental equation is valid both for single-slice and for multislice CT. Short Review of Single-Slice Spiral CT The most commonly used single-slice spiral interpolation schemes are the 360° and 180° linear interpolations (360LI and 180LI): ∑ The slice width [i.e., the full width at half maximum (FWHM) of the slice sensitivity profile (SSP)] significantly increases with increasing pitch (see Fig. 2). This is a consequence of the increasing axial distance of the projections used for spiral interpolation. ∑ The image noise is independent of the pitch, if the tube current (mA) is left unchanged. 3 4 Technical Principles and Applications of Multislice Spiral CT Fig. 3. Adaptive axial interpolation for a 4-slice CT-system: slice sensitivity profile (SSP) of the 2-mm slice (for 4×1-mm collimation) for selected pitch values.The functional form of the SSP, and hence the slice width, is independent of the pitch. Consequently, MPRs of a spiral z-resolution phantom scanned with 2-mm slice width show clear separation of the 1.5-mm and 2-mm cylinders for all pitch values ∑ The patient dose decreases with increas- ing pitch, according to Eq. 3. ∑ Spiral artifacts gradually increase with increasing pitch. Due to its narrower SSP, the 180° linear interpolation is almost exclusively used for single-slice CT scanning, despite its increased susceptibility to artifacts and its increased image noise: for the same mAs, noise is about 15% higher than in sequential mode. Four-Slice Spiral CT: 180° and 360° Multislice Linear Interpolation Versus Adaptive Axial Interpolation If 180° or 360° linear interpolation techniques are simply extended to multislice spiral scanning (180MLI or 360MLI), a complicated dependence of both slice width and image noise on the pitch results. As a consequence, multislice CT scanners relying on 180MLI or 360MLI techniques offer only few discrete pitch values to the user, such as 3/4 and 6/4. To maintain a free selection of the pitch according to the clinical needs of an examination, a generalized nonlinear spiral weighting approach, the adaptive axial interpolation is recommended (as shown in the work of Schaller et al. 2000). That paper introduces a new concept in multislice spiral Technical Principles and Applications of Multislice Spiral CT Fig. 4. Axial sampling scheme with four slices. Although the sampling pattern and the sampling density vary with pitch, the sampling distance in the center of rotation is never larger than the subbeam collimation for any pitch factor up to 2 (volume pitch up to 8) scanning: the functional form of the SSP and consequently the slice width, is completely independent of the pitch. As an example, Fig. 3 shows the SSP of the 2-mm slice (for 4 ×1-mm collimation) for selected pitch values.A major reason why a pitch-independent SSP can be realized is the axial sampling scheme with multiple slices (see Fig. 4). Although the sampling pattern and the sampling density vary with the pitch, the sampling distance in the center of rotation is never larger than the subbeam collimation for any volume pitch up to 8 (corresponding to pitch factor P≤ 2). For Pvol >4 (P>1), the complementary rays have to be taken into account. To achieve a constant SSP, appropriate spiral weighting functions are used, whose functional forms are automatically adapted to the pitch and the desired slice width. Image Noise and Patient Dose With the adaptive axial interpolation, the image noise would decrease with decreasing pitch if the tube current mA was left unchanged, due to the increasing axial sampling density (overlapping spiral sampling). To maintain constant image noise, the tube Fig. 5. With the 4-slice CT scanner evaluated, the tube current is automatically adapted to the pitch to compensate for the increasing axial sampling density with decreasing pitch. As a consequence, both image noise and patient dose are independent of the pitch current (mA) is adapted to the pitch of the spiral scan as an automatic procedure (Ohnesorge 1999). The user selects a certain image noise level and hence a certain image quality by choosing an effective mAs value. The tube current is then automatically ad- 5 6 Technical Principles and Applications of Multislice Spiral CT a b Fig. 6. a SSPs for slice widths of 1 mm, 1.25 mm, 1.5 mm, 2 mm, 3 mm, 4 mm, and 5 mm, which are available for 4 × 1-mm collimation (not shown are the SSPs for slice widths of 6 mm, 7 mm, 8 mm, and 10 mm). b SSPs of the 3-mm slice for 4 × 1-mm and 4 ×2.5-mm collimation. The slice width (FWHM) is equal, but the profile is more rectangular for the narrow collimation (4 × 1 mm) justed to the pitch and the rotation time according to the following (and see also Eq. 3): Adaptive Axial Interpolation: Key Properties mA=eff. mAs × 1/trot × P In summary, multislice spiral scanning with adaptive axial interpolation has the following properties: freely selectable pitch, slice width independent of pitch, image noise independent of pitch, and lastly patient dose independent of pitch and simply given by Dose=eff. mAs × CTDI. Spiral artifacts gradually increase with increasing pitch. (See “Short Review of Single-Slice Spiral CT” for a comparison with single-slice spiral CT.) Using this adaptive axial interpolation, slice width and collimation are no longer directly related as with single-slice spiral CT (Schaller et al. 2000). Instead, for each collimation a variety of different slice widths are available. For instance, from the data taken at 4 × 1-mm collimation, any slice width between 1.0 mm and 10.0 mm may be reconstructed (as an example, the SSPs up to 5 mm are shown in Fig. 6a). Hence, from the same data set both narrow slices for highcontrast details (or as an input for 3D postprocessing) and wide slices for low-contrast (4) This relation is graphically sketched in Fig. 5. As a consequence, in a deviation from single-slice spiral scanning, not only the image noise but also the patient dose is independent of the pitch. Introducing Eq. 4 into Eq. 3 simply yields: Dose=eff. mAs × CTDI (5) The spiral dose is therefore constant and equal to the dose of a sequential scan with the same mAs. Technical Principles and Applications of Multislice Spiral CT information (and/or overview and filming) may be derived. On the other hand, for each slice width (e.g., 3 mm) at least two different collimation settings are available: a narrow collimation to acquire the data set with highest axial resolution, i.e., closest to isotropic resolution, and a wider collimation for short examination times (in this example, 4×1 mm and 4×2.5 mm).With regard to image quality, narrow collimation is preferable to wide collimation, due to better suppression of partial volume artifacts and a more rectangular slice sensitivity profile (see Fig. 6b), even if the pitch has to be increased for equivalent volume coverage. Similar to single-slice spiral CT, narrow collimation scanning is the key to the reduction of artifacts and improved image quality. Applications Standard Applications As mentioned in the introduction, clinical applications benefit from multislice technology in several ways: ∑ Shorter scan time (important for exam- ple in cardiac imaging, CTA) ∑ Extended scan range (important for CTA, chest-abdomen scans) ∑ Improved axial resolution (beneficial for all reconstructions). Some protocols even benefit from a combination of all of these advantages. Consider a thorax exam with a scan range of 30 cm. In order to cover that range in a reasonable time of around 25 s with a single-slice CT scanner using 1 s rotation time, a collimation of 7 mm can be used at a pitch of 2. The breakthrough that multislice technology has brought is not the fact that this exam can now be performed in a much shorter time (6 s), but that it can deliver close to isotropic resolution (with 1-mm reconstructions) in this time. Thus, a typical thorax protocol uses a collimation of 4× 1 mm at a volume pitch of 6–7 (e.g., Combi Thorax, a thorax examination technique reconstructing different slice widths from the same CT raw data). In combination with the improved rotation speed of 0.5 s, a scan range of 30 cm can be covered in 21 s. Figure 7 shows an example of thorax images obtained with this protocol. Please note that the close-to-isotropic resolution enables three-dimensional (3D) renderings of diagnostic quality and that multiplanar reformats (MPRs) and oblique maximum intensity projections (MIPs) are of a resolution similar to the original axial images. We expect that the availability of multislice CT technology will change the way radiologists think about CT imaging. In CT, one traditionally distinguishes between axial and in-plane resolution. It must be appreciated that this distinction is made mainly for historical reasons. Before the introduction of spiral CT, axial resolution was determined by slice collimation only, while in-plane resolution was determined by the convolution kernel. With spiral CT, collimation is no longer the only factor determining axial resolution, but the spiral interpolation function also has to be considered. This has been a first step towards decoupling the slice width of the images from the beam width determined by the collimation. Multislice CT represents a further step to be taken: adaptive axial interpolation allows for reconstruction of arbitrary slice widths from a given collimation (as long as the desired slice width is not smaller than the collimation). In many applications, narrow collimation data are recommended independently of the slice width desired for primary viewing. In practice, two different slice widths are commonly reconstructed by default: thick slices for filming and thin slices for 3D postprocessing and evaluation (please refer to the individual protocols). Alternatively, one can reconstruct closeto-isotropic high-resolution volumes and still limit the image noise by making use of thick MPRs. Hence, images with the desired slice width can be obtained in arbitrary directions. In this approach, the axis of rotation and the corresponding axial plane of 7 8 Technical Principles and Applications of Multislice Spiral CT Fig. 7. Case study using a fast high-resolution thorax protocol. Collimation 4 ×1 mm, pitch factor 2, reconstructed slice-width 1.25 mm. Left: axial images show the central thrombosis of the right subclavian vein. Right: maximum intensity projection (MIP) images show different views of the filiform stenosis of the right brachiocephalic vein proximal to the confluence of the superior vena cava. (Images courtesy of Dr. Lell, University of Erlangen, Germany) Technical Principles and Applications of Multislice Spiral CT reconstruction is no longer a limit for CT imaging. The transition from CT as a crosssectional slice modality to a volume imaging modality has finally been made. Figure 8 shows an example of an abdominal case study that has been diagnosed interactively on a 3D workstation (Virtuoso; Siemens Medical Solutions, Germany) using a volume-rendering technique (VRT) by pushing a clip plane through the volume. Special Applications Cardiac CT Fig. 8. VRT images rendered on a 3D workstation. The 3D volume can be explored by interactively navigating clip planes and manipulating the VRT settings. The images demonstrate a renal donor study. The dual-phase CT angiogram provides definition of both the potential donor’s renal artery(s) (top) as well as the venous anatomy (bottom). This study is used as the guide for laparoscopic nephrectomy. Note the two left renal arteries. (Images courtesy of Dr. Fishman, Baltimore, USA) One of the most exciting new applications of multislice CT is the ability to image the heart. Increased rotation speed combined with dedicated ECG-synchronized reconstruction algorithms effectively allow one to freeze the heart motion (Ohnesorge et al. 2000a,b; Becker et al. 2000). The details of this new technique have been discussed in several recent publications, therefore we restrict this chapter to a brief overview. One important application of cardiac CT is the quantitative evaluation of coronary calcification as a risk indicator in asymptomatic patients, which previously was a domain of electron beam CT technology (EBT). Studies have shown that ECG-gated spiral imaging with reconstruction of overlapping images can significantly reduce interscan variability (Ohnesorge and Flohr 2002). Good repeatability of quantitative measurements is prerequisite for longitudinal studies, such as controlling the same individual for effectiveness of medication. Newly developed software for quantitative evaluation of coronary calcium allows efficient calculation of the established Agatston score (as well as other score system values, such as lesion volume scores and others). Due to the improved signal-to-noise ratio when compared with EBT and the higher axial resolution that can be achieved with 1-mm collimation, it has been shown that also noncalcified (soft) plaques can be visualized with high accuracy when using CTA 9 10 Technical Principles and Applications of Multislice Spiral CT Fig. 9. CT angiography of the coronary vessels. Left: normal anatomy in VRT renderings from standard viewing directions labeled according to American Heart Association conventions. (Images courtesy of Dr. Becker, Grosshadern, Munich, Germany). Right: noncalcified, soft plaques. (Images courtesy of Dr. Schröder, Universitätsklinikum Tübingen, Germany) Technical Principles and Applications of Multislice Spiral CT (Becker et al. 2000). This might turn out to be a promising tool for assessing risk for myocardial infarction. Figure 9 shows an example of coronary CTAs without pathology (left column) as well as several soft plaques (right column). Lung Cancer Screening Another possible future application within the arena of preventive care is the early detection of lung cancer (Henschke 1999). Basic requirements here are the ability to cover the entire lung in a single breathhold at sufficient resolution to detect small, suspicious nodules while keeping the dose to an acceptable level. In principle this is also possible using single-slice CT, but substantial workflow improvements can be achieved using multislice CT. In the early lung cancer action project (ELCAP) study (Henschke et al. 1999), suspicious nodules were found in around 25% of the screened population (and these patients accordingly received further work-up). Generally accepted schemes for work-up of small nodules is to follow and monitor their growth, or to surgically remove them, depending on various factors. However, accurate volume assessment of small nodules requires high-resolution data sets and could not be based on the ELCAP initial screening study. Therefore, the pertinent patients had to be rescheduled. With multislice CT, the screening scan can be done at high resolution, obviating the need for rescheduling. We propose a protocol using a 4× 1-mm collimation at 0.5-s rotation and volume pitch 7 (pitch factor 1.75), covering a 30-cm range in 21 s.With 120 kV and 20 eff. mAs, the effective patient dose is below 1 mSv, which is less than the natural background radiation exposure of half a year. Recent Developments: 16-Slice Scanning Since their introduction in 1998, 4-slice CT systems have been accepted as a clinical standard. The main advantage of the new technology can be summarized as rapid close-to-isotropic imaging with the ability to freeze cardiac motion for low to moderate heart rates using ECG synchronization. To further increase acquisition speed and to allow for true isotropic resolution in routine clinical examinations, the tendency toward even narrower collimation and higher number of slices continues. Improved temporal resolution for a better clinical stability of ECG-gated multislice CT examinations of the heart and the coronary arteries, and for examination of patients with higher heart rates, requires even shorter gantry rotation times. In 2001, the first 16-slice CT scanners were introduced, representing the next generation of multislice CT. Similar to established 4-slice systems, these scanners use a detector with, for example, 24 detector rows offering simultaneous acquisition of 16 slices with 0.75-mm or 1.5-mm beam collimation. Figure 10 shows a schematic drawing of the detector (Siemens) and a picture of a detector module. The key difficulty for image reconstruction with 16-slice CT systems is the fact that, in contrast to single-slice CT, the acquired rays are no longer perpendicular to the axis of rotation, but are tilted by the cone angle.While neglect of this effect in all currently available 4-slice CT systems is justified in theory, it is mandatory to account for the cone angle in systems with 16 slices. A newly developed image reconstruction technique adaptive multiple plane reconstruction (AMPR) (Schaller 2001; Flohr et al. 2002) delivers high-quality images at optimum dose usage over a wide range of pitch values. As an intermediate step, employing the AMPR approach, a variety of partial images on double oblique image planes are calculated, which are individually adapted to the spiral path and to the multislice detector 11 12 Technical Principles and Applications of Multislice Spiral CT Fig. 