Cross-species characterization of transcranial ultrasound propagation

Transcranial ultrasound stimulation (TUS) has shown promising prospects as a non-invasive neuromodulation technique for both animals and humans. However, ultrasonic propagation characteristics within the brain differ significantly from those in free space. There is currently a lack of comprehensive studies on the effects of skull thickness on focal point position, full width at half maximum (FWHM), and acoustic intensity.

This study investigates the transcranial acoustic field characteristics of 500 kHz focused ultrasound, with a focus on the impact of skull thickness.

The study combined finite element simulations to evaluate the effects of skull thickness on 500 kHz focused ultrasound with experimental investigations across multiple species (mouse, rat, pig, and human).

The simulation and experimental results indicate that the skull changes focal length (-4.4-4.7 mm) and axial focal region (-7.93-7.59 mm), and the skull causes significant attenuation of acoustic intensity, which increases with skull thickness. The attenuation rate of human skulls is greater than 80 %. We found that the skull thickness has little effect on focal point position (<0.9 mm) and focal region (<1.44 mm) in lateral and vertical directions.

Skull thickness has great influence on focal length, axial focal region and acoustic intensity, but has little effect on focal point position and focal region in lateral and vertical directions. And improving axial spatial resolution is a potential method to reduce changes of axial focal region.