Investigating the impact of magnetisation transfer and water exchange via permeability on diffusion MRI measurements

Motivation: Magnetisation transfer (MT) and water exchange across permeable membranes operate on a similar length scale to diffusion and may impact the measured diffusion-weighted MRI (dMRI) signal. This could bias resulting parameter estimates when performing microstructural modelling. Goal(s): To investigate how magnetisation transfer and water exchange affect dMRI measurements, particularly pore size estimations. Approach: Monte-Carlo simulations were used to model the dMRI signal affected by MT and cross-membrane exchange in a parallel-plate geometry. Errors in plate separation estimations represent their impact on dMRI estimates. Results: MT had a limited effect on dMRI pore size estimation, while cross-membrane water exchange can cause large overestimations. Impact: Pore size estimates from diffusion-weighted MRI have been found to be minimally affected by magnetisation transfer but might be significantly biased by large membrane/structure permeability. New signal models incorporating diffusion and complementary phenomena can now be explored using Monte-Carlo simulations.