10. Adaptive array detector of a recently introduced 16-slice CT system. Left: schematic drawing. By proper combination of the signals of the 24 detector rows, the basic collimations of 16 ×0.75 mm and 16 ×1.5 mm can be realized. Right: picture of a detector module, which consists of 16 ×24 detector elements Fig. 11. Schematic of the adaptive multiple plane reconstruction, AMPR. Left: depending on the spiral pitch, the multislice raw data are divided into overlapping segments. As an intermediate step, a variety of partial images on double oblique image planes are calculated, which are individually adapted to the spiral path and to the multislice detector geometry and fan out like the pages of a book. Right: the final images are obtained by an axial interpolation between the tilted partial image planes, similar to an MPR geometry, and these fan out like the pages of a book (see Fig. 11a). The final images with full dose utilization are obtained by an appropriate axial interpolation between the tilted partial image planes, similar to an MPR (Fig. 11b). The shape and the width of the interpolation function are freely selectable; different slice sensitivity profiles (SSP) and hence different slice widths can therefore easily be adjusted in this z-reformation step. Furthermore, the spiral concept introduced with adaptive axial interpolation can be maintained with AMPR: the spiral pitch is freely selectable, the slice width is independent of the pitch. Both patient dose and image noise are independent of the pitch, due to an automatic adjustment of the tube current according to Eq. 4. For the CT scanner evaluated, the pitch factor ranges between 0.5 and 1.5. Figure 12 shows images of a pelvis phantom scanned with 16× 1.5-mm collimation, 0.5-s gantry rotation time, pitch factor P=1, corresponding to a table feed of 48 mm/s, on the left side for a reconstruction neglecting the cone angle of the measurement rays, on the right side for AMPR. The conventional approach without consideration of the cone-beam geometry leads to severe artifacts and geometrical distortions of high-contrast objects (Fig. 12, left). Cone artifacts are considerably reduced with the AMPR algorithm, and the spatial integrity of Technical Principles and Applications of Multislice Spiral CT Fig. 12. Axial slice (top) and MPR (bottom) of a pelvis phantom scanned with a recently introduced 16slice CT system, 16× 1.5-mm collimation, 2-mm reconstructed slice width, 0.5-s rotation time, pitch factor 1.0, i.e., table feed 48 mm/s. Left: conventional multislice spiral reconstruction neglecting the cone angle of the measurement rays. Cone-beam artifacts are indicated by arrows. Right: AMPR. Conebeam artifacts are effectively suppressed the objects is restored (Fig. 12, right). Using 16 × 0.75-mm collimation and overlapping image reconstruction, it is possible to maintain an axial resolution of about 0.6 mm independent of the pitch. This is demonstrated by Fig. 13, which shows MPRs of a z-resolution phantom scanned at pitch factors P=0.75, 1.0, 1.25, and 1.5. Overlapping images with 0.75-mm slice width and 0.4mm increment were reconstructed, and MPRs in the axial direction were generated. Independent of the pitch, all cylinders down to 0.6-mm diameter can be clearly resolved and the MPRs are free of geometric distortions. With an in-plane resolution of about 0.5 mm using a standard body kernel and an axial resolution of 0.6 mm, the ideal of true isotropic resolution for routine applications has finally been reached with state-of-theart 16-slice CT-systems. For ECG-gated scanning, the CT scanner evaluated offers a minimum gantry rotation time of 0.42 s to provide a temporal resolution of up to 105 ms for clinically robust cardiac imaging even at higher heart rates. Improved axial resolution goes hand in hand with considerably reduced scan times, facilitating the examination of uncooperative patients and reducing the amount of contrast agent needed – but also requiring optimized contrast agent protocols. Furthermore, new clinical applications will 13 14 Technical Principles and Applications of Multislice Spiral CT manage the huge amounts of data generated and not cause a bottleneck in the flow of clinical diagnosis and treatment. References Fig. 13. MPRs of a z-resolution phantom scanned with 16× 0.75-mm collimation at pitch factors P = 0.75, 1.0, 1.25, and 1.5, reconstruction slice width of 0.75 mm. Independent of the pitch, all cylinders down to a 0.6-mm diameter can be clearly resolved and the MPRs are free of geometric distortions, thus proving the spatial integrity of the 3D image evolve as a result of the tremendously increased volume scan speed. CTA examinations in the pure arterial phase will become feasible. A CTA of the circle of Willis with 0.75-mm collimation, 0.5-s rotation time, and pitch factor 1.5 requires only 3.5 s for a scan range of 100 mm (table feed 36 mm/s). Examining the entire thorax (350 mm) with 0.75-mm collimation, 0.5-s rotation time, and pitch factor 1.375 (table feed 33 mm/s) can be done in 11 s. In conclusion, 16-slice technology will allow for isotropic imaging in virtually any application. Consequently, the number of slices reconstructed will increase even further, and those involved with network and workstation performance can be expected to experience great pressure to properly Becker C, Knez A, Ohnesorge B, Schöpf UJ, Reiser MF (2000) Imaging of non-calcified coronary plaques using helical CT with retrospective gating. AJR:175 Flohr T, Stierstorfer K, Bruder H, Simon J, Schaller S (2002) New technical developments in multislice CT. Part 1: approaching isotropic resolution with sub-millimeter 16-slice scanning. RöFo 174:839–845 Henschke CI, McCauley DI, Yankelevitz DF, Naidich DP, McGuinness G, Miettinnen OS, Libby DM, Pasmantier MW, Koizumi J, Altorki AK, Smith JP (1999) Early lung cancer action project, overall design and findings from baseline screening. Lancet 354:99–105 Ohnesorge B, Flohr T, Schaller S, KlingenbeckRegn K, Becker C, Schöpf UJ, Brüning R, Reiser MF (1999) Technische Grundlagen und Anwendungen der Mehrschicht-CT. Radiologe 39:923–931 Ohnesorge B, Flohr T, Becker CR, Kopp AF, Knez A, Baum U, Klingenbeck-Regn K, Reiser MF (2000a) Cardiac imaging by means of electrocardiographically gated multisection spiral CT – initial experience. Radiology 217:564– 571 Ohnesorge B, Flohr T, Becker C, Knez A, Kopp A, Fukuda K, Reiser M (2000b) Herzbildgebung mit schneller, retrospektiv EKG-synchronisierter Mehrschichtspiral CT. Radiologe 40: 111–117 Ohnesorge B, Flohr T, Fischbach R, Kopp AF, Knez A, Schröder S, Schöpf UJ, Crispin A, Klotz E, Reiser MF, Becker CR (2002) Reproducibility of coronary calcium quantification in repeat examinations with retrospectively ECG-gated multisection spiral CT. Eur Radiol 12:1532– 1540 Schaller S, Flohr T, Klingenbeck K, Krause J, Fuchs T, Kalender WA (2000) Spiral interpolation algorithm for multi-slice spiral CT. Part I: Theory. IEEE Trans Med Imag 19:822–834 Schaller S, Stierstorfer K, Bruder H, Kachelriess M, Flohr T (2001) Novel approximate approach for high-quality image reconstruction in helical cone beam CT at arbitrary pitch. Proc SPIE Int Symp Med Imag 2001 4-row Scanning 16 4-row Scanning Head Routine CCT Indications. Differential diagnosis cerebral infarct, intracranial bleeding, traumata (including skull fractures, see “Comments”), unconsciousness, atrophy, central neural disturbances of unclear origin, hydrocephalus. Patient Positioning. Supine, arms bilaterally downward, use of headrest recommended. Topogram 3D Reconstructions MIP No MPR No VRT No Other No Criteria of Good Image Quality 1. Symmetric positioning of the patient’s head. 2. Absence of motion artifacts. Fig. 1. Region: from skull base upward (use gantry tilt if necessary) Caveat 1. If the patient tends to move, positioning devices should be used in addition to the headrest. Example of Axial Scan Fig. 2 a, b Routine CCT Scan Parameters Parameter Mode Spiral 1 (skull base) Spiral 2 (cerebrum) Collimation 4 ¥ 1 mm 4 ¥ 2.5 mm Pitch factor 0.65–0.75 0.65–0.75 Reconstruction 4 mm 5–8 mm Rotation time 0.75 s 0.75 s Scan orientation Caudo-cranial Caudo-cranial Scanner settings 120 kV, 300 eff. mAsa 120 kV, 300 eff. mAsa Kernel (algorithm) Soft (brain) Soft (brain) Window (width/center) 120/45 80/35 Contrast medium No Administration Volume Flow rate Scan delay a All mAs values in the scan protocols are effective mAs values; please refer to the technical overview chapter for definition. Comments The decision whether spiral or sequential data acquisition will be utilized in the future will be the subject of further debate. For the detection or exclusion of skull fractures, a subsequent (second) reconstruction of the raw data with a high-resolution bone kernel is recommended. Even though this second reconstruction is usually sufficient for an overview, for suspected temporal bone fractures the protocol “Temporal Bone and Inner Ear,” and for maxillofacial fractures the protocol “Routine Sinuses” (under “Neck”) must be added. In the example given in Fig. 2a, an ischemia with secondary bleeding on the left in a young adult is shown. In Fig. 2b, early signs are visible of a partial infarction of the left MCA territory. 17 18 4-row Scanning Head Contrast-Enhanced CCT Indications. Exclusion or detection of brain tumor, cerebral metastasis, or intracranial abscess. Patient Positioning. Supine, arms bilaterally downward, use of headrest recommended. Topogram 3D Reconstructions MIP a In selected cases MPR In selected cases VRT No Other In selected casesa MIP or SSD Criteria of Good Image Quality 1. Low noise. 2. Enhanced density from contrast material in the sagittal sinus. 3. Symmetric positioning. Fig. 1. Region: from skull base upward (use gantry tilt if necessary) Caveats Example of Axial Scan Fig. 2a–c. 1. If the patient tends to move, positioning devices should be used. 2. Identical slice positions should be ensured for contrast-enhanced CCT and unenhanced CCT. Contrast-Enhanced CCT Scan Parameters Parameter Collimation Mode Spiral 1 (skull base) Spiral 2 (cerebrum) 4 ¥ 1 mm 4 ¥ 2.5 mm Pitch factor 0.65–0.75 0.65–0.75 Reconstruction 4 mm 5–8 mm Rotation time 0.75 s 0.75 s Scan orientation Caudo-cranial Caudo-cranial Scanner settings 120 kV, 300 eff. mAs 120 kV, 300 eff. mAs Kernel (algorithm) Soft (brain) Soft (brain) Window (width/center) 120/45 80/35 Contrast medium Yes Administration Monophasic Volume 100 ml Flow rate 3 ml/s Scan delay 40 s Start second spiral immediately Comments The decision whether spiral or sequential data acquisition will be utilized in the future, will be the subject of further debate. One of the advantages of spiral (helical) thin-collimation scanning is shown in Figs. 1 and 2. In Fig. 2a, there is a left frontal hyperdense spot. The thin-collimation spiral data allowed further reconstruction of MIPs (Fig. 2b) and SSD (Fig. 2c) from the same data set, without exposing the patient to a second scan. The diagnosis was developmental venous abnormality (DVA). 19 20 4-row Scanning Head Temporal Bone and Inner Ear Indications. Posttraumatic fracture of the temporal bone, cholesteatoma and chronic otitis media as preoperative work-up, otosclerosis, tumors of the cerebellopontine angle (if MRI is not possible), postsurgical complications. Patient Positioning. Supine, arms bilaterally downward, use headrest. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Oblique coronal and oblique sagittal (along and perpendicular to temporal bone axis; see “Comments”). Criteria of Good Image Quality 1. Sufficient delineation of ossicles, tympanic cavity, and mastoid cells. 2. MPR reconstruction devoid of stepping artifacts. Fig. 1. Region: upper mastoid cells to lower end of mastoid (avoid lenses) Caveats Example of Axial Scan Fig. 2a, b. 1. Patient positioning and gantry tilt must avoid direct exposure of the lenses. 2. The temporal bone needs a separate MPR with an FOV (<9 cm) for each side. Temporal Bone and Inner Ear Scan Parameters Parameter Mode Spiral Collimation 2 ¥ 0.5 mm Pitch factor 1.0 Reconstruction Slice 0.5 mm, increment 0.2 mm for MPR, 0.5/1 mm filming Rotation time 0.75–1.0 s Scan orientation Cranio-caudal Scanner settings 120 kV, 120 eff. mAs Kernel (algorithm) Ultra sharp Window (width/center) 2,000/300 Contrast medium No Administration Volume Flow rate Scan delay Comments In our setting, the axial image data acquisition and the subsequent coronal (and sagittal) MPRs are replacing the image acquisition in both planes. However, there can also be a direct coronal acquisition performed in either supine or prone position. In the protocol suggested, however, the quality of the coronal MPRs are sufficient to replace the primary coronal image acquisition. Figure 2a shows the detail possible with a 0.5-mm data acquisition and a reconstruction using the high-resolution kernel on a patient with a transverse fracture of the temporal bone. Figure 2b shows an MPR of the same patient; a double-angulated reconstruction plane allows visualization of the extent of the fracture. A marked reduction of dose can be considered e.g., for children, then 120 kV, 80–100 mAs should be sufficient. 21 22 4-row Scanning Head CTA Intracranial Aneurysm Indications. Suspected inzidental intracranial aneurysm, detection of intracranial aneurysm after subarachnoid hemorrhage, suspected arterial occlusion (see “Comments”), noninvasive diagnosis of suspected occlusion, AV malformations. Patient Positioning. Supine, arms downward, use of headrest recommended. Topogram 3D Reconstructions MIP a Yesa MPR Yes VRT Yes Other No STS MIPs or thin MPRs give the best information (e.g., 3-mm thickness, 1.5-mm increment). Criteria of Good Image Quality Fig. 1. Region: the scan range should be adapted to the suspected area (sample for circle of Willis) 1. High contrast of the arterial vessels. 2. No or little contrast media in the veins. 3. Thin overlapping reconstructions for good reconstruction quality. Caveats Example of Axial Scan Fig 2 a–d 1. Timing of the contrast injection is critical (a test bolus injection or bolus tuning is recommended). 2. A routine (unenhanced) CCT should precede this protocol. CTA Intracranial Aneurysm Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 1.0–1.5 Reconstruction Slice 1.25 mm, increment 0.8 mm Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 90–180 eff. mAs Kernel (algorithm) Soft Window (width/center) 400/100 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 20 s (test bolus or bolus tuning recommended) Comments Depending on the individual need, various postprocessing procedures can be used. Initially, axial slices can be reconstructed (Fig. 2a). For an overview,VRT can be seen in Fig. 2b, where the aneurysm at the carotid bifurcation is visualized. However, a close-up reconstruction using VRT (Fig. 2c) can show the exact relationship of the aneurysmal sac, the aneurysmal neck, and the neighboring vessels. Also, a sagittal MPR may be of help (Fig. 2d). When MPRs or other reconstructions are planned, the reconstruction increment should be reduced to 0.6 mm with 50% overlap. The tube voltage recommended for cerebral CTA is currently under discussion and may be reduced even below 100 kV; the mAs should be varied depending on the scan range and the noise reduction necessary. 23 24 4-row Scanning Head Venous Sinus CTA Indications. Suspected thrombosis of the cerebral sinuses or thrombosis of the large cerebral veins. Patient Positioning. Supine, arms downward. Topogram 3D Reconstructions a MIP Yesa MPR No VRT Yesa Other No Either postprocessing procedure recommended. Criteria of Good Image Quality 1. Sufficient contrast enhancement of all sinuses/veins. 2. Thin overlapping axial reconstructions for high-quality MIP. Fig. 1. Region: coverage of the entire brain is necessary Caveats Example of Axial Scan 1. Venous filling takes time. 2. Axial slices and MIPs both have to be read in order to reach a diagnosis. 3. A routine head protocol (CCT) should precede this protocol. Fig. 2 a–c. (Case courtesy of Dr. B. Ertl-Wagner) Venous Sinus CTA Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 1.0–1.5 Reconstruction Slice 1.25 mm, increment 1 mm Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 90–180 eff. mAs Kernel (algorithm) Soft Window (width/center) 120/45 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 100 s Comments This protocol can be used to detect or exclude a thrombosis of the superior sagittal sinus, the sigmoid sinus, or the large cephalic veins. CTA is not capable of detecting or excluding a cavernous sinus thrombosis or of the cephalic veins. Figure 2a shows an example of an axial cut in a female patient with bleeding and an extensive sinus vein thrombosis, Fig. 2b is a coronal MIP reconstruction, and Fig. 2c is a MIP reconstruction showing the full extent of the thrombosis in the superior sagittal sinus. 25 26 4-row Scanning Head Cerebral Perfusion Indications. Suspected early stage of cerebral infarction, cerebral ischemia pretherapy. Patient Positioning. Supine, arms downward, use of headrest recommended. Topogram 3D Reconstructions a MIP No MPR No VRT No Other Yesa Special postprocessing is necessary to derive blood flow, blood volume, and other hemodynamic parameters (see “Comments”). Criteria of Good Image Quality Fig. 1. Region: two parallel slices in the region of the basal ganglia (avoid lenses) 1. No head movement during the repeated scans. 