The distortions of the free water model for diffusion MRI data when assuming single compartment relaxometry and proton density.

To document the bias of thefree water model of diffusion MRI (dMRI) signal vis-à-vis amodel which, in addition to diffusion, incorporates compartment-specific proton density (PD), T1 recovery during repetition time (TR), and T2 decay during echo time (TE).Both models assume that volume fractionof the total signal in any voxel arises from the free water compartment () such as cerebrospinal fluid or edema, and the remainder (1) from hindered water () which is constrained by cellular structures such as white matter (WM). Theandmodels are compared on a synthetic dataset, using a range of PD, T1 and T2 values. We then fit the models to anhealthy brain dMRI dataset. For bothanddata we use experimentally feasible TR, TE, signal-to-noise ratio (SNR) and physiologically plausible diffusion profiles.From the simulations we see that the difference between the estimatedandis largest for mid-range ground-truth, and it increases as SNR increases. The estimation of volume fractionis sensitive to the choice of model,or, but the estimated diffusion parameters are robust to small perturbations in the simulation.is more accurate and precise than. In the white matter (WM) regions of theimages,is lower than.In dMRI models for free water, accounting for compartment specific PD, T1 and T2, in addition to diffusion, improves the estimation of model parameters. This extra model specification attenuates the estimation bias of compartmental volume fraction without affecting the estimation of other diffusion parameters.