GAMMA-KNIFE IRRADIATION-INDUCED CHANGES IN THE NORMAL RAT-BRAIN STUDIED WITH H-1 MAGNETIC-RESONANCE SPECTROSCOPY AND IMAGING

Rationale and Objectives. The pathogenesis of brain injury following r adiosurgery is poorly understood. To better elucidate the relationship between blood-brain barrier disruption and metabolic derangements, we used magnetic resonance (MR) imaging and H-1 MR spectroscopy to detec t early changes from focused single-fraction, high-dose irradiation in jury in rat brains. Methods. Using the Leksell gamma knife, we irradia ted the frontoparietal cortex of 11 male Wistar rats with a single dos e of 120 Gy. Four weeks later, we sequentially performed water-suppres sed H-1 MR spectroscopy and gadopentetate dimeglumine-enhanced T1-weig hted MR imaging. Metabolic maps were created of n-acetylaspartate (NAA ), creatine and choline (Cr/Cho), and lactate from the MR spectroscopy data set. Detection of irradiation injury among the tested modalities was assessed by receiver operating characteristic analysis and by qua ntitative signal intensity changes. Pathologic confirmation of irradia tion damage was obtained in all rats. Results. Gadopentetate dimeglumi ne-enhanced T1-weighted MR imaging was the only imaging modality that detected statistically significant signal intensity changes (P < .05). No reproducible changes in the metabolites of interest could be detec ted by 1H MR spectroscopy. Conclusion. In our animal model, blood-brai n barrier disruption was a reproducible, integral finding of single-fr action, high-dose irradiation injury. No reproducible metabolic derang ements of ischemia or necrosis were detected by H-1 MR spectroscopy, p ossibly because of dose-latency effects or sensitivity issues.