Acute changes in MRI diffusion, perfusion, T(1), and T(2) in a rat model of oligemia produced by partial occlusion of the middle cerebral artery.

Oligemic regions, in which the cerebral blood flow is reduced without impaired energy metabolism, have the potential to evolve toward infarction and remain a target for therapy. The aim of this study was to investigate this oligemic region using various MRI parameters in a rat model of focal oligemia. This model has been designed specifically for remote-controlled occlusion from outside an MRI scanner. Wistar rats underwent remote partial MCAO using an undersize 0.2 mm nylon monofilament with a bullet-shaped tip. Cerebral blood flow (CBF(ASL)), using an arterial spin labeling technique, the apparent 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 CBF(ASL) to 35 +/- 5% of baseline throughout the middle cerebral artery territory. During the entire period of the study there were no 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 conclusion, this study demonstrates the feasibility of partially occluding the 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 edema. We attribute the acute change in T(2) to increased amounts of deoxyhemoglobin; the mechanisms underlying the change in T(1) require further investigation.