Pulsed Transcranial Ultrasound Stimulation Immediately After The Ischemic Brain Injury is Neuroprotective

Tengfei Guo, Hangdao Li, Yifan Lv, Hongyang Lu, Jinhai Niu, Junfeng Sun, Guo-Yuan Yang, Chuancheng Ren, Shanbao Tong

IEEE Transactions on Biomedical Engineering 2015, 62, 2352-2357 · 10.1109/tbme.2015.2427339

rodentstrokebehaviourhistology molecularcerebral haemodynamics

Abstract

Goal We applied a low-intensity pulsed transcranial ultrasound stimulation (pTUS) to the ischemic cortex after a distal middle cerebral artery occlusion (dMCAO) to study whether pTUS is capable of protecting brain from ischemic injury. Methods Rats were randomly assigned to Sham (n = 6), Control (n = 16), and pTUS (n = 16) groups. The pTUS-treated rats were subjected to 60-min ultrasonic stimulation immediately after the ischemia. After 48 h, the sensorimotor-related behavioral outcomes were assessed by a neurological severity score (NSS), and the permanent brain injury was assessed by the histologic analysis of TTC staining of brain slices. Results pTUS group showed significantly lower NSS (n = 10, 5.5 ± 2.5) than the Control group ( n = 10, 10.5 ±1.4) (p Conclusion Both behavior and histological results suggested that pTUS on ischemic core immediately after ischemic stroke could be neuroprotective. Significance The noninvasiveness and high spatiotemporal resolution of pTUS makes it a unique neuromodulation technique in comparison with the current TMS and tDCS.

Abstract via europepmc.

Speciesrat (Sprague-Dawley)

Subjects16, 9swept animals

Sessions per subject1

Randomisedyes

Blindingsingle

Sham / controlnone

Auditory controlnot reported

Readout timingboth

Anaesthesiaanaesthetised

Readoutsbehaviour, histology molecular, cerebral haemodynamics — Neurological severity score (NSS); TTC staining for cortical infarct volume; laser speckle imaging (LSI) of cerebral blood flow; MPO immunohistochemistry for neutrophil infiltration

Direction of effectexcitatoryThe pTUS parameters (established via motor output/EMG responses in pilot work, indicating excitatory neuromodulation) were applied to the ischemic cortex immediately after dMCAO; treated rats had lower NSS, smaller infarct volume, fewer infiltrating neutrophils, and increased regional cerebral blood flow than untreated controls.

Adverse eventsnot reportedEstimated brain temperature rise was <0.01C for the frequency/intensity used over 60 min of stimulation; ISATA values used were all under the threshold reported for thermal or cavitational damage, though the authors note a theoretical risk of haemorrhage for unhealthy vessels.

Exposures

Exposure 1: Collimated 0.5 MHz pTUS to ischemic/somatosensory cortex

Target: cerebral cortex — “ischemic cortex (ischemic core after distal MCAO); in a separate cerebral-blood-flow experiment, 'the overall somatosensory cortex'”
Device: Olympus / Panametrics · Olympus · V301

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	500	✓✓✓
Pulse duration (ms)	0.4	✓✓✓⚑
Pulse repetition frequency (Hz)	1,500	✓✓✓
Duty cycle (%)	not reportedpulse duration × PRF gives 60%
Sonication duration (s)	0.4, 0.67swept	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported	⚑
Free-field Ispta (W/cm²)	not reported	⚑
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
Isppa, domain unspecified (W/cm²)	2.16	✓✓✓
Ispta, domain unspecified (W/cm²)	0.086	✓✓✓

Protocol, in the paper’s words

Each tone pulse comprised 200 acoustic cycles at 0.5 MHz (NC = 200) repeated at a tone-burst PRF of 1.5 kHz. In stroke experiments, 360 trials (0.4 s sonication per trial, 10 s intertrial interval) of collimated pTUS were delivered to the ischemic cortex immediately after dMCAO for a total of 60 min, using 600 tone bursts per trial (NTB = 600). In a separate cerebral-blood-flow experiment on non-ischemic rats, three blocks of 12 trials (2 min intertrial, 10 min interblock interval) were tested with NTB = 600, 800 or 1000, giving per-trial sonication durations of about 0.40-0.67 s. Ultrasound power was reported as spatial-average pulse-average (ISAPA, 2.155 W/cm2) and spatial-average temporal-average (ISATA, 43-86 mW/cm2 depending on NTB) intensities, not spatial-peak values.

Flags from extraction

exposures[0].timing.pulse_duration_ms — Not stated directly as a duration; computed via the permitted cycles-per-pulse / frequency conversion from NC = 200 acoustic cycles at 0.5 MHz.
exposures[0].free_field.isppa_w_cm2 — Paper reports only spatial-average intensities (ISAPA 2.155 W/cm2, ISATA 43-86 mW/cm2 depending on NTB), not the spatial-peak ISPPA/ISPTA quantities requested by this field; left not_reported rather than conflating spatial-average with spatial-peak intensity.
exposures[0].free_field.ispta_w_cm2 — Same as above: only spatial-average temporal-average intensity (ISATA) is reported, which is a distinct quantity from spatial-peak ISPTA.
n_subjects — 38 rats were split into dMCAO-control (n=16, no ultrasound), dMCAO-pTUS (n=16, ultrasound-exposed) and Sham-surgery (n=6, no ultrasound, no dMCAO) groups; a separate cohort of 9 rats was used for the cerebral-blood-flow experiment. Only the 16 pTUS-treated stroke rats and the 9 CBF-experiment rats received ultrasound; these are recorded as two group sizes since the paper gives no combined total and it is unclear whether any animals overlap between experiments (e.g. the n=6 immunohistochemistry subset).
sham_type — The paper's 'Sham' group refers to sham surgery for the stroke model (no dMCAO), not a sham/inactive-ultrasound condition; the ultrasound comparator ('Control') simply received no ultrasound device application, so sham_type is recorded as 'none'.