FIG 5. Patient 18.

A–C, Contrast-enhanced gradient-echo images (26/6/1) and PRESS spectra (1000/144/1; voxel resolution, 1.0 cm³) acquired 1 day before (A) and 2 months (B) and 4 months (C) after radiosurgery. Voxel shifting was used to obtain a spectrum centered within the 15-Gy isodose line (shown in red). Although a hemorrhage present at the time of gamma knife treatment complicated radiologic interpretation, elevated Cho was clearly well outside the gamma knife target. At the last measured time point, the Cho/NAA ratio of the treated voxel (average dose, 18.5 Gy) was reduced to values comparable to normal tissue, while tumorlike spectral patterns remained present posteriorly. Resection was recommended at this time, during which biopsy samples were obtained that verified the new contrast enhancement as residual/recurrent GBM, including some necrosis.