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MRI of focal cerebral ischemia using 17O‐labeled water

This work presents a novel approach for quantifying low concentrations of H217O in vivo and explores its utility for assessing cerebral ischemia. Oxygen‐17 enriched water acts as a T2 shortening contrast agent whose effect can be suppressed by decoupling at the 17O frequency during TE interval in a spin‐echo MR image. Serial T2‐weighted echo planar images were acquired in phantoms and rat brain with decoupler power alternated every eight images. The resulting periodic signal change (proportional to H217O concentration) was detected by cross‐correlating the square‐wave decoupler power timecourse with the signal intensity in each voxel. Natural abundance (0.037 atom%) images of H217O in rat brain were generated. The transverse relaxivity of H217O in brain was estimated, R2 = 2.4 ± 0.5 s−1(atom%)−1. After bolus injection of 1 ml of 10 atom% H217O, brain H217O concentration was estimated at 0.06 ± 0.01 atom%. In the rat focal ischemia model, 17O cross‐correlation maps compared well with diffusion and Gd‐DTPA perfusion images to indicate infarct location. Magn Reson Med 43:876–883, 2000. © 2000 Wiley‐Liss, Inc.