Microscopic Propagator Imaging (MPI) with Diffusion MRI
This method addresses the need for more specific biomarkers in neuroscience and medical imaging to directly link changes to microstructure integrity, though it appears incremental as it builds on existing diffusion MRI techniques.
The authors tackled the problem of measuring microscopic tissue properties in diffusion MRI by introducing Microscopic Propagator Imaging (MPI), which retrieves indices specific to microstructures like axons, independent of mesoscopic organization, and demonstrated it on synthetic and human data.
We propose Microscopic Propagator Imaging (MPI) as a novel method to retrieve the indices of the microscopic propagator which is the probability density function of water displacements due to diffusion within the nervous tissue microstructures. Unlike the Ensemble Average Propagator indices or the Diffusion Tensor Imaging metrics, MPI indices are independent from the mesoscopic organization of the tissue such as the presence of multiple axonal bundle directions and orientation dispersion. As a consequence, MPI indices are more specific to the volumes, sizes, and types of microstructures, like axons and cells, that are present in the tissue. Thus, changes in MPI indices can be more directly linked to alterations in the presence and integrity of microstructures themselves. The methodology behind MPI is rooted on zonal modeling of spherical harmonics, signal simulation, and machine learning regression, and is demonstrated on both synthetic and Human Diffusion MRI data.