Abstract
PURPOSE : Flat-panel computed tomography (FpCT) improves spatial resolution and allows better visualization of atherosclerotic lesions than does clinical 64-channel CT scanning (64-CT). In this rabbit study, we demonstrated that noninvasive in vivo FpCT imaging can quantify the different components within atherosclerotic plaque. METHODS: Six anesthetized Watanabe homozygous hyperlipidemic rabbits were scanned with 64-CT (image thickness, 0.625 mm) and FpCT (image thickness, 0.150 mm). Iohexol (2 ml/kg) was administered via an ear vein for each scan. Scanning was performed during full inspiration at 30, 60, and 90 seconds after injection (64-CT) or immediately after injection (FpCT). Small field-of-view images (16-mm) were generated perpendicular to the center line of the aorta at 1-mm intervals; including minimum-thickness images and 2-mm–thick volumetric images using average-, maximum-, and minimum-intensity projection. Vessel wall thickness and area, lipid pools, and calcific deposits were measured on the 2-mm–thick, average-intensity images. The aortas were serially sectioned (~2.0 to 2.5 mm in thickness) in proximal-to-distal fashion for histologic correlation with CT. RESULTS: ANOVA showed a significant correlation - FpCT vs 64-CT, P =0.017; 64-CT vs histology (HS), P =0.012; FpCT vs HS, P <0.001 - in mean wall thickness and vessel wall area as measured by both scanning techniques and by HS (n=192 sections). Plaque with a large necrotic lipid core was observed in 98 FpCT images, 7 64-CT images, and 87 histologic sections. Both FpCT and HS (gold standard) allowed the detection of lipid pools as small as 0.3 mm diameter; 64-CT allowed detection of lipid pools of 1.5 mm diameter or more. In both FpCT and HS images, but not 64-CT images, we identified lesions composed of <5% lipid. Calcific deposits of <1 mm diameter were recognized only in FpCT and HS images. The histopathologic data for plaque eccentricity and circumference, number of lipid pools, and minimal distance of each component from the vascular lumen was better correlated with the FpCT data than the 64-CT data. CONCLUSION: FpCT provides better quantification of plaque components than does 64-CT and is a promising tool for characterizing plaque composition.
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