Research Support
Dual-Source CT:
What is it and How Do I Test it?
• National Institute of Health
– EB04898, CA75333, AR27065, HR46158
Cynthia H. McCollough, Ph.D.
CT Clinical Innovation Center
Department of Radiology
Mayo Clinic College of Medicine
Rochester, MN
• Flight Attendant Medical Research Institute
• Siemens Medical Solutions
• Bayer Healthcare
• RTI Electronics
Tube A: 50 cm FOV
Tube A: 50 cm FOV
Tube B: 26 cm FOV
Tube B: 26 cm FOV
Each tube/detector pair has:
80 kW generator
32 x 0.6 mm detector array
Double z sampling with Z-FFS
No gantry tilt
I. Single Tube Operation - Performs Same as a Sensation 64
Temporal Resolution =
Rotation Time 330 ms
=
2
2
= 165 ms
83 ms vs. 165 ms
(same raw data, same phase)
II. Dual Tube Operation - x 2 Improved Temporal Resolution
Single tube recon
Dual tube recon
Temporal Resolution =
Rotation Time 330 ms
=
4
4
= 83 ms
RCA
RCA
LAD
Mean HR=90 bpm
LAD
Dose
82 ms
•
•
125 ms
165 ms
McCollough et al., Radiology 243(3):775-784 (2007)
70
MDCT
DSCT
0.2
MDCT pulsed
DSCT 310 ms
0.2
DSCT 210 ms
0.2
DSCT 110 ms
0.2
60
Continuous irradiation (spiral acquisition) with two
x-ray tubes would double the radiation dose
Four dose reduction strategies:
–
–
–
–
Cardiac beam shaping filter (bowtie filter)
3-D adaptive noise filtration
Variable pitch values (based on heart rate)
ECG-pulsing with arrhythmia detection and
adjustable temporal windows
III. Dual Source (Obese) Mode
Use both tubes at same kV to double
the available power to 160 kW
50
40
30
0.2
0.265
0.36
0.46
20
10
No ECG
pulsing
Pulsing
No ECG
pulsing
Pulsing
No ECG
pulsing
Pulsing
No ECG
pulsing
Pulsing
0
<55
55-70
70-90
Heart Rate (bpm)
>90
•Reconstructed images are the
SUMMATION of Tube A and B
•Avoids need to trade off exam speed
(pitch) or narrow slices (collimation)
for photon flux
•Allows much higher mAs for
– Obese patients
– 80 kVp imaging
IV. Material Specific Imaging
Use each tube at a different kV to exploit
the kV-dependent nature of CT #
80kV
Bone
670 HU
Iodine
296 HU
Applications of Dual-Energy CT
• Iodine imaging
– Automated bone removal in CT angiography
– Plaque removal
– Blood pool imaging (Perfused blood volume)
• Soft tissue imaging
– Enhanced visualization of tendons & ligaments
– Virtual non-contrast (Iodine removal)
Bone
450 HU
Iodine
144 HU
140kV
• Dose reduction
• Material characterization
TR Johnson et al. Eur Radiology 17(6):1510-1517 (2007)
Applications of Dual-Energy CT
Direct subtraction of bone in
complicated anatomical regions
• Iodine imaging
– Automated bone removal in CT angiography
– Plaque removal
– Blood pool imaging (Perfused blood volume)
• Soft tissue imaging
– Enhanced visualization of tendons & ligaments
– Virtual non-contrast (Iodine removal)
• Dose reduction
• Material characterization
Courtesy of University Hospital of Munich - Grosshadern / Munich, Germany
Applications of Dual-Energy CT
• Iodine imaging
Contrast enhanced Nephrographic phase
– Automated bone removal in CT angiography
– Plaque removal
– Blood pool imaging (Perfused blood volume)
• Soft tissue imaging
– Enhanced visualization of tendons & ligaments
– Virtual non-contrast (Iodine removal)
DE image from same scan
Virtual non-contrast
• Dose reduction
• Material characterization
