Glymphatic System Visualized by Chemical-Exchange-Saturation-Transfer Magnetic Resonance Imaging

Abstract

Dysfunction of the glymphatic system may play a significant role in the development of neurodegenerative diseases. However, <i>in vivo</i> imaging of the glymphatic system is challenging. In this study, we describe an unconventional MRI method for imaging the glymphatic system based on chemical exchange saturation transfer, which we tested in an <i>in vivo</i> porcine model of impaired glymphatic function. The blood, lymph, and cerebrospinal fluid (CSF) from one pig were used for testing the MRI effect <i>in vitro</i> at 7 Tesla (T). Unilateral deep cervical lymph node ligation models were then performed in 20 adult male Sprague-Dawley rats. The brains were scanned <i>in vivo</i> dynamically after surgery using the new MRI method. Behavioral tests were performed after each scanning session and the results were tested for correlations with the MRI signal intensity. Finally, the pathological assessment was conducted in the same brain slices. The special MRI effect in the lymph was evident at about 1.0 ppm in water and was distinguishable from those of blood and CSF. In the model group, the intensity of this MRI signal was significantly higher in the ipsilateral than in the contralateral hippocampus. The correlation between the signal abnormality and the behavioral score was significant (Pearson's, <i>R</i>² = 0.9154, <i>p</i> < 0.005). We conclude that the novel MRI method can visualize the glymphatic system <i>in vivo</i>.