Longitudinal [¹⁸F]FMISO PET Evaluation of Hypoxic Tissue in a Rat Model of Hindlimb Ischemia

Peripheral artery disease (PAD) is a vascular condition caused by atherosclerosis that can reduce blood flow and occlude certain arteries. Hypoxia induces angiogenesis, leading to the proliferation and expansion of the capillary network, thereby reducing cellular ischemia. Several studies have suggested that hypoxia should be considered a major target for diagnosing and monitoring treatment of PAD. However, its in vivo detection in hindlimb ischemia models remains unexplored. In this preclinical study, hypoxia was assessed using longitudinal [¹⁸F]Fluoromisonidazole ([¹⁸F]FMISO) PET/CT imaging, in comparison with perfusion and glucose metabolism evaluated by [^99mTc]Tetrofosmin ([^99mTc]TTF) SPECT and [¹⁸F]Fluorodeoxyglucose ([¹⁸F]FDG) PET/CT, respectively, in a rat model of hindlimb ischemia. PAD was induced in 29 rats through the occlusion of the femoral, epigastric, popliteal, saphenous and iliac arteries in the left hind limb and longitudinal PET/CT and SPECT scans were conducted to assess disease progression postsurgery. Our results showed that the hindlimb ischemia rat model exhibited hypoxic tissue during the first 3 h postischemia, when the hypoxic volume reached its maximum. This volume then rapidly decreased over time, particularly after 26 h postsurgery. The hypoxic region exhibited a precise spatial overlap with the area of hypoperfusion; however, hypoperfusion was most pronounced during the first week postocclusion and gradually resolved between days 7 and 30. In contrast, [¹⁸F]FDG uptake showed a modest increase in the hypoxic region beginning at 3 days postischemia and appeared to persist beyond the period of hypoperfusion, remaining detectable up to 14 days postischemia. These findings demonstrate the presence of hypoxic tissue in the ischemic hindlimb and open the possibility for new therapies aimed at reducing ischemic damage associated with hindlimb ischemia.