Comparison of water exchange measurements between filter-exchange and diffusion time-dependent kurtosis imaging in human brain

Motivation: Trans-membrane water exchange rate has been measured by several MRI methods but reported with largely variant results. Goal(s): To explore whether Filter-exchange imaging (FEXI) and time-dependent DKI are comparable for water exchange measurements on the same subjects in human brain. Approach: Eight healthy volunteers underwent FEXI and DKI(t) acquisitions on a 3T scanner. ROI-based analysis was performed to determine correlations between FEXI-derived AXR and DKI(t)-derived 1/τex. Results: A significant correlation between AXR and 1/τex was found only in axial direction in white matter. This correlation should be interpreted cautiously because structural disorder has non-negligible effects on D(t) and K(t) in Kärger model. Impact: While a significant correlation was observed between AXR and 1/τex in the axial direction, this study suggests cautious use of DKI(t) for water exchange measurements due to potential deviations from the Kärger model's constant diffusivity assumption in the human brain.