Simplified Anisotropic IVIM using Spherical Means and an Application in the Placenta

Motivation: The intravoxel incoherent motion (IVIM) model can separately assess diffusion in tissue and perfusion in vasculature. However, anisotropic extensions to IVIM that model coherently orientated vasculature are complex and difficult to fit. Goal(s): Enhance the IVIM model to account for macroscopic anisotropy in vascular structures, while minimizing the increase in model complexity. Approach: We model perfusion and diffusion compartments using constrained tensors and estimate the tensor parameters via the spherical mean. Results: Our spherical mean anisotropic IVIM approach quantifies and maps anisotropy in perfusion and diffusion compartments and captures microstructural and microcirculatory alterations in the placenta during pregnancy. Impact: Existing anisotropic IVIM models are complex and clinically impractical. We demonstrate a spherical mean approach that simplifies the disentanglement of perfusion- and diffusion-related anisotropy. This can enable rapid quantification of biomarkers for detecting microcirculatory and microstructural changes in anisotropic tissue.