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Ultrasound Flow Imaging Study on Rat Brain with Ultrasound and Light Stimulations

Junhang Zhang, Chen Gong, Zihan Yang, Fan Wei, Xin Sun, Jie Ji, Yushun Zeng, Chi-feng Chang, Xunan Liu, Deepthi S. Rajendran Nair, Biju B. Thomas, Qifa Zhou

Bioengineering 2024 · 10.3390/bioengineering11020174

rodenthealthycerebral haemodynamicsinvasive electrophysiology

Abstract

Functional ultrasound (fUS) flow imaging provides a non-invasive method for the in vivo study of cerebral blood flow and neural activity. This study used functional flow imaging to investigate rat brain's response to ultrasound and colored-light stimuli. Male Long-Evan rats were exposed to direct full-field strobe flashes light and ultrasound stimulation to their retinas, while brain activity was measured using high-frequency ultrasound imaging. Our study found that light stimuli, particularly blue light, elicited strong responses in the visual cortex and lateral geniculate nucleus (LGN), as evidenced by changes in cerebral blood volume (CBV). In contrast, ultrasound stimulation elicited responses undetectable with fUS flow imaging, although these were observable when directly measuring the brain's electrical signals. These findings suggest that fUS flow imaging can effectively differentiate neural responses to visual stimuli, with potential applications in understanding visual processing and developing new diagnostic tools.

Abstract via europepmc.

Speciesrat (Long-Evans)
Subjects5 animals
Sessions per subjectnot reported
Randomisednot reported
Blindingnot reported
Sham / controlnone
Auditory controlnot reported
Readout timingonline
Anaesthesiaanaesthetised
Readoutscerebral haemodynamics, invasive electrophysiology — Functional ultrasound power Doppler CBV imaging (L22-14v, Verasonics); multi-electrode array recording in visual cortex
Direction of effectmixed or unclearUltrasound stimulation of the eye evoked EEG responses in visual cortex (larger at 90 Vpp than 30 Vpp) but produced no significant response in visual cortex or LGN on fUS activation maps or CBV.
Adverse eventsnot reported

Exposures

Exposure 1: Ultrasound stimulation of the rat eye/retina

Target: retina — “rats' eyeballs; retinas”
Device: custom-built

Pulse timing
Waveformnot reported
Fundamental frequency (kHz)3,500✓✓✓
Pulse duration (ms)50✓✓✓
Pulse repetition frequency (Hz)1✓✓✓
Duty cycle (%)not reportedpulse duration × PRF gives 5%
Sonication duration (s)not reported
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 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

Stimulation at two output voltages, 30 Vpp and 90 Vpp, for a 50 ms duration with a 1 s interval; fUS imaging used 90 Vpp with the same parameters. A hydrophone test used a 3.5 MHz sine wave in burst mode with 20 cycles.

Flags from extraction

  • n_subjects — Five rats stated for the comparative light/ultrasound imaging experiment; number for the EEG experiment not stated (10 trials).
  • exposures[0].timing.waveform — Unclear whether the 50 ms stimulus is a single burst or a train; the 20-cycle burst is mentioned only for hydrophone characterisation.
  • exposures[0].device.family — Author contributions say a co-author fabricated the stimulation transducer; no maker named.
  • exposures[0].free_field.pressure_kpa — Only output voltages (30 and 90 Vpp) given; a hydrophone profile is in Fig. 1c but no pressure value is in the text.