MRI of focal cerebral ischemia using O-17-labeled water

This work presents a novel approach for quantifying low concentrations of ( H2O)-O-17 in vivo and explores its utility for assessing cerebral ischemia. Oxygen-17 enriched water acts as a T-2 shortening contrast agent whose eff ect can be suppressed by decoupling at the O-17 frequency during TE interva l in a spin-echo MR image. Serial T-2-weighted echo planar images were acqu ired in phantoms and rat brain with decoupler power alternated every eight images. The resulting periodic signal change (proportional to (H2O)-O-17 co ncentration) was detected by cross-correlating the square-wave decoupler po wer timecourse with the signal intensity in each voxel. Natural abundance ( 0.037 atom%) images of (H2O)-O-17 in rat brain were generated. The transver se relaxivity of (H2O)-O-17 in brain was estimated, R-2 = 2.4 +/- 0.5 s(-1) (atom%)(-1). After bolus injection of 1 ml of 10 atom% (H2O)-O-17, brain ( H2O)-O-17 concentration was estimated at 0.06 +/- 0.01 atom%. In the rat fo cal ischemia model, O-17 crosscorrelation maps compared well with diffusion and Gd-DTPA perfusion images to indicate infarct location. Magn Reson Med 43:876-883, 2000. (C) 2000 Wiley-Liss, Inc.