Beth Israel Deaconess Medical center Harvard Medical School PART I. Technical Advances of Fluoroscopy with Special Interests in Automatic Dose Rate Control (ADRC) Logic of Cardiovascular Angiography Systems Pei-Jan Paul Lin Department of Radiology Beth Israel Deaconess Medical Center and Harvard Medical School Boston, MA 02215 Review of Fluoroscopy Equipment 1) Conventional Fluoroscopy Unit 2) Special Procedures Fluoroscopy Unit a) Extension of conventional fluoroscopy. b) Pedestal Type examination table fluoroscopy and over-head hanger synchronized lateral plane. 3) Fluoroscopy Systems with Positioners for a) b) c) d) Cardiac Catheterization. Neuro Angiography. Visceral Angiography. Electrophysiology Laboratory. Review of Basic Automatic Brightness Controlled Fluoroscopy Systems. And Some historical overview. The “Legacy” Fluoroscopy 1) Compartment for full size cassettes, 2) Either Conventional or Pedestal type examination table, 3) Image Intensifier, a) Input Phosphor, and Output Phosphor. b) Image intensifier is an Electron Optical Device. c) Optical Distributor mounted on I.I. to accommodate Cameras, i.e.; • Photospot (photofluorographic) Camera, • Cine (cinematographic) Camera, and • Closed Circuit Television Camera TV Camera TV Camera 100 mm Photo Spot Camera Optical Distributer Image Intensifier Tower 35 mm Cine Camera Optical Distributer 100 mm Photo Spot Camera Image Intensifier Image Intensifier Cassette Compartment Four way floating tabletop / Stepping capable Four way motorized tabletop 15/90 Tilting Examination Table Typical Upper and Lower GI Fluoroscopy Equipment . C-arm connection Examination Pedestal X-ray Tube Assembly 1 Up to this point may be considered “Legacy Fluoroscopy” Equipment. • Irrespective of the geometrical configuration, the fluoroscopy is equipped with “Automatic Brightness Control” (ABC) circuit. • The TV chain is equipped with “Automatic Gain Control” (AGC). • The primary imaging parameter may be “tube potential”, “tube current”, or “pulse width” for pulsed fluoroscopy. Mechanical Structure for Mounting on the C-Arm Flat Panel Image Detector Four way floating tabletop / Stepping capable C-arm connection Examination Pedestal X-ray Tube Assembly Internal Structure of Image Intensifier Input Phosphor (-) Input Phosphor Output Phosphor Thin Aluminum Layer Fluorescent Screen Aluminum Substrate Fluorescent Screen Photocathode Output Phosphor X-ray Photons Electrons Electrons Light Photons Electron Flux Anode (+) Electrode (Focusing) Image Intensifier Tube Total Brightness Gain of Image Intensified Fluorocopy System “Gains” of Image Intensifier Brightness Gain = Intensifier Luminance Patterson B-2 Luminance Luminance (cd/m2) Conversion Factor = Radiation Input (mR/sec) Minification Gain = Input Phosphor Output Phosphor (a) Fluorescent screens are made of Cesium Iodide (CsI) which has a higher absorption of X-rays than the older silver-activated zinccadmium sulfide. (b) Photocathode is a photoemissive metal; a combination of antimony and cesium. 2 Flux Gain: Electrons are accelerated (~30kV) Typical flux gain values; 50~60 For a 9” mode image intensifier with 1” output phosphor, the minification gain is (9/1)X(9/1)=81. The Flux gain is approximately ~50. Therefore, the total brightness gain is = 81 X 50 = 4050. 