2. Measurable arterial input function as vascular reference. 3. Injection of compact bolus. Caveats Example of Axial Scan Fig.2 a–c. Right MCA occluded by embolic thrombus 1. No movement must occur during the scan; sometimes restraints have to be used. 2. Large-caliber venous access is necessary. 3. An unenhanced CCT should precede this protocol. Cerebral Perfusion Scan Parameters Parameter Mode Sequential multiscan Collimation 4 ¥ 5 mm Pitch factor 0, no table feed Reconstruction 2 ¥ 10 mm Rotation time 1.0 s Scan orientation Caudo-cranial Scanner settings 120 kV, > 110 mAs Kernel (algorithm) Soft Window (width/center) 120/45 Contrast medium Yes Administration Monophasic Volume 40–50ml Flow rate 8 ml/s (5–10 ml/s) Scan delay 0 s, repeat scanning Comments Perfusion CT is a modern imaging procedure for visualizing local cerebral perfusion. The findings on the perfusion maps are positive much earlier than on a normal CCT scan. Thus, perfusion CT is used for early detection of ischemia. Various parameters can be calculated from this dynamic examination: 1. Relative cerebral blood flow (CBF) can be calculated as CBF=CBV/MTT or as max. gradient of curve/max. peak enhancement. CBF is reduced in the patient with embolic MCA occlusion shown in Fig. 2a. 2. Relative cerebral blood volume (CBV) represents the intravascular volume within a given cerebral structure (Fig. 2b). 3. Other parameters such as “time to peak” (TTP; Fig. 2c), which detects a delayed arrival of the contrast bolus. In suspected acute cerebral ischemia, in order to save time the perfusion scan should immediately follow the routine CCT. In most centers, prerequisites for a therapeutic lysis are a normal CCT, positive clinical signs, and a vascular study (perfusion CT and angiography or ultrasound) indicative of vascular occlusion. The findings on the rCBF/rCBV maps are positive much earlier than a normal CCT scan. Thus, it can be used for early detection of ischemia. The lenses should not be in the scan planes. 27 28 4-row Scanning Neck Routine Neck Indications. Suspected cervical lymph nodes, lymphoma, abscesses, phlegmonous inflammation, staging and restaging thyroid goiter (hyperthyroidism). Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions If many dental fillings are present, two different spiral acquisitions with angulation are used. The shoulder should be lowered as much as possible. Image reconstruction in the axial plane is recommended. MIP No MPR No VRT No Other No Criteria of Good Image Quality 1. Contrast opacification of arteries and veins more than 120 HU. 2. No swallowing artefacts. 3. Gantry parallel to C4–C5 intervertebral space. Fig. 1. Region: hard palate to upper mediastinum (parallel to hard palate or dental fillings) Example of Axial Scan Caveats 1. Motion artifacts should be minimized. 2. Dental artifacts may obscure enlarged retropharyngeal nodes (artifacts are minimized with 1-mm collimation). Fig. 2. Routine Neck Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 2.5 Pitch factor 1.375–1.5 Reconstruction 5 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 150 eff. mAs Kernel (algorithm) Soft Window (width/center) 380/50 Contrast medium Yes Administration Monophasic Volume 80–110 ml Flow rate 3 ml/s Scan delay 45 s Comments The short investigation time with the breathhold technique decreases the likelihood of movement artifacts. A flexible FOV should be used to enlarge areas of interest (anterior portion of the neck). Thin-collimation imaging decreases dental artifacts. If severe artifacts are present, angulation of the gantry may be necessary.An example of the routine neck technique in a patient with hypopharyngeal and supraglottic infiltration is shown in an axial slice in Fig. 2. 29 30 4-row Scanning Neck Routine Sinuses Indications. Trauma to facial skeleton (including LeFort fractures), inflammatory disease (benign sinusitis), septum deviation and exclusion of cysts or polyps for preoperative workup, polyposis, preoperative work-up for corrective surgery. Patient Positioning. Supine, all scans are performed in the axial plane, arms downward, use headrest. Topogram 3D Reconstructions See “Comments”. Alternatively, also direct coronal image acquisition in either supine or prone position as possible. a MIP No MPR Yesa VRT No Other No For sinusitis and polyposis, image reconstruction in the coronal plane is recommended and may alone be sufficient for image reading. For trauma and fractures, image reconstruction in at least the axial and the coronal plane is recommended. Criteria of Good Image Quality 1. Artifact-free reconstructions of all sinuses and of the entire facial skeleton. 2. Absence of motion artifacts. Fig. 1. Region: including frontal sinus to alveolar ridge (dental roots; axial scan) Example of Reconstruction Quality Fig. 2a, b. Caveat 1. Dental artifacts should not alter the scan quality or obscure the sinuses. Routine Sinuses Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.875–1.25 Reconstruction 2 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 70–100 eff. mAs Kernel (algorithm) Bone Window (width/center) 2,000/300 Contrast medium No Administration Volume Flow rate Scan delay Comments Since the lenses are within the scanned region, a reduction of the tube current is strongly suggested. Due to the high percentage of artifacts caused by dental fillings, we suggest the general use of this protocol with axial scanning and the reading of coronal MPRs alone for the workup of benign sinus disease. Alternatively, coronal acquisition can be performed and reconstructed. Due to the high contrast of tissue versus air, tube current can be reduced to about 70 mAs. This helps reduce the dose. However, a clear indication for the CT is warranted. Use this protocol for benign sinusitis (Fig. 2) or fractures only. For the staging and differentiation of tumor or mucoceles, the “Sinus Tumors” protocol is recommended. For the appropriate appreciation of fractures, the reading of the MPRs in axial and coronal planes are recommended. The data acquired can also be used for virtual endoscopy (Fig. 3). While this technique is still under investigation, benefits may include safer endonasal surgery, especially of the ethmoids. Fig. 3. 31 32 4-row Scanning Neck Sinus Tumors Indications. Fungal disease of the sinuses, granulomatosis, mucocele, papilloma, carcinoma of the sinuses, other sinonasal tumors and tumor-like conditions. Patient Positioning. Supine, arms downward, use headrest. Topogram 3D Reconstructions MIP No MPR Yes VRT No Other No Image reconstructions in axial and coronal planes in both soft tissue and bone kernel are recommended. MPR reconstructions in the soft-tissue kernel should be made with 3–4-mm reconstruction thickness for optimal quality. Fig. 1. Region: including frontal sinus to alveolar ridge (dental roots) Criteria of Good Image Quality Example of Axial Scan 1. Artifact-free reconstructions of the entire facial skeleton including infratemporal space. Caveat 1. For lymph node staging, an additional investigation is necessary (see “Routine Neck”). Fig. 2. (Case courtesy of Dr. L. Jaeger) Sinus Tumors Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.875 Reconstruction 2 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 140 eff. mAs Kernel (algorithm) Soft tissue and bone Window (width/center) 450/60 + 2,000/300 Contrast medium Yes Administration Monophasic Volume 100 ml Flow rate 3 ml/sec Scan delay 40 s Comments A higher dose compared to the “Routine Sinuses” protocol is necessary in order to visualize the soft tissue. For the detection or exclusion of bone erosion, the bone kernel is necessary. If lymph node extension is not known, add the protocol “Routine Neck.” Alternatively, a direct coronal image acquisition in either the supine or prone position is possible. If a tumor with intracranial infiltration is suspected, coronar reconstructing (MPR) and a contrast enhanced MRI should be performed. Figure 2 shows an example of aspergillosis of the right maxillary sinus. 33 34 4-row Scanning Neck Nasopharynx and Oropharynx Indications. Complications of inflammation such as abscesses, tumors in the naso- or oropharynx of either benign or malignant origin, masses of the salivary glands, suspected arrosion of skull base. Patient Positioning. Supine, arms (and shoulders) downward, remove dental prostheses and necklaces, etc. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Image reconstructions in coronal planes in soft tissue are recommended in all cases of suspected skull base infiltration, in extensive tumor extension, and in postsurgical cases where anatomy is obscured. Criteria of Good Image Quality Fig. 1. Region: frontal sinus to upper mediastinum 1. High-quality axial scans. 2. Sufficient opacification of the vessels. Caveat Example of Axial Scan 1. For lymph node staging, an additional spiral is necessary (see “Routine Neck”). Fig. 2 a–c. (Case courtesy of Dr. L. Jaeger) Nasopharynx and Oropharynx Scan Parameters Parameter Mode Spiral Collimation a 4 ¥ 1 mm Pitch factor 1.375–1.5 Reconstruction 2–3 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 140–150 eff. mAs Kernel (algorithm) Soft and bonea Window (width/center) 450/60 + 2,000/300 Contrast medium Yes Administration Monophasic Volume 100 ml Flow rate 3 ml/s Scan delay 40 s Coronal MPR reconstructions in bone kernel could be made to exclude skull base infiltration; otherwise the skull base should be evaluated by bone kernel and/or direct coronal cuts, as necessary. Comments In order to visualize the mass and to define its maximum extent and the differential diagnosis, both CT and MRI may be necessary. For the detection or exclusion of bone erosion, bone kernel or coronal MPRs are necessary. If lymph node extension is not known, add the “Routine Neck” protocol. Figure 2 shows a tumor of the left nasopharynx invading the skull base (Fig. 2a), the osseous part of the middle cranial fossa (Fig. 2b). While the osseous destructions is best observed in the coronal MPRs of the CT, the MRI has superior sensitivity to detect intracranial infiltrations (Fig. 2c). 35 36 4-row Scanning Neck Larynx and Hypopharynx Indications. Laryngeal fractures, laryngeal inflammation of unknown origin, benign and malignant laryngeal tumors, laryngoceles, tumors of the hypopharynx. Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram See “Comments.” With regard to both “e” – phonation and breathhold, attempt should be made to avoid artifacts from lots of dental fillings. The shoulder(s) should be lowered as much as possible. 3D Reconstructions MIP No MPR Yes VRT No Other No Image reconstructions in the coronal and sagittal planes with soft-tissue kernels are recommended (for fractures, bone kernel). Criteria of Good Image Quality 1. High-quality coronal reconstructions. 2. Breathhold imaging of both spirals. Caveats Fig. 1. Region: from the mandible to the subglottic region; two spirals, breathhold and “e” phonation Example of Axial Scan 1. The scan level to scan the larynx varies with each patient; check should be made that the entire larynx is on the scan. 2. The patient should be properly instructed before the examination. Larynx and Hypopharynx Scan Parameters Parameter Spiral 1 (breathhold) Spiral 2 (phonation) 4 ¥ 1 mm 4 ¥ 1 mm Pitch factor 1.375–1.5 1.375–1.5 Reconstruction Slice 1 mm, increment 0.5 mm Slice 1 mm, increment 0.5 mm Rotation time 0.75 s 0.75 s Scan orientation Cranio-caudal Cranio-caudal Scanner settings 120 kV, 180 eff. mAs 120 kV, 180 eff. mAs Kernel (algorithm) Softa Softa Window (width/center) 450/60 450/60 Contrast medium Yes Administration Monophasic Volume 100 ml Collimation a Mode Flow rate 3 ml/s Scan delay 40 s Start second spiral immediately For fractures, alter the suggested protocol with bone kernel reconstruction in breathhold, if possible. Comments Breathhold imaging is a general requirement. For the differentiation of T2 and T3 laryngeal carcinoma, the movement of the vocal cord is crucial. Repeat scanning of the larynx with “e” phonation; quiet breathing and the Valsalva maneuver then become necessary. Vocal cord paralysis is readily possible to document. Every third image is filmed. While the axial image is important and gives very high spatial resolution (Fig. 2a), coronal (Fig. 2b) and sagittal (Fig. 2c) MPR reconstructions significantly contribute to the understanding of the infiltration pattern. They are recommended especially for preoperative staging. For nodal staging, add a spiral examination of the neck (“Routine Neck” protocol). Fig. 2 a–c. 37 38 4-row Scanning Neck CTA Carotids Indications. Suspected stenosis, occlusion or dissection of the common or internal carotid artery or parts thereof. Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions a MIP No MPR Yesa VRT Yes Other No STS-MPR can be used for reconstructions; however, segmentation will be necessary in the skull base. Criteria of Good Image Quality 1. High opacification of the carotid artery. 2. Little contrast in the jugular vein. Fig. 1. Region: from 3–4 cm above the sella turcica to the collarbone Caveats 1. Scan and contrast timing is critical. 2. A test bolus injection is recommended. Example of Axial Scan Fig. 2 a–c. (Case courtesy of Dr. B. Wintersperger, Munich) CTA Carotids Scan Parameters Parameter Mode Spiral Collimation a 4 ¥ 1 mm Pitch factor 1.375–2.0 Reconstruction Slice 1.5 mm, increment 0.8 mm Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 100–150 eff. mAs Kernel (algorithm) Soft Window (width/center) 380/50 Contrast medium Yes Administration Monophasic Volume 100 ml Flow rate 3–5 ml/s Scan delay 12 sa A test bolus or bolus triggering is recommended for the exact timing of the injection. The best reconstruction quality will be achieved when the artery has the maximum contrast opacification, and the jugular vein the minimum. Comments As the scan of the entire carotid will take about 20 s (at 1 mm the current maximum table speed is 16 mm/s), the caudo-cranial direction is recommended for bifurcation stenosis. If the suspected disease is in the more cranial part (e.g., dissection of the ICA), cranio-caudal scanning may be better. For a quick overview,VRT reconstructions seem to be very efficient. However, maximum reproducibility is achieved by axial scans in area measurements. If no MPR reconstruction is planned, the reconstruction increment can be as large as 5 mm. When MPRs are planned, the reconstruction increment should be reduced to 0.8 mm with 50% overlap. Figure 2 shows a CTA of the carotids in a young male patient with an ICA occlusion (dissection) on the left side. Coronal and sagittal MPR reconstructions of the left ICA in this patient are seen in Fig. 2a,b. An example of a VRT reconstruction (same patient) can be seen in Fig. 2c. 39 40 4-row Scanning Chest Routine Chest and HR-Chest Indications. Mediastinal and axillary lymph nodes; tumors of the anterior, medial, and posterior mediastinum; posterior mediastinum, including thyroid goiter; staging; thoracic abnormalities (e.g., situs inversus viscerum); abscesses. Patient Positioning. Supine position, arm(s) elevated over the head (in asbestosis prone position also, see “Comments”). Topogram 3D Reconstructions MIP No MPR No VRT No Other No The chest routine program is not optimized for the secondary reconstructions of either lung or mediastinum. For these options, please refer to treatments in this book on combithorax, chest aortic arch, or chest CTA. Fig. 1. Region: from lung apices, to under the diaphragm (including the adrenals in bronchial carcinomas) Criteria of Good Image Quality 1. Caudo-cranial acquisition. 2. Breathhold acquisition. 3. Sufficient contrast in arteries and veins. Example of Axial Scan Caveat 1. For screening of lung nodules or inflammatory changes only, the low-dose protocol should be used (see “Comments”). Fig. 2 a, b. (Case courtesy of Dr. U. J. Schoepf, Boston, US) Routine Chest and HR-Chest Scan Parameters Parameter Mode Spiral a b Collimation 4 ¥ 2.5 mma Pitch factor 1.5 Reconstruction 6 mm lung and 6 mm soft tissue Rotation time 0.5 s Scan orientation Caudo-cranialb Scanner settings 120 kV, 90–120 eff. mAs Kernel (algorithm) Soft tissue, lung Window (width/center) 420/50, 1,500/–600 Contrast medium Yes Administration Monophasic Volume 80 ml Flow rate 3.0 ml/s Scan delay 35 s Scan time is usually below 15 s, which in breathhold is well tolerated by most patients. Since the sensitive lower parts are scanned first, caudo-cranial scan orientation helps to minimize artifacts from breathing.Artifacts from venous inflow are also reduced.The reconstructions should be cranio-caudal. Comments This protocol is designed to serve as a routine protocol (soft and lung window; see Fig. 2a,b). Demarcation of the esophagus is optimized when giving a swallow of barium suspension shortly before initiation of the scan. For screening, detection, or exclusion of pulmonary nodes or infiltrates only, a low-dose high resolution HR lung protocol as follows is recommended: – Collimation: 4¥2.5 mm – Pitch factor 1.5 – Reconstruction: 3 mm – Scanner setting: 120 kV, 10–20 mAs (!) – Rotation time: 0.5–0.75 s – Kernel (algorithm): lung – Window: lung window 1,500/–600 Administration of contrast material is not necessary. This protocol drastically reduces the dose of the CT scan at the expense of more noise. To detect or exclude asbestosis or orthostatic changes, an additional scan of this protocol in the prone position is recommended. ECG triggering may be used in selected cases to minimize motion artifacts (soft and lung window: Fig. 2) (Schoepf et al. 1999). 