Objectives: ...In the current study, we aimed to establish a clinical magnetic resonance imaging (MRI) study protocol for visualizing lymphatic vessels as part of the GLS in humans. More importantly, we aimed to describe the dynamic changes of a contrast agent in these lymphatic vessels over time.

Materials and methods: Twenty volunteers with an unremarkable neurological/psychiatric history were included in this 3T MRI study. Serial MRI sequence blocks were performed at 3 predefined time points (TP)...The time course of the signal intensities was examined by generalized linear mixed models. The data were adjusted for age, cognitive function (Montreal-Cognitive-Assessment test), and sleep quality (Pittsburgh Sleep Quality Index questionnaire).

Results: The GLS was best visualized in the 2D T2-FLAIR and 3D T1-SPACE sequences, enabling further SI measurement. In precontrast (TP 1), the SI within the GLS was significantly higher than in CSF and significantly lower than in GM and WM. In post-GBCA, a significant increase (TP 2) and decrease (TP 3), respectively, of the GLS SI values were noted (86.3 ± 25.2% increase and subsequent decrease by 25.4 ± 9% in the 3D T1-SPACE sequence). The SI values of CSF, GM, and WM did not change significantly between the 3 TPs.

Conclusions: A clinical MRI study protocol was established for the visualization of lymphatic vessels as an important part of the GLS and therefore the brain's clearing mechanism of interstitial solutes. Furthermore, dynamic changes in the GLS were described over time, possibly reflecting the clearing function of the GLS. This might constitute the basis for evaluating the GLS function in manifold neurological pathologies in the future.