2 GE Detector Design • The flat panel image detector technology as a whole (at a minimum) will have to; (1) have a similar electronic gain in order to maintain the input sensitivity enjoyed by the image intensifier television chain, (2) hence, a comparable input sensitivity to maintain the same patient exposure. Contact Leads For Read-Out Electronics Contact Fingers Glass Substrate Scintillator (CsI) Opticlad Reflector Amorphous Silicon Array Graphite Cover Scintillator Epoxy Seal aSi Array Glass Substrate Courtesy of General Electric Heath Care Systems, Inc. Basic GE Detector Physics Basic GE Detector Physics X-Ray Photons X-Ray Photons Cesium Iodide (CsI) X-ray absorption Cesium Iodide (CsI) Light Light emission Amorphous Silicon Panel (Photodiode/Transistor Array) Electrons Read Out Electronics Light absorption Electron-hole generation Conversion to digital signal Digital Data IQ, fast readout, low noise, no significant image retention Courtesy of General Electric Health Care Systems, Inc. Automatic Brightness Control • There are there primary imaging parameters that may be employed to drive the ABC circuit, namely; 1) The tube potential “kVp”, 2) The tube current “mA”, or 3) The exposure time, more accurately; “pulse width” for a pulsed fluoroscopy system. DETECTOR DETECTOR Light Amorphous Silicon Panel (Photodiode/Transistor Array) Electrons Read Out Electronics Cesium iodide scintillator absorbs X-Ray photons and converts them to light Low-noise photodiode array absorbs light and converts it into an electronic charge... Each photodiode represents a pixel or picture element... Charge at each pixel is read out by low- noise electronics and turned into digital data sent to an image processor Digital Data IQ, fast readout, low noise, no significant image retention Courtesy of General Electric Health Care Systems, Inc. • System (3), “Exposure Time system” is similar to the radiographic automatic exposure control (AEC), it “phototimes” each fluorscopic pulse. • Usually, the tube potential and tube current are manually selected. • This method of brightness control has long been retired, and will not be discussed further. 3 TV Camera Let us go through the operation logic of a “kVp-primary” fluoroscopic ABC, as the one shown here in this slide. (a) Suppose, the x-ray tube potential and current are adjusted properly for a given steady situation. Optical Distributer TV Camera Amplifier Video Amplifier Optical Sensor kVp-primary ABC Circuit Image Intensifier Photomultiplier Amplifier TV Monitor Reference Voltage r e m a C V T S o ln -p P m a C V rT ie d g f iT ra nie lf p m A o d rV i ts n e g a Im ire fa ,O s .S u h P c n rfiR p m ltC o V e g m A o tM V T G a u -iA k c tlL n C ry o m e Automatic Gain Control Voltage Comparator Lock-in Memory "kVp" Control Module "mA" Control Module X-ray Tube Characteristic Table Generator Characteristic Table Generator Power Train X-ray Tube Adapted from Reference #1 Optical Distributer TV Camera Amplifier Video Amplifier Optical Sensor Image Intensifier Photomultiplier Amplifier (d) The “mA-control module” receives a signal from the “kVp-control Module”, and will increase the tube current in accordance to a preprogrammed value based on the “fluoroscopy loading curve”. (e) As the x-ray tube current rises, the required increase in tube potential is reduced to perhaps 5 kVp, rather than 10 kVp. TV Camera TV Camera (b) Assume that a patient has swallowed a large amount of barium meal. Therefore, a sudden increase in x-ray absorption had occurred. (c) The voltage comparator detects that a decrease in voltage from the photomultiplier amplifier. A signal is sent to the “kVp-control Module” to increase the tube potential by 10 kVp. [If the current remained the same.] r e m a C V T fig d S o ln -p P m a C V rT e fie ln p m A o d rV T a i ts n e g a Im fticra e A m ,O s .S u h P n R p lC o V g n V T G a u -iA k c tlL C ry o m e M Automatic Gain Control TV Camera Amplifier Video Amplifier Optical Sensor TV Monitor Reference Voltage Optical Distributer Image Intensifier Photomultiplier Amplifier TV Monitor Reference Voltage r e m a C V T S o ln -p P m a C V rT ie d g f T in ra lf p m A o d V e tsi n e g