41 42 4-row Scanning Chest Pulmonary Embolism Indications. Detection or exclusion of suspected pulmonary embolism, evaluation of atypical chest pain. Patient Positioning. Supine, arms elevated above the head. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No MIP reconstructions can be used to detect embolism in rather subtle cases (see Fig. 2 b). Criteria of Good Image Quality 1. Sufficient contrast in pulmonary arteries. 2. Absence of motion artifacts. Fig. 1. Region: concentrated on central hilar portion, from above the aortic arch Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. U.J. Schoepf ) Caveat 1. The high flow of contrast material injected may cause artifacts from the superior vena cava. Pulmonary Embolism Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 1.5–1.75 Reconstruction 3 mm, for MPR reconstructing 1 mm with 0.5 mm increment Rotation time 0.5 s Scan orientation Caudo-cranialb Scanner settings 120 kV, 140 eff. mAs Kernel (algorithm) Soft/mid Window (width/center) 420/60 and 1,500/–600 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 4.0 ml/s Scan delay 16 sc a Scan time is usually below 15 s, which is well tolerated in breathhold by most patients. Since the sensitive lower parts are scanned first, the caudo-cranial scan orientation helps to minimize artifacts from breathing. Also, artifacts from venous inflow are reduced. The reconstructions should be cranio-caudal. c This interval should be determined by a test bolus injection or a bolus tracking. b Comments The protocol can be used to exclude or to detect pulmonary embolism (Fig. 2a). The MPR can help to view the full extent of the thrombotic material (Fig. 2b). Using MSCT, the source of embolization, as for example the right heart, can also be visualized. Demarcation of the esophagus is optimized when giving a barium suspension shortly before beginning the scan. 43 44 4-row Scanning Chest Combi Thorax Indications. Evaluation of the lung tissue in conjunction with detailed analysis of the mediastinal structures, e.g., in sarcoidosis; alternatively, to evaluate bronchogenic carcinoma or other chest disease. Patient Positioning. Supine, arms elevated above the head. Topogram 3D Reconstructions MIP Yes MPR Yes VRT No Other No MIP reconstructions of the Combi Thorax in the coronal and sagittal planes are superior for visualization of the pulmonary arteries, while MPR reconstructions have been found to be superior for central and peripheral bronchi and lung parenchymal changes (Eibel et al 1999). Fig. 1. Region: including from below the diaphragm to the lung apices Criteria of Good Image Quality Example of Axial Scan 1. Absence of motion artifacts. 2. Low noise. 3. Sufficient contrast in vessels. Caveat 1. This Combi Thorax protocol should be used for the combined evaluation of HR lung and soft-tissue mediastinum. Fig. 2a–c. (Case courtesy of Dr. U.J. Schoepf ) Combi Thorax Scan Parameters Parameter Mode Spiral a b Collimation 4 ¥ 1 mma Pitch factor 1.5–1.75 Reconstruction Soft: 8 mm; lung: 1 mm Rotation time 0.5 s Scan orientation Caudo-cranialb Scanner settings 120 kV, 90–140 eff. mAs Kernel (algorithm) Soft, hard Window (width/center) 420/60, 1,500/–600 Contrast medium Yes Administration Monophasic Volume 80 ml Flow rate 2.5 ml/s Scan delay 35 s Scan time is usually below 25 s, which in breathhold is well tolerated by most patients. Since the sensitive lower parts are scanned first, the caudo-cranial scan orientation helps to minimize artifacts from breathing. Artifacts from the venous inflow are also reduced. The reconstructions should be cranio-caudal. Comments The Combi Thorax protocol is ideal for the work-up of cases in which the combined investigation of lung parenchyma and mediastinal and hilar soft tissue is necessary. A case with sarcoidosis (Fig. 2) shows both the lung tissue in 1-mm reconstruction thickness with the high-resolution kernel (Fig. 2a,b) and the soft tissue with the soft-tissue kernel (Fig. 2c), as generated for one spiral data set. Demarcation of the esophagus can be optimized by giving a barium suspension shortly before starting the scan. 45 46 4-row Scanning Chest CTA Aortic Arch Indications. Detection or exclusion of aortic aneurysms, bleeding, dissection, or thrombosis of the ascending aorta, arch, and descending aorta. Patient Positioning. Supine, arm elevated over the head. Topogram 3D Reconstructions a MIP Yes MPR Yesa VRT No Other No MPR helps to visualize the cranio-caudal extent of the disease (see Fig. 2). Criteria of Good Image Quality 1. High contrast of the arterial vessels. 2. Little or no contrast media in the veins. 3. High quality of secondary reconstructions. Fig. 1. Region: including lung apices to below the diaphragm, or to the distal end of any aneurysm (must include supra-aortic arches) Example of Axial Scan Fig. 2 a, b. (Cases courtesy of Dr. B. Ohnesorge) Caveat 1. The timing of the contrast injection is critical and should be determined by a test bolus or bolus tracking. CTA Aortic Arch Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mma Pitch factor 1.5–2.0 Reconstruction Slice 1.25–2 mm, 1 mm increment Rotation time 0.5 s Scan orientation Caudo-cranialb Scanner settings 120 kV, 110–150 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/50 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3.0 ml/s Scan delay 15 s a Scan time is usually low and breathhold is well tolerated by most patients. b The caudo-cranial scan orientation helps to minimize artifacts from breathing since the sensitive lower parts are scanned first. Artifacts from venous inflow are also reduced. The reconstructions should be cranio-caudal. Comments In patients with possible alteration of the circulation time, a bolus timing technique or use of a test bolus is recommended for optimal contrast in the spiral acquisition. The protocol can be adapted to extend coverage to the chest and abdomen (using 4¥2.5 mm). Triggering improves the image quality, especially in the ascending portion of the aorta (see Fig. 2a). MPR can improve the visualization of, for instance, dissections, as shown in Fig. 2b. 47 48 4-row Scanning Heart Coronary Artery Screening Indications. Suspected coronary artery disease; symptomatic patients, atypical chest pain; asymptomatic patients, risk stratification. Patient Positioning. Supine, arms elevated, ECG trigger on. Topogram 3D Reconstructions MIP a Fig. 1. Region: scan from above the tracheal bifurcation to the diaphragm Example of Axial Scan No MPR No VRT No Other a Calcifications are postprocessed to determine the Agatston score, a volume or mass score. Postprocessing can take place at the scanner's console or at a separate workstation. Elevated values of these scores are known to correlate with an increased risk of coronary artery disease (CAD) (see the second table). Criteria of Good Image Quality 1. Motion-free visualization of the coronaries and the coronary calcifications. 2. Focused FOV. 3. Heart rates of less than 70 beats per minute are optimal. Caveats Fig. 2. 1. Variation of the trigger delay may be necessary. 2. Automated programs for deriving scores need supervision. 3. The lung window also needs to be read! 4. ECG gating and the coverage of the entire heart (Fig. 1) is necessary for sufficient image quality (see Fig. 2) and score reproducibility. Set the trigger to 40–70% of the ECG R interval. Coronary Artery Screening Scan Parameters Parameter Mode Sequential Collimation 4 ¥ 2.5 mm Pitch factor 0.375 Reconstruction 3 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 133 eff. mAs Kernel (algorithm) Heart view medium Window (width/center) 370/50 Contrast medium No Administration Volume Flow rate Scan delay Comments For direct visualization of the lumen of the coronary arteries, please add the protocol “CTA Coronary Arteries.” Clinical interpretation of the calcium score should be made according to suggestions based on the articles of Haberl et al. 2001 and of Janowitz et al. 1991, among others (see “References”). a Agatston scorea Interpretation Clinical implication Possible therapeutic implications 0 Negative score Negative predictive value for CAD 90 %–95 % None 1–10 Minimal calcium deposits Stenosis unlikely General preventive treatment 11–100 Small calcium deposit(s) CAD possible Another evaluation required 101–400 Severe calcium deposits Stenosing CAD possible > 400 Excessive calcium deposits High probability for stenosing CAD Treatments of risk factors and dedicated cardiological therapy Indication for stress ECG, catheterization as indicated The table is modified from Rumberger et al. 1999.The applicability of the MSCT data to the Agatston score is dealt with in the work by Knez et al. 2002 and Kopp et al. 2002 (see “References”). 49 50 4-row Scanning Heart CTA Bypasses Indications. Follow-up after coronary bypass surgery. Patient Positioning. Supine. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yes Other No STS MPRs or STS MIPs are recommended. Criteria of Good Image Quality Fig. 1. Region: from the aortic arch to below the heart 1. High contrast in the coronary arteries and in the bypass. 2. Adapted FOV. Example of Axial Scan Caveats 1. A test bolus is recommended for good timing of the contrast injection. 2. FOV must cover the entire heart plus aortic root. Fig. 2. (Case courtesy of Dr. C. Becker) CTA Bypasses Scan Parameters Parameter Mode Spiral Collimation a b 4 ¥ 1 mm Pitch factor 0.375 Reconstruction 1.25 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 260–400 eff. mAs Kernel (algorithm) Soft/mid Window (width/center) 500/80 Contrast medium Yes Administration Biphasica Volume 40 ml 80 ml Flow rate 4 ml/s 2 ml/s Scan delay b 10 s later Adapted from C. Becker (unpublished data). Determined by test bolus or bolus tracking. Comments Retrospective ECG gating and the coverage of the entire heart and proximal aorta is necessary for optimal image quality. Using this protocol, a heart rate of less than 70 is optimal. If necessary, premedication (beta-blocker) can be considered. Alternatively, a prospectively ECG-triggered sequential scan may also be used (4 ¥2.5 mm collimation, 0.5 s, 120 mAs at 120 kV). Figure 2 shows a patent sequential bypass at the level of the aortic insertion (the frontal bypass graft was revised with a stent). 51 52 4-row Scanning Heart CTA Coronary Arteries Indications. Suspected coronary artery disease. Patient Positioning. Supine, arms elevated, ECG trigger on. Topogram 3D Reconstructions a Fig. 1. Region: from above the tracheal bifurcation to the diaphragm MIP Yesa MPR No VRT Yes Other No Oblique (45° parallel to main stem) STS MIPs are recommended (3 mm slice thickness, 1.5 mm increment) for the visualization of the main stem, LAD and RCA. Criteria of Good Image Quality 1. Absence of motion artifacts. 2. High contrast in coronary arteries. 3. Heart rates of less than 70 beats per minute are optimal. Example of Axial Scan Caveats 1. A test bolus should always be used. 2. Offline postprocessing is required. 3. All of the coronary system must be opacified (proximal, mid, and distal). Fig. 2. (Case courtesy of Dr. C. Becker) CTA Coronary Arteries Scan Parameters Parameter Mode Spiral Collimation a b 4 ¥ 1 mm Pitch factor 0.375 Reconstruction Slice 1.25 mm, increment 0.8 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 400 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium Yes Administration Biphasica Volume 40 ml 80 ml Flow rate 4 ml/s 2 ml/s Scan delay b 10 s later Adapted from C. Becker (unpublished data). To be determined by test bolus or bolus tracking. Comments ECG gating and the coverage of the entire heart is necessary to derive sufficient image quality and score reproducibility. If the heart rate exceeds 70 beats/min, oral premedication (beta-blockers) can be considered. An illustration of high-contrast opacification is given in Fig. 2, which is an example of partially calcified and partially soft plaques. 53 54 4-row Scanning Abdomen Routine Abdomen Indications. Screening, detection, or exclusion of abscesses; control scans; follow-ups. Patient Positioning. Supine, arms elevated above the head. Topogram 3D Reconstructions MIP No MPR No VRT No Other No Criteria of Good Image Quality 1. Absence of gross motion artifacts. 2. Good contrast opacification of arteries, veins, and the portal system. Fig. 1. Region: from above the diaphragm to the symphysis pubis Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. C. Hong) Caveat 1. For the detection or exclusion of venous thrombosis, vary the injection time. Routine Abdomen Scan Parameters Parameter Mode Spiral a Collimation 4 ¥ 2.5 mm Pitch factor 1.0–1.5 Reconstruction 5–8 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 165–200 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium i. v. + oral + rectala Administration i. v., monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 65 s Oral contrast media for the optimal distention of the stomach should be administered immediately before scanning, and for the bowel up to 2 h (with 900 ml) before scanning.The rectal administration of water or methylcellulose should be immediately before scanning. Comments To further reduce radiation, especially in young patients, the tube currents should be adapted to the habitus and can be reduced to 120 mAs. The patient should do deep breathing before the beginning of the spiral scan. A normal abdominal slice with a patent vena cava is shown in Figure 2a. To exclude venous thrombosis of the pelvis or the inferior vena cava (Fig. 2b), the scan delay should exceed 65 s. The injection rate of the contrast material may also be varied. 55 56 4-row Scanning Abdomen Venous Upper Abdomen Indications. Detection or exclusion of liver abscesses, follow-up of liver metastasis, suspected portal thrombosis, portal obstruction. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No For planned reconstructions, a 1.5-mm reconstruction interval is recommended (and the reconstruction thickness can be 3 mm). Criteria of Good Image Quality Fig. 1. Region: from the diaphragm to the iliac crest 1. Absence of breathing artifacts. 2. A venous phase providing positive contrast in the portal veins and inferior vena cava. Caveat Example of Axial Scan 1. The scan delay can be as long as 80 s to safely exclude a portal venous thrombus. Fig. 2. Venous Upper Abdomen Scan Parameters Parameter Mode Spiral Collimation a 4 ¥ 2.5 mm Pitch factor 1.0–1.5 Reconstruction Slice 5–8 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 165–200 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium Yes Administration Monophasica Volume 120 ml Flow rate 3 ml/s Scan delay 65 s Administration of the oral contrast media for optimal distention of the stomach should take place immediately before scanning, and for the bowel up to 2 h (with 900 ml) before scanning. Comments To reduce radiation, especially in young patients, the tube currents should be adapted to the habitus and can be reduced to 120 mAs. Patients should be instructed to breathe deeply before scanning. Water should be given before scanning for better filling of the stomach. The MDCT data can be used to reconstruct coronal and sagittal planes (in a 4¥2.5-mm spiral, a reconstruction thickness of 3 mm and a reconstruction increment of 1.5 mm are recommended). These additional reconstructions may help to localize metastases in the individual liver segments. Figure 2 shows a case with multiple metastases to segments 2, 4a, 7, and 8. 57 58 4-row Scanning Abdomen Biphasic Abdomen Indications. Known liver metastasis; hepatocellular carcinoma; restaging, including lymph node staging. Patient Positioning. Supine, arm elevated to the head. Topogram 3D Reconstructions a MIP No MPR Optionala VRT No Other No For planned segmental resection of the liver, the MPR reconstructions are especially helpful when the tumor is near large vascular structures (such as the hepatic veins) or the central portal structures. In these cases, sagittal and coronal reconstructions are strongly recommended. Criteria of Good Image Quality Fig. 1. Region: entire liver biphasic – (1) spiral acquisition, dotted lines; and (2) venous abdomen acquisition, solid lines 1. Good arterial and venous contrast opacification of the liver parenchyma. 