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Monitoring time dependence with diffusion MRI provides observables sensitive to restricted diffusion and exchange. Probing these phenomena by simply varying the diffusion time is a challenge because they have opposite effects on the diffusion-weighted signal and may cancel each other. A theoretical framework was recently proposed for disentangling the effects using free gradient waveforms. Here we explore the potential of the approach for neuroimaging in vivo using a high-performance gradient system. Results demonstrate unprecedented ability to disentangle the effects of restriction and exchange. Maps of the exchange rate show plausible contrast in both cortical and subcortical regions of the brain.
Chakwizira et al. (Wed,) studied this question.