Spatially Constrained Probability Distribution Model of Incoherent Motion (spim) Improves Longitudinal Reproducibility of Quantitative Diffusion Weighted Mri

Purpose: Diffusion-weighted MRI (DW-MRI) of the body is a non-invasive imaging technique that enables characterization of tissue microenvironments through measurement of variations in the mobility of water molecules due to cellularity, cell membrane integrity, and compartment they are located. Quantitative DW-MRI has a well-established role in the detection, characterization and follow-up of a variety of abdominal abnormalities including liver fibrosis, tumors and active inflammation . Several quantitative DW-MRI techniques have been proposed to model water molecule motion and quantify diffusion changes associated with abnormalities. The Intra-voxel incoherent motion (IVIM) model represents the diffusion signal decay with a bi-exponential function that has one decay rate parameter for the slow diffusion associated primarily with the Brownian motion of water molecules, and a second decay rate parameter for the fast diffusion component associated primarily with the bulk motion of intravascular molecules in the micro-capillaries. However, in biological systems fast diffusion can occur over a large range of length and time scales due to widely varying vessel sizes and flow rates, and the IVIM model cannot represent this heterogeneity in diffusion components. We recently introduced the Spatially-constrained Probability distribution model of Incoherent Motion (SPIM). The SPIM model represents the heterogeneity of the diffusion scales with a twocomponent probability distribution mixture model of incoherent motion and spatial homogeneity of the diffusion parameters with a spatially smoothing prior. The SPIM model allows for the precise characterization of the diffusion components even from relatively low SNR DW-MRI images. In this work, we evaluate the effect of the incoherent motion model used on longitudinal reproducibility of parameters estimation in data collected from both healthy volunteers and Crohn’s disease patients.