Abstract 14673: Imaging of Hypoxia and Inflammation in Carotid Atherosclerosis With 18F-Fluoromisonidazole and 18F-Fluorodeoxyglucose Positron Emission Tomography
Background: Positron emission tomography (PET) imaging of atherosclerosis with 18F-fluorodeoxyglucose (FDG) gives a non-invasive surrogate of inflammation. FDG PET can be used to track the response to drugs and potentially to predict risk of future vascular events. FDG uptake correlates with the presence of macrophages, but not perfectly (r=0.7). Hypoxia also exists within atherosclerosis. Published in vitro data suggest that hypoxia, as well as inflammation, contributes to the observed FDG signal. PET imaging with 2-nitroimidazoles like 18F-fluoromisonidazole (FMISO) is used to measure hypoxia within tumors, a marker of a poorer prognosis. Here, we demonstrate the first use of FMISO PET to image and measure hypoxia in carotid plaque. We also examined the relationship between symptoms, FDG and FMISO uptake in the same subjects.
Methods: 15 patients (7 symptomatic and 8 asymptomatic, mean age 71±6 years, 27% female) with carotid atherosclerosis underwent PET imaging with FDG and FMISO. Symptomatic individuals underwent imaging 15±11 days after stroke or transient ischemic attack (TIA). 300MBq of FMISO was injected and static images acquired 165 minutes later. PET data were co-registered with contrast CT, and regions-of-interest drawn around the carotid artery. FDG and FMISO uptake were quantified as target-to-background ratios (TBR).
Results: Carotid artery FMISO and FDG uptake correlated positively (r2=0.38; p<0.001). Median carotid arterial TBR for FDG was 1.79 (IQR 1.33-2.25). Mean FMISO TBR was 1.06±0.07. FMISO uptake, but not FDG, was higher in culprit plaques than asymptomatic lesions (1.11±0.08 vs. 1.04±0.06; p<0.05).
Conclusions: Imaging of hypoxia in carotid atherosclerosis is feasible. These data suggest that culprit lesions after TIA or stroke are more hypoxic than asymptomatic disease. The correlation between FDG and FMISO uptake suggests that hypoxia significantly contributes to the observed FDG uptake in atherosclerosis PET studies.
- © 2013 by American Heart Association, Inc.