Acute changes in MRI diffusion, perfusion, T-1, and T-2, in a rat model ofoligemia produced by partial occlusion of the middle cerebral artery

Oligemic regions, in which the cerebral blood flow is reduced without impai red energy metabolism, have the potential to evolve toward infarction and r emain a target for therapy. The aim of this study was to investigate this o ligemic region using various MRI parameters in a rat model of focal oligemi a. This model has been designed specifically for remote-controlled occlusio n from outside an MRI scanner. Wistar rats underwent remote partial MCAO us ing an undersize 0.2 mm nylon monofilament with a bullet-shaped tip. Cerebr al blood flow (CBFASL) using an arterial spin labeling technique, the appar ent diffusion coefficient of water (ADC), and the relaxation times T-1 and T-2 were acquired using an 8.5 T vertical magnet. Following occlusion there was a decrease in CBFASL to 35 +/- 5% of baseline throughout the middle ce rebral artery territory. During the entire period of the study there were n o observed changes in the ADC. On occlusion, T-2 rapidly decreased in both cortex and basal ganglia and then normalized to the preocclusion values. T- 1 values rapidly increased (within approximately 7 min) on occlusion, In co nclusion, this study demonstrates the feasibility of partially occluding th e middle cerebral artery to produce a large area of oligemia within the MRI scanner. In this region of oligemic flow we detect a rapid increase in T-1 and decrease in T-2. These changes occur before the onset of vasogenic ede ma. We attribute the acute change in T-2 to increased amounts of deoxyhemog lobin; the mechanisms underlying the change in T-1 require further investig ation. (C) 2000 Wiley-Liss, Inc.