Characterisation of compartmental diffusion and transverse relaxation properties of rat ischaemic tissue after stroke

Motivation: Conventional multi-echo NODDI, where the intrinsic diffusivity is fixed to a brain-wide value, has limited applicability in tissue pathologies where this parameter is significantly altered, e.g. ischaemic stroke. Goal(s): A recently proposed estimation method for multi-echo NODDI with released intrinsic diffusivity is applied here to investigate the diffusion and relaxation properties of ischaemic tissue. Approach: Model fitting is achieved via non-linear least-squares with an additional l2-norm regularisation term to impose fitting stability. Results: All compartmental diffusion and transverse relaxation parameters, in particular the tissue intrinsic diffusivity, at the ischaemic core are significantly affected compared to the contralateral side. Impact: The application of multi-echo NODDI to investigate microstructural properties of ischaemic tissue is enabled by releasing the intrinsic diffusivity (conventionally fixed to a brain-wide value), which is greatly affected in this tissue pathology.