Proton MR spectroscopic evaluation of suspicious brain lesions after stereotactic radiotherapy

BACKGROUND AND PURPOSE: The radiologic assessment of suspicious brain lesio ns after stereotactic radiotherapy of brain tumors is difficult. The purpos e of our study was to define parameters from single-voxel proton MR spectro scopy that provide a probability measure for differentiating neoplastic fro m radiation-induced, nonneoplastic lesions. METHODS: Seventy-two lesions in 56 patients were examined using a combined MR imaging and MR spectroscopy protocol (point-resolved spectroscopy, TE = 135 ms). Signal intensities of cholines, creatines, N-acetyl aspartate, and the presence of lactate and lipid resonances were correlated to final diag noses established by clinical and MR imaging follow-up, positron emission t omography studies, or biopsy/surgery. Statistical analysis was performed us ing the t test, linear discriminant analysis, and k nearest-neighbor method . RESULTS: Significantly increased signal intensity ratios I-tCho/I-tCr (P < .0001) and I-tCho/I-NAA (P < .0001) were observed in neoplastic (n = 34) co mpared with nonneoplastic lesions (n = 32) and contralateral normal brain ( n = 33). Analysis Of I-tcho/I-tCr and I-tCho/I-NAA data yielded correct ret rospective classification as neoplastic and nonneoplastic in 82% and 81% of the lesions, respectively. Neither I-NAA/I-tCr nor signal intensitities of lactate or lipids were useful for differential diagnosis. CONCLUSION. Metabolic information provided by proton MR spectroscopy is use ful for the differentiation of neoplastic and nonneoplastic brain lesions a fter stereotactic radiotherapy of brain tumors.