Imaging of Hypoxic–Ischemic Penumbra with 18F-fluoromisonidazole PET/CT and Measurement of Related Cerebral Metabolism in Aneurysmal Subarachnoid Hemorrhage

This study aimed to characterize hypoxic, but salvageable, tissue imaged by 18 F-fluoromisonidazole ( 18 F-FMISO), combining with perfusion-computed tomography (PCT) for regional cerebral blood flow (rCBF) measurement and metabolism by microdialysis (MD) in aneurysmal subarachnoidal hemorrhage (SAH) patients. 18 F-FMISO positron-emission tomography (PET)/CT was performed within the period of possible vasospasm (day 6.8±3 after SAH) in seven SAH patients. In parallel, rCBF was determined within the MD region of interest (MD-ROI) ( n=5). The MD catheter was inserted into the brain parenchyma with highest risk for ischemia; extracellular levels of glutamate and energy metabolites were registered at time of PET and hourly for 10 days. Twelve-month outcome was evaluated. In asymptomatic patients ( n=3) no hypoxia was detected and glutamate levels were low (<10 mmol/L), whereas symptomatic patients had higher glutamate concentrations ( P<0.001). Increased 18 F-FMISO uptake within the MD-ROI ( n=3) was related to higher glutamate levels, while rCBF was above the ischemic range. Hypoxia (increased 18 F-FMISO uptake) was present in symptomatic patients and associated with relevant metabolic derangement of extracellular glutamate levels, whereas energy metabolism and rCBF were preserved. This technique has the potential to improve our understanding of the role of cellular hypoxia in aneurysmal SAH.