Associations Between Pericarotid Fat Density and Image-based Risk Characteristics of Carotid Plaque

In this study, we aimed to evaluate the associations between pericarotid fat density (PFD) and various risk characteristics of carotid plaque.We retrospectively evaluated consecutive patients who were subjected to both high-resolution MRI and carotid artery CT angiography CTA at our institution between January 2016 and April 2021. The section of the carotid artery with the most severe lumen stenosis was selected from each patient for analysis. Two separated regions of interest (ROI) (each with an area of 2.5 mm2 and located at least 1 mm from the outer margin of the carotid artery wall) were defined in the perivascular fat tissue. The mean value of PFD (mean HU) was measured on the plaque side and the same axial non-plaque side. Then, the bilateral difference (D-value HU) was calculated (plaque side mean HU minus non-plaque side mean HU). According to carotid plaque risk characteristics (American Heart Association VI type [AHA VI], intraplaque hemorrhage [IPH], thinning and/or rupture of the fibrous cap [TRFC], lipid-rich necrotic core [LRNC], and calcification [CA]), the associations between PFD and five different risk characteristic subgroups were analyzed. The Student's t-test, Mann-Whitney U test, and Chi-square test were used to compare differences between different risk subgroups. Receiver operating characteristic (ROC) curve analysis was used to evaluate the predictive efficacy of PFD for carotid plaque risk characteristics. P < 0.05 was considered statistically significant.A total of 71 eligible patients (mean age 61.25 ± 10.35 years, 57 male) were examined in this study. For the plaque side and the non-plaque side, the mean PFD values were -36.25 ± 20.65 HU and -66.87 ± 15.00 HU, respectively. In the non-AHA VI and AHA VI subgroups, the values for the mean HU of the plaque side were -49.50 ± 20.53 and -33.55 ± 19.78, respectively (P = 0.014). The D-value HU was higher for the AHA VI group compared to the non-AHA VI group (33.61 ± 16.72 vs. 15.91 ± 14.52, respectively; P = 0.001). Compared to the non-IPH subgroup, the IPH subgroup had a higher mean HU value for the plaque side (-47.68 ± 18.26 vs. -29.63 ± 19.16, respectively; P < 0.001) and a higher D-value HU (17.80 ± 13.27 vs. 38.03 ± 15.46, respectively; P < 0.001). Compared to the low risk non-TRFC subgroup, the TRFC subgroup had a higher D-value HU (24.51 ± 16.16 vs. 33.55 ± 17.65, respectively; P = 0.042). The D-value of PFD was found to be a significant predictor of both AHA VI classification (AUC: 0.79; SE: 64.41%; SP: 83.33%; P = 0.0001) and IPH (AUC: 0.83; SE: 88.89%; SP: 65.38%; P < 0.0001).Our study found that PFD was significantly associated with high risk AHA VI plaque characterization, IPH, and TRFC. Therefore, PFD has the potential to be used as an indirect clinical marker of plaque instability.