Diffusion-weighted chemical exchange saturation transfer MRI in the human brain at 7T

Abstract

Metabolite diffusion provides information on unique intracellular environments that are not captured by water diffusion. Conventional diffusion-weighted magnetic resonance spectroscopy (DW-MRS) is a useful tool for probing metabolite diffusion, but lacks spatial information. In this study, we utilized diffusion-weighted chemical exchange saturation transfer (DW-CEST) to investigate the spatial distribution of the diffusion-based brain metabolite characteristics in the human brain. DW-CEST was performed on a phantom and five healthy subjects using a 7T human MRI, and diffusion-based CEST signals of water (Diff LD, water ) and amide (Diff LD, amide ) were compared. As expected, diffusion-weighted Z-spectra decreased as a function of the b-value. In the phantom experiments, Diff LD, amide signals were relatively preserved regardless of amide concentration, while they were effectively suppressed in non-amide regions. In the human brain, Diff LD, amide signals showed a trend toward higher values in WM than in GM, in contrast to Diff LD, water , which showed no significant anatomical contrast between the two regions. In both the phantom and human brains, Diff LD, amide was about 7 times lower and 3 times lower than Diff LD, water , respectively. In alignment with previous literature, these results suggest that the proposed DW-CEST method and the derived biomarker Diff LD, amide have potential for examining diffusion-based metabolite characteristics with higher spatial resolution than DW-MRS, warranting further investigation.