MRI-Based Demonstration of The Normal Glymphatic System in a Human Population: A Systematic Review

Abstract The glymphatic system has been described as the exchange between cerebrospinal fluid and interstitial fluid. Recently, many studies have demonstrated the presence of the glymphatic system based on MRI. The purpose of our study is to systematically review the studies demonstrating normal glymphatic system in a human population using MRI, and to find a detailed imaging protocol for the glymphatic system. We searched the MEDLINE and EMBASE databases to identify studies with human participants that contained MRI-based demonstrations of the normal glymphatic system. We extracted data on the imaging sequence, imaging protocol, and the targeted anatomical structures on each study. According to studies using contrast-enhanced MRI, peak enhancement was sequentially detected first in the CSF space, followed by the brain parenchyma, the meningeal lymphatic vessel (MLV), and finally the cervical lymph nodes, which corresponds to the glymphatic flow. Non-contrast flow-sensitive MRI showed similar results of glymphatic inflow from the CSF space to the brain parenchyma and efflux from the brain parenchyma to the MLV. Based on current systematic review, we recommended T1-weighted MRI using contrast material to visualize the glymphatic system. Our result can increase understanding of the glymphatic system and may lay the groundwork for future development of a standard imaging protocol.