Gamma knife irradition-Induced changes in the normal rat brain studied with ¹H magnetic resonance spectroscopy and imaging

Rationale and Objectives.: The pathogenesis of brain injury following radiosurgery is poorly understood. To better elucidate the relationship between blood-brain barrier disruption and metabolic derangements, we used magnetic resonance (MR) imaging and ¹H MR spectroscopy to detect early changes from focused single-fraction, high-dose irradiation injury in rat brains. Methods.: Using the Leksell gamma knife, we irradiated the frontoparietal cortex of 11 male Wistar rats with a single dose of 120 Gy. Four weeks later, we sequentially performed water-suppressed ¹H MR spectroscopy and gadopentetate dimeglumine-enhanced T1-weighted 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 quantitative signal intensity changes. Pathologic confirmation of irradiation damage was obtained in all rats. Results.: Gadopentetate dimeglumine-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 detected by ^1H MR spectroscopy. Conclusion.: In our animal model, blood-brain barrier disruption was a reproducible, integral finding of single-fraction, high-dose irradiation injury. No reproducible metabolic derangements of ischemia or necrosis were detected by ¹H MR spectroscopy, possibly because of dose-latency effects or sensitivity issues.