Identification of Fibrous Cap Status by MRI

Several image weightings (T1, T2, PD, 3D TOF) are used together by a radiologist to make the diagnosis of a FC [97]. A dark rim on 3D TOF is associated with a thick cap and a thin cap is associated with its absence. A ruptured cap is indicated by the absence of a dark rim in the presence of other markers like a focal contour abnormality or a bright gray region near the lumen [97] usually best seen in flow suppressed black blood images. Figures 8.22-8.24 show typical appearances of thick, thin, and ruptured caps, respectively. It has to be noted that various cap states can occur within the same slice.

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Figure 8.22: Thick cap—presence of dark rim on 3D TOF due to a thick cap (arrow). The site of apparent rupture on histology (color) is artifactual and caused by surgical incision (arrow).

Figure 8.23: Thin cap—absence of dark rim on 3D TOF due to a thin cap (arrow). The apparent focal contour abnormality on T1 (arrow) is due to calcium and not a real contour abnormality.
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