2. No breathing artifacts (especially critical in the MPRs). Example of Axial Scan Caveat 1. For the imaging in breathhold and correct contrast injection, timing is essential for optimal contrast. Fig. 2 a, b. (Cases courtesy of Dr. C. Hong) Biphasic Abdomen Scan Parameters Parameter a Mode Spiral 1 (dotted line) Spiral 2 (solid line) Collimation 4 ¥ 2.5 mm 4 ¥ 2.5 mm Pitch factor 1.0–1.5 1.25–1.5 Reconstruction 5–8 mm, for MPR 3 mm 5–8 mm, for MPR 3 mm Rotation time 0.5 s 0.5 s a Scan orientation Cranio-caudal Caudo-cranial Scanner settings 120 kV, 165–220 eff. mAs 120 kV, 165–220 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 420/60 420/60 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 35 s 65 s This orientation is advantageous for better contrast of liver veins in a second spiral acquisition. Comments The diagnostic quality of the MPR reconstructions can be appreciated in Fig. 2, showing two patients with hepatocellular carcinoma. One patient (Fig. 2a) displays a huge lesion but no thrombosis, and the other patient (Fig. 2b) has a central thrombosis of the portal venous system. Patient should do deep breathing before the beginning of the spiral. To exclude a secondary venous thrombosis of the vena cava, the scan delay of spiral 2 may exceed 80 s. 59 60 4-row Scanning Abdomen Biphasic Liver (Including CTAP) Indications. Hepatocellular carcinoma, differentiation of hepatic lesions, small bowel metastasis, cholangiocellular carcinoma, etc. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No 1-mm axial reformatting is recommended if MPR reconstructions are desired. Criteria of Good Image Quality 1. Contrast enhancement, arterial: initial parenchymal contrast and high-contrast vessels. 2. No breathing artifacts. Fig. 1. Region: from above the diaphragm to the upper iliac crest Caveats Example of Axial Scan 1. In the two spiral acquisitions, the delay (35 s, 55 s) is critical. 2. No oral contrast medium is required. Fig. 2 a, b. (Case courtesy of Dr. C. Hong) Biphasic Liver (Including CTAP) Scan Parameters Parameter Mode Spiral 1 Spiral 1 + 2 Collimation 4 ¥ 2.5 mm 4 ¥ 2.5 mm Pitch factor 1.0–1.5 1.0–1.5 Reconstruction Slice 5 mm, increment 5 mm Slice 5 mm, increment 5 mm Rotation time 0.5 s 0.5 s Scan orientation Cranio-caudal Caudo-cranial Scanner settings 120 kV, 155–220 eff. mAs 120 kV, 155--220 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 420/60 420/60 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 20 s 55 s Comments If an endocrine-active tumor is suspected, the arterial phase is important (especially in gastrinomas and Zollinger-Ellison syndrome). The arterial phase gives high contrast in highly vascularized metastases of renal cell or breast carcinomas. For the differential diagnosis of liver lesions, it may be necessary to perform a dynamic scan (5–10 mm slice thickness, table feed 0, start delay about 15 s, approximately 1 image/s). The patient must hold their breath for the entire length of scanning (approximately 40 s). This dynamic series can be evaluated using ROI time/density curves (differentiation of focal nodular hyperplasia, adenoma, and hemangioma). This protocol can also be used to perform a CT arterial portography (CTAP). Here, an intra-arterial catheter must be placed with the tip in the superior mesenteric artery or the splenic artery, with the injection of 60 cc contrast diluted 1:1 with saline, and a scan delay of 15 s. Arterial plus venous scanning has been employed in Fig. 2. Figure 2a shows a liver metastasis with marked hyperdensity in the arterial phase. Using thin overlapping slices (reconstruction increment 1.5 mm), MPRs of the same patient can be created, as seen in Fig. 2b. In case of a suspected gallbladder or cholangio-cellular carcinoma, an increased scan delay is recommended, as these tumors tend to have a prolonged contrast uptake. Metastases are usually supplied by the hepatic artery and thus enhance less than the liver parenchyma. The patient should do deep breathing before the start of the spiral scan. To reduce radiation, especially in young patients, the tube currents should be adapted to the habitus and can be reduced to 120 mAs. 61 62 4-row Scanning Abdomen CT Enteroclysis Indications. Evaluation of the small bowel, inflammatory processes such as Crohn's disease and their complications, wall thickness, and metastasis to the small bowel. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions MIP a No MPR Yesa VRT No Other No It is strongly recommended that MPRs be done in the coronal and sagittal planes. Criteria of Good Image Quality 1. Distention of the small bowel. 2. Clear bowels. 3. Use of paraffin methylcellulose (PMC) solution to induce hypodensity of lumen. Fig. 1. Region: from above the diaphragm to below the symphysis pubis Caveat 1. The methylcellulose solution must be given via a nasogastric tube; oral introduction is not recommended. Example of Axial Scan Fig. 2a–c. (Cases courtesy of Dr. G.F. Rust) CT Enteroclysis Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 1.0–1.5 Reconstruction Slice 1.25 mm, increment 0.6 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 165 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium i. v., Enteral Administration i. v., Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 35 s Comments All of the named indications are currently under investigation (work in progress). CT enteroclysis offers distinct advantages over MR enteroclysis, such as high spatial resolution in very short acquisition times. In contrast, MR enteroclysis has superior soft-tissue contrast and does not use ionizing radiation. Patient preparation: Approximately 18 h before the examination, internal cleaning needs to be initiated. In addition to fluid load, the patients are given antigas medication (e.g., Lefax®, Asche, Germany). A nasoduodenal tube (e.g. 8 Fr, 150 cm, Guerbet, Germany) is inserted in all of our patients. This tube must be placed beyond the duodenal-jejunal junction. The enteral contrast material (paraffin solution) should be given via the nasogastric tube only, and after reflux has been ruled out. Two ampoules of, for instance, Buscopan® should be given i.v. shortly before the CT examination. PMC solution is recommended as a negative contrast material. A low pump rate of between 30 and 70 ml per minute (the mean value for the patients we examined was 40 ml/min) is suggested. A normal case is shown in Fig. 2 (Fig. 2a being axial, Fig. 2b sagittal, and Fig. 2c coronal MPR reconstructions). 63 64 4-row Scanning Abdomen Biphasic Pancreas Indications. Suspected tumors of the pancreas, differential diagnosis of pancreatic lesions. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No In selected cases, MPR reconstructions can help to determine the cranio-caudal infiltration pattern. Criteria of Good Image Quality 1. High contrast and clear visualization of vessel structures surrounding the pancreas. 2. Duodenal “C” properly distended. Fig. 1. Region: focused on the pancreas and surroundings Example of Axial Scan Fig. 2 a–c. Caveats 1. Oral contrast material (water) is required. 2. The patient should be instructed to breathe deeply before scanning. 3. The FOV should be adapted to the pancreas. Biphasic Pancreas Scan Parameters Parameter Spiral 1 Spiral 2 4 ¥ 1 mm 4 ¥ 1 mm Pitch factor 0.75–1.5 0.75–1.5 Reconstruction Slice 2 mm, increment 1 mm; for MPRs slice 1.25 mm, increment 0.5 mm Slice 2 mm, increment 1 mm; for MPRs slice 1.25 mm, increment 0.5 mm Rotation time 0.5 s 0.5 s Collimation a Mode Scan orientation Cranio-caudal Caudo-cranial Scanner settings 120 kV, 165–250 eff. mAs 120 kV, 165–250 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 420/60 420/60 Contrast medium Yesa Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 35 s 70 s For the optimal distention of the stomach, oral contrast media should be administered immediately before scanning, and for the bowel up to 2 h (with 900 ml) before scanning. Comments This is a dedicated examination for suspected pancreatic disease (other than pancreatitis) and local metastasis only. For the diagnosis of pancreatitis, a different protocol is recommended (e.g., “Routine Abdomen CT”). Distention of the duodenum with water (for negative contrast) is recommended. The duodenal wall then shows a positive contrast. Some authors recommend giving water in a right-sided position and scanning in supine position; others recommend use of an agent such as Buscopan. Patients should do deep breathing before the start of the spiral scan. Using this protocol, an optimal image quality can be achieved in the axial, coronal, and sagittal planes (Fig. 2a–c). 65 66 4-row Scanning Abdomen Routine Kidney Indications. Follow-up of renal tumors, inflammations, infarcts of the kidneys. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Optional, either of the two spirals can be reconstructed using MPR: the first without contrast enhancement (unenhanced) and the second with a delayed contrast enhancement (parenchymal; excretory phase) Criteria of Good Image Quality Fig. 1. Region: from mid-liver to mid-pelvis 1. Absence of breathing artifacts. 2. Timing of the second spiral to obtain parenchymal contrast. Caveat Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. U. Mueller-Lisse) 1. This protocol is intended for the followup of known lesions. For the differentiation of renal tumors, the protocol “Renal Differential Diagnosis and Tumors” should be used. Routine Kidney Scan Parameters Parameter a Mode Spiral 1 Spiral 2 Collimation 4 ¥ 2.5 mm 4 ¥ 2.5 mm Pitch factor 1.0–1.5 1.0–1.5 Reconstruction 5 mm 5 mm Rotation time 0.5 s 0.5 s Scan orientation Cranio-caudal Cranio-caudal Scanner settings 120 kV, 165–200 eff. mAs 120 kV, 165–200 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 420/60 420/60 Contrast medium Unenhanceda Yes Administration Monophasic Volume 80 ml Flow rate 3 ml/s Scan delay 40 s To contrast the renal pelvis, a dose of 20 ml can be injected 5 min before each spiral. Comments MDCT images are recommended of the kidney in the precontrast phase, the nephrographic phase, and the excretory phase (Mueller-Lisse and Oberneder (2001). Since the natural CT contrast between the renal cortex and the lesions is often small, contrast enhancement with iodinated contrast medium is frequently required to allow diagnosis. To exclude renal vein and vena cava thrombosis, the second (contrast enhanced) spiral can be extended to the right atrium. If a renal artery stenosis is suspected, no oral contrast material should be given and a protocol with 4¥1-mm collimation and a reconstruction increment of 0.5 mm should be used (see the protocol “CTA Abdomen”). The contrast injection should be at least 100 ml at a rate of 3 ml/s and the delay should be 25 s. Figure 2 shows an example of a renal cyst in the unenhanced spiral (Fig. 2a) and in the excretory (Fig. 2b) phase. 67 68 4-row Scanning Abdomen Renal Differential Diagnosis and Tumors Indications. Differential diagnosis of renal masses. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Coronal MPRs are optimal (in 3-mm reconstruction thickness and < 2-mm increment). Criteria of Good Image Quality Fig.1. Region:from mid-liver to mid-pelvic region Example of Axial Scan 1. Absence of breathing artifacts (especially on MPR). 2. Timing of the spirals to obtain optimal nephrographic and excretory phase contrast. Caveats 1. This protocol is designed for the differentiation of renal lesions. 2. Due to the triple spiral, the radiation exposure is relatively high, mandating careful selection of appropriate patients. 3. This protocol is recommended for tumors. Fig. 2 a, b. (Case courtesy of Dr. U. Mueller-Lisse) Renal Differential Diagnosis and Tumors Scan Parameters Parameter Mode Spiral 1 Spiral 2 Spiral 3 Collimation 4 ¥ 1 mm 4 ¥ 1 mm 4 ¥ 2.5 mm Pitch factor 1.0–1.5 1.0–1.5 1.0–1.5 Reconstruction 1.25 mm 1.25 mm 5 mm Rotation time 0.5 s 0.5 s 0.5 s Scan orientation Cranio-caudal Caudo-cranial Cranio-caudal Scanner settings 120 kV, 155–200 eff. mAs 120 kV, 155–200 eff. mAs 120 kV, 155–200 eff. mAs Kernel (algorithm) Soft Soft Soft Window (width/center) 420/60 420/60 420/60 Contrast medium Unenhanced after preinjectiona Yes Yes Multiphasic Multiphasic Volume 20 mla 100 ml Flow rate 3 ml/s 3 ml/s Scan delay 40 s 70 s Administration a 100 s Preinjection of 20 ml for the positive contrast of the renal pelvis. Comments MDCT images of the kidneys are possible in the precontrast phase, nephrographic phase, and excretory phase. Because the natural CT contrast between the renal cortex and the lesions is often small, contrast enhancement with iodinated contrast medium is frequently required so as to allow diagnosis. Significantly more renal lesions are detected during the nephrographic phase (equal contrast in renal cortex and medulla) than during the corticomedullary phase with its strong renal cortical enhancement and less enhancement of the renal medulla. [See Fig. 2 (renal cell carcinoma) and the reference in “Routine Kidney” protocol.] Peak renal enhancement occurs 35–45 s after injection. This can be evaluated by a test bolus imaging series that covers the renal parenchyma. To exclude renal vein and inferior vena cava thrombosis, the second spiral can be extended to the right atrium. In suspected masses of the renal pelvis, a late spiral (>100 s) may be considered (spiral 3). The second “standard” plane of view in MDCT of the kidney should be coronal. To reduce radiation, especially in young patients, the tube currents should be adapted to the habitus and can be reduced to 120 mAs. 69 70 4-row Scanning Abdomen Rectal Tumors Indications. Staging of tumors of the rectum, preoperative work-up. Patient Positioning. Supine, arms above the head. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No For the second spiral acquisition in the pelvic region, the MPR reconstructions are helpful in delineating infiltrations in the rectum or bladder. Criteria of Good Image Quality 1. Sufficient distention of rectum. 2. Timing of the venous injection. Fig. 1. Region: (1) from diaphragm to the upper iliac crest; (2) from the upper iliac crest to below the symphysis pubis (spiral 1, dotted lines; spiral 2, solid lines) Caveat 1. Stool retention will reduce image quality; therefore, a careful preparation of the patient is of paramount importance. Example of Axial Scan Fig. 2 a, b. (From Kulinna et al. 2001) Rectal Tumors Scan Parameters Parameter Collimation Mode Spiral 1 (upper abdomen) Spiral 2 (pelvis) 4 ¥ 2.5 mm 4 ¥ 1 mm Pitch factor 1.25–1.5 1.0–1.5 Reconstruction 8 mm 1.25 mm Rotation time 0.5 s 0.5 s Scan orientation Cranio-caudal Cranio-caudal Scanner settings 120 kV, 165–200 eff. mAs 120 kV, 165–200 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 420/60 420/60 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 65 s To start after first spiral Comments The well-known beam-hardening artifacts are markedly reduced with this protocol. Especially in young patients, a dose reduction should be considered (scanner settings <200 mAs). Water or methylcellulose (solution) should be administered rectally immediately before scanning. Alternatively, water or gel (e.g., ultrasound gel) can be given; however, for the distention of the entire rectum, methylcellulose is seen as optimal. Two spirals are recommended, (1) to cover the upper abdomen and (2) as a thin collimation spiral to provide raw data for the MPR reconstructions of the pelvis (dotted lines in Fig. 1). It is also possible to cover the entire abdomen with a thin collimation spiral, but the amount of data is markedly increased. For the second spiral, breathhold is not necessary. In Fig. 2, the optimal distention of the rectum with methylcellulose suspension is shown: a rectal carcinoma is seen in axial (Fig. 2a) and sagittal MPR reconstructions (Fig. 2b). 71 72 4-row Scanning Abdomen CTA Abdomen Indications. To quantify or to exclude aneurysms of the abdominal aorta, to measure the diseased portions of the abdominal aorta before minimally invasive or open intervention, to detect or exclude aortic rupture or retroperitoneal bleeding. Patient Positioning. Supine, arm elevated over the head. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT No Other No MIPs or MPRs help to visualize the cranio-caudal extent of the aneurysms (see Fig 2). Criteria of Good Image Quality 1. High contrast in the abdominal aorta throughout the scan. 2. Little contrast in the parenchymal organs and negative contrast in the bowel. Fig. 1. Region: from above the diaphragm to below symphysis pubis Caveat Example of Axial Scan 1. Axial images and reconstructions must visualize aortic branches such as renal arteries, superior mesenteric artery, etc. Fig. 2 a–c. (Case courtesy of Dr. B. Wintersperger) CTA Abdomen Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm (4 ¥ 2.5 mm)a Pitch factor 1.0–2.0 Reconstruction Slice 2 mm, increment 1 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 130–180 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/50 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3.0 ml/s Scan delay 18 sb 4 ¥ 2.5 mm can be used, e.g., for reevaluation if details such as the renal arteries are of less importance and a higher volume coverage is important. b In patients with possible alteration of the circulation time, a test bolus application or bolus tracking is recommended to achieve optimal contrast in the spiral acquisition. a Comments If a renal artery stenosis is suspected, no oral contrast material should be given and a protocol should be instituted with 4¥1-mm collimation and a reconstruction increment of 0.5 mm. The contrast injection should be at least 100 ml at a rate of 3 ml/s with a delay of 25 s. Figure 2 shows a patient with an intrarenal aortic aneurysm. While the renal arteries are appreciated on the axial images (e.g., Fig. 2a), the full extent of the lesion can be visualized on either MIP (Fig. 2b) or MPR (Fig. 2c) reconstructions. 