This study sought to discover which atherosclerotic plaque components co-localize with enhanced [(18)F]-fluorodeoxyglucose (FDG) uptake in carotid positron emission tomography (PET) images. Although in vivo PET currently lacks the resolution, high-resolution ex vivo FDG-microPET with histology validation of excised carotid plaque might accomplish this goal. Thirteen patients were injected with FDG before carotid endarterectomy. After excision, the plaque specimens were scanned by microPET and magnetic resonance imaging, and then serially sectioned for histological analysis. Two analyses were performed using generalized linear mixed models: (1) a PET-driven analysis which sampled high and low FDG uptake areas from PET images to identify their components in matched histology specimens; and (2) a histology-driven analysis where specific plaque components were selected and matched to corresponding PET images. In the PET-driven analysis, regions of high FDG uptake were more likely to contain inflammatory cells (p < 0.001) and neovasculature (p = 0.008) than regions of low FDG uptake. In the histology-driven analysis, regions with inflammatory cells (p = 0.001) and regions with loose extracellular matrix (p = 0.001) were associated with enhanced FDG uptake. Furthermore, areas of complex inflammatory cell infiltrate (co-localized macrophages, lymphocytes and foam cells) had the highest FDG uptake among inflammatory subgroups (p < 0.001). In conclusion, in carotid plaque, regions of inflammatory cell infiltrate, particularly complex one, co-localized with enhanced FDG uptake in high-resolution FDG-microPET images. Loose extracellular matrix and areas containing neovasculature also produced FDG signal. This study points to the potential ability of FDG-PET to detect the cellular components of the vulnerable plaque.
Keywords: Atherosclerosis; Carotid plaque; FDG; Inflammation; MicroPET; Vulnerable plaque.