Neuroimaging assessment of memory-related brain structures in a rat model of acute space-like radiation

Abstract

Purpose: To investigate the acute effects on the central nervous system (CNS) of 56Fe radiation, a component of high-energy charged particles (HZE) in space radiation, using quantitative magnetic resonance imaging (MRI) non- invasively. Materials and Methods: Sprague-Dawley rats were exposed to whole-brain 56Fe (0, 1, 2, and 4 Gy). At 1 week postirradiation, MRI scans were made using T2-weighted (T2WI), diffusion-weighted (DWI), and contrast enhanced T1-(CET1) imaging. T2 relaxation time and apparent diffusion coefficient (ADC) values were obtained from memory- related brain regions of interest (ROIs). Histopathology was correlated using ex vivo tissues. Results: No overt abnormalities were visualized using T2WI and DWI at 1 week postradiation. CET1 values did not differ significantly between the irradiated and control animals. Compared to 0 Gy, there were significant prolongations in T2 values and reductions in ADC after irradiation. In the absence of evident neuronal pathology, immunohistochem- istry revealed astrocytic activation in 4 Gy animals. Conclusion: At 1 week after whole-brain 56Fe exposure, T2 and ADC values can differentiate radiosensitivity in regions critical for hippocampal-related memory. MRI may provide noninvasive assessment of the initial molecular/cellular disturbances in vivo after HZE irradiation. © 2009 Wiley-Liss, Inc.