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Measuring Noncalcified Coronary Atherosclerotic Plaque Using Voxel Analysis with MDCT Angiography: A Pilot Clinical Study

¹ Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Ave., WCC-302, Boston, MA 02215.
² Department of Cardiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA.

View larger version (11K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —Voxel analysis definitions. Diagram of arterial segment shows eight radial lines at 45° intervals across artery for generation of voxel attenuation plot. Voxels A and B are placed in epicardial fat, C at epicardial fat-wall interface, D and E spanning wall, and F and G in lumen. Each 400-µ voxel was sampled eight times in each cross section to obtain average density value (in Hounsfield units) in 41 normal segments. These values were used to determine attenuation value at interface of epicardial fat and outer wall and inner wall-lumen interface and to establish wall thickness of 800 µ.

View larger version (10K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —Voxel analysis definitions. Diagram of arterial segment shows voxel lines across computer-generated 3D segment to determine wall boundaries and volume of segment considered normal on MDCT angiography (lines 1 and 2) and percentage of luminal stenosis in area of plaque using voxel technique (line 3).

View larger version (46K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —Using voxel analysis to measure percentage of stenosis. Images from 3D volume rendering. Cross-sectional voxel lines are depicted above plaque (line 1) and below plaque (line 2) to determine normal wall (yellow) boundaries and normal lumen (red). Line 3 through plaque (green) measures luminal stenosis. Voxel line across eccentric plaque (line 3) calculated luminal narrowing to be 44%.

View larger version (82K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —Using voxel analysis to measure percentage of stenosis. MDCT angiography (B) and catheter coronary arteriography (C) with fiducial markers show left main (LM), left circumflex (LCX), and left anterior descending (LAD) coronary arteries with diagonal (D1 and D2) and septal (S) branches.

View larger version (85K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —Using voxel analysis to measure percentage of stenosis. MDCT angiography (B) and catheter coronary arteriography (C) with fiducial markers show left main (LM), left circumflex (LCX), and left anterior descending (LAD) coronary arteries with diagonal (D1 and D2) and septal (S) branches.

View larger version (25K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D —Using voxel analysis to measure percentage of stenosis. Attenuation plot of segment in A across eccentric plaque extends voxel line (line 3) to H and I. Note that density of wall (voxel E) is less than in normal segments because of volume averaging of lower-density plaque in plaque-containing segment.

View larger version (21K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3 —Plot across normal and plaque-containing arterial segments shows attenuation values in Hounsfield units. Values were obtained by measuring 2,296 voxels in 41 normal segments (56 voxels per segment) and 448 voxels in eight abnormal segments (56 voxels per segment). Each voxel represents an average of eight separate measurements. Plaque-containing segment always showed significantly lower attenuation values than its respective normal segment (p < 0.05). Attenuation values of voxel C and at epicardial fat-wall interface were not significantly different between normal and plaque-containing segments.

View larger version (18K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4 —Plaque volumes from eight segments (one per patient) as measured by two independent observers with excellent correlation (R2 = 0.9671) of plaque volumes in cubic millimeters. Insert shows correlation line for reader 2 (y-axis) and reader 1 (x-axis).

View larger version (22K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5 —Bar graph shows percentage of stenosis measured on quantitative coronary arteriography (QCA) is represented on y-axis and measured using voxel method on x-axis. Luminal stenosis comparing QCA with voxel analysis shows good correlation (R2 = 0.55, p = 0.04). Voxel technique tended to underestimate diameter of stenosis. Insert shows diameter of stenosis measured on catheter coronary arteriography.

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