a Im s,O .S u h cP n rfiR p m C lta o V e g A o tM V T G a u ck-iA lL n ryC m e Automatic Gain Control Voltage Comparator Lock-in Memory Voltage Comparator Lock-in Memory "kVp" Control Module "mA" Control Module "kVp" Control Module "mA" Control Module X-ray Tube Characteristic Table X-ray Tube Characteristic Table Generator Characteristic Table Generator Characteristic Table Generator Power Train X-ray Tube Generator Power Train X-ray Tube Adapted from Reference #1 Optical Distributer TV Camera Amplifier Video Amplifier Optical Sensor Image Intensifier X-ray Tube Photomultiplier Amplifier (h) During this transition time, the TV monitor image brightness is maintained to a constant by the Automatic Gain Control in the video chain. The reaction time of the AGC is approximately 40~60 mSec. This short reaction time of the AGC circuit essentially ensures a constant brightness level is presented to the human eyes. TV Camera TV Camera (f) A newly established steady state is then presented to the output phosphor of the image intensifier with a constant brightness again. (g) This whole process may take somewhere around 1 to 2 seconds. Adapted from Reference #1 r e m a C V T fig d S o ln -p P m a C V rT e fie ln p m A o d rV T a i ts n e g a Im fticra e A m ,O s .S u h P n R p lC o V g n V T G a u -iA k c tlL C ry o m e M Automatic Gain Control TV Camera Amplifier Video Amplifier Optical Sensor TV Monitor Reference Voltage Optical Distributer Image Intensifier Photomultiplier Amplifier TV Monitor Reference Voltage r e m a C V T S o ln -p P m a C V rT ie d g f T in ra lf p m A o d V e tsi n e g a Im s,O .S u h cP n rfiR p m C lta o V e g A o tM V T G a u ck-iA lL n ryC m e Automatic Gain Control Voltage Comparator Lock-in Memory Voltage Comparator Lock-in Memory "kVp" Control Module "mA" Control Module "kVp" Control Module "mA" Control Module X-ray Tube Characteristic Table X-ray Tube Characteristic Table Generator Characteristic Table Generator Characteristic Table Generator Power Train X-ray Tube Adapted from Reference #1 Generator Power Train Adapted from Reference #1 4 TV Camera Let us go through the operation logic of a “mA-primary” fluoroscopic ABC, as the one shown here in this slide. (a) Suppose, the x-ray tube potential and current are adjusted properly for a given steady situation. Optical Distributer TV Camera Amplifier Video Amplifier Optical Sensor mA-primary ABC Circuit Image Intensifier Photomultiplier Amplifier TV Monitor Reference Voltage r e m a C V T S o ln -p P m a C V rT ie d g f T in ra lf p m A o d V e tsi n e g a Im s,O .S u h cP n rfiR p m C lta o V e g A o tM V T G a u ck-iA lL n ryC m e Automatic Gain Control Voltage Comparator Lock-in Memory "mA" Control Module "kVp" Control Module X-ray Tube Characteristic Table Generator Characteristic Table Generator Power Train X-ray Tube Adapted from Reference #1 Irrespective of the image receptor system, i.e., whether the image receptor is an image intensifier or a flat panel image detector, the subject of discussion does not change. The primary theme of this presentation is on the Automatic Brightness Control, or the updated version, called Automatic Dose Rate Control (ADRC) Logic which is available and installed on either of these image receptors. Optical Distributer TV Camera 100 mm Photo Spot Camera 35 mm Cine Camera Image Intensifier Flat Panel Detector Ionization Chamber #2 Ionization Chamber #2 PMMA Phantom PMMA Phantom 38 cm 38 cm Ionization Chamber #1 2.07 in Ionization Chamber #1 2.07 in Examination Tabletop Examination Tabletop SID= 110 cm SID= 110 cm X-ray Tube Assembly X-ray Tube Assembly TV Camera Evaluation of the characteristics of an ABC controlled “legacy” fluoroscopy system. Fluoroscopic Parameters (Normal Level) Optical Distributer 38 cm Ionization Chamber #2 PMMA Phantom Or, Copper Sheets Ionization Chamber #1 3.97 in Examination Tabletop SID= 110 cm X-ray Tube Assembly The phantom material may have been (1) aluminum, (2) copper, and (3) PMMA Plastic. Pressed wood had also been Employed without consistent results. The accuracy of the fluoroscopic “kVp” & “mA” should be assessed with appropriate measurement devices so that the “power Loading” can be correctly calculated. 