Identifying hypoxic tissue after acute ischemic stroke using PET and F-18-fluoromisonidazole

Objective: To show that PET with F-18-fluoromisonidazole (F-18-FMISO) can d etect peri-infarct hypoxic tissue in patients after ischemic stroke. Backgr ound: PET with O-15-labeled oxygen and water is the only established method for identifying the ischemic penumbra in humans. We used PET with F-18-FMI SO in patients after ischemic stroke to identify hypoxic but viable peri-in farct tissue likely to represent the ischemic penumbra, and to determine ho w long hypoxic tissues persist after stroke. Methods: Patients with acute h emispheric ischemic stroke were studied using PET with F-18-FMISO either wi thin 48 hours or 6 to II days after stroke onset. The final infarct was def ined by CT performed 6 to 11 days after stroke. Tracer uptake was assessed objectively by calculating the mean activity in the contralateral (normal) hemisphere, then identifying pixels with activity greater than 3 SDs above the mean in both hemispheres. Positive studies were those with high-activit y pixels ipsilateral to the infarct. Results: Fifteen patients were studied ; 13 within 48 hours of stroke, 8 at 6 to 11 days, and 6 during both time p eriods. Hypoxic tissue was detected in 9 of the 13 patients studied within 48 hours of stroke, generally distributed in the peripheries of the infarct and adjacent peri-infarct tissues. None of the 8 patients studied 6 to 11 days after stroke exhibited increased F-18-FMISO activity. All 6 patients s tudied both early and late exhibited areas of increased activity during the early but not the late study. Conclusions: PET with F-18-FMISO can detect peri-infarct hypoxic tissue after acute ischemic stroke. The distribution o f hypoxic tissue suggests that it may represent the ischemic penumbra. Hypo xic tissues do not persist to the subacute phase of stroke (6 to 11 days).