Sodium T2*-weighted MR imaging of acute focal cerebral ischemia in rabbits

Changes in T-2*-weighted tissue sodium (Na-23) signal following acute ischemia may help to identify necrotic tissue and estimate the duration of ischemia. Sodium signal was monitored in a rabbit model of acute (0-4 h) focal cerebral ischemia, using gradient echo Na-23 MR images (echo time = 3.2 ms) acquired continuously in 20-min intervals on a 4-Tesla MRI. 2,3,5-Triphenyl-tetrazolium chloride staining was used to identify regions of necrosis. In necrotic tissue, average Na-23 image signal intensity decreased by 11% +/- 8% during the first 40 min of ischemia followed by a linear increase (0.19%/min) to 25% +/- 14% greater than baseline after 4 h of ischemia. The time course of Na-23 signal change observed in necrotic tissue following focal ischemia in this rabbit model is consistent with an initial decrease in Na-23 T-2* relaxation time followed by an increase in tissue sodium concentration and provides further evidence that tissue Na-23 signal may offer unique information regarding tissue viability that is complementary to other MR imaging techniques. (C) 2004 Elsevier Inc. All rights reserved.