Advanced diffusion-weighted magnetic resonance imaging in the evaluation of white matter axons in patients with idiopathic normal pressure hydrocephalus

Masaaki Hori; Kouhei Kamiya; Ryusuke Irie

doi:10.4103/1673-5374.221149

摘要：With the increasing application of regenerative medicine in vivo, non-invasive and accurate methods for estimating the white mat-ter axons in neuronal tissue have become increasingly important. As a non-invasive method for patients, magnetic resonance (MR) imaging has demonstrated potential as a promising tool for evalu-ating axons in vivo. In particular, diffusion-weighted MR imaging (dMRI) and its applications, such as white matter tractography and the metrics derived from dMRI data (i.e., mean diffusivity and frac-tional anisotropy (FA)), have been used for the semi-quantitative measurement of normal and diseased axons of neuronal tissues, particularly in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and idiopathic normal pressure hy-drocephalus (iNPH), because the diagnosis and monitoring of the status of neurodegenerative diseases are usually estimated based on clinical symptoms, gene abnormalities and imaging findings. Moreover, recent advances in MR imaging, such as more com-plicated and dedicated dMRI analyses, are emerging and can be compared with conventional dMRI. Unlike the previous conven-tional dMRI, recent advances in dMRI are based on the theory of the non-Gaussian assumption of water molecule diffusivity and/or compartment model analysis because the Gaussian assumption of water molecule diffusion in the tissue made by conventional dMRI theory has drawbacks and limitations that restrict the more accu-rate estimation of the microstructures of actual neuronal tissues. In actual neuronal tissues, Gaussian distributions of water molecules are rarely observed because tissue microstructures, such as cell membranes, organelles and myelin sheaths, can act as barriers to water molecules. Therefore, emerging and advanced dMRI analyses have the potential to provide new and additional information re-garding the actual neuronal tissue microstructures compared with conventional dMRI.