Evaluating cardiac hypoxia in hibernating myocardium: Comparison of ^99mTc-MIBI/¹⁸F-fluorodeoxyglucose and ¹⁸F-fluoromisonidazole positron emission tomography-computed tomography in relation to normal, hibernating, and infarct myocardium

Abstract

The aim of this prospective study was to explore the feasibility of 18F-fluoromisonidazole (18F-FMISO) cardiac positron emission tomography/computed tomography (PET/CT) in the detection of cardiac hypoxia in patients of ischemic heart disease (IHD) and to compare the uptake pattern with that of 99mTc-MIBI and 18F-fluorodeoxyglucose (18F-FDG). Twenty-six patients suffering from IHD were evaluated in this study. The patients initially underwent 99mTc-MIBI rest/stress myocardial perfusion imaging and 18F-FDG cardiac PET/CT as a part of their routine cardiac imaging. Patients with hibernating myocardium on these scans further underwent 18F-FMISO Cardiac PET/CT. Controls were also considered in the form of patients with scarred and normal myocardium. On visual assessment, increased 18F-FMISO uptake was noted in the hibernating myocardium compared to scarred or normal myocardium. On semiquantification analysis, there was overlap in the uptake values with a range of maximum standardized uptake value (SUVmax) in hibernating, scarred, and normal myocardium being 0.8–2.2 g/dl, 0.7–1.8 g/dl, and 0.7–1.6 g/dl, respectively. On individual patient-specific comparison in subjects harboring both hibernating and scarred myocardium, it was observed that SUVmax of 18F-FMISO in hibernating myocardium was highest, followed by scarred myocardium and normal myocardium, respectively. The ratio of 18F-FMISO SUVmax of hibernating to the normal myocardium in these subjects was always more than 1, and never less than the ratio of SUVmax of scarred to normal myocardium. Thus, in this mixed population study, it was observed that on an individual patient basis, hypoxic myocardium consistently showed higher 18F-FMISO uptake than surrounding scarred and normal myocardium. The ratio of 18F-FMISO SUVmax of hibernating to normal myocardium was higher than the ratio of scarred to the normal myocardium in all patients. On overall basis, however, there was considerable overlap in the SUV values among hibernating, scarred, and normal myocardium resulting in difficulty in differentiation of these entities with FMISO cardiac PET. 18F-FDG cardiac PET/CT remains the standard and superior method to determine hibernating myocardium in patients of IHD due to its superior contrast. The limitation of FMISO is poor signal to noise ratio because of high background uptake from the blood pool. Cardiac PET/CT with superior hypoxia tracers needs to be further examined for imaging cardiac hypoxia.