Stroke is the third leading cause of death in North America and occurs when blood flow to the brain is interrupted or reduced (ischemia). During conditions of ischemia, metabolic and structural changes detectable by MR occur rapidly in brain tissue. Such changes include the production of lactate, alteration in the relative concentration of oxy- and deoxy-hemoglobin, the redistribution of ²³Na ions, and decreased ¹H₂0 diffusion. These tissue changes also result in altered ¹H₂0 relaxation times (T₁, T_1ρ, T₂, T₂*) and hence can generate contrast within MR images. However, such changes may be subtle during the acute phase of stroke damage (i.e. less than six hours) when critical decisions regarding patient treatment are usually based on the duration of ischemia and the likelihood that affected tissue may be salvaged. The combination of metabolic imaging techniques with perfusion and/or diffusion weighted imaging has shown promise for the prediction of future tissue death - a key determinant in patient therapy. The goals of this work are to develop new MRI imaging methods - particularly based on T_2ρ image contrast - to identify disuse damage in acute stroke, and to use metabolic markers of tissue damage measured by ¹H MR spectroscopy to predict tissue survival and the efficacy of neuroprotective agents.

Single coronal slices representative of the 3D histology and P-LASER images acquired during a single study. The TTC histology image (A) shows viable tissue as red and infarcted tissue as white. The corresponding CP-LASER-EPI images, taken at 20 minutes post ischemia with TE = 30.0 ms (B, 0 CP-MLEV pulses), and TE = 129.8 ms (C, 20 CP-MLEV pulses), and at 4 hours post ischemia with TE = 129.8 ms (D, 20 CP-MLEV pulses) demonstrate the increased signal intensity in CP-LASER-EPI images in the ischemic region.