Quantitative in vivo proton MR spectroscopic evaluation of the irradiated rat brain

Purpose: To investigate if in vivo localized proton magnetic resonance spectroscopy (MRS) can detect putative metabolic changes in the irradiated rat brain and quantitatively measure brain metabolite changes in this model. Materials and Methods: A total of 20 adult male Fischer 344 rats were exposed to a fractionated regimen of whole brain irradiation (WBI) (total 45 Gy, given as five Gy fractions. twice per week for 4.5 weeks); 10 control rats received sham irradiation. A total of 52 weeks after WBI, all animals were subjected to high-resolution MRI and in vivo proton MRS to determine structural and brain metabolite changes. Brain metabolites were measured by using single-voxel MRS. Quantitative analysis of detectable metabolites was performed by using the spectral analysis method, LCModel. Results: Significant differences in brain metabolite concentrations were detected in rat brains irradiated with a clinically relevant fractionated radiotherapy regimen in 52 weeks, in comparison to age-matched sham-irradiated rats. Conclusion: These findings indicate that quantitative in vivo MRS may serve as a sensitive imaging tool to noninvasively detect neurochemical changes in the irradiated brain.