cardiovascular computed tomography

7/31/2019 Cardiovascular Computed Tomography

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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

cardiovascular computed tomography

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