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CT imaging techniques
J D Schuijf
Department of Cardiology,
Leiden University Medical Center,
Leiden, the Netherlands
Nice 2010
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• Calcium scoring
• CT angiography
Acquisition and Patient selection
Advances and Dose reduction
• Additional information/ imaging techniques
LV function
Myocardial perfusion imaging
Outline
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Hallmark:
• Presence and extent of coronary calcifications as
marker for CAD
Calcium scoring (EBCT/MSCT)
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No contrast
Images acquired at
predefined phase
4 x 3mm collimation
Low radiation dose 1-3 mSv
Calcium scoring (EBCT/MSCT)
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Calcium scoring (EBCT/MSCT)
Very extensive plaque burden>1,000
Extensive plaque burden401-1,000
Moderate plaque burden101-400
Mild plaque burden11-100
Minimal plaque burden1-10
No identifiable
atherosclerotic plaque0
Calcified Plaque BurdenCAC Score
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Limitations calcium scoring
No direct relation between extent
calcium and angiographic
severity of disease
extensive calcium without obstruction
limited calcium with high grade stenosis
Non-calcified lesions are not visualized…
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MSCT coronary angiography
•Direct visualization of the coronary arteries
•Detection of significant CAD (stenosis >50%
luminal narrowing)
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2000 2010
4-slice CT 64-slice CT16-slice CT256/ 320-row
CT
Rapid development
Dual-source
CTHigh-pitch
spiral CT
Adapted from G Pundziute
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Mollet, N. R et al. Heart 2005;91:401-407
MSCT scanning
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Mollet, N. R et al. Heart 2005;91:401-407
Sequential CT scanning
-Prospective triggering
- 1 phase acquired
Spiral CT scanning
-Retrospective gating
-Recontruction in all
phases
ECG
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Breath hold of approx 8 seconds
Collimation 64 x 0.5 mm
Rotation time: 0.4s or faster
Contrast agent bolus 4-6 ml/s
ECG is simultaneously acquired
to allow retrospective
reconstruction of the data
4D dataset
Registration of the ECG
Retrospective 64-slice CT
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Recontructed Images gated to ECG
Reconstructed at 75% ; 0.5 mm at 0.3 mm increment
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Protocol Issues
• Iodinated contrast
• Radiation
• Temporal resolution relatively
limited, images reconstructed over
several heartbeats: heart rate should
be stable and low
• Breath hold required
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Contra-indications for MSCT
Contrast
• Known or suspected contrast allergy
• Renal insufficiency
Radiation
• Pregnancy
• Age
• Recent imaging with radiation?
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Contra-indications for MSCT
Heart rate
• Atrial fibrillation
• High heart rate and contra-
indications for beta-blockers
Breath hold
• Not able to hold breath
• Not able to lie still
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HR below 60 bpm
• Improved image quality with lower heart rates
• Higher diagnostic accuracy
• More options for dose reduction
• Administration of beta-blockers at HR >60
bpm
Low HR High HR.....
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(Klass et al J Comput Assist Tomogr 2009;33: 199Y203)
Nitroglycerine
With Nitro
Without Nitro
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0
10
20
30
40
50
Dose (mSv)
Range of medians: 5.7 to 36.5 mSv
Estimated radiation dose 64-slice
Hausleiter et al ACC 2008/JAMA 2009
50 study sites, different vendors, 4% 16-slice
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Automatic exposure control
adaption of tube current to pat.‘s anatomy
ECG pulsing
modulation of tube current to pat.‘s ECG
100 kV tube voltage
instead of conventional ≥ 120 kV tube voltage
adapted to pat‘s posture
Sequential scanning (step and shoot)
instead of conventional spiral scan technique
Dose saving algorithms
Hausleiter et al ACC 2008/JAMA 2009
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Automatic exposure control– 64-slice systems – Hausleiter et al JAMA 2009
62.1 37.90
50
100(%)
Frequency of use
15.4 15.80
10
20
30(mSv)
Estimated dose
automatic exposure controlwithwithout
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ECG pulsing
Maximum output only during diastole
Noisy images during systole
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ECG pulsing– 64-slice systems –Hausleiter et al JAMA 2009
(%)
Frequency of use
21.3 78.70
50
100
ECG pulsingwithwithout
(mSv)
Estimated dose
20.9 16.70
10
20
30
20%
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100 kV tube voltage– 64-slice systems –Hausleiter et al JAMA 2009
(%)
Frequency of use
kV tube voltage100≥ 120
0
50
100
94.25.8
0
50
100
Image quality
(%)
97.3 97.3
(mSv)
Estimated dose
0
10
20
30
17.4 8.7
50%
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Mollet, N. R et al. Heart 2005;91:401-407
Sequential CT scanning
-Prospective triggering
- 1 phase acquired
Spiral CT scanning
-Retrospective gating
-Recontruction in all
phases
Retrospective vs prospective
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Spiral vs. sequential scanning– 64-slice systems –Hausleiter et al JAMA 2009
(%)
Frequency of use
scanningsequentialspiral
0
50
100
93.86.2
(mSv)
Estimated dose
0
10
20
30
17.6 5.6
68%
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Prospective ECG triggering
30 pts
Heart rate 56 +/- 8 bpm;
Dose 2.1+/- 0.7 mSv
(range: 1.0–3.3)
Herzog . et al. Eur Heart J 2008
Sensitivity 100%
Specificity 83%
PPV 90%
NPV 100%
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Herzog et al Heart 2009;95:1656-1661
Radiation dose
Good image quality, good diagnostic
accuracy at doses even lower than invasive
coronary angiography
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Husmann, L. et al. Eur Heart J 2008 29:191-197
During computed tomography coronary angiography scanning with prospective ECG-gating (SnapShot Pulse technology), data are acquired
with a z-coverage of 40 mm (indicated by white lines)
Artefacts
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4 x 1 16 x 0.5 64 x 0.5 320 x 0.5
2000 2001 2004 2007
Coverage
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Coverage in a single heart beat
56 year old male, family history for CAD +++
Prospective ECG-triggering 75%
320-row CT: 1 heart beat
100 kV
Rule out significant CAD at 2.7 mSv
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High-pitch spiral CT
Prospective triggering with very fast pitch
128 DSCT, 2 x 128 x 0.6 mm
Entire period of data acquisition 260 ms, placed in diastole
Temp resolution of each slice is 75 ms (0.28s rotation time)
Achenbach S. et al. Eur Heart J 2009
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High-pitch spiral CT
Achenbach S. et al. Eur Heart J 2009
estimated effective dose 0.89 mSv