Neuroimaging assessment of memory-related brain structures in a rat model of acute space-like radiation.
OBJECTIVE
To investigate the acute effects on the central nervous system (CNS) of (56)Fe radiation, a component of high-energy charged particles (HZE) in space radiation, using quantitative magnetic resonance imaging (MRI) noninvasively.


METHODS
Sprague-Dawley rats were exposed to whole-brain (56)Fe (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, immunohistochemistry revealed astrocytic activation in 4 Gy animals.


CONCLUSIONS
At 1 week after whole-brain (56)Fe 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.
Huang
Lei
L
Department of Radiation Medicine, Loma Linda University School of Medicine, Loma Linda, California, USA.
Smith
Anna
A
Cummings
Peter
P
Kendall
Edward J
EJ
Obenaus
Andre
A
D000818:Animals; D003359:Cosmic Radiation; D038524:Diffusion Magnetic Resonance Imaging; D004307:Dose-Response Relationship, Radiation; D018728:Entorhinal Cortex / Q000473:pathology / Q000528:radiation effects*; D006624:Hippocampus / Q000473:pathology / Q000528:radiation effects*; D007091:Image Processing, Computer-Assisted; D007124:Immunoenzyme Techniques; D007503:Iron Isotopes; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011829:Radiation Dosage; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013788:Thalamus / Q000473:pathology / Q000528:radiation effects*
D007503:Iron Isotopes