Measuring water exchange in myelinated white matter using Magnetization Transfer (MT)-weighted constant gradient diffusion MRI (MT-cgdMRI)

In white matter, myelin forms a barrier for water exchange between the intra-axonal and extra-axonal compartments. Although myelin is not directly visible in conventional diffusion MRI (dMRI), it may affect dMRI measurements via exchange. In this study, we compared two ways to combine magnetization transfer (MT) preparation with constant gradient dMRI (cg-dMRI) to study the effects of myelin on water exchange rate. Our results demonstrate that MT preparation can modulate the sensitivity of cg-dMRI to exchange by suppressing signals from a portion of exchanging spins and that placing MT preparation is more effective before diffusion encoding than during diffusion encoding.