MRI investigation of glymphatic responses to Gd‐DTPA infusion rates

The glymphatic system is a newly identified waste clearance pathway in brain discovered and investigated predominately using in vivo two‐photon confocal microscopy. Magnetic resonance imaging (MRI), in contrast to two‐photon confocal microscopy, provides dynamic and real‐time pictures of the glymphatic system in whole brain. We employ MRI to investigate the response of the glymphatic system to the rate of infusion of Gd‐DTPA (magnevist). Wistar rats were subjected to a surgery of inserting a tube into the cisterna magna for infusion during MRI. Three infusion rates were chosen for 20 min infusions of diluted magnevist into the cerebrospinal fluid (CSF) of rat brain. Glymphatic response was imaged using dynamic MRI 3D measurement for 5 hr. Robust correlations were found in all ventricles between the peak intensities of image enhancement and infusion rates, with additional correlations between the peak times of MRI image enhancement and infusion rates in the fourth ventricle. An infusion rate of 2.92 μL/min induced an evident accumulation of tracer in the fourth ventricle near the cisterna magna. In hippocampal tissue, image enhancements exhibited low correlation with the infusion rates. However, an infusion rate of 1.67 μL/min provided a high image enhancement, but less tracer accumulation near the cisterna magna. Contrast‐enhanced MRI provides a suitable tool for investigating image contrast infusion rate response of the glymphatic system in rat brain. Considering both T(1) and T(2)(*) effects in response to the infused magnevist into CSF, the infusion rate of 1.67 μL/min appears suitable for MRI study of the glymphatic system in rat.