A phased array ultrasound system with a robotic arm for neuromodulation

Jongbum Seo, Hyunsoo Shin, Sungtaek Cho, Sungon Lee, Wooseok Ryu, Su-Cheol Han, Da Hee Kim, Goo Hwa Kang

Medical Engineering & Physics 2023 · 10.1016/j.medengphy.2023.104023

nonhuman primatehealthybehaviour

Abstract

Background Ultrasonic neuromodulation (UNMOD) provides a non-invasive brain stimulation. However, the high-resolution region-specificity of UNMOD with a single element transducer combined with a mechanical positioning system could have limits due to the intrinsic positioning error from mechanical systems. Objective/hypothesis A phased array system could lead to highly selective neuromodulation with electronic control. Methods A specialized phased-array system with a robotic arm is implemented for a rhesus monkey model. Various primary motor cortex areas related to tail, hand, and mouth were stimulated with a 200 μm step size. The ultrasonic parameters were I SPTA of 840 mW/cm 2 , pulse repetition frequency of 100 Hz, and a 5% duty factor at 600 kHz. The induced movement were recorded and analyzed. Results Separate digits, mouth, and tongue motions were successfully induced by electronically controlling the focus. The identical body part movement could be induced when the focus was moved back to the identical primary motor cortex with electronic control. Accordingly, the reproducibility of UNMOD could be partially validated with rhesus monkey model. Conclusion A phased-array system appears to have a potential for the non-invasive and region-selective neuromodulation method.

Abstract via europepmc.

Speciesrhesus macaque (rhesus monkey)

Subjects2 animals

Sessions per subjectnot reported

Randomisednot reported

Blindingnot reported

Sham / controlnone

Auditory controlnot reported

Readout timingonline

Anaesthesiaanaesthetised

Readoutsbehaviour — camcorder recording of induced tail, digit, mouth and tongue movement

Direction of effectexcitatoryTail, finger, thumb, jaw, lower lip and tongue movements were induced depending on focus position (200 um steps); response delay averaged 12 s.

Adverse eventsnot reportedA 2D Pennes bioheat simulation gave a temperature rise of about 0.5 C at the focus after 60 s; no in vivo safety assessment is described.

Exposures

Exposure 1: Phased-array UNMOD of monkey motor cortex (tail, hand, mouth areas)

Target: primary motor cortex — “primary motor cortex areas related to tail, hand, and mouth”
Device: IGT / Imasonic · Imasonics, France ✓

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	600	✓✓✓
Pulse duration (ms)	not reportedimplied by duty cycle ÷ PRF: 0.5 ms (not stated by the paper)	⚑
Pulse repetition frequency (Hz)	100	✓✓✓
Duty cycle (%)	5	✓✓✓
Sonication duration (s)	60	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	0.84	✓✓✓⚑
In-situ estimate	not reported
In-situ pressure (kPa)	not reported
In-situ Isppa (W/cm²)	not reported
In-situ Ispta (W/cm²)	0.42	✓✓✓

Protocol, in the paper’s words

Each stimulation was 1 min at a 5% duty factor and 100 Hz PRF; the focus was electronically steered in 200 um steps around reference points, with stimulation off for about 1 min between points.

Flags from extraction

exposures[0].free_field.ispta_w_cm2 — Paper says the intensity used was obtained from the basic calibration in water, so placed in free_field; the abstract prints the unit as 'mW/cm' without the square.
exposures[0].timing.pulse_duration_ms — Not stated; not computed from duty factor and PRF.
n_subjects — Two subjects for tail experiments and two for digit-level experiments; assumed here to be the same animals only in the sense of 'two subjects' stated; not confirmed.
exposures[0].in_situ — A thermal simulation used 420 mW/cm2 at the focus, apparently after skull attenuation, but the paper does not state the domain; not recorded.