Revealing membrane integrity in human brain using oscillating-gradient diffusion sequence in two frequency-varying regimes

Motivation: In vivo evaluation of membrane integrity has been achieved through diffusion frequency-dependence, measured by using oscillating-gradient spin-echo (OGSE) sequence. However, the observed frequency-dependence in previous studies is inconsistent due to two different ways of varying frequency. Goal(s): To compare and interpret the frequency-dependent kurtosis, measured by using OGSE of varying frequency with either (1) a fixed number of oscillations or (2) a fixed total waveform time. Approach: We performed in vivo frequency-dependent kurtosis measurements in brains by using OGSE in two approaches and explained results based on adiabatic KÄrger exchange model. Results: The theory coincided with observations and yielded membrane exchange time estimations. Impact: We measured frequency-dependent kurtosis in human brains using oscillating-gradient-spin-echo sequence with either a fixed number of oscillations or a fixed total waveform time. The observed kurtosis frequency-dependence in two approaches were orthogonal, providing a novel way to evaluate water exchange.