110 Tube Potential (kVp) 1.31 in Image Intensifier The geometry of experimental arrangement Is not critical as long as “clinical” situation Is simulated. 3.5 120 3.0 Tube Potential 100 2.5 Tube Current 90 2.0 80 1.5 70 Tube Current (mA) • A few slides ago, it was mentioned that the “mA-control module” receives a signal from the “kVp-control Module”, and will increase the tube current in accordance to a preprogrammed value based on the “fluoroscopy loading curve”. • The fluoroscopy loading curve is at the heart of the ABC, and verification and/or evaluation of fluoroscopy ABC logic can be obtained through a simple experimental setup. 1.0 60 0.5 50 40 0.0 0 1 2 3 4 5 6 7 8 9 10 11 Nominal PMMA Phantom Thickness (inches) 5 These two fluoroscopy loading curves can be compared to verify the system operation against the manufacturer supplied Technical Data Sheets. Power Loading Rate 350 Fluoroscopy Loading Curves 3.5 Power Loading Fluoroscopy Curve, Normal Level 3.0 250 Fluoroscopy Curve, High Level Tube Current (mA) Power Loading Rate (W/sec) 300 200 150 100 50 2.5 2.0 1.5 1.0 0.5 0.0 0 0 2 4 6 8 10 12 40 50 Nominal PMMA Phantom Thickness (inches) The image intensifier input exposure rate (air kerma rate) beyond the 10” phantom thickness will starts to fall down due to the ABC Logic that limits generator to 110 kVp/3.0 mA Patient Entrance Exposure Rate 130 7 Image Intensifier Input Exposure Rate 120 6 110 5 100 4 90 3 80 2 70 1 60 0 50 0 • 2 4 6 8 Nominal PMMA Phantom Thickness (inches) Image Intensifier Input Exposure Rate (μ R/sec) Patienn Entrance Exposure Rate (R/min) 140 8 70 80 90 Tube Potential (kVp) 120 10 TV Camera The Philips Eleva System evaluated in this study was equipped with the following features; Evaluation of the characteristics of an ABC controlled “legacy” fluoroscopy system. Optical Distributer a) 17/25/31 cm active phosphor sizes. (3) Image Intensifier 2) Fluoroscopy Operation: 1.31 in a) Continuous Fluoroscopy Mode. (2) b) Pulsed Fluoroscopy Mode. (2) c) Low Dose Level & High Dose Level Modes. (2) 38 cm 3) Anti-scatter Grid may be removed.(2) • 110 • Let us conduct the same test on a typical “Upper/Lower GI” Study fluoroscopy system (Philips Eleva System). • With Phantom Materials of; Copper and Aluminum. • Compare the data to find out what thickness aluminum is equivalent to what thickness of copper. The geometry of experimental arrangement Is not critical as long as “clinical” situation Is simulated. 1) Image Intensifier Format: Tri mode I.I. The permutation of available modes under fluoroscopic operation configuration ~ 48 Not all available modes of combination were evaluated. Ionization Chamber #2 PMMA Phantom Or, Copper Sheets Ionization Chamber #1 Examination Tabletop 3.97 in • 100 PART II. Evaluation of ABC Logic Exposure Rate vs. PMMA Phantom Thickness 9 60 SID= 110 cm The phantom material may have been (1) aluminum, (2) copper, and (3) PMMA Plastic. Pressed wood had also been Employed without consistent results. The accuracy of the fluoroscopic “kVp” & “mA” should be assessed with appropriate measurement devices so that the “power Loading” can be correctly calculated. X-ray Tube Assembly 6 These graphs show that (1) the “Low Level” modes employ lower “kVp” than the “Normal Level” modes. And, the