cardiovascular computed tomography
TRANSCRIPT
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Computed TomographyComputed Tomography
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Coronary Artery DiseaseCoronary Artery Disease
Dr. Surinder SinghDr. Surinder Singh
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Terminology Scanners
Electron-beam CT
Developed specifically for cardiac imagingIt is very fast: 50 to 100 ms per image slice
Multidetector CT
Acquire multiple slices per rotation
Modes
Sequential 2-D mode
The stop and shoot mode
EBCT is performed in this mode
Spiral mode
3-D volumetric series
Cardiac MDCT is usually performed in this mode.
Image assessment
Conventional Axial3D Multi lanar
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Principle of Electron Beam TomographyPrinciple of Electron Beam Tomography
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64-slice MSCT (Normal Study)64-slice MSCT (Normal Study)
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Procedure Beta-blockade (HR < 70 bpm)
Patient positioning and explanation
Calcium scoring sequence obtained
Coronary angiogram study is then planned
60ml of 400mg iomeprol is injected at 5ml/s,followed by 30ml of NS at same speed
The sequence is triggered with a 4s delay,when the contrast in the ascending aortareaches 100HU
The averages scan time is 12 seconds
Images are reconstructed at 40-75% of the RRinterval depending on the preview series
Stenotic lesion, images reconstructed in adifferent phase to rule out a phase artifact
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Calcium ScoringCalcium Scoring
Technique of measuring the extent of calcification in theTechnique of measuring the extent of calcification in thecoronary arteriescoronary arteries
A calcium score of more than 400 is considered severeA calcium score of more than 400 is considered severe
Methods Methods
Agatston Score (EBCT/MDCT) area ofAgatston Score (EBCT/MDCT) area of
calcification x coefficient (1-4)calcification x coefficient (1-4)Volume equivalent plaque area x slice thicknessVolume equivalent plaque area x slice thickness
Mass equivalent plaque volume x mean plaqueMass equivalent plaque volume x mean plaque
densitydensity
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Coronary CalciumCoronary Calcium
Surrogate marker for coronary atherosclerosisSurrogate marker for coronary atherosclerosis
Quantity of coronary calcium correlates closely withQuantity of coronary calcium correlates closely with
Extent of atherosclerotic plaque burdenExtent of atherosclerotic plaque burden
Likelihood of future cardiac eventsLikelihood of future cardiac events
Detection of large amounts does not imply significant stenosisDetection of large amounts does not imply significant stenosis
Absence rules out significant stenosis with high NPV - 99% by EBCTAbsence rules out significant stenosis with high NPV - 99% by EBCT
& 60% by MDCT& 60% by MDCT
Coronary calcium is not associated with propensity of plaque ruptureCoronary calcium is not associated with propensity of plaque rupture
Overall accuracy of EBCT in range of TMT and nuclear imaging forOverall accuracy of EBCT in range of TMT and nuclear imaging for
predicting signifiant CAD.predicting signifiant CAD.
