MRI study suggests an optimal time of day for evaluating glymphatic function
New findings suggest that the early morning hours may be the best time to assess glymphatic function on imaging.
The glymphatic system is responsible for eliminating metabolic waste from the brain. Some of this waste, such as amyloid-β and tau proteins, are toxic and can lead to adverse neurological conditions, making the function of the glymphatic system critical for neural health.
Sleep plays an important role in glymphatic activity. Most glymphatic clearance occurs during sleep and prior studies have indicated that poor sleep habits are associated with poor glymphatic function. With this in mind, researchers proposed the idea that there may be certain times of day that are optimal for examining the clearance process.
“Understanding these variations is important for optimizing the timing of clinical imaging studies and interpreting glymphatic measurements accurately. For instance, misinterpreting glymphatic function due to unaccounted diurnal variations could lead to incorrect assessments in clinical or research settings,” Yangsean Choi, with the Department of Radiology and Research Institute of Radiology at the University of Ulsan College of Medicine in the Republic of Korea, and colleagues explained. “Given that MRI scans are commonly conducted at various times during the day, recognizing these diurnal variations could help clinicians and radiologists better interpret the results of diffusion tensor image analysis along the perivascular space (DTI-ALPS).”
Diffusion tensor MRI is the modality of choice for evaluating glymphatic function. For the study, researchers retrospectively analyzed all patients who underwent the exam at a single center between January and August 2023. The team took note of what time each scan was completed and compared the time of day (dawn, early morning, daytime, and evening/night) to patients’ ALPS index values.
Among the more than 500 exams studied, those conducted in the hours around dawn had the highest mean ALPS index, followed by early morning, evening/night and then daytime. The daytime values were significantly lower than those observed during the exams completed around dawn, suggesting the daytime hours might be the least optimal time to evaluate glymphatic function.
“Our study highlights the significant differences in glymphatic function across various times during the day, demonstrating that glymphatic activity is not solely influenced by arousal states but is also modulated by circadian rhythms,” the team noted. “While prior studies have predominantly focused on the relationship between sleep and glymphatic clearance, our findings emphasize the role of intrinsic circadian oscillations in regulating glymphatic dynamics.”
The group suggested that additional work is needed to better understand intra-individual differences in glymphatic activity over a 24-hour period.
Learn more about the findings here.
In addition to her background in journalism, Hannah also has patient-facing experience in clinical settings, having spent more than 12 years working as a registered rad tech. She began covering the medical imaging industry for Innovate Healthcare in 2021.