Cross-species characterization of transcranial ultrasound propagation

Background: 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. Objective: This study investigates the transcranial acoustic field characteristics of 500 kHz focused ultrasound, with a focus on the impact of skull thickness. Methods: 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). Results: 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 (