Is the inversion time important? A study of the reciprocal influence of inversion time and b-value on diffusion and longitudinal relaxation in MRI

The nervous tissue microstructure can be characterized by sensitizing the MRI signal to diffusion. The advent of multi-parametric sequences enabled the collection of diffusion data at different echo and inversion times. While the link between diffusion and transverse relaxation has undergone several investigations, in this work we characterize the relationship between the diffusion and longitudinal relaxation, and quantify the reciprocal influence of b-values and inversion time on the quantification of T1 and of diffusion metrics, interpreting our findings on in vivo data in the light of numerical simulations, and showing evidence that longitudinal relaxation locally modifies the diffusion contrast.