O. Dzyubak, Tuesday 2:42 pm, Rm L100J
Implications for Performance Testing
Image Quality
• Single source mode: No change from any MDCT
• Dual source cardiac mode: optional
– Use demo ECG mode
– Coronary CTA: 120 kVp, 240 mAs/rot, 0.33 sec, 32x0.6, pitch
auto selected, 3 mm, B26f, retrospectively-gated spiral mode
– ACR phantom: CT number accuracy
– Large (> 30 cm diameter) water or uniform acrylic phantom
• Uniformity and noise in axial and coronal images
– mAs/rot represents mAs sum from both tubes
(not effective mAs = mAs/pitch)
Implications for Performance Testing
Image Quality
• Dual energy mode: Suggested
– Mixed image (0.3 • 80 kV + 0.7 • 140 kV)
– DE abdomen: 140/80 kVp, 95/400 eff. mAs, 0.5 s,
14x1.2 mm, pitch < 0.7, 5 mm, D30f, spiral
– ACR CT phantom: CT number accuracy
• Fat (polyethylene) and bone (Teflon) expected to have
different CT numbers relative to 120 kVp
• Check accuracy of water and air CT numbers
– Large (> 30 cm) water or uniform acrylic phantom
• Uniformity and noise in axial and coronal images
Implications for Performance Testing
Image Quality
• Dual source non-cardiac (obese) mode: Optional
– Average image (0.5 • Tube A + 0.5 Tube B)
– Obese XXL: 120 kVp, 300 eff. mAs, 0.5 s, 24x1.2 mm,
pitch < 1.0, 5 mm, B20f, spiral
– ACR phantom: CT number accuracy
– Large (> 30 cm) water or uniform acrylic
phantom
• Uniformity and noise in axial and coronal images
Implications for Performance Testing
Dose
• Must test both tubes, recommend to do separately
• Tube A: No change from any MDCT
– CTDIw in head and body phantoms for routine head and body
– CTDIair for all collimations at routine kVp
– CTDIair for all kVp settings at routine collimation
– IEC 61223-2-6-Ed2 (Constancy Testing)
• Tube B: Fewer collimations available
• HVL for both tubes at acceptance testing
(required after any tube chance in some states)
• Change of one tube does NOT affect other tube
• Doses are additive
Body Dose Measurement
Cardiac Dose Measurement
(Body CTDI phantom, Body filter)
(Body CTDI phantom, Head filter)
80kVp
100kVp
120kVp
QC(A,B)
AT (A)
AT (A)
QC(A,B)
QC(A,B)
QC(A) QC(A) QC(A,B)
AT (B) AT (B)
CTDIw
32x0.6(UHR)
AT (A,B)
UHR =Ultra high resolution focalspot.
140kVp
2x1
1x5
1x10
14x1.2
24x1.2
32x0.6
QC(A)
AT (B)
AT = acceptance test only. QC = AT + scheduled QC or after tube change
Head Dose Measurement
(Head CTDI phantom, Head filter)
80kVp
120kVp
QC(A,B)
AT(A)
AT(A)
QC(A,B)
QC(A,B)
QC(A) QC(A) QC(A,B)
AT(B) AT(B)
CTDIw
32x0.6(UHR)
AT(A,B)
UHR =Ultra highresolutionfocalspot.
2x1
1x5
1x10
14x1.2
24x1.2
32x0.6
100kVp
140kVp
QC(A)
AT(B)
AT = acceptance test only. QC = AT + scheduled QC or after tube change
80kVp
120kVp
QC(A,B)
AT(A)
AT(A)
QC(A,B)
QC(A) QC(A) QC(A,B)
AT(B) AT(B)
CTDIw
32x0.6(UHR)
AT(A,B)
UHR =Ultra highresolutionfocalspot.
2x1
1x5
1x10
24x1.2
32x0.6
100kVp
140kVp
QC(A)
AT(B)
AT = acceptance test only. QC = AT + scheduled QC or after tube change
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Dose Measurement – Service mode
Mayo CT Clinic Innovation Center and Dept. of Radiology
L Yu, MR Bruesewitz, JM Kofler, AN Primak, AP Dzyubak, X Liu
JG Fletcher, TJ Vrtiska, EE Williamson, JF Breen, DM Hough
Additional Reference: Flohr, TG et al., European Radiology 16:256-268 (2006)