Biomedical Sciences
Wen-Shiang Chen, MD, PhD
Professor
National Taiwan University College of Medicine
Taipei City, Taipei, Taiwan (Republic of China)
Meng-Ting Lin, MD, PhD
Attending physician / Assistant professor
National Taiwan University Hospital
Taipei City, Taipei, Taiwan (Republic of China)
Chueh-Hung Wu, MD, PhD (he/him/his)
Associate Professor
National Taiwan University College of Medicine
Taipei City, Taipei, Taiwan (Republic of China)
The glymphatic system is crucial for brain waste clearance, and its dysfunction is linked to various neurodegenerative diseases. Imaging the glymphatic system, the dynamics of perivascular spaces (PVS), remains challenging. This study aimed to employ contrast-enhanced superb microvascular imaging (SMI) to achieve real-time visualization and quantification of glymphatic flow dynamics in rat brains. Furthermore, we assessed the effect of focused ultrasound (FUS) stimulation on the flow dynamics.
Design:
Adult rats received either nanobubbles (< 450 nm) or microbubbles ( >1 µm) injections via the cisterna magna (CM) or intravenous (IV) routes (as positive control). The SMI-derived vascularity index (VI) was quantified at baseline and multiple post-injection time points to measure PVS-associated flow. To evaluate the modulation effect of glymphatic transport, FUS (0.5 MHz, 1 Hz PRF, 0.6 MPa, 1% duty cycle, 10 min total: 5 + 5 min) was applied following CM nanobubbles injection. The resulting VI was quantified at baseline (pre-FUS), and again at 5 and 10 minutes post-FUS stimulation.
Results: CM injection of nanobubbles resulted in a significant increase in VI compared to baseline (p = 0.0011), whereas microbubbles showed no signal enhancement (p = 0.6241). The nanobubbles-derived signal was transient, peaking at 5 minutes post-injection (p < 0.0001) and declining by 20 minutes (p < 0.0001). Furthermore, subsequent FUS stimulation robustly amplified the nanobubbles-enhanced VI, showing a significant increase after the first 5-minute session (p = 0.0005), which was sustained after a second session.
Conclusion:
This research establishes nanobubble-enhanced SMI as a viable platform for quantifying PVS dynamics, demonstrating that nanobubbles, unlike microbubbles, overcome size-exclusion limitations. This ultrasound-based strategy bridges a critical gap between superficial optical imaging and macroscopic MRI, offering a powerful, accessible tool to probe glymphatic dysfunction in deep parenchymal structures and assess FUS-mediated modulation of glymphatic dynamics.
