NMR Imaging and Spectroscopy of the Mammalian Central Nervous System after Heavy Ion Radiation

Abstract

NMR imaging, NMR spectroscopy, and histopathologic techniques were used to study the proton relaxation time and related biochemical changes in the rodent brain after in vivo helium beam irradiation with single doses of 10, 20, 30, and 50 Gy. Two-dimensional Fourier transform spin-echo imaging and saturation recovery with projection reconstruction were used to measure the NMR relaxation parameters. These parameters were correlated with proton spectroscopy and histopathology. Additional high resolution in vitro proton spectroscopy was performed on brain extracts to observe chemical changes that could not be seen in vivo. The major findings from these experiments were that at 4-14 days postirradiation, image intensity and T1 relaxation time decreased on the irradiated side and increased on the nonirradiated side relative to nonirradiated control animals. In vivo surface coil proton spectroscopy methods demonstrated changes in lipid and phosphatidylcholine (p-choline) peaks. In vitro studies of the aqueous fraction of brain extracts showed radiation-induced changes in lactate, 4-aminobutyric acid, and p-choline peak areas. In the organic fraction, radiation-induced changes were observed in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine. With histology and Evans blue injections, blood-brain barrier alterations were seen as early as 4 days after a dose of 50 Gy.