larger the active phosphor size employs lower “kVp” than smaller active phosphor sizes, (2) at the same time the larger active phosphor size with “Lower Level” fluoroscopy has a wider dynamic range in coverring the patient (phantom) thickness. The x-ray current graphs show similar trends as that of the previous slide on “kVp”. Tube Currentl vs. Phantom Thickness 4.0 Tube Potential vs. Phantom Thickness 120 T u b e C u r r en t (m A ) T ube P otential (k V p) 110 100 90 80 17 cm Mode, (N) 25 cm Mode, (N) 31 cm Mode, (N) 17 cm Mode, (L) 25 cm Mode, (L) 31 cm Mode, (L) 70 60 50 3.0 2.0 17 cm Mode, mA (N) 25 cm Mode, mA (N) 31 cm Mode, mA (N) 17 cm Mode, mA (L) 25 cm Mode, mA (L) 31 cm Mode, mA (L) 1.0 0.0 0 40 0 2 4 6 8 10 12 14 2 4 6 8 10 12 14 16 Nominal PMMA Phantom Thickness (inches) 16 Nominal PMMA Phantom Thickness (inches) Low level IIIAKR is approximately 0.7~0.75 μGy/sec, and the Normal level IIIAKR is 1.1 μGy/sec for the 31 cm active phosphor size, and 1.25 microGy/sec, and 1.35 μGy/sec for the 25 cm and 17 cm active phosphor sizes, respectively. Image Intensifier Input Air Kerma Rate vs. Phantom Thickness With Anti-scatter "Grid-".in 3.0 Air Kerma Rate 80 2.0 cm Mode, cm Mode, cm Mode, cm Mode, cm Mode, cm Mode, (N) (N) (N) (L) (L) (L) 70 17 25 31 17 25 31 60 Air Kerma Rate (mGy/min) 17 25 31 17 25 31 2.5 (μGy/sec) Image Intensifier Input Air Kerma Rate The “Air Kerma Rate” graphs show and confirm the same trends described in previous slides. Essentially, this fluoroscopy system is able to penetrate 10” to 14” of PMMA equivalent patient thickness depending on the mode of operation. This is typical of fluoroscopy systems employed for upper/lower GI studies. 1.5 1.0 0.5 0.0 50 40 cm Mode cm Mode cm Mode cm Mode cm Mode cm Mode (N) (N) (N) (L) (L) (L) 30 20 10 0 0 2 4 6 8 10 12 14 16 0 Nominal Phantom Thickness (inches) 2 4 6 8 10 12 Nominal Phantom Thickness (inches) 14 16 Fluoroscopy Loading Curve Phantom Thickness Equivalence 4.0 100 3.5 Air Kerma Rate (mGy/min) 3.0 Tube Current (mA) 90 Aluminum Phantom Copper Phantom PMMA Phantom 2.5 2.0 1.5 Aluminum Copper PMMA 80 70 60 50 40 30 20 10 1.0 0 0 0.5 10 20 30 40 50 60 70 80 Phantom Thickness (mm for Al, X0.1 mm for Cu, "inches" divide by 6 for PMMA) 90 0.0 40 50 60 70 80 90 Tube Potential (kVp) 100 110 120 7 “mA-primary” ABC Logic Aluminum (mm) Aluminum (inches) PMMA (inches) 3.67 [3-3/4] 5-1/2 10 0.8 19 3/4 20 1.6 38 1-1/2 40 3.2 80 58 5.6 76 3 • A GE Advantx fluoroscopy system is equipped with the “mA-primary” ABC Logic. • The tube potential may be pre-selected, and defaulted to 75 kVp for fluoroscopy operation. This is the minimum “kVp” unless the “kVp” is manually selected at a lower value. • The tube potential is increased by a preset value (5, or 10 kVp) when the Patient Air Kerma Rate approaches the regulatory limitation. • The system is calibrated to work at a given “kVp” while the “mA” is varied in accordance to the attenuation the optical sensor “sees”. TV Camera Amplifier Video Amplifier Optical Sensor Photomultiplier Amplifier Image Intensifier 7.3 [7-1/2] 9.3 [9-1/2] 2-1/4 Optical Distributer TV Monitor Reference Voltage Automatic Gain Control Voltage Comparator Lock-in Memory "mA" Control Module "kVp" Control Module X-ray Tube Characteristic Table Generator Characteristic Table Generator Power Train X-ray Tube The same set of data obtained on the Philips System is also obtained. This slide shows the Tube Potential and Tube Current as functions of the PMMA Phantom Thickness. NOTE: the default “kVp” values for the 60 kVp, and the 75 kVp are represented here. Fluoroscopic Parameters (With Grid) 9 130 120 8 Tube Potential (60) Tube Potential (75) Tube Current (60) Tube Current (75) 110 100 7 6 90 5 80 4 70 