A Miniature Ultrasound Source for Neural Modulation
Samantha F. Schafer, Haley Croke, Andres Kriete, Hasan Ayaz, Peter A. Lewin, Catherine R. von Reyn, Mark E. Schafer
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 2023 · 10.1109/tuffc.2023.3322963
Abstract
This work describes a unique ultrasound (US) exposure system designed to create very localized ( [Formula: see text]) sound fields at operating frequencies that are currently being used for preclinical US neuromodulation. This system can expose small clusters of neuronal tissue, such as cell cultures or intact brain structures in target animal models, opening up opportunities to examine possible mechanisms of action. We modified a dental descaler and drove it at a resonance frequency of 96 kHz, well above its nominal operating point of 28 kHz. A ceramic microtip from an ultrasonic wire bonder was attached to the end of the applicator, creating a 100- [Formula: see text] point source. The device was calibrated with a polyvinylidene difluoride (PVDF) membrane hydrophone, in a novel, air-backed, configuration. The experimental results were confirmed by simulation using a monopole model. The results show a consistent decaying sound field from the tip, well-suited to neural stimulation. The system was tested on an existing neurological model, Drosophila melanogaster, which has not previously been used for US neuromodulation experiments. The results show brain-directed US stimulation induces or suppresses motor actions, demonstrated through synchronized tracking of fly limb movements. These results provide the basis for ongoing and future studies of US interaction with neuronal tissue, both at the level of single neurons and intact organisms.
Abstract via europepmc.
Exposures
Exposure 1: 96 kHz miniature microtip source over the Drosophila central brain
Target: drosophila neurons — “the center of the right hemisphere of the central brain”
Device: custom-built · modified dental ultrasonic descaler (Langevin stack) with 100 um ceramic wire-bonder microtip
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 96 | ✓✓✓ |
| Pulse duration (ms) | not reportedimplied by duty cycle ÷ PRF: 0.5 ms (not stated by the paper) | ⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓ |
| Duty cycle (%) | 50 | ✓✓✓⚑ |
| Sonication duration (s) | 5 | ✓✓✓ |
| Free-field pressure (kPa) | 14 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable |
Tone bursts at 96 kHz, 1 kHz pulse repetition rate, duty cycle varied (30-80 %) with 50 % most consistent, delivered for 5 s inside a 15-s recording; 4-8 trials per fly with 8 min recovery. Bursts were always longer than 30 cycles because the source is resonant.
Flags from extraction
exposures[0].unspecified_domain.pressure_kpa— 'Estimated pressure level of 14 kPa' with no statement of domain; calibration used an air-backed hydrophone at 100 um from the tip and a monopole calculation gave 20 kPa.exposures[0].timing.duty_cycle_pct— Duty cycle varied between 30-80 % (methods) or 20-80 % (discussion); 50 % is the proof-of-concept value recorded.exposures[0].timing.pulse_duration_ms— Not stated.n_subjects— Only 'representative examples from six flies' and 4-8 trials per fly are given; total not stated.anaesthesia— Flies were cold-anaesthetised for preparation then head-fixed and behaving during sonication; recorded as awake.