A Soft Housing Needle Ultrasonic Transducer for Focal Stimulation to Small Animal Brain
Taewon Choi, Sungjun Bae, Minah Suh, Jinhyoung Park
Annals of Biomedical Engineering 2020, 48, 1157-1168 · 10.1007/s10439-019-02431-w
Abstract
Conventional acoustic brain stimulators that transmit low frequency (< 1 MHz) bursts in a pulse repetition frequency with large-sized transducers are barely compatible with small animal models because of broad beam width, possible stimulation of auditory pathways, and blocking of field-of-view for in vivo imaging of brain hemodynamics and neuronal activities. A miniaturized ultrasound stimulator with higher stimulation frequencies will enhance spatial specificity and enable simultaneous eliciting and monitoring brain activities. Moreover, the use of non-periodic pulse sequences may reduce unintended stimulations on auditory cortex, which might be caused by transmitting periodic bursting patterns. A platform for ultrasound brain stimulations for small animal models, including a soft housing 10 MHz needle transducer with a beam size of 680 μm, random transmission sequences, and optical imaging systems, was developed. The platform can deliver focal stimulations to the visual and barrel cortex of mice and monitor subsequent brain activities. The stimulated sites in both the visual and primary somatosensory cortices (S1) showed approximately two to three times higher neuronal calcium signal levels than those in peripheral regions. Activities in the auditory cortex were elicited by periodic sequence stimulation, while it was reduced by 67 and 35% for barrel and visual cortex stimulation with the random sequence, respectively.
Abstract via europepmc.
Exposures
Exposure 1: Barrel cortex stimulation (periodic and random sequences)
Target: primary somatosensory cortex — “barrel cortex”
Device: custom-built
| Waveform | pulsed, other_patterned | |
|---|---|---|
| Fundamental frequency (kHz) | 10,000 | ✓✓✓ |
| Pulse duration (ms) | 0.333 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 1,500 | ✓✓✓ |
| Duty cycle (%) | 50pulse duration × PRF gives 49.95% | ✓✓✓ |
| Sonication duration (s) | 0.2 | ✓✓✓ |
| Free-field pressure (kPa) | 200 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 0.662 | ✓✓✓⚑ |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Each stimulus imaging trial consisted of recording for 5 s pre-stimulation, 200 ms stimulation, and 24.8 s post-stimulation periods, with a data session of 50 trials averaged into a single 30-s data period. The T1 trigger signal comprised 50 trigger pulses with a pulse repetition period of 30 s (total trigger pulse train length 25 min); periodic sequences used a fixed PRF of 1.5 kHz while random sequences jittered the pulse start time within each 666-us repetition period to maintain the same 50% duty cycle without a fixed audible PRF.
Exposure 2: Visual cortex stimulation (periodic and random sequences)
Target: primary visual cortex — “visual cortex”
Device: custom-built
| Waveform | pulsed, other_patterned | |
|---|---|---|
| Fundamental frequency (kHz) | 10,000 | ✓✓✓ |
| Pulse duration (ms) | 0.333 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 1,500 | ✓✓✓ |
| Duty cycle (%) | 50pulse duration × PRF gives 49.95% | ✓✓✓ |
| Sonication duration (s) | 0.2 | ✓✓✓ |
| Free-field pressure (kPa) | 200 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | 0.662 | ✓✓✓ |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Each stimulus imaging trial consisted of recording for 5 s pre-stimulation, 200 ms stimulation, and 24.8 s post-stimulation periods, with a data session of 50 trials averaged into a single 30-s data period. The T1 trigger signal comprised 50 trigger pulses with a pulse repetition period of 30 s (total trigger pulse train length 25 min); periodic sequences used a fixed PRF of 1.5 kHz while random sequences jittered the pulse start time within each 666-us repetition period to maintain the same 50% duty cycle without a fixed audible PRF.
Flags from extraction
exposures[0].free_field.ispta_w_cm2— paper states '0.662 W/cm2' immediately after mentioning the 50% duty cycle, suggesting a duty-cycle-averaged (Ispta) intensity, but the paper never labels it Isppa or Ispta explicitly; recorded as Ispta with this uncertainty flagged.exposures[0].timing.waveform— study compares a periodic pulse train (fixed 1.5 kHz PRF) against a non-periodic 'random' sequence with the same duty cycle; both are combined here as one exposure per target with waveform listed as ['pulsed','other_patterned'].auditory_control— the paper's 'random' pulse-timing sequence is designed specifically to reduce auditory-cortex activation compared with a periodic sequence, but this is a property of the stimulus design rather than a standard auditory-masking control, so it is recorded as 'other'.n_sessions_per_subject— each mouse received 50 repeated 30-s trials per condition (see Table 1 for which of the 5 mice received which conditions), but the paper does not state a number of discrete sessions.