3 60 2 50 1 0 40 0 Note: This is a 10 year old system and the IIIAKR has been increased to account for the decreased image intensifier efficiency. At the 6” of phantom thickness, there is a singular point that corresponds to a jump in Tube Potential. Tube Current (mA) (mGy/min) Copper (mm) Tube Potential (kVp) Air Kerma Rate TV Camera Thickness Equivalence (Philips Eleva System) 2 4 6 8 10 Nominal PMMA Phantom Thickness (inches) 12 14 The phantom thickness equivalence graphs are charted on this slide. The points of discontinuity correspond to the phantom thickness that triggered the generator to increase the tube potential. Phantom Thickness Equivalence Air Kerma Rate vs. Phantom Thickness 100 10.0 100 70 8.0 7.0 Air Kerma Rate (mGy/min) 80 80 70 60 60 6.0 50 5.0 40 4.0 30 3.0 20 2.0 10 1.0 10 0 0.0 0 0 2 4 6 8 10 Nominal PMMA Phantom Thickness 12 14 Aluminum Copper PMMA 90 9.0 PAKR (60) PAKR (75) IIIAKR (60) IIIAKR (75) Image Intensifier Input Air Kerma Rate (μGy/sec) Air Kerma Rate (mGy/min) 90 50 40 30 20 0 10 20 30 40 50 60 70 80 90 Phantom Thickness (mm for Al, X 0.1 mm for Cu, divide by 6 "inches" for PMMA) 8 This chart may be used to convert the phantom thickness from one material to another, amongst copper, aluminum, and PMMA plastic. Philip Eleva GE Advantx Cu (mm) Al (mm) Al (inches) Al (mm) Al (inches) 0.8 19 0.75 22 0.87 3.65 2.5 1.6 38 1.5 36 1.42 5.5 4.3 3.2 58 2.25 68 2.7 7.3 7.3 5.6 76 3 82 3.2 9.3 9 Thickness Equivalence (Fussed) PMMA (inches) 10 5 8 4 6 3 4 2 PMMA Aluminum 2 1 Linear (PMMA) Linear (Aluminum) 0 Aluminum Thickness (inches) GE Advantx PMMA Thickness (inches) Philip Eleva 0 0 1 2 3 4 5 6 7 Copper Thickness (mm) PART III. The ADRC; new generation of ABC • • • • Application of filters using aluminum, copper and high atomic number elements for patient exposure reduction had been studied for use in radiographic examinations. On the other hand, the introduction of copper filters for spectral shaping during fluoroscopic imaging procedures had been available for the past decade, However, extensive application of spectral shaping filters started in its earnest as the interventional angiography procedures become widely practiced in the US in the early 1990s. Use of spectral shaping filters contributed to minimize the patient (skin entrance exposure) air kerma dramatically while the image quality is optimized and maintained. New Generation of Cardiovascular Fluoroscopy Systems are equipped with; 1) High Frequency Inverter Type Generator a) Precise switching time ( 1 msec) b) Better Pulse Shape (less over/under shoot) 2) Spectral Shaping Filters a) 0.2 ~ 0.9 mm copper (beam hardening) b) On a rotating wheel in collimator assembly (interchangeable filters during fluoroscopy) 3) High Heat Capacity X-ray Tube a) High Anode Heat Capacity (2 MHU) b) High X-ray Tube Housing Heat Capacity (3 MHU) c) To counter attenuation by spectral shaping filter Excerpt from Reference #2 Automatic Dose Rate Control (ADRC) Logic Automatic Dose Rate Control (ADRC) Logic (a) A sophisticated software programming to control the copper filter thickness in response to x-ray attenuation. (a) The fluoroscopy system employed is a Siemens Biplane angiography system AXIOM Artis dBA. (b) The ADRC is designed to control various imaging parameters including; (1) focal spot size, (2) kVp, (3) mA, (4) pulse width, etc. during fluoroscopy. (b) Operated under 22 cm flat panel image receptor mode. [It is a 48 cm flat panel.] (c) The heavy copper filter preferentially removed low energy photons and the mean x-ray beam energy is, thus, increased. (d) For the same applied tube potential this would require a higher “tube current” to produce an acceptable image quality. --- Hence, a “high power” x-ray tube