Metabolite diffusion up to very high b in the mouse brain In Vivo: Revisiting the potential correlation between relaxation and diffusion properties

Purpose:To assess the potential correlation between metabo-lites diffusion and relaxation in the mouse brain, which is ofimportance for interpreting and modeling metabolite diffusionbased on pure geometry, irrespective of relaxation properties(multicompartmental relaxation or surface relaxivity).Methods:A new diffusion-weighted magnetic resonance spec-troscopy sequence is introduced, dubbed “STE-LASER,” whichpresents several nice properties, in particular the absence ofcross-terms with selection gradients and a very clean localiza-tion. Metabolite diffusion is then measured in a large voxel in themouse brain at 11.7 Tesla using a cryoprobe, resulting in excel-lent signal-to-noise ratio, up to very highb-values under differentecho time, mixing time, and diffusion time combinations.Results:Our results suggest that the correlation betweenrelaxation and diffusion properties is extremely small or evennonexistent for metabolites in the mouse brain.Conclusion:The present work strongly supports the interpre-tation and modeling of metabolite diffusion primarily based ongeometry, irrespective of relaxation properties, at least undercurrent experimental conditions