A SPECT-based method for dynamic imaging of the glymphatic system in rats

The glymphatic system is a brain-wide waste drainage system that promotes cerebrospinal fluid circulation through the brain to remove waste metabolites. Currently, the most common methods for assessing glymphatic function are ex vivo fluorescence microscopy of brain slices, macroscopic cortical imaging, and MRI. While all these methods have been crucial for expanding our understanding of the glymphatic system, new techniques are required to overcome their specific drawbacks. Here, we evaluate SPECT/CT imaging as a tool to assess glymphatic function in different anesthesia-induced brain states using two radiolabeled tracers, [In-111]-DTPA and [Tc-99m]-NanoScan. Using SPECT, we confirmed the existence of brain state-dependent differences in glymphatic flow and we show brain state-dependent differences of CSF flow kinetics and CSF egress to the lymph nodes. We compare SPECT and MRI for imaging glymphatic flow and find that the two imaging modalities show the same overall pattern of CSF flow, but that SPECT was specific across a greater range of tracer concentrations than MRI. Overall, we find that SPECT imaging is a promising tool for imaging the glymphatic system, and that qualities such as high sensitivity and the variety of available tracers make SPECT imaging a good alternative for glymphatic research.

Automated summary

SPECT/CT imaging is a promising tool for assessing the glymphatic system, as it overcomes the limitations of other imaging modalities such as fluorescence microscopy, cortical imaging, and MRI. The study shows that SPECT imaging can accurately visualize the flow of cerebrospinal fluid and identify brain state-dependent differences in glymphatic function. Compared to MRI, SPECT imaging has higher sensitivity and is capable of detecting a wider range of tracer concentrations, making it a valuable alternative for glymphatic research.