Transcranial focused ultrasound stimulation enhances cerebrospinal fluid movement: Real-time in vivo two-photon and widefield imaging evidence
Seunghwan Choi, Jeungeun Kum, Seon Young Hyun, Tae Young Park, Hyungmin Kim, Sun Kwang Kim, Jaeho Kim
Brain Stimulation 2024, 17, 1119-1130 · 10.1016/j.brs.2024.09.006
Abstract
Background Cerebrospinal fluid (CSF) flow is crucial for brain homeostasis and its dysfunction is highly associated with neurodegenerative diseases. Restoring CSF circulation is proposed as a key strategy for the treatment of the diseases. Among the methods to improve CSF circulation, focused ultrasound (FUS) stimulation has emerged as a promising non-invasive brain stimulation technique, with effectiveness evidenced by ex vivo studies. However, due to technical disturbances in in vivo imaging combined with FUS, direct evidence of real-time in vivo CSF flow enhancement by FUS remains elusive. Objective To investigate whether FUS administered through the skull base can enhance CSF influx in living animals with various real-time imaging techniques. Methods We demonstrate a novel method of applying FUS through the skull base, facilitating cortical CSF influx, evidenced by diverse in vivo imaging techniques. Acoustic simulation confirmed effective sonication of our approach through the skull base. After injecting fluorescent CSF tracers into cisterna magna, FUS was administered at the midline of the jaw through the skull base for 30 min, during which imaging was performed concurrently. Results Enhanced CSF influx was observed in macroscopic imaging, demonstrated by the influx area and intensity of the fluorescent dyes after FUS. In two-photon imaging, increased fluorescence was observed in the perivascular space (PVS) after stimulation. Moreover, particle tracking of microspheres showed more microspheres entering the imaging field, with increased mean speed after FUS. Conclusion Our findings provide direct real-time in vivo imaging evidence that FUS promotes CSF influx and flow in the PVS.
Abstract via europepmc.
Exposures
Exposure 1: FUS through skull base targeting ventricular choroid plexus
Target: other — “choroid plexus of lateral ventricles (LV) and the third ventricle (3V)”
Device: Ultran · The Ultran Group · GPS500-D19-P38 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 100 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 1 | ✓✓✓ |
| Duty cycle (%) | 10pulse duration × PRF gives 10% | ✓✓✓ |
| Sonication duration (s) | 1,800 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 5 | ✓✓✓ |
| Free-field Ispta (W/cm²) | 0.5 | ✓✓✓ |
| In-situ estimate | simulationsingle value | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | 8.07 | ✓✓✓ |
| In-situ Ispta (W/cm²) | 0.807 | ✓✓✓ |
FUS was administered at the midline of the jaw through the skull base for 30 min, aimed at the choroid plexus of the lateral and third ventricles, concurrent with in vivo CSF tracer imaging. Parameters (100 ms PD, 10% DC, 1 Hz PRF) were selected based on a prior study showing these were the most effective compared to higher duty cycles (up to 50%) or longer pulse durations (up to 750 ms or continuous wave) for enhancing CSF-mediated particle transport.
Flags from extraction
n_subjects— Paper reports multiple different sample sizes across separate imaging/histology analyses (e.g. two-photon n=11, macroscopic AUC n=10, MCA ROI n=20, microspheres from 3-4 mice, histology n=14-19) without stating a single total number of unique FUS-exposed mice, and it is unclear whether these are overlapping or distinct animals.sham_type— The 'Control' group's exact mechanism (no transducer vs. inactive transducer) is not described in the available text.direction_of_effect— Study outcome is CSF/glymphatic flow, not a conventional neuromodulation readout; direction_of_effect vocabulary does not have a clean fit, coded as not_assessed.