When Perfusion Meets Diffusion – in vivo Measurement of Water Extraction and Permeability in Human Brain

Introduction While water was initially considered as a freely diffusible tracer in arterial spin labeling (ASL) perfusion MRI, emerging evidence suggested a limited degree of water exchange between the vascular (capillary) and tissue compartments (1, 2). Quantification of water extraction fraction and permeability is important for accurate perfusion quantification in ASL methods, and may provide clinically relevant information regarding the functional status of the microvasculature. In this study, water extraction fraction was estimated by differentiating the amount of labeled water in the vascular and tissue space based on their distinct diffusion characteristics, using diffusion weighted (DW) ASL perfusion MRI. By resorting to the single-pass approximation (SPA) model (3), we further estimated the water permeability of human brain.