Abstract 5829: Lipid Deposition and Quantitation in Carotid Endarterectomy Plaque Samples Using High Resolution Magnetic Resonance Imaging (MRI) Technique
Patients with carotid plaque undergo endarterectomy based on empirical guidelines, primarily the magnitude of stenosis. There is significant peri-operative morbidity and mortality associated with this procedure, and unfortunately many patients undergoing endarterectomy are found to have stable fibrotic plaque unlikely to cause thromboembolus. Patients who would derive benefit from carotid endarterectomy are those with lipid rich, vulnerable plaque at high risk of rupture. The purpose of this study was to validate the use of MRI as a means of characterizing lipid deposition in carotid plaque, thereby facilitating development of a non-invasive, quantitative predictor of plaque stability. To this end MR spectroscopy (MRS) was used to quantify major lipid species found in carotid plaques, including cholesteryl ester (CE), free cholesterol (FC), and triglyceride (TG), using phantoms of these lipids, and mixtures of them at known ratios for standardization. Twenty carotid plaque samples were obtained from patients (10 symptomatic, 10 asymptomatic) undergoing endarterectomy. A 3-D interleaved water-fat MRI protocol was implemented at 11.7 T to assess lipid deposition and plaque composition. At selected locations in each plaque, the content of different lipid species was estimated using MRS. After MRI/MRS, the plaques were sectioned and subjected to histological and biochemical analyses to confirm the plaque composition by MRI/MRS assessment. By MRS we observed that plaque lipid consists largely of CE and FC, with minimal TG. We also observed the distribution of CE and FC to vary spatially within any given lipid rich region. Further, by MRI/MRS we were able to correlate the size and composition of a plaque with the clinical status of the patient. Plaques from symptomatic patients were either large (>320 mm3) or >45% lipid rich and <10% calcified. Plaques from asymptomatic patients were either small (<320 mm3) or >10% calcified. The fraction of a plaque that was lipid rich inversely correlated with patient’s HDL level. Our data confirmed that plaque calcification may be associated with plaque stabilization. Longer term prospective non-invasive imaging studies could be warranted to investigate the relationship between events and lipid content in the plaque.