1 H-MR spectroscopy of the rat hippocampus after whole brain irradiation: an in vivo study

Objective To study the relationships between dynamic changes of the hippocampus metabolites,cognitive impairment and uhrastructural changes of hippocampus in rots during the initial 4 weeks after 6 MV X-ray whole-brain irradiation.Methods 65 rats were randomly divided into four groups as sham control(n=5),10 Gy,20 Gy and 30 Gy groups(n=20).The learning and memory ability was measured with the Y maze test 4,8 weeks,2,6 months after irradiation.1H-MRS was performed after 2 or 4 weeks'brain irradiation.The ultrastrnctural changes of the hippoeampus were observed by electronic microscope.Results The learning and memorizing ability of irradiation groups was significantly different from that of control group.Compared with control group,the NAA/Cr and Cho/Cr ratio in the left hippocampus in 10 Gy,20 Gy and 30 Gy groups at 2 weeks and 4 weeks decreased significantly.Neuronal mitochondria edema,endothelial cells swelling and lamina dissociation in myelin sheath were demonstrated in various degrees by electmmicmscope at 4 weeks following whole brain irradiation.Conclusions1H-MRS can be used to non-invasively monitor the metabolic changes,both quantitatively and dynamically,of the irradiated rat brain.1H-MRS is superior to MRI in detecting early abnormality of the brain.Tlle NAA/Cr and Cho/Cr ratio in irradiated hippocampus could reflect the severity of the brain injury to some extent. Key words: Magnetic resonance spectroscopy;  Radiation brain lesions;  Rat;  Microscopy; Electron;  Cognition