Association between Carotid Bifurcation Angle and Vulnerable Plaque Volume Using Black Blood Magnetic Resonance Imaging

Figures

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  Fig. 1. Measurement of plaque volume and the proportion of plaque volume. A) Plaque was measured using a manual operator-defined region of interest drawn over the entire plaque (within solid lines) on axial magnetic resonance imaging (MRI) of the area with the bifurcation. The relative overall signal intensity (roSI) was calculated as the signal intensity of the entire plaque/reference signal intensity, where the reference is the sternocleidomastoid muscle tissue (dotted line). Next, plaques were extracted above and below the bifurcation in the same manner. Plaques were defined as areas with roSI ≥ 1.0, and volumes of these plaques were then measured in increments of 1.0, 1.1, and 1.2, up to 2.0. B) For roSI ≥ 1.0, plaque volume was 3.39 mL. C) For roSI ≥ 1.1, plaque volume was 2.74 mL (80.8% of the volume for roSI ≥ 1.0). D) For roSI ≥ 1.2, plaque volume was 2.33 mL (68.7% of the volume for roSI ≥ 1.0). E) For roSI ≥ 1.3, plaque volume was 2.03 mL (59.9% of the volume for roSI ≥ 1.0). F) For roSI ≥ 1.4, plaque volume was 1.71 mL (50.4% of the volume for roSI ≥ 1.0). G) For roSI ≥ 1.5, plaque volume was 1.51 mL (44.5% of the volume for roSI ≥ 1.0). H) For roSI ≥ 1.8, plaque volume was…

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  Fig. 2. Relation between relative plaque volume, roSI, and bifurcation angle. A: Measurement of relative plaque volume per roSI. *p = 0.0085; **p = 0.019; *** p = 0.0031. Relative plaque volume was significantly higher in Group B from roSI ≥ 1.3 to ≥1.5 and also tended to be higher in Group B for the other thresholds. B: Correlation between vulnerable relative plaque volume and the ICA angle. C: Correlation between vulnerable relative plaque volume and the ECA angle.

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  Fig. 3. Process of carotid plaque formation. A) Normal carotid artery. B) First, with increasing bulb diameter and tortuosity, the ICA angle in the carotid artery increases. C) The low-wall shear stress (WSS) region due to an increased ICA angle leads to plaque formation consistent with that site. Low WSS is observed in the outer ICA (arrows). D) Lower WSS promotes atherosclerotic plaque formation, and vulnerable plaque volume also increases. The ECA angle does not contribute to increased plaque formation on the internal carotid side.