is required. (c) Pulsed fluoroscopy rate @ 15 pulses/sec. (d) Fluoroscopy curve name: 80kV10RAF2kW (e) Equipped with spectral shaping filters of; 0.2, 03, 0.6, and 0.9 mm of copper. (f) The small focal spot (0.6 mm) is the default. (g) SID = 105 cm, Source-to-chamber #1 = 60 cm. 9 Evaluation of the Automatic Dose Rate Control (ADRC) Logic Tube Potential (kVp) and Filter Thickness (mmCu) vs. PMMA Thickness (inches) Flat Panel Detector 120 Iso-center Tube Potential (kVp) PMMA Phantom 45 cm Ionization Chamber #1 Examination Tabletop 2.75 in 15 cm 105 cm Copper Filter (mmCu) Tube Potential (kVp) 100 1.0 0.8 80 0.6 0.4 0.2 60 X-ray Tube Assembly Geometrical Arrangement 0 2 Pulse Width (mSec) 60 40 20 6 8 10 12 14 16 14 12 10 8 0 2 4 30 cm 1.0 0.8 80 0.6 0.4 Input Sensitivity in front of the Flat Panel Image Detector 0.2 60 100 80 60 40 20 Patient Skin Dose (Air Kerma) 16 14 12 10 Input Sensitivity (μGy/sec) Copper Filter (mmCu) Tube Potential (kVp) 100 Tube Current (mA) 8 10 cm Copper Filter (mm) Tube Potential (kVp) 20 cm Entrance Exposure rate (mGy/min) 10 cm 120 6 10 12 14 Nominal Phantom Thickness (inches) Nominal Phantom Thickness (inches) Pulse Width (mSec) Tube Current (mA) 80 4 14 Pulse Width (mSec) vs. PMMA Thickness (inches) 100 2 4 6 8 10 12 Nominal Phantom Thickness (inches) Adapted from Reference #2 Tube Current (mA) vs. PMMA Thickness (inches) 0 Copper Filter (mm) .95 in Ionization Chamber #2. 20 cm 30 cm 0.9 0.8 0.7 0.6 100 10 1 8 0.1 0 2 4 6 8 10 12 Nominal Phantom Thickness (inches) 14 0 2 4 6 8 10 12 14 Nominal Phantom Thickness (inches) 10 Why is it possible to have a “Better Image Quality” & “Lower Patient Dose” at the same time? • Image quality is “better” because of consistently lower tube potential is employed---higher image contrast! • Radiation dose to the patients, especially, small and average size patient, is significantly reduced due to the use of spectral shaping filters --- considerably amount of low energy portion of spectrum is removed before hitting the patient. • There are many fluoroscopy curves designed by the manufacturers tailored to fit specific types of examination. – Some 256 fluoroscopy curves are available. – Cardiac vs. Neuro vs. Visceral angiography – For adults ? Or for pediatric patients? • Needs to verify the preprogrammed fluoroscopy curves for the intended use of the system. • Not only the acceptance testing of the hardware is necessary, but also evaluation of the software becomes increasingly important. Fluoroscopy Curve 70kV10RAF3kW Fluoroscopy Curve 70kV10RAF3kW Tube Potential & Copper Filter vs. PMMA Thickness (3 kW) Pulse Width & Tube Current vs. PMMA Thickness (3kW) 120 0.9 180 0.8 160 Copper Filter 100 0.6 90 0.5 80 0.4 70 0.3 60 0.2 50 T ube C urrent (m A) 0.7 C o p p e r F ilte r ( m m C u ) 10 140 120 8 100 80 Tube Current P ulse Width 0.1 0 2 4 6 8 10 12 14 16 40 18 4 0 2 4 6 PMMA Thickness (inches) 8 10 12 14 16 18 PMMA Thickness (inches) Data Source: AAPM TG 125 Data Source: AAPM TG 125 Fluoroscopy Curve 70kV10RAF2kW Fluoroscopy Curve 70kV10RAF2kW Tube Potential & Copper Filter vs. PMMA Thickness (2 kW) Tube Current & Pulse Width vs. PMMA Thickness (2 kW) Tube Potential 0.8 110 Copper Filter 0.7 100 0.6 90 0.5 0.4 80 70 0.3 60 0.2 50 0.1 T ube C urrent (m A) 120 C o p p e r F ilte r ( m m C u ) 0.9 130 T u b e P o te n tia l (k V p ) 6 60 70 8.0 60 7.0 50 6.0 40 5.0 30 4.0 Tube Current 20 P u ls e W id th ( m s ) T u b e P o te n tia l ( k V p ) Tube Potential 110 12 P u ls e W id th ( m S e c ) 130 3.0 Pulse Width (mSec) 0 2 4 6 8 10 12 14 10 2.0 0 2 4 6 8 10 12 14 PMMA Thickness (inches) PMMA Thickness (inches) Data Source: AAPM TG 125 Data Source: AAPM TG 125 11 Fluoroscopy Curve 70kV10RAF2kW (Pediatric) Fluoroscopy