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Low-Intensity Focused Ultrasound Stimulation on Fingertip Can Evoke Fine Tactile Sensations and Different Local Hemodynamic Responses

Liuni Qin, Mingyang Dou, Lili Niu, Laixin Huang, Fei Li, Shichun Bao, Xinping Deng, Guanglin Li, Yanjuan Geng

IEEE Transactions on Neural Systems and Rehabilitation Engineering 2024 · 10.1109/tnsre.2024.3493925

human healthyhealthybehaviourother

Abstract

Low-intensity focused ultrasound stimulation (LIFUS) has been proved effective in eliciting vibrotactile in addition to warm, cold and nociceptive pain when applied to human peripheral endings. However, if it can evoke fine tactile sensations has been rarely investigated by far despite the importance of fine tactile feedback in motor control. To explore this issue, 14 healthy volunteers were recruited in this study. A psychophysical experiment was firstly conducted to determine the appropriate range of pulse repetition frequency (PRF) and acoustic intensity (AI). Then, participants were asked to perceive and discriminate different tactile stimulations under LIFUS, so as to evaluate if multiple fine tactile sensations could be reliably elicited by modulating the PRF and AI. For objective assessment, the local blood perfusion volume (BPV) response beneath stimulated fingertip was recorded and characterized. Our results showed that four types of tactile sensations, including tapping, vibrating, electrical, and pressure could be reliably elicited by modulating the PRF and AI within a specific range, and there was a significant impact of PRF and AI on both participants' tactile discrimination and amplitude features of BPV response. This study would facilitate the application of LIFUS to some human-machine interaction scenarios, and shed valuable insights on the physiological mechanisms of peripherally applied ultrasound stimulation.

Abstract via europepmc.

Specieshuman
Subjects14 participants
Sessions per subjectnot reported
Randomisedyes
Blindingnot reported
Sham / controlnone
Auditory controlnot reported
Readout timingonline
Anaesthesianot applicable
Readoutsbehaviour, other — psychophysical pairwise comparison and sensation discrimination accuracy; local blood perfusion volume by laser speckle imaging (moorLDI2-HIR)
Direction of effectexcitatoryFingertip stimulation evoked tapping, vibrating, electrical and pressure sensations depending on PRF and intensity, with differing local blood perfusion responses. Peripheral stimulation, not transcranial.
Adverse eventsnot reportedThermocouple maximum temperature increase of 0.72 degC; estimated maximum rise 0.95 degC; participants told to withdraw the finger on pain.

Exposures

Exposure 1: Fingertip LIFUS, 250 kHz transducer

Target: other — “fingertip (right index finger)”
Device: other named manufacturer · Pantsd Inc., China · HN81C-750-250KC ✓

Pulse timing
Waveformpulsed
Fundamental frequency (kHz)250✓✓✓
Pulse duration (ms)not reported
Pulse repetition frequency (Hz)4, 88swept✓✓✓⚑
Duty cycle (%)3✓✓✓
Sonication duration (s)1, 2swept✓✓✓
Pressure and intensity, by domain
Free-field pressure (kPa)not reported
Free-field Isppa (W/cm²)10.28, 28.02swept✓✓✓
Free-field Ispta (W/cm²)0.22, 0.84swept✓✓✓
In-situ estimatenot reported
In-situ pressure (kPa)not reported
In-situ Isppa (W/cm²)not reported
In-situ Ispta (W/cm²)not reported
Protocol, in the paper’s words

Pulsed ultrasound at 3% duty cycle with PRF selected per sensation (tapping 4-7 Hz, vibrating 14-24 Hz, electrical 63-72 Hz, pressure 80-88 Hz), 1 s or 2 s per stimulus (2 s in experiments 2 and 3), followed by 5 s rest in experiment 2 and 1 min inter-trial interval in experiment 3.

Exposure 2: Fingertip LIFUS, 500 kHz transducer

Target: other — “fingertip (right index finger)”
Device: other named manufacturer · NDT Inc., USA · IBP0.512 ✓

Pulse timing
Waveformpulsed
Fundamental frequency (kHz)500✓✓✓
Pulse duration (ms)not reported
Pulse repetition frequency (Hz)4, 88swept✓✓✓
Duty cycle (%)3✓✓✓
Sonication duration (s)1, 2swept✓✓✓
Pressure and intensity, by domain
Free-field pressure (kPa)1,790✓✓✓
Free-field Isppa (W/cm²)10.28, 35.33swept✓✓✓
Free-field Ispta (W/cm²)0.31, 1.15swept✓✓✓
In-situ estimatenot reported
In-situ pressure (kPa)not reported
In-situ Isppa (W/cm²)not reported
In-situ Ispta (W/cm²)not reported
Protocol, in the paper’s words

Pulsed ultrasound at 3% duty cycle with PRF selected per sensation (tapping 4-7 Hz, vibrating 14-24 Hz, electrical 63-72 Hz, pressure 80-88 Hz), 1 s or 2 s per stimulus (2 s in experiments 2 and 3), followed by 5 s rest in experiment 2 and 1 min inter-trial interval in experiment 3.

Flags from extraction

  • n_subjects — 14 recruited; 8 took part in experiment 1 and 12 in experiments 2 and 3
  • exposures[0].unspecified_domain.isppa_w_cm2 — Range across Table I (experiment 2) rows for this transducer; experiment 1 used up to 56.7 W/cm2 for 500 kHz; AI-voltage relation was calibrated in a water bath but intensity domain is not stated explicitly
  • exposures[0].timing.pulse_repetition_frequency_hz — PRF range from Table I across four sensation types; experiment 1 swept 2-90 Hz
  • exposures[0].target — Peripheral fingertip stimulation; no target term fits, recorded as other
  • sham_type — 'No stimulation' trials were interleaved, otherwise no sham
  • exposures[1].unspecified_domain.pressure_kpa — Highest peak pressure of 1.79 MPa given for the whole study without frequency; not entered