73 74 4-row Scanning Spine Cervical Spine Indications. Disk protrusion, disk herniation, suspected fractures, spondylolisthesis, unclear MR findings when performed as post-myelographic CT, MR contraindications. Patient Positioning. Supine, arms parallel to the body, shoulders down, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No We recommend using MPRs in an angulated fashion regularly in the way shown in Fig 1b. Using the thin 1-mm raw data, the angulated slice thus obtained reduces noise and achieves superior detail. Criteria of Good Image Quality 1. Zoomed images (FOV smaller than 90 mm). 2. Angulation of the reconstructions parallel to the disks. Caveat 1. The axial acquisition must cover the entire scanned volume, while the reconstructions must be angulated to the individual disk level. Example of Axial Scan Fig. 1. a For the scanning protocol, region to be adapted to the region of interest, as seen. b For the reconstructions, angulate reconstructions as shown perpendicular to cervical canal Fig. 2 a, b. Cervical Spine Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.625–1.0 Reconstruction Angulated axial and sagittal slices: slice 2–3 mm, increment 1.5 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 200 eff. mAs Kernel (algorithm) Soft; if fracture, bone kernel Window (width/center) 420/60, 2000/300 or adapteda Contrast medium No Administration Volume Flow rate Scan delay a After the myelographic intralumbar injection of contrast material in CT, a window of 1,200/400 is recommended. Comments The combination of angulated axial and sagittal reconstructions is most advantageous. Figure 2a shows the sagittal MPR reconstruction of a male patient with an anterior listhesis after a motor vehicle accident. Figure 2b shows an example of a postmyelographic examination in a female patient with persistent pain after ventral osteosynthesis. The myelographic contrast helps to delineate nawaring of the spinal cord and the CSF. 75 76 4-row Scanning Spine Thoracic Spine Indications. Disk protrusion, disk herniation, suspected fractures, spondylolisthesis, postmyelographic CT, MR contraindications. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP No MPR Yesa VRT Optional (see “Comments”) Other No MPRs in sagittal and axial orientation are recommended. The axial MPRs must be angulated to the individual disk level. Criteria of Good Image Quality 1. Focused images (FOV smaller than 90 mm). Fig. 1. Region: to be adapted to the region of interest Example of Axial Scan Fig. 2 a–c. (c: Case courtesy of Dr. U.J. Schoepf ) Caveat 1. The axial reconstructions must cover the entire volume of interest. Thoracic Spine Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.625–1.0 Reconstruction Angulated axial and sagittal slices: slice 2–3 mm, increment 1.5 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 250 eff. mAs Kernel (algorithm) Soft; if fracture, bone kernel Window (width/center) 420/60, 2000/300 or adapteda Contrast medium No Administration Volume Flow rate Scan delay a After the myelographic intralumbar injection of contrast material in CT, a window of 1,200/400 is recommended. Comments The combination of angulated axial and sagittal MPR reconstructions is most advantageous. For the detection of fractures, even in patients with severe osteoporosis, sagittal MPRs (Fig. 2a) can show type and extent of fracture. Alternatively, VRTs can be used for a threedimensional data visualization (Fig. 2b). A combination of CT and myelography is recommended for increased contrast if an intraspinal process is suspected (Fig. 2c) (disk protrusion). 77 78 4-row Scanning Spine Lumbar Spine Indications. Disk protrusion, disk herniation, suspected fractures, spondylolisthesis, unclear myelographic finding (as post-myelographic CT), MR contraindications. Patient Positioning. Supine, arms elevated, legs elevated for comfort. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No We recommend using MPRs in an angulated fashion regularly in the way shown in Fig. 1b. Using the thin 1-mm raw data, the angulated slices obtained in this manner yield low noise and superior detail. Criteria of Good Image Quality 1. Zoomed images (FOV about 90 mm). 2. Angulation parallel to the disks. Caveat 1. The axial scan must cover the entire volume while the reconstructions are angulated to the individual disk level. Fig. 1. a For the scanning protocol, region to be adapted to that of interest in lumbar spine, as seen. b For the reconstructions, slices as seen Lumbar Spine Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.625–1.0 Reconstruction Angulated axial and sagittal slices: slice 2–3 mm, increment 1.5 mm Rotation time 0.75–1.0 s Scan orientation Cranio-caudal Scanner settings 120 kV, 300 eff. mAs Kernel (algorithm) Soft; if fracture, bone kernel Window (width/center) 420/60, 2000/300 or adapteda Contrast medium No Administration Volume Flow rate Scan delay a After the myelographic intralumbar injection of contrast material in CT, a window of 1,200/400 is recommended. Comments The combination of angulated axial and sagittal MPRs is most advantageous. The reconstructions are based on one unangulated spiral, as shown in Fig. 1a. The positions of the angulated MPRs are shown in Fig. 1b.An example of the image quality is given in Fig. 2a and of the sagittal reconstruction in Fig. 2b (patient with L5/S1 disk herniation). A combination of CT and myelography is recommended for increased contrast if an intraspinal or intradural process is suspected. Example of Axial Scan Fig. 2 a, b. 79 80 4-row Scanning Peripherals Wrist Indications. Complicated wrist trauma, atypical distal radial fracture, scaphoid fracture or other carpal fracture unclear on conventional X-ray. Patient Positioning. Prone, arm elevated over the head. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No MPRs are obligatory in coronal, optional in sagittal plane. Criteria of Good Image Quality 1. High resolution kernel. 2. Absence of motion artifacts through stable positioning. Fig. 1. Region: from metacarpals to distal radius shaft Caveat 1. If the hand cannot be positioned above the head, please refer to “Comments”. Example of Axial Scan Fig. 2 a, b. Wrist Scan Parameters Parameter Mode Spiral Collimation 2 ¥ 0.5 mm Pitch factor 1.0 Reconstruction Slice 0.5 mm, increment 0.25 mm Rotation time 0.75–1.0 s Scan orientation Distal to proximal Scanner settings 120 kV, 100–150 eff. mAs Kernel (algorithm) Bone (high resolution) Window (width/center) 2,000/300 Contrast medium No Administration Volume Flow rate Scan delay Comments High-resolution imaging of the wrist should always include MPR reconstructions. Stable positioning is the key to getting good image quality. An example of an occult scaphoid is shown in Fig. 2a (coronal) and Fig. 2b (sagittal view). If the hand cannot be positioned over the head, position it in supine position on the belly. Tube current must then be increased to more than 300 mAs to get sufficient noise suppression. 81 82 4-row Scanning Peripherals Shoulder Indications. Suspected occult or complicated fractures, preoperative evaluation, postarthrographic evaluation e.g. of the anterior labrum. Patient Positioning. Supine, examined arm downward, contralateral side up (see Fig. 1). Topogram 3D Reconstructions a Fig. 1. Region: including clavicle, acromion, and the proximal humerus (the contralateral arm should be elevated) MIP No MPR Yesa VRT No Other No Coronal and sagittal MPRs are recommended, angulated parallel and perpendicular to the axis of the scapula. Criteria of Good Image Quality 1. Low noise. 2. Absence of motion artifacts. 3. In arthrographic evaluation, sufficient filling. Caveat 1. High tube current is usually necessary. Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. C. Glaser) Shoulder Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 1.0 Reconstruction Slice 1 mm, increment 0.5 mm Rotation time 1.0–1.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 200–250 eff. mAs Kernel (algorithm) Bone Window (width/center) 2,000/300 Contrast medium None or arthrographic Administration Volume Flow rate Scan delay Comments The elevation of the contralateral arm is aimed to reduce the X-ray beam absorption as much as possible. Figure 2 shows a 13-year-old boy with a suspected fracture. While slight incongruence in the articular portion is visible in the axial image (Fig. 2a), the coronal reconstruction (Fig. 2b) shows that no fracture is present. 83 84 4-row Scanning Peripherals Ankle Indications. Complicated fracture of the distal tibia, talus, or calcaneus, especially when a surgical intervention is planned. Patient Positioning. Supine, foot rest adapted, knee bend elevated and made comfortable with cushions. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No MPRs are obligatory in the coronal and sagittal planes. Criteria of Good Image Quality Fig. 1. Region: from distal calf including calcaneus (use foot rest!) 1. Absence of patient motion or metal artifacts. Caveat 1. Reconstructions for MPRs should include one side only. 2. The use of positioning devices is especially important for a comfortable and stable position. Example of Axial Scan Fig. 2 a, b. Ankle Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.5–0.75 Reconstruction Slice 1 mm, increment 0.5 mm Rotation time 0.75–1.0 s Scan orientation Proximal-distal Scanner settings 120 kV, 100–200 eff. mAs Kernel (algorithm) Bone Window (width/center) 2,000/300 Contrast medium No Administration Volume Flow rate Scan delay Comments High-resolution imaging of the ankle should always include sagittal MPR reconstructions. While a lot of details such as intra-articular fragments and destructions in this male patient with postraumatic arthrosis are visible in axial images (Fig. 2a), reconstructions in the coronal plane give the best overview (Fig. 2b). 85 86 4-row Scanning Peripherals Knee Indications. Suspected trauma on conventional x-rays, occult suspected depression of the articular surface, presurgical evaluation. Patient Positioning. Supine. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No MPR reconstructions are obligatory in the sagittal and coronal planes. Criteria of Good Image Quality Fig. 1. Region: from the distal femur to beyond the tibial plateau 1. Absence of motion artifacts. Caveats 1. To detect or exclude injury of the menisci or the cruciform ligaments, MRI is recommended. 2. Reconstructions should focus on one side only. Example of Axial Scan Fig. 2 a, b. Knee Scan Parameters Parameter Mode Spiral Collimation 4 ¥ 1 mm Pitch factor 0.5–0.75 Reconstruction Slice 1 mm, increment 0.5 mm Rotation time 0.75–1.0 s Scan orientation Proximal-distal Scanner settings 120 kV, 200 eff. mAs Kernel (algorithm) Bone Window (width/center) 2,000/300 Contrast medium No Administration Volume Flow rate Scan delay Comments To take full advantage of MSCT, reconstructions of lateral and medial injuries from the axial data (Fig. 2a) as applied to the coronal plane are recommended (see Fig. 2b). Sagittal reconstructions are optimal for anterior and posterior processes. 87 88 4-row Scanning Peripherals Trauma Indications. Quick evaluation of patients with major trauma and suspected injuries of the spine, chest and abdomen. Patient Positioning. Supine. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Imaging of trauma patients should include sagittal MPR reconstructions of the spine (see “Comments”). Criteria of Good Image Quality 1. Good contrast opacification of both vessels and parenchymal organs. 2. For MPRs of the spine, low noise at the cervicothoracic junction. Fig. 1. Region: from collar bones to symphysis pubis Example of Axial Scan Fig. 2. Caveat 1. Reconstructions of the spinal canal necessitate thin overlapping reconstructions in addition to the soft-tissue images. Trauma Scan Parameters Parameter Mode Spiral Collimation a 4 ¥ 2.5 mm Pitch factor 1.25–2.0 Reconstruction a Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 120–150 eff. mAs Kernel (algorithm) (1) Soft; (2) bonea Window (width/center) (1) 420/60; (2) 2,000/300 Contrast medium Yes Administration Monophasic Volume 150 ml Flow rate 3 ml/s Scan delay 45 s The reconstructions for parenchymal organ injury in 6-mm-thick slices should be (1) followed by a thin reconstruction of the spinal canal, (2) made with an adapted FOV and at least sagittal reconstructions,and (3) a possible third reconstruction in a lung window for lung parenchymal changes. Comments Figure 2 shows a case of splenic rupture. For the different reconstruction protocols see protocols “Routine Chest”, Routine Abdomen” and Spine (e.g.“Thoracic Spine”). Depending on the medical situation, this protcol can be completed by a CT study of the head, the temporal bone, HR thorax, peripherals or a CTA study of the region of interest. 89 90 4-row Scanning Peripherals Peripheral CTA Indications. Peripheral stenotic or occluding artery disease. Patient Positioning. Supine, arms elevated. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yesa Other No All reconstruction methods can be used (see Fig. 2). Criteria of Good Image Quality 1. High contrast opacification of the arterial run-off vessels. Caveats Fig.1. Region:from the renal arteries down to the ankles Example of Axial Scan 1. A stenotic process on only one side may pose a problem in the contrast material timing. 2. Spatial resolution has to be sufficient. Fig. 2 a, b. Peripheral CTA Scan Parameters Parameter Mode Spiral Collimation a 4 ¥ 2.5 mm Pitch factor 1.5–2.0 Reconstruction Slice 3 mm, increment 1.5 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 110–160 eff. mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium Yes Administration Monophasic Volume 150 ml Flow rate 3 ml/s Scan delay 25–30 sa A test bolus injection or bolus tracking is recommended. Comments The collimation of 4¥2.5 mm is preferred because it offers higher table feed than the 4¥1-mm collimation. Thin overlapping reconstructions maintain the quality of the reconstruction. A MIP reconstruction (Fig. 2a) and a VRT reconstruction (Fig. 2b) are shown in a patient with severe arteriosklerotic stenosis of the crossover bypass graft. The peripheral run-off is documented on both sides. 91 92 4-row Scanning Interventions Drainages Indications. Local fluid collection with suspected inflammation, abscesses, cysts, pericardial effusion not drainable by US-guided approach. Patient Positioning. Supine; may be varied to prone if the safest (and shortest) path to reach the area of interest is ventral, or to sagittal for similar considerations. Topogram 3D Reconstructions a Fig. 1. Region: Patient positioning in the CT scanner Example of Axial Scan MIP No MPR No VRT No Other Fluoroscopya Fluoroscopy is recommended, especially when the patient is unable to cooperate well and when the area of interest is within the basal parts of the lung, the heart, or the upper abdomen. Criteria of Good Image Quality 1. Documentation of the drainage when the needle is in position before and after aspiration. Caveat 1. A follow-up spiral must be done after drainage is in place. Comments Fig. 2. (From Bruening et al. 2002) Patient must be informed and must have signed an informed consent form prior to the investigation. Further patient preparation includes a venous drip, premedication, if necessary, and local anesthesia. Data on blood coagulation and patient file must be available. Sterile table preparation: – Syringe of 10–50 ml; needle for local anesthesia; scalpel; sterile clothing and gloves; Seldinger needle (18 G); guide wire (0.035 F, 75 cm) Drainages Scan Parameters Parameter Mode Sequential Collimation 5 mm Table feed 0 Reconstruction 5 mm Rotation time 0.5 s Scan orientation No table movement Scanner settings 120 kV, 70–150 mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium No Administration Volume Flow rate Scan delay Unsterile table preparation: – Spray; sterile drainage sets (8–20 F); suture set Procedure: 1. Perform and review spiral data (in expiration) and move the table to an optimal position. 2. Mark the optimal entry point with either pen or barium paste (e.g., Mikrotrast). 3. Give local anesthesia. 4. Use a scalpel for incision. 5. Use a Seldinger puncture needle for entry into the chest or abdomen. 6. Proceed under fluoroscopic or single-shot CT control. 7. Verify the needle tip as within the fluid collection. 8. Insert the guide wire, extract the needle. 9. Use dilators to prepare for entry of the drain (or drains). 10. Introduce drain(s). 11. Aspirate as much as possible with the syringe; send the specimen to microbiology laboratory. 12. Link the drain(s) to an external reservoir. 13. Fix drain(s) with a suture. 14. Perform control scans. 