Curve 70kV10RAF2kW (Pediatric) Tube Potential & Copper Filter vs. PMMA Thickness (2 kW) 130 1 Tube Current & Pulse Width vs. PMMA Thickness (2 kW) 70 120 10 0.9 Tube Potential (kVp) 90 0.6 80 0.5 70 0.4 60 0.3 8 50 7 40 6 30 5 Tube Current (mA) Pulse Width (ms) 20 50 Pulse Width (ms) 0.7 Tube Current (mA) 100 9 60 0.8 Copper Filter (mmCu) Copper Thickness (mmCu Tube Potential (kVp) 110 4 0.2 40 10 0.1 0 2 4 6 8 10 3 0 12 2 4 6 8 PMMA Thickness (inches) PMMA Thickness (inches) • The fluoroscopy is employed to find the passage and manipulate the catheter and/or the guide wire to the point of interests. • The mission of the ADRC for fluoroscopy may be accomplished but is just the starting point for the acquisition of diagnostic information. • In other words, the “acquisition mode” of the examination, as opposed to the “fluoroscopic mode” lies ahead. TV Camera What’s beyond the ADRC Logic? 12 Data Source: AAPM TG 125 Optical Distributer Data Source: AAPM TG 125 10 TV Camera Amplifier Video Amplifier TV Monitor Automatic Gain Control Cine Camera Control & Synchronization Control Lock-in Memory Cine Camera Filming Rate Selector Image Intensifier Photomultiplier Amplifier Reference Voltage Focal Spot Size Selector Voltage Comparator Pulse Width Selector "kVp" Control Module "mA" Control Module Cine Run Time Selector Pulse Width Control Module Controller Block A Power Rating Check X-ray Tube Anode Heat Sensor Generator Anode Heat capacity Pre-exposure Calculator Duty Cycle Compensation Overload Protection X-ray Tube Characteristic Table Generator Characteristic Table Controller Block B Comparison of Patient Exposure/Air Kerma Rate Comparison of Input Sensitivities 23/2 5 c m Im a ge In tens ifie r Inp u t Pho sp ho r (Ac tive ) S ize Cu rr en t P r ac tice Lo w Le ve l F luo r osc opy No r m a l L ev e l F luo ros co py 2 5 μ R/s e c 5 0 μ R/s e c 23/25 cm Image Intensifier, Patient Exposure Rate Current Practice Used To Be 5 0 μ R/s e c Low Level Fluoroscopy > 1 R/min 3 R/min 7 5 -100 μ R/s e c Normal Level Fluoroscopy 3 R/min 6 R/min Us ed T o B e Hig h Lev e l F lu oro sc opy 7 5 μ R/s e c N/A High Level Fluoroscopy 5 R/min N/A 10 0 m m P ho to sp o t Ca m er a 5 0 -1 00 μ R/fr a m e 1 0 0 -2 00 μ R/fr a m e 100 mm Photospot Camera 100 mR/frame 200 mR/frame 1 00 μ R/fr a m e Digital Photofluorography 75~100 mR/frame 200 mR/frame Digital Subtraction Angiography 100~300 mR/frame 500 mR/frame 35 mm Cine Camera 30~80 R/min 70~160 R/min Digital Cine Photofluorography 20~60 R/min N/A D ig ita l P ho to fluo r og r aphy 25 -10 0 μ R/fr a m e D ig ita l Su b tr ac tion An g iog r aphy 1 0 0 -5 00 μ R/fr a m e 3 5 m m C in e Ca m er a 1 0 -2 0 μ R/fr a m e 1 5-3 0 μ R/fr a m e D ig ita l C in e Ph o to flu or o gra phy 7 -12 μ R/fr a m e N/A 50 0 -1 00 0 μ R/fr a m Due primarily to the better image intensifier, television chain. Data Date: 2001 Due primarily to the better image intensifier & television chain. Data Date: 2001 12 We have come a long way from this! References & Other Reading Material 1. 2. 3. 4. PP Lin, “Acceptance testing of automatic exposure control systems and automatic brightness stabilized fluoroscopic equipment”, in Quality Assurance in Diagnostic Radiology, AAPM Monograph No. 4, New York: Am. Inst. Phys., pp 10-27 (1980) PP Lin, “The operation logic of automatic dose control of fluoroscopy systems in conjunction with spectral shaping filters”, Med. Phys. Vol 34 no 8, pp 3169-3172 (2007) PP Lin, “Cine and Photospot Cameras”, in Encyclopedia of Medical Devices and Instrumentation, John G. Webster Editor, John Wiley & Son, Publisher, 1st Edition, Vol. 2, pp 681-693 (1988) AAPM TG 125 Home Page. E-mail Address: plin@bidmc.harvard.edu Photo: Courtesy of Siemens Medical Systems 13