The association of lesion eccentricity with plaque morphology and components in the superficial femoral artery: a high-spatial-resolution, multi-contrast weighted CMR study

Abstract

Background: Atherosclerotic plaque morphology and components are predictors of subsequent cardiovascular events. However, associations of plaque eccentricity with plaque morphology and plaque composition are unclear. This study investigated associations of plaque eccentricity with plaque components and morphology in the proximal superficial femoral artery using cardiovascular magnetic resonance (CMR).

Methods: Twenty-eight subjects with an ankle-brachial index less than 1.00 were examined with 1.5 T high-spatial-resolution, multi-contrast weighted CMR. One hundred and eighty diseased locations of the proximal superficial femoral artery (about 40 mm) were analyzed. The eccentric lesion was defined as [(Maximum wall thickness- Minimum wall thickness)/Maximum wall thickness] >or= 0.5. The arterial morphology and plaque components were measured using semi-automatic image analysis software.

Results: One hundred and fifteen locations were identified as eccentric lesions and sixty-five as concentric lesions. The eccentric lesions had larger wall but similar lumen areas, larger mean and maximum wall thicknesses, and more calcification and lipid rich necrotic core, compared to concentric lesions. For lesions with the same lumen area, the degree of eccentricity was associated with an increased wall area. Eccentricity (dichotomous as eccentric or concentric) was independently correlated with the prevalence of calcification (odds ratio 3.78, 95% CI 1.47-9.70) after adjustment for atherosclerotic risk factors and wall area.

Conclusions: Plaque eccentricity is associated with preserved lumen size and advanced plaque features such as larger plaque burden, more lipid content, and increased calcification in the superficial femoral artery.

Figure 1

Example of cross-sectional CMR images with four contrast weightings. The multi-contrast weighted images were matched using bifurcation (arrowhead) of common femoral artery as a fiducial marker. (CFA: common femoral artery; CFV: common femoral vein; SFA: superficial femoral artery; DFA: deep femoral artery).

Figure 2

Delineation of eccentricity measurement. (a), Eccentricity Index = (A - B)/A. A (Maximum wall thickness) and B (Minimum wall thickness) can be measured by CASCADE automatically. The eccentric lesion is defined as EI ≥ 0.5, concentric lesion as EI < 0.5; (b) and (c), Examples of femoral arterial plaques with eccentricity index of 0.31 and 0.83, respectively. A big calcification can be seen in the eccentric plaque (dark area). (blue: outer wall boundary; red: lumen).

Figure 3

Example of signal pattern of calcification and lipid rich necrotic core (LRNC) in multi-contrast weighted CMR. (a) The calcification shows low intensity signal on all four contrast weightings (arrowhead) (b) The typical image pattern of LRNC is iso-intensity on TOF, iso/high-intensity on T1WI and low intensity on PD and T2WI. In the posterior vessel wall of superficial femoral artery, a crescent shaped LRNC can be identified (arrowhead).

Figure 4

Example of concentric and eccentric lesions in multi-contrast weighted CMR. Cross-sectional TOF and PD weighted images show examples of femoral arterial plaques with eccentricity index of 0.39 (concentric) and 0.78 (eccentric), respectively. The eccentric lesion has significant larger wall area (27.50 mm² vs.15.23 mm²), total vessel area (87.65 mm² vs. 61.55 mm²), maximum wall thickness (5.09 mm vs. 2.27 mm) and mean wall thickness (2.43 mm vs. 2.27 mm), but still preserves larger lumen area (27.50 mm² vs. 15.23 mm²). A big piece of calcification (CA), which shows dark signal on all weightings, can be detected in eccentric plaque.