High-fidelity transcranial ultrasound multi-focal stimulation via physics-aware hologram technique
Moon Hwan Lee, Mohd Afzal Khan, Akm Ashiquzzaman, Eunbin Lee, Jonghun Lee, Euiheon Chung, Hyuk-Sang Kwon, Jae Youn Hwang
Brain Stimulation 2026 · 10.1016/j.brs.2026.103158
Abstract
Introduction Transcranial ultrasound stimulation (TUS) is an emerging non-invasive neuromodulation modality that offers deep brain access with high spatial precision. However, its broader application is limited by the difficulty of reliably generating complex transcranial acoustic fields, particularly for multi-target stimulation through the skull. These limitations can lead to focal distortion, off-target exposure, and reduced reliability of neuromodulation outcomes. Materials and methods Here, we introduce a physics-aware thickness-only acoustic hologram (TOAH) technique for precise transcranial ultrasound neuromodulation. Unlike conventional approaches that rely on simplified phase-based approximations, TOAH directly generates fabrication-ready holographic implementations while preserving consistency between numerical field synthesis and physical acoustic realization. This enables accurate formation of single-, dual-, and tri-focal stimulation patterns under transcranial conditions. We validated TOAH through in silico simulations, ex vivo acoustic measurements through skulls, and in vivo experiments. Results Compared with state-of-the-art methods, TOAH improved focal reconstruction, energy confinement, and multi-focal balance while reducing off-target acoustic leakage. Human-skull simulations further supported robust multi-focal reconstruction under clinically relevant transcranial conditions. In a neuropathic pain mouse model, bilateral thalamic stimulation induced measurable changes in neuronal activity, reflected by reduced c-Fos expression, together with preliminary improvements in pain-related behavioral responses. These findings support the capability of the proposed technique to enable spatially localized and reproducible neuromodulation in vivo. Conclusion Collectively, this work provides a practical proof-of-concept strategy for achieving high-precision, multi-target transcranial neuromodulation and supports further investigation for neuroscience research and future therapeutic applications.
Abstract via europepmc.
Exposures
Exposure 1: Dual-foci transcranial stimulation of bilateral VP thalamic nuclei via TOAH hologram lens
Target: ventral posterior nucleus — “bilateral ventral posterior nuclei (VP) of the thalamus”
Device: custom-built · custom single-element transducer (13 mm aperture, PZT-4) with 3D-printed thickness-only acoustic hologram (TOAH) lens and coupling cone ✓
| Waveform | theta burst | |
|---|---|---|
| Fundamental frequency (kHz) | 2,000 | ✓✓✓⚑ |
| Pulse duration (ms) | 3 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 200 | ✓✓✓⚑ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 60% | ⚑ |
| Sonication duration (s) | 120 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | measurementsingle value | |
| In-situ pressure (kPa) | 750, 730swept | ✓✓✓ |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | 1.13, 1.07swept | ✓✓✓ |
An FPGA board gated a function generator producing a 2 MHz sinusoidal signal, delivered as repeated tone bursts (tone burst duration 3 ms, pulse repetition period 5 ms) with a 200 ms inter-stimulation interval, applied for 120 s total per session, described as continuous theta-burst ultrasound stimulation (cTBUS) parameters adapted from prior work. In vivo, ultrasound was delivered on days 8 and 11 after CCI surgery, with a final stimulation on day 14 after the last behavioural assessment (3 sessions total).
Flags from extraction
sham_type— 'SC' groups are a sham surgical/CCI procedure (nerve exposure without ligation), not a sham ultrasound arm; there is no inactive-transducer or sham-US condition, so sham_type is coded none.n_sessions_per_subject— Session count (3) is inferred from the described treatment days (8, 11, and a final session on day 14) rather than an explicit statement of total session number.exposures[0].timing.pulse_repetition_frequency_hz— PRF (200 Hz) is a unit conversion from the stated pulse repetition period (PRP = 5 ms), not an independently stated PRF value.exposures[0].timing.duty_cycle_pct— Duty cycle is not explicitly stated; computing it from TBD/PRP (3/5 ms) would require arithmetic not performed here.exposures[0].fundamental_frequency_khz— 2 MHz center frequency is the PZT element specification confirmed elsewhere as the driving frequency used in vivo (FPGA-gated 2 MHz sinusoidal signal).