(A)True-positive 16-detector coronary computed tomography angiography (CTA). (a)Axial images show a calcified and uncalcified plaque in the proximal left anterior descending (LAD) (arrow). (b)A cross section through the plaque shows calcium on the periphery and a low-attenuation, soft plaque obstructing much of the lumen (arrow). A small residual lumen with contrast is visible at approximately the one-o’clock position in the vessel lumen. The axial image is overlaid in the lower left-hand corner and the plane of the cross section is shown (line). (c)Catheter angiography shows an eccentric stenosis (75% diameter, arrow) corresponds to the plaque observed at CT. From Ropers et al. (38). (B)False-positive 16-detector coronary CTA. (a)A multiplanar reformat of the CT data, intended to display the LAD in a projection equivalent to a right anterior oblique projection at catheter angiography. Extensive calcification can be found along the course of the LAD artery. Proximally, there is a heavily calcified plaque, which is shown bisected with a white line. (b)A cross section of the vessel (the plane defined by the line in a). The cross section is entirely white, meaning it appears the vessel lumen is completely replaced with calcified plaque. (c)A catheter angiogram. At the site of the calcified plaque shown in (a)and (b)(line bisecting the LAD), there is mild stenosis but not the occlusion, as shown on the CT images from (a)and (b). For technical reasons, calcium appears to occupy more space on CT scans than it does in reality. For this reason, stenosis caused by calcified plaques is overestimated by CT. From Hoffmann et al. (40).