Early detection of irreversible cerebral ischemia in the rat using dispersion of the magnetic resonance imaging relaxation time, T-1p

The impact of brain imaging on the assessment of tissue status is likely to increase with the advent of treatment methods for acute cerebral ischemia. Multimodal magnetic resonance imaging (MRI) demonstrates potential for sel ecting stroke therapy patients by identifying the presence of acute ischemi a, delineating the perfusion defect, and excluding hemorrhage. Yet, the ide ntification of tissue subject to reversible or irreversible ischemia has pr oven to be difficult. Here, the authors show that T-1 relaxation time in th e rotating frame, so-called T-1 rho, serves as a sensitive MRI indicator of cerebral ischemia in the rat. The T-1 rho prolongs within minutes after a drop in the CBF of less than 22 mL 100 g(-1) min(-1). Dependence of T-1 rho on spin-lock amplitude, termed as T-1 rho dispersion, increases by approxi mately 20% on middle cerebral artery (MCA) occlusion, comparable with the m agnitude of diffusion reduction. The T-1 rho dispersion change dynamically increases to be 38% +/- 10% by the first 60 minutes of ischemia in the brai n region destined to develop infarction. Following reperfusion after 45 min utes of MCA occlusion, the tissue with elevated T-1 rho dispersion (yet nor mal diffusion) develops severe histologically verified neuronal damage; thu s, the former parameter unveils an irreversible condition earlier than curr ently available MRI methods. The T-1 rho dispersion as a novel MRI index of cerebral ischemia may be useful in determination of the therapeutic window for acute ischemic stroke.