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MeaningMeaning
Negative test (score 0) = athersclerotic plaque unlikelyNegative test (score 0) = athersclerotic plaque unlikelyLow risk of future CV eventsLow risk of future CV events
Positive test = Atherosclerotic disease +/- obstructivePositive test = Atherosclerotic disease +/- obstructive
Greater calcium greater likelihood of occlusionGreater calcium greater likelihood of occlusion
If significant obstruction test will be positiveIf significant obstruction test will be positive
Calcification is a sign of neither stability nor instabilityCalcification is a sign of neither stability nor instability
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Acquisition Protocol for coronaryAcquisition Protocol for coronary
calciumcalciumEBCT
Prospective
MDCT
Retrospective
MDCT
Prospective
No. of Image 40 80 80
Rotation Time 50 ms 420 ms 420 ms
Slice thickness 3mm 3mm 3mm
Radiation dose 1.3 mSv 1- 3 mSv 1.8 mSv
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Coronary LuminalCoronary Luminal
StenosisStenosis 2D provide highest2D provide highest
diagnostic accuracydiagnostic accuracy
3D reconstruction adds no3D reconstruction adds no
further informationfurther information
HR restrictionHR restriction
Problem severeProblem severecalcification,calcification,
arrhythmiasarrhythmias
Can not differentiate severeCan not differentiate severe
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64-slice MSCT64-slice MSCT
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Soft PlaquesSoft Plaques High resolution MDCT
Cannot comment on the
vulnerability of the
plaque
Senstivity & SpecificitySenstivity & Specificitynot yet testednot yet tested
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Acquisition Protocol for coronaryAcquisition Protocol for coronary
arteriesarteries
EBCT MDCT
Slice 4 64
Rotation time 50ms 330ms
ECG gating Prospective Retrospective
Contrast required 160ml 60ml
Radiation dose 1 2 mSv 5 10 mSv
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Accuracy of 16 slice MDCT (S.Korea 2005)Accuracy of 16 slice MDCT (S.Korea 2005)
Vessel AnalysisVessel Analysis
0
10
20
30
40
50
60
70
80
90
100
LAD% LCx % RCA% LM%
Sensitivity
Specificity
Accuracy
PPV
NPV
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Accuracy of 64-slice MSCT AngiographyAccuracy of 64-slice MSCT Angiography
European Heart Journal ; August 2005European Heart Journal ; August 2005 67 pts. (50 male, 17 female) referred for suspected CAD67 pts. (50 male, 17 female) referred for suspected CAD
Underwent invasive CAG and 64-slice MSCTUnderwent invasive CAG and 64-slice MSCT
% Total LM LAD LCx RCA
Sensitivity 94 100 95 94 93
Specificity 97 100 95 92 96
PPV 87 100 88 80 87
NPV 99 100 98 98 98
Image quality - excellent 61% , good 31% & adequate 8%
best results in proximal segments
Impaired image quality - severely calcified vessel walls (commonest) Most motion artifacts - mid RCA
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Imaging StentsImaging Stents Metal artifacts prevent adequateMetal artifacts prevent adequate
visualization of coronary lumenvisualization of coronary lumen
Special "stent" algorithm that allowsbetter intra-stent, luminal visualization
Can reliably evaluate at the leading /Can reliably evaluate at the leading /trailing endstrailing ends
However in patients with small calibrestents, this may not be easy
Flow beyond a stent does not implypatency, since there could be retrogradefilling of the vessel via collaterals.
Not currently reliable to assess ISRNot currently reliable to assess ISR
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Imaging GraftsImaging Grafts
High accuracy forHigh accuracy forestablishing patency andestablishing patency and
occlusionocclusion
Limitations concerningLimitations concerningstenosis at the site ofstenosis at the site of
anastomosis.anastomosis.
Internal mammary grafts,which are smaller, often are
partially obscured by
artifacts from metallic
surgical clips
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Image Assessment ProtocolImage Assessment ProtocolLa Radiologia Medica 2005La Radiologia Medica 2005
0%
10%
20%30%
40%
50%
60%70%
80%
90%
100%
Sensitivity Specificity NPV PPV
Conventional
3D
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CT for Significant Coronary StenosisCT for Significant Coronary Stenosis
83%77%
84%
94%
80%84%
89.50%
97%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Sensitivity Specificity
EBCT
4- Slice
16 Slice
64- Slice
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Radiation DoseRadiation Dose Calcium scanning
EBCT 0.5 to 0.7 mSv, 16-slice MDCT (prospective gating) 0.8 to 1.5 mSv MDCT (retrospective gating) up to 6.2 mSv .
Coronary angiography EBCT 1.5 and 2.0 mSv for male and female patients, respectively 16-slice MDCT 6.7 to 10.9 mSv for male patients and 8.1 to 13.0 mSv for
female patients.
For both EBT and MDCT, the radiation dose increases with thinnerslices and more overlapping images
Routine conventional coronary angiography - 2.1 and 2.5 mSv for male
and female patients, respectively
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FutureFuture
Hybrid TechniquesHybrid TechniquesMRI/CT/NuclearMRI/CT/Nuclear
MicroCTMicroCT
16 li MSCT i
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16-slice MSCT angiograms
Thi 16 li MSCT
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Thin 16-slice MSCT