Electrophysiological Source Imaging of Brain Networks Perturbed by Low-Intensity Transcranial Focused Ultrasound
Kai Yu, Abbas Sohrabpour, Bin He
IEEE Transactions on Biomedical Engineering 2016, 63, 1787-1794 · 10.1109/tbme.2016.2591924
Abstract
Objective Transcranial focused ultrasound (tFUS) has been introduced as a noninvasive neuromodulation technique with good spatial selectivity. We report an experimental investigation to detect noninvasive electrophysiological response induced by low-intensity tFUS in an in vivo animal model and perform electrophysiological source imaging (ESI) of tFUS-induced brain activity from noninvasive scalp EEG recordings. Methods A single-element ultrasound transducer was used to generate low-intensity tFUS ( ) and induce brain activation at multiple selected sites in an in vivo rat model. Up to 16 scalp electrodes were used to record tFUS-induced EEG. Event-related potentials were analyzed in time, frequency, and spatial domains. Current source distributions were estimated by ESI to reconstruct spatiotemporal distributions of brain activation induced by tFUS. Results Neuronal activation was observed following low-intensity tFUS, as correlated to tFUS intensity and sonication duration. ESI revealed initial focal activation in cortical area corresponding to tFUS stimulation site and the activation propagating to surrounding areas over time. Conclusion The present results demonstrate the feasibility of noninvasively recording brain electrophysiological response in vivo following low-intensity tFUS stimulation, and the feasibility of imaging spatiotemporal distributions of brain activation as induced by tFUS in vivo. Significance The present approach may lead to a new means of imaging brain activity using tFUS perturbation and a closed-loop ESI-guided tFUS neuromodulation modality.
Abstract via europepmc.
Exposures
Exposure 1: Low-intensity tFUS of rat anterior cortex
Target: frontal lobe — “right/left anterior cortex”
Device: Olympus / Panametrics · Olympus · V389 ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | not reported | ⚑ |
| Pulse repetition frequency (Hz) | 2,000 | ✓✓✓ |
| Duty cycle (%) | not reported | |
| Sonication duration (s) | 0.005, 0.05, 0.2swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | measurementmean or range across subjects | |
| In-situ pressure (kPa) | 18.3, 27.9, 45.9swept | ✓✓✓ |
| In-situ Isppa (W/cm²) | 0.0007, 0.0014, 0.0046swept | ✓✓✓ |
| In-situ Ispta (W/cm²) | 0.0001, 0.0002, 0.0006swept | ✓✓✓ |
tFUS pulses were produced in a burst mode by a single-element focused transducer using a single-pulse burst mode (rather than a tens-of-cycles tone-burst) at a 2 kHz pulse repetition frequency, delivered through a conical collimator to a scalp site, with 3 s intersonication intervals. Three sonication intensities (SI1-SI3) were tested at a fixed 200 ms sonication duration in one experiment; a second experiment compared 5, 50, and 200 ms sonication durations at a fixed intensity (Ispta 0.6 mW/cm2). A sham condition used the same 200 ms sonication with the transducer aimed away from the animal.
Flags from extraction
exposures[0].target.terms— Figures describe the sonicated site only as 'right anterior cortex' / 'left anterior cortex'; no more specific named cortical subregion is given, so mapped to frontal_lobe as the closest match.exposures[0].in_situ.method— Intensities/pressures were measured with a calibrated hydrophone placed behind a piece of freshly excised Wistar rat skull, i.e. measured through skull, matching the 'measurement' in_situ method.exposures[0].timing.pulse_duration_ms— Paper contrasts its 'single-pulse burst mode' with the tone-burst mode (tens of cycles per pulse) used in prior studies, but never states the duration of an individual pulse in ms; only the pulse repetition frequency (2 kHz) of pulses within the sonication train is given, so pulse_duration_ms is left not_reported (burst-rule ambiguity).