15. Keep the patient in bed for at least 6 hours. Figure 2 shows the placement of a pigtail catheter in a pericardial effusion, using a lateral approach. 93 94 4-row Scanning Interventions Biopsies Indications. Histology specimen needed from structures deep to the surface, e.g., lung, pancreas, liver, retroperitoneal lymph nodes. Patient Positioning. Supine; may be varied to prone if the safest (and shortest) path to reach the area of interest is ventral, or to sagittal for similar considerations. Topogram 3D Reconstructions MIP a No MPR No VRT No Other Fluoroscopya Fluoroscopy is recommended, especially when the patient is unable to cooperate well and the area of interest is within the basal parts of the lung or the upper abdomen. Criteria of Good Image Quality Fig. 1. Biopsy device 1. The needle in position before and after the biopsy to document the exact position. Example of Axial Scan Caveat 1. One or more follow-up scans after the conclusion of the procedure are strongly recommended in order to exclude complications (e.g., subclinical bleeding or pneumothorax). Comments Fig. 2. Example of a lung nodule biopsy in the prone position. (From Muehlstaedt et al. 2002) Before the procedure is initiated, the patient must be informed and have signed an informed consent form 24 h prior to the investigation. Further patient preparation includes a venous drip, premedication as necessary, and local anesthesia. Data on blood coagulation and the patient file must be available. Before performing the biopsy, it is strongly recommended to scan the region of interest in the planned position of the patient, usually with contrast, to include the neighboring tissues. Biopsies Scan Parameters Parameter Mode Sequential/fluoroscopy Collimation 5 mm Table feed 0 Reconstruction 5 mm Rotation time 0.5 s Scan orientation No table movement Scanner settings 120 kV, 70–150 mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium Optional Administration Volume Flow rate Scan delay Sterile table preparation: – Syringe (10 cc); needle for local anesthesia; scalpel; sterile clothing; biopsy needle [16, 18, or 20 G; length 10–16 cm (see Fig. 1)] Unsterile table preparation: – Sterile gloves (packed); spray; biopsy device; cases for the specimen to be sent to microbiology, pathology, and/or cytology (no formalin for microbiology specimen) Procedure: 1. Review the spiral data and move the table to the optimal position. 2. Mark the optimal entry point with either a pen or barium paste. 3. Give local anesthesia. 4. Make the incision. 5. Introduce the needle into the chest or abdomen. 6. Carry out further procedures under fluoroscopic or single-shot CT control. 7. Verify the needle is in the correct position and that there is enough room for the needle tip to be advanced (up to 25 mm!; see Fig. 2) 8. Adjust the biopsy device. 9. Perform the biopsy. 10. Before removing the needle, perform a control scan to document the exact position of the needle tip within the lesion! This is important, if the biopsy is negative 11. Perform the control scan. Figure 2 shows a patient with a single pulmonary nodule, biopsied in the prone position using this protocol. 95 96 4-row Scanning Interventions Sympaticolysis Indications. Advanced peripheral arteriosclerotic disease otherwise untreatable. Patient Positioning. Prone. Topogram 3D Reconstructions a MIP No MPR No VRT No Other Fluoroscopya Fluoroscopy can be used, especially when the patient is unable to cooperate well. Criteria of Good Image Quality 1. Clear visualization of the lumbar spine and the great abdominal vessels at the L3 level. Fig. 1. Region: the region of interest in the prone position Example of Axial Scan Caveat 1. Documentation of an exact positioning with a test injection with contrast medium is necessary before the injection of concentrated alcohol. Fig. 2. The injected mixture of alcohol, contrast material and local anesthesia in a patient with chronic symptomatic arteriosclerosis of the pelvis and legs Sympaticolysis Scan Parameters Parameter Mode Sequential/fluoroscopy Collimation 5 mm Table feed 0 Reconstruction 5 mm Rotation time 0.5 s Scan orientation No table movement Scanner settings 120 kV, 70–150 mAs Kernel (algorithm) Soft Window (width/center) 420/60 Contrast medium No Administration Volume Flow rate Scan delay Comments Patient must be informed and must have signed an informed consent form prior to the investigation. Further patient preparation includes a venous drip, premedication as necessary, and local anesthesia. Data on blood coagulation and the patient file must be available. Sterile table preparation: – Syringe (ml); needle for local anesthesia; sterile clothing and gloves, Fransen needle (18 or 20 G) Unsterile table preparation: – Spray; alcohol (96%); contrast material (1 ml); local anesthesia Procedure: 1. Perform and review the CT data (in prone position) and move the table to the optimal position at the level of lumbar vertebra 4. 2. Mark the optimal entry point; the optimal point of injection is ventral to the lumbar vertebra. Therefor, a lateral entry may be necessary. 3. Give local anesthesia. 4. Proceed under fluoroscopic or single-shot CT control. 5. Verify the needle position with the tip in front of the lumbar vertebra and clear of the great vessels. 6. Carry out a test injection (1 ml contrast + 1 ml local anesthesia). 7. Perform control scans. 8. Inject the therapeutic agent (8 ml 96% alcohol + 1 ml contrast + 1 ml local anesthesia) until pain occurs. 9. Perform control scans. 10. Retract the needle. 11. Keep the patient in bed for at least 4 h. 97 16-row Scanning 100 16-row Scanning Head Routine CCT Indications. Suspected infarct, bleeding, trauma (including fractures, see “Comments”), unconsciousness of unclear origin, atrophy, central neural disturbances of unclear origin, hydrocephalus. Patient Positioning. Supine, arms bilaterally downward, use of headrest recommended. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Coronal or sagittal MPRs may assist in selected cases. Criteria of Good Image Quality 1. Symmetric positioning of the patient’s head. 2. Absence of motion artifacts. Fig. 1. Region: from the base of the skull upward (exposure of lenses should be avoided by patient positioning) Caveat Example of Axial Scan 1. If patient tends to move, positioning devices should be used in addition to the headrest. Fig. 2 a, b. (Case courtesy of Dr. B. Ertl-Wagner) Routine CCT Scan Parameters Parameter Mode Spiral 1 (infratentorial) Spiral 2 (supratentorial) Collimation 0.75 mm 1.5 mm Pitch factor 0.57 0.57 Reconstruction 4 mm 8 mm Rotation time 0.75 s 0.75 s Scan orientation Caudo-cranial Caudo-cranial Scanner settings 120 kV, 260–350 eff. mAs 120 kV, 260–400 eff. mAs Kernel (algorithm) Soft (brain) Soft (brain) Window (width/center) 100/45 80/35 Contrast medium No No Administration Volume Flow rate Scan delay Comments Especially when using the 16-row scanner, helical data acquisition is very tempting and preliminary testing at our institution gave comparable results to sequential scanning quality. It remains controversial, however, whether the established sequential scans can be substituted by helical multislice CT; confirmation by controlled studies is needed. Alternatively to the above protocols with two separate spirals, one single spiral with 0.75-mm collimation can be considered. For the detection or exclusion of skull fractures, a subsequent (second) reconstruction of the raw data (especially of spiral 1) with a high-resolution bone kernel is recommended. To avoid artifacts at the skull base, the use of algorithms designed for their reduction is recommended. Figure 2 shows an investigation of a calcifying breast cancer metastasis to the brain. Indications for contrast material administration as in the 4 row protocols 101 102 16-row Scanning Head Temporal Bone and Inner Ear Indications. Posttraumatic fracture of the temporal bone, cholesteatoma and chronic otitis media, otosclerosis. Patient Positioning. Supine, arms bilaterally downward, use headrest. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No Axial acquisition and MPRs in oblique coronal and oblique sagittal (along and perpendicular to the temporal bone) are recommended. Criteria of Good Image Quality Fig. 1. Region: from upper mastoid cells to lower end of mastoid (avoid direct exposure of lenses) 1. Sufficient delineation of ossicles, tympanic cavity, and mastoid cells. 2. MPR reconstruction without stepping artifacts. Caveats Example of Axial Scan 1. Patient positioning without gantry tilt must avoid direct exposure of the lenses. 2. The temporal bone needs a separate MPR with a FOV (<9 cm) for each side. Fig. 2 a, b. (Case courtesy of Dr. B. Ertl-Wagner) Temporal Bone and Inner Ear Scan Parameters Parameter Mode Spiral Collimation 0.75 mm Pitch factor 1.0 Reconstruction 0.75 mm Rotation time 1.0 s Scan orientation Caudo-cranial Scanner settings 120 kV, 120 eff. mAsa Kernel (algorithm) Ultra-hard (inner ear) Window (width/center) 2,000/30 Contrast medium No Administration Volume Flow rate Scan delay a A further reduction of dose can be considered for children (120 kV, 70–100 mAs). Comments In our setting, the axial image data acquisition and the subsequent coronal (and sagittal) MPRs as described are replacing the image acquisition in both planes. Figure 2a (axial MPR) and 2b (coronal MPR) show reconstructions of a normal inner ear, incus-malleus articulation, and mastoid. 103 104 16-row Scanning Head CTA Intracranial Aneurysm Indications. Suspected intracranial aneurysm; thrombosis of basilar or other intracranial artery (if no angiographic correlation can be achieved); suspected occlusions; malformations; variants. Patient Positioning. Supine, arms downward, use of headrest recommended. Topogram 3D Reconstructions a Fig. 1. Region: adapted to the suspected area MIP Yesa MPR Yesa VRT Yesa Other No Both MIP and MPR as well as VRTs can be beneficial for the detection or exclusion of an aneurysm and should be routinely used as an adjunct to the axial scans. Criteria of Good Image Quality 1. High contrast of the arterial vessels. 2. No or little contrast media in the veins. Caveats Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. R. Hofmann) 1. Timing of the contrast injection is critical (a test bolus injection is recommended). 2. This protocol should follow a routine (unenhanced) CCT. CTA Intracranial Aneurysm Scan Parameters Parameter Mode Spiral Collimation 0.75 mm Pitch factor 0.57–1.25 Reconstruction 0.5–1.0 mm Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kVa, 100–200 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Administration Volume 100–120 ml Flow rate 3–4 ml/s Scan delay 35 sb a The tube voltage recommended for cerebral CTA is currently under discussion and may be reduced to even below 100 kV. b For the optimal timing of the contrast injection, a test bolus tracking technique is recommended. The timing should also take into consideration the desired scan length. With the protocol suggested here, table feed is 24–30 mm/s. Comments This protocol should follow a routine CCT protocol. Figure 2 reveals a small fusiform aneurysm in a female with complex developmental abnormalities of the cerebral vessels of the right posterior artery. 105 106 16-row Scanning Neck Routine Neck Indications. Cervical lymph nodes, lymphoma, abscesses, staging and restaging, thyroid goiter (hyperthyroidism). Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No For staging and restaging, coronal and sagittal MPR may be helpful. Image reconstruction in the axial plane is recommended. Criteria of Good Image Quality Fig. 1. Region: from the hard palate to the upper mediastinum (parallel to hard palate),or adapted to the area of interest 1. Good contrast opacification. 2. Absence of swallowing or gross motion artifacts. Example of Axial Scan Caveat 1. Dental artifacts may obscure enlarged retropharyngeal nodes. Fig. 2 a, b. (Case courtesy of Dr. W. Flatz) Routine Neck Scan Parameters Parameter Mode Spiral Collimation 1.5 mm Pitch factor 1.33 Reconstruction 5 mm Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 150 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 80–120 ml Flow rate 3 ml/s Scan delay 45 s Comments The even shorter investigation time of 16-row scanners in conjunction with the breathhold technique decreases the likelihood of movement artifacts. A flexible FOV should enlarge areas of interest (anterior portion of the neck). Thin collimation imaging decreases dental artifacts and may be necessary if the region of interest is at the same level. A carcinoma of the left hypopharynx with contact to the left supraglottic larynx is shown in Fig. 2a (axial) and 2b (coronal MPR). 107 108 16-row Scanning Neck Larynx and Hypopharynx Indications. Laryngeal fractures, laryngeal inflammation of unknown origin, benign and malignant tumors, laryngoceles. Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions MIP No MPR Yes (obligatory) VRT No Other No MPR reconstructions in the coronal and sagittal planes using soft tissue kernels are strongly recommended (for fractures, bone kernel). Fig. 1. Region: from the tip of epiglottis to the subglottic region in two spirals: breathhold and “e” phonation. The shoulders should be lowered as much as possible Criteria of Good Image Quality 1. High quality coronal reconstructions. 2. Breathhold imaging of both spirals. Caveats Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. W. Flatz) 1. The level for scanning the larynx varies with each patient; the entire larynx must be on the scan. 2. The patient must be properly instructed before the examination. Larynx and Hypopharynx Scan Parameters Parameter Mode Spiral 1 (breathhold) Spiral 2 (“e” phonation) Collimation 0.75 mm 0.75 mm Pitch factor 1.0–1.33 1.0–1.33 Reconstruction 1 mm for MPR, 3 mm 1 mm for MPR, 3 mm Rotation time 0.5 s 0.5 s Scan orientation Cranio-caudal Cranio-caudal Scanner settings 120 kV, 150–200 eff. mAs 120 kV, 150–200 eff. mAs Kernel (algorithm) Soft Soft Window (width/center) 450/60 450/60 Contrast medium Yes Administration Monophasic Volume 100 ml Flow rate 3 ml/s Scan delay 40 s Start second spiral immediately Comments Breathhold scanning is a requirement for good imaging of laryngeal carcinoma. The combination of the two spirals in breathhold and “e” phonation becomes important when infiltration of the vocal cord is suspected. For routine scanning to rule out carcinoma, breathhold maybe sufficient. MPR reconstructions are very important for understanding the anatomy (Fig. 2a,b). They are recommended in every investigation in coronal orientation. For nodal staging, add the “Routine Neck” protocol. 109 110 16-row Scanning Neck CTA Carotids Indications. Suspected stenosis, occlusion or dissection of the common or internal carotid artery or parts thereof. Patient Positioning. Supine, arms downward, remove dental prostheses, necklaces, etc. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yesa Other No Various forms of postprocessing exist. STS/ MPR are recommended, but MIP or VRT can also be used. Segmentation may be necessary in the skull base. Criteria of Good Image Quality Fig. 1. Region: from 3–4 cm above the sella turcica to the sternal notch 1. High opacification of the carotid artery, but little contrast in the jugular vein. Caveats Example of Axial Scan Fig. 2 a, b. 1. Scan and contrast timing is critical; a test bolus injection is recommended. 2. Huge scan ranges increase the radiation dosage. CTA Carotids Scan Parameters Parameter Mode Spiral Collimation a 0.75 mm Pitch factor 1.0 Reconstruction 3 mm; 1 mm for 3D reconstructions Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 120–200 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 100–120 ml Flow rate 3 ml/s Scan delay 12–15 sa A test bolus of the aortic arch is recommended for the exact timing of the injection (+ 3 s).The best reconstruction quality will be attained when the artery has a maximum contrast opacification,and the jugular vein the minimum. Comments For a quick overview, VRT reconstructions seem to be very efficient. If no MPR reconstruction is planned, the reconstruction increment can be as high as 5 mm. When MPRs are planned, the reconstruction slice width should be reduced to 1 mm, increment 0.5 mm. Figure 2a shows an MPR and a VRT reconstruction in a young female to rule out carotid occlusion after a chiropractic maneuver. 111 112 16-row Scanning Chest Routine Chest Indications. Mediastinal and axillary lymph nodes; tumors of the anterior, medial, and posterior mediastinum; staging. Patient Positioning. Supine position, arm(s) elevated over the head. Topogram 3D Reconstructions MIP No MPR Yes VRT No Other No The chest routine program is not optimized for the secondary reconstructions of either lung or mediastinum. However, if MPR reconstructions are desired, a thin reconstruction increment is important. Fig. 1. Region: from the lung apices to below the diaphragm (in bronchial carcinoma including the adrenals) Criteria of Good Image Quality 1. Breathhold acquisition. Caveat 1. For screening of lung nodules or inflammatory changes only, the low-dose protocol should be used (see “Comments”). Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. R. Eibel) Routine Chest Scan Parameters Parameter Mode Spiral Collimation 1.5 mm Pitch factor 1.25–1.5 Reconstruction 6 mm Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 100–150 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 and 1,500/600 Contrast medium Yes Administration Monophasic Volume 80 ml Flow rate 3 ml/s Scan delay 30 s Comments This is meant to serve as a routine protocol. The reconstructions should be cranio-caudal. Detection of an intrapulmonary scar in ruling out primary bronchogenic carcinoma in the right upper lobe is the subject of Fig. 2. 113 114 16-row Scanning Chest Pulmonary Embolism Indications. Detection or exclusion of suspected pulmonary embolism, evaluation of atypical chest pain. Patient Positioning. Supine, arms elevated above the head. Topogram 3D Reconstructions MIP a Yesa MPR Yesa VRT No Other No Coronal and axial MIP or MPR reconstructions are used to detect embolism in subtle cases. Criteria of Good Image Quality Fig. 1. Region: from above the aortic arch with concentration on the central hilar portion 1. Sufficient contrast in the pulmonary arteries. 2. Absence of motion artifacts. Caveat 1. The high flow of contrast material injected may cause artifacts from the superior vena cava. Example of Axial Scan Fig. 2 a, b. (Cases courtesy of Dr. R. Eibel) Pulmonary Embolism Scan Parameters Parameter Mode Spiral Collimation a 0.75 mm Pitch factor 1.25–1.5 Reconstruction 5 mm; 1 mm for 3D reconstructions Rotation time 0.5 s Scan orientation Caudo-cranial Scanner settings 120 kV, 100–150 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 120ml Flow rate 4 ml/s Scan delay 16 sa The delay should be determined by a test bolus injection or bolus tracking (pulmonary artery). Comments The protocol can be used to exclude or to detect pulmonary embolism. The MPR can help in viewing the full extent of the thrombotic material. Using MSCT, the source of embolization (as for example in the right heart) can also be visualized. Figure 2a reveals a small embolus in the paracardial segment of the right lung; Fig. 2b shows a normal MPR. 115 116 16-row Scanning Chest CTA Aortic Arch Indications. Detection or exclusion of aortic aneurysms, bleeding, dissection, or thrombosis of the ascending aorta, arch, and descending aorta. Patient Positioning. Supine, arms elevated over the head, ECG gating on. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yesa Other No Reconstructions using either technique helps in viewing the vessel lumen itself and the relationship to neighboring structures. Criteria of Good Image Quality Fig. 1. Region: from above the lung apices to below the diaphragm (or lower tip of aneurysm). Put ECG pads on! 1. High contrast of the arterial vessels. 2. Little or no contrast media in the veins. 3. Good quality secondary reconstructions. Caveat Example of Axial Scan 1. Timing of the contrast injection is critical and should be determined by bolus tracking or a test bolus. Fig. 2 a, b. (Case reconstructions by Dr. Loke Gie Haw) CTA Aortic Arch Scan Parameters Parameter Mode Spiral a Collimation 1.5 mm Pitch factor 0.28–0.32 (ECG-gating) Reconstruction 3–6 mm; 2 mm for 3D reconstructions Rotation time 0.42–0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 200–250 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3–5 ml/s Scan delay 15 sa If an alteration of the circulation time is suspected, the use of a bolus tracking technique or a test bolus (+ 5 s) is recommended. Comments ECG gating is recommended to reduce pulsation artifacts. A detail of the region of the origin of the vertebral arteries is given in Fig. 2a (hypoplastic, but not stenotic vertebral artery on the right). Figure 2b demonstrates the possibility of reconstructing details such as the brachial artery. 117 118 16-row Scanning Heart Coronary Artery Screening Indications. Suspected coronary artery disease. Symptomatic patients, atypical chest pain; asymptomatic patients, risk stratification. Patient Positioning. Supine, arms elevated, ECG gating on. Topogram 3D Reconstructions MIP a Fig. 1. Region: from above the tracheal bifurcation to the diaphragm No MPR No VRT No Other a Calcifications are postprocessed to determine the Agatston score, or a volume or mass score. Elevated values of these scores are known to correlate with an increased risk of coronary artery disease. Criteria of Good Image Quality Example of Axial Scan 1. Motion-free visualization of the coronaries and the coronary calcifications. 2. Focused FOV. Caveats 1. Variation of the trigger delay may be necessary. 2. Automated programs for deriving scores need supervision. 3. The lung window should also be read. 4. Heart rates less than 70 beats per minute are optimal (see comments). Fig. 2. (Case courtesy of Dr. C. Becker) Coronary Artery Screening Scan Parameters Parameter Mode Spiral Collimation 1.5 mm Pitch factor 0.28–0.32 Reconstruction 3 mm Rotation time 0.42 sa Scan orientation Cranio-caudal Scanner settings 120 kV, 133 eff. mAs Kernel (algorithm) Cardiac Window (width/center) 450/60 Contrast medium No Administration Volume Flow rate Scan delay a This is to be ECG-gated. Comments ECG gating and coverage of the entire heart is necessary in order to derive sufficient image quality and score reproducibility. Set the trigger to 40–70% (default 60%) of the ECG R duration. Instead of spiral acquisition, sequential scanning is also possible (120 kV, 30 mAs, rotation time 0.42 s, 1.5 mm per slice). If the heart beat exceeds 70 beats/min, oral premedication using a beta blocker may be considered. For direct visualization of the lumen of the coronary arteries, please add the “Coronary Artery Screening” protocol. For the interpretation of the coronary artery scores, please refer to the third table in the “Coronary Artery Screening” protocol (page 49) as well as to the literature cited therein. An example of subtle calcifications in the LAD is given in Fig. 2. 119 120 16-row Scanning Heart CTA Coronary Arteries Indications. Suspected coronary artery disease. Patient Positioning. Supine, arms elevated, ECG gating on. Topogram 3D Reconstructions a Fig. 1. Region: from above the tracheal bifurcation to the diaphragm MIP Yesa MPR No VRT No Other Yesa Oblique (45°, parallel to main stem) STS MIPs are recommended (3 mm slice thickness, 1.5 mm increment) for the visualization of the main stem, as well as LAD and RCA projections. Criteria of Good Image Quality 1. Absence of motion artifacts. 2. High contrast in coronary arteries. Example of Axial Scan Caveats 1. A test bolus should be used. 2. All parts of the arteries must be opacified (proximal, mid, and distal). Fig. 2 a, b. (Case courtesy of Dr. C. Becker) CTA Coronary Arteries Scan Parameters Parameter Mode Spiral Collimation 0.75 mm Pitch factor 0.28–0.32 Reconstruction 1 mmd Rotation time 0.42 sa Scan orientation Cranio-caudal Scanner settings 120 kV, >400 eff. mAs Kernel (algorithm) Cardiac Window (width/center) 450/60 Contrast medium Yes Administration Biphasicb Volume 40 ml 80 ml Flow rate 4 ml/s 2 ml/s Scan delay c 10 s later a ECG gated. b Adapted from C. Becker (unpublished data). c To be determined by test bolus or bolus tracking. d Reconstruction slice width 0.75 mm should be restricted to detail diagnosis of stents or severely calcified coronary arteries. Comments ECG gating and coverage of the entire heart is necessary for sufficient image quality. Set the trigger to 60% of ECG R duration. Individual patient optimization may be required, which is best achieved by a series of test images with different phase settings at the level of mid-RCA. The LAD and RCA may require separate optimizations of the reconstruction phase. Using this protocol, heart rates of less than 70 beats per minute are optimal. If the rate exceeds 70 beats/min, oral premedication using beta blockers should be considered. The quality that may be achieved with this technique is illustrated in Fig. 2a, where highcontrast opacification and motion-free visualization of the LAD is shown. The quality of STS MIPs may be appreciated in Fig. 2b. 121 122 16-row Scanning Abdomen Routine Abdomen Indications. Screening, detection or exclusion of abscesses, control scans, follow-ups. Patient Positioning. Supine, arms elevated above the head. Topogram 3D Reconstructions MIP Yes MPR Yes VRT No Other No Criteria of Good Image Quality 1. Absence of gross motion artifacts. 2. Good contrast opacification of arteries and veins. including the portal system. Caveat Fig. 1. Region: from above the diaphragm to the symphysis pubis Example of Axial Scan Fig. 2 a, b. (Case courtesy of Dr. A. Wieser) 1. For the detection or exclusion of venous thrombosis, vary the injection time. Routine Abdomen Scan Parameters Parameter Mode Spiral Collimation 1.5 mm Pitch factor 1.0–1.5 Reconstruction 5–6 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 140–165 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium i. v. + oral + rectala Administration i.v., monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 25–80 sb a Oral contrast for the optimal distention of the stomach should be given immediately before, and for the bowel up to 2 h (with 900 ml) before scanning.Water or methylcellulose should be rectally administered immediately before scanning. b Depending on the desired contrast, the scan delay may be varied from 25 s for portal venous contrast to over 80 s for systemic venous contrast. Comments To reduce radiation, especially in young patients, the tube currents should be adapted to the habitus and can be reduced to 120 mAs. The patient should do deep breathing before beginning the spiral. Liver metastases the left liver segments are shown in Fig. 2a; at the same time Fig. 2b, using appropriate sagittal reconstructions, reveals sclerotic plaques of the abdominal aorta. 123 124 16-row Scanning Abdomen CTA Abdomen Indications. To quantify or to exclude aneurysms of the aorta, to measure the diseased portions of the abdominal aorta before minimally invasive or open intervention, to detect or exclude aortic rupture or retroperitoneal bleeding. Patient Positioning. Supine, arm elevated over the head. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yesa Other No All of the reconstructions help to visualize the three-dimensional extent and should be used in addition to the axial data. Criteria of Good Image Quality 1. High contrast in the abdominal aorta throughout the scan. 2. Little contrast in the parenchymal organs and no or negative contrast in the bowel. Fig. 1. Region: adapted to the area of interest Caveat Example of Axial Scan Fig. 2 a, b. 1. Axial images and reconstructions must visualize aortic branches such as the renal arteries and superior mesenteric artery. CTA Abdomen Scan Parameters Parameter Mode Spiral a Collimation 0.75 mm Pitch factor 1.00–1.25 Reconstruction 5 mm; for 3D reconstructions 0.75–1.0 mm Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 130–200 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 120 ml Flow rate 3 ml/s Scan delay 18 sa In patients with possible alteration of the circulation time, a bolus tracking technique or a test bolus application (+ 8 s) is recommended so as to achieve optimal contrast in the spiral acquisition. Comments This protocol can be adapted to an extended coverage to include neck, chest, and abdomen (using a collimation of 1.5 mm with a pitch factor of >1). Figure 2 shows an infrarenal aortic aneurysm (reconstruction of the aneurysm in VRT by Dr. Loke Gie Haw). 125 126 16-row Scanning Spine Spine Indications. Suspected disk protrusion or herniation; suspected fractures, spondylolisthesis; unclear findings such as from a post-myelogram CT; MRI contraindications. Patient Positioning. Supine, arms downward for cervical spine, arms elevated for thoracic and lumbar spine. Topogram 3D Reconstructions a MIP No MPR Yesa VRT No Other No We recommend using MPRs in an angulated fashion regularly in the manner of Fig. 1. Using the thin axial raw data, the slices angulated in this way yield low noise and superior detail. Criteria of Good Image Quality 1. Zoomed images (FOV about 90 mm). 2. Angulation parallel to the disks. Caveat 1. The axial scan must cover the entire volume while the reconstructions are angulated to the individual disk level. Fig. 1 a, b. Region: adapted to the area of interest. Depending on the region, Fig. 1a for scanning protocol, Fig. 1b for reconstructions Spine Scan Parameters Parameter Mode Spiral Collimation 0.75 mm Pitch factor 0.50–0.75 Reconstruction Angulated axial and sagittal slices 3 mm thick, 1.5 mm increment Rotation time 0.75 s Scan orientation Cranio-caudal Scanner settings 120 kV, 330 eff. mAs Kernel (algorithm) Soft; if fracture, bone kernel Window (width/center) 450/60; 2,000/300 or adapteda Contrast medium No Administration Volume Flow rate Scan delay a After a myelographic intralumbar injection of contrast material a window of 1200/400 is recommended. Comments The combination of angulated axial and sagittal MPR reconstructions is most advantageous. This way an angulation of the gantry is not necessary for any spinal investigation. The MPR reconstructions can be routinely used and viewed instead of the axial cuts. Figure 2 shows findings in a young man with anterior listhesis on L4–L5 and consecutive disk protrusion in the lumbar spine at the level L4–L5. Example of Axial Scan Fig. 2 a, b. (Case by Dr. A. Wieser) 127 128 16-row Scanning Peripherals Peripheral CTA Indications. Peripheral stenotic or occluding artery disease. Patient Positioning. Supine, arms downward. Topogram 3D Reconstructions a MIP Yesa MPR Yesa VRT Yesa Other No All reconstruction methods can be used (VRT is shown in Fig. 2 b). Criteria of Good Image Quality 1. High contrast opacification of the arterial run-off vessels throughout the scan range. Caveat 1. A stenotic process on only one side may be a problem in the contrast material timing. 2. Spatial resolution has to be sufficient. Fig. 1. Region: from the renal arteries or pelvis down to the ankle Example of Axial Scan Fig. 2 a, b. Peripheral CTA Scan Parameters Parameter Mode Spiral Collimation a 1.5 mm Pitch factor 1.25–1.50 Reconstruction 6.0 mm; 2 mm for 3D reconstruction Rotation time 0.5 s Scan orientation Cranio-caudal Scanner settings 120 kV, 130–150 eff. mAs Kernel (algorithm) Soft Window (width/center) 450/60 Contrast medium Yes Administration Monophasic Volume 150 ml Flow rate 3 ml/s Scan delay 25–30 sa A bolus tracking technique or test bolus injection (+ 16 s) is recommended. Comments Depending on the scan range, the collimation can be varied; the collimation in conjunction with the pitch factor offers increased table feed. Thin overlapping reconstructions maintain the quality of the 3D reconstructions. An arteriosclerotic portion of the abdominal aorta and pelvic arteries are shown in Fig. 2a. Please note that the calcified plaques can also be viewed on the VRTs (as in Fig. 2b). 129 131 References Bruening R, Muehlstaedt M, Knez A, et al (2002) Computed tomography – fluoroscopy guided drainage of pericardial effusions. Invest Radiol 37:328–332 Eibel R, Bruening R, Schoepf UJ, et al (1999) Image analysis in multislice spiral CT of the lung with MPR and MIP reconstructions. Radiologe 39:952–957 Haberl R, Becker A, Leber A, Knez A, Becker C, Lang C, Brüning R, Reiser M, Steinbeck G (2001) Correlation of coronary calcification and angiographically documented stenoses in patients with suspected coronary artery disease: results of 1,764 patients. J Am Coll Cardiol 37:451–457 Janowitz WR, Agatston AS, Viamonte M Jr (1991) Comparison of serial quantitative evaluation of calcified coronary artery plaque by ultra-fast computed tomography in persons with and without obstructive coronary artery disease. Am J Cardiol 68:1–6 Knez A, Becker C, Becker A, Leber A, White C, Reiser M, Steinbeck G (2002) Determination of coronary calcium with multi-slice spiral computed tomography: a comparative study with electron-beam CT. Int J Cardiovasc Imaging 18:295–303 Kopp AF, Ohnesorge B, Becker C, Schröder S, Heuschmid M, Küttner A, Kuzo R, Claussen CD (2002) Reproducibility and accuracy of coronary calcium measurements with multi-detector row versus electron-beam CT. Radiology 225:113–119 Kulinna C, Scheidler J, Bruening R, et al (2001) MDCT of the rectum. In: Reiser M, Modic M, Takahashi M, Bruening R (eds) Multislice CT. Springer, Berlin Heidelberg New York, pp 61–68 Muehlstaedt M, Bruening R, Diebold J, et al (2002) CT/fluoroscopy-guided transthoracic needle biopsy: sensitivity and complication rate in 98 procedures. J Comput Assist Tomogr 26:191–196 Mueller-Lisse UL, Oberneder, R (2001) Multidetector CT of the kidney. In: Reiser M, Modic M, Takahashi M, Bruening R (eds) Multislice CT. Springer, Berlin Heidelberg New York, pp 23–34 Rumberger JA, Brundage BH, Rader DJ, Kondos G (1999) Electron beam computed tomographic coronary calcium scanning: a review and guidelines for use in asymptomatic persons. Mayo Clin Proceed 74:243–252 Schoepf UJ, Becker CR, Bruening RD, et al (1999) Electrocardiographically gated thin-section CT of the lung. Radiology 212:649–654
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