Flat Panel Volume Computed Tomography of the Coronary Arteries

Rationale and Objectives

Multidetector-row computed tomography (MDCT) has evolved into a sensitive diagnostic tool for the noninvasive detection of coronary artery stenosis, but remains limited by spatial resolution. Flat panel volume computed tomography (fpVCT) offers a higher spatial resolution. In a postmortem investigation of autopsy specimens, the accuracies of fpVCT for measuring the severity of coronary artery stenosis and the size of atherosclerotic plaque components were determined.

Methods and Materials

In 25 autopsy cases, hearts were isolated, the left anterior descending coronary arteries filled with contrast agent, and depicted with a prototype fpVCT unit with a slice thickness of 0.25 mm. Transections of the left anterior descending coronary arteries were reconstructed and compared with histopathologic sections using light microscopy.

Results

FpVCT measurements of luminal stenosis ( r = 0.81), total plaque area ( r = 0.88), calcified plaque area ( r = 0.92), noncalcified plaque area ( r = 0.83), and lipid core size ( r = 0.67; P < .02) correlated well with histopathology ( P < .0001). The limits of agreement for measuring any plaque component were three times smaller than those reported for MDCT.

Conclusions

Postmortem coronary fpVCT provides an accurate and reproducible method for the quantitative assessment of both luminal stenosis and atherosclerotic plaque size. Because of its high spatial resolution, the method should be sufficiently accurate to reliably detect the lipid pools of vulnerable plaques.

Multirow-detector computed tomography (MDCT) has evolved into a potential noninvasive tool for the detection of coronary artery stenosis and its use is regarded as appropriate in certain clinical scenarios . However, grading stenosis remains inaccurate in comparison to catheter angiography . The detection of severe stenosis is still insufficient, both on the vessel and the segment levels, even with the most recent 64-row MDCT technology . These important shortcomings have been ascribed to a lack of spatial resolution, since even the most advanced 64-row MDCT units have a slice thickness, as defined by detector element size in the z-axis direction, of no less than 0.5–0.75 mm, which is only a fraction of the spatial resolution of conventional coronary angiography of about 0.2 mm. A voxel resolution of 0.63 mm implies that a normal distal coronary artery lumen of 1.5 mm diameter is represented by no more than two to three computed tomography (CT) voxels, which limits the accuracy of grading stenoses. MDCT has also been assessed for its potential for identifying the vulnerable plaque in the future , and its spatial resolution has been found to limit its accuracy in this application as well .

Use of high-resolution flat panel volume computed tomography (fpVCT) detectors has been suggested as one method to improve the spatial resolution, and prototype CT units based on flat panel technology have become available .

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Methods

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Results

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Assessment of Coronary Stenosis

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Table 1

Reproducibility of Measuring Coronary Stenosis Severity

Parameter Method Correlation Coefficient r = Median Difference (mm 2 ) 95% Limits of Agreement (mm 2 ) Total vessel fpVCT 0.86 5.7 −6; 18 Histo 0.98 0.35 −1.6; 2.3 Lumen area fpVCT 0.76 −0.31 −3.8; 3.2 Histo 0.99 −0.02 −0.6; 0.6 % stenosis fpVCT 0.9 0.01 −0.17; 0.15 Histo 0.93 0.01 −0.11; 0.14

Histo: histology; fpVCT: flat panel volume computed tomography.

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Assessment of Plaque Composition

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Table 2

Reproducibility of Plaque Area Measurements from Two Independent Observers

Plaque Area Method Correlation Coefficient r = Median Difference (mm 2 ) 95% Limits of Agreement (mm 2 ) Total fpVCT 0.87 −0.2 −5.5; 5.1 Histo 0.9 −1.6 −5.4; 2.3 Calcified fpVCT 0.75 −0.004 −2.6; 2.6 Histo 0.79 0.07 −1.1; 1.2 Noncalcified fpVCT 0.8 −0.03 −5.2; 5.2 Histo 0.93 −0.29 −2.9; 2.3 Lipid core fpVCT 0.39 −0.19 −1.5; 1.1 Histo 0.45 −0.12 −1.5; 1.1

Histo: histology; fpVCT: flat panel volume computed tomography.

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Table 3

Comparison of fpVCT Plaque Measurements with Histology on a Per-vessel Basis

Plaque Area Method Median (25; 75% CI) (mm 2 ) Correlation Coefficient r = Median Difference (mm 2 ) 95% CI (mm 2 ) Total fpVCT 98 (68; 122) Histo 55 (43; 70) 0.95 41 −6; 88 Calcified fpVCT 6.2 (2.6; 16) Histo 2.9 (0.5; 9.3) 0.92 6 −8; 20 Noncalcified fpVCT 83 (65; 105) Histo 63 (50; 83) 0.94 18 −10; 41 Lipid core fpVCT 2.6 (0.6; 4.5) Histo 3.2 (0.8; 5.8) 0.69 −0.8 −5.2; 3.5

Histo: histology; fpVCT: flat panel volume computed tomography.

Table 4

Reproducibility of Plaque Area Measurements from Two Independent Observers on a Per-vessel Basis

Plaque Area Method Correlation Coefficient r = Median Difference (mm 2 ) 95% Limits of Agreement (mm 2 ) Total fpVCT 0.94 3.2 −28; 35 Histo 0.93 23 −9; 55 Calcified fpVCT 0.96 0.05 −7.2; 7.4 Histo 0.74 −1 −8.6; 6.6 Noncalcified fpVCT 0.93 0.4 −27; 28 Histo 0.94 4.2 −17; 26 Lipid core fpVCT 0.67 2.7 −2.6; 8.1 Histo 0.51 1.8 −5.7; 9.3

Histo: histology; fpVCT: flat panel volume computed tomography.

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Image Noise and Contrast

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Discussion

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Quantitative fpVCT Measurements of Coronary Artery Stenosis Severity

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Quantitative fpVCT Measurements of Atherosclerotic Plaque Components

Comparison with coronary angiography

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Comparison with 16- and 64-row MDCT

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Comparison with intracoronary ultrasound

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Clinical Implications

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References

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Flat Panel Volume Computed Tomography of the Coronary Arteries

Rationale and Objectives

Methods and Materials

Results

Conclusions

Methods

Results

Assessment of Coronary Stenosis

Assessment of Plaque Composition

Image Noise and Contrast

Discussion

Quantitative fpVCT Measurements of Coronary Artery Stenosis Severity

Quantitative fpVCT Measurements of Atherosclerotic Plaque Components

Comparison with coronary angiography

Comparison with 16- and 64-row MDCT

Comparison with intracoronary ultrasound

Clinical Implications

References

Further Reading

An Integrated Model for Radiology Education

Assessment of Performance Improvement in Content-based Medical Image Retrieval Schemes Using Fractal Dimension

Cardiac Imaging, 3rd Edition