EXPERIMENTAL MR STUDY OF CEREBRAL RADIATION-INJURY - QUANTITATIVE T2 CHANGES OVER TIME AND HISTOPATHOLOGIC CORRELATION

PURPOSE: To use the pig brain as a large-animal model to examine the e ffects of high-dose single-fraction irradiation on MR images, T2 relax ation time, and histologic integrity. METHODS: A total of 24 Meishan p igs were studied: 20 irradiated animals and 4 unirradiated controls. A high dose was delivered to the right hemisphere of the animals, using a 12-MeV electron beam. Ten animals received 40 Gy at the 90% isodose , and 10 animals received 60 Gy. Quantitative measurement of T2 relaxa tion time was compared with qualitative analysis of T2-weighted images and histologic studies. RESULTS: Quantitative analysis revealed a rep roducible increase of the T2 parameter within the irradiated areas. Th e T2 kinetic could be analyzed in two phases, which appeared before th e visualization of ventricle compression, necrosis, and edema. The fir st is characterized by vascular inflammation and the latter by radiati on necrosis and edema. Both are dose dependent. CONCLUSION: These resu lts underline the ability of quantitative MR for early diagnosis of br ain radiation lesions in vivo.