Purpose: To use magnetic resonance (MR) imaging to examine the short-term (6 months) natural history of the lipid-rich necrotic core (LRNC) in carotid artery plaques by examining the placebo group of a multicenter clinical trial.
Materials and methods: Study procedures and consent forms were approved by the institutional review board for this HIPAA-compliant study. Written informed consent was obtained for all enrolled subjects. Subjects in the placebo group of a multicenter clinical trial who showed LRNC at screening MR imaging had a follow-up MR imaging examination after 6 months. Lumen and wall volumes and LRNC volume and percentage were measured on images from both examinations by readers who were blinded to the time sequence. Plaque progression was calculated as annualized change in common coverage by using the carotid artery bifurcation as a landmark. Associations of clinical and imaging variables with LRNC progression were examined by using linear regression analysis.
Results: Fifty-nine of 73 (81%) subjects completed the study, with a mean interval ± standard deviation of 6.9 months ± 1.0. The mean progression rates per year ± standard deviation of LRNC volume and percentage were -5.2 mm(3) ± 34.3 (P = .249) and -1.74% ± 6.27% (P = .038), respectively. Of the clinical and imaging variables examined, presence of intraplaque hemorrhage (IPH) was significantly associated with LRNC progression (P = .001). Plaques with IPH had increased LRNC volume per year (62.9 mm(3) ± 46.2 vs -8.8 mm(3) ± 29.9, P < .001) and percentage per year (3.67% ± 1.85% vs -2.03% ± 6.30%, P = .126) compared with those without IPH. Spearman correlation analysis showed that change in LRNC positively correlated with change in wall volume (ρ = 0.60, P < .001), but not with change in lumen volume (ρ = -0.17, P = .201).
Conclusion: Serial MR imaging of the carotid artery allowed observation of changes in LRNC over a short follow-up period and demonstrated the complexity of plaque progression patterns related to tissue composition. LRNC progression may be influenced not only by clinical characteristics, but also and to a large extent by plaque characteristics such as IPH.