Diffusion Imaging for Mapping Hydraulic White Matter Parameters in Convection Enhanced Delivery

Motivation: Intraparenchymal brain infusions using convection enhanced delivery (CED) require predictive modeling to plan catheter locations to visualize end distributions. Currently, diffusion MRI indirectly estimates extracellular volume fraction (ECVF) and creates hydraulic conductivity maps. Goal(s): To directly measure ECVF parameters using advanced biophysical diffusion models. Approach: Quantitative brain maps of ECVF from a pre-existing database were generated with diffusion model SANDI. These were compared with prior ECVF estimates determined via invasive physiological techniques. Results: SANDI modeling predicted ECVF ranges of 0.14-0.26 in white matter across 12 cases, consistent with consensus values around 0.20 estimated from physiology. Impact: SANDI can quantitatively measure extracellular volume fractions in white matter. Previous methods estimated these parameters indirectly. Direct parametrization could be used for more accurate estimates of end-state biologic distributions in proposed trials of monogenic pediatric neurodegenerative gene therapy trials.