Transcranial focused ultrasound stimulation with high spatial resolution
Seongyeon Kim, Yehhyun Jo, Geon Kook, Cristina Pasquinelli, Hyunggug Kim, Kipom Kim, Hyang-Sook Hoe, Youngshik Choe, Hyewhon Rhim, Axel Thielscher, Jeongyeon Kim, Hyunjoo Jenny Lee
Brain Stimulation 2021, 14, 290-300 · 10.1016/j.brs.2021.01.002
Abstract
Background Low-intensity transcranial focused ultrasound stimulation is a promising candidate for noninvasive brain stimulation and accurate targeting of brain circuits because of its focusing capability and long penetration depth. However, achieving a sufficiently high spatial resolution to target small animal sub-regions is still challenging, especially in the axial direction. Objective To achieve high axial resolution, we designed a dual-crossed transducer system that achieved high spatial resolution in the axial direction without complex microfabrication, beamforming circuitry, and signal processing. Methods High axial resolution was achieved by crossing two ultrasound beams of commercially available piezoelectric curved transducers at the focal length of each transducer. After implementation of the fixture for the dual-crossed transducer system, three sets of in vivo animal experiments were conducted to demonstrate high target specificity of ultrasound neuromodulation using the dual-crossed transducer system (n = 38). Results The full-width at half maximum (FWHM) focal volume of our dual-crossed transducer system was under 0.52 μm 3 . We report a focal diameter in both lateral and axial directions of 1 mm. To demonstrate successful in vivo brain stimulation of wild-type mice, we observed the movement of the forepaws. In addition, we targeted the habenula and verified the high spatial specificity of our dual-crossed transducer system. Conclusions Our results demonstrate the ability of the dual-crossed transducer system to target highly specific regions of mice brains using ultrasound stimulation. The proposed system is a valuable tool to study the complex neurological circuitry of the brain noninvasively.
Abstract via europepmc.
Exposures
Exposure 1: Motor cortex stimulation (dual-crossed transducer)
Target: motor cortex — “motor cortex”
Device: other named manufacturer · Hagisonic Inc. ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 5,000 | ✓✓✓ |
| Pulse duration (ms) | not reportedimplied by duty cycle ÷ PRF: 1 ms (not stated by the paper) | |
| Pulse repetition frequency (Hz) | 500 | ✓✓✓ |
| Duty cycle (%) | 50 | ✓✓✓ |
| Sonication duration (s) | 0.4 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 1 | ✓✓✓⚑ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | 0.13 | ✓✓✓ |
| In-situ Ispta (W/cm²) | not reported |
The stimulation parameters were center frequency of 5 MHz, duration of 0.4 s, pulse repetition frequency (PRF) of 500 Hz, duty cycle of 50%, and intensity of 1 W/cm2 (~130 mW/cm2 accounting for skull attenuation effects). A separate beam-profile characterization measured a maximum intensity of 1189 mW/cm2 (~155 mW/cm2 accounting for skull attenuation), which is not necessarily the same measurement as the stated in vivo exposure.
Exposure 2: Habenula stimulation (dual-crossed transducer)
Target: habenula — “habenula”
Device: other named manufacturer · Hagisonic Inc. ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 5,000 | ✓✓✓ |
| Pulse duration (ms) | not reportedimplied by duty cycle ÷ PRF: 1 ms (not stated by the paper) | |
| Pulse repetition frequency (Hz) | 500 | ✓✓✓ |
| Duty cycle (%) | 50 | ✓✓✓ |
| Sonication duration (s) | 0.4 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 1 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | deratingsingle value | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | 0.13 | ✓✓✓ |
| In-situ Ispta (W/cm²) | not reported |
Using the same protocol as the cortical stimulations, neuromodulation of the habenula was conducted: center frequency of 5 MHz, duration of 0.4 s, PRF of 500 Hz, duty cycle of 50%, and intensity of 1 W/cm2 (~130 mW/cm2 accounting for skull attenuation effects).
Flags from extraction
sham_type— Controls for habenula c-Fos comparison were off-target stimulation (active_control_site) and a 'no stimulation' arm that does not map cleanly to a vocabulary sham type; recorded as 'other'.exposures[0].free_field.isppa_w_cm2— Paper states 'intensity' without specifying spatial-peak pulse-average vs temporal-average; recorded as Isppa by convention. A separate beam-profile measurement elsewhere in the paper reports 1189 mW/cm2 free field / 155 mW/cm2 in situ, which may or may not be the same quantity as the 1 W/cm2 stated stimulation parameter.timing.pulse_duration_ms— Only PRF (500 Hz) and duty cycle (50%) are given; pulse duration would require arithmetic and is not stated directly, so left not_reported.