A novel numerical approach to stimulation of a specific brain region using transcranial focused ultrasound.

One of the biggest challenges associated with transcranial application of focused ultrasound is the presence of skull in wave propagation resulting in the attenuation and diffraction of sound waves, which leads to disruption and shifting of the acoustic focus in the brain. In this study, we were motivated to find an optimal transducer position to effectively deliver sufficient acoustic energy to the target in the brain whilst minimizing the effects of skull on wave propagation in a computationally inexpensive way. We hypothesized that the placement of a single-element focused ultrasound transducer which gives the lowest reflection coefficient would be the optimal position. We tested our hypothesis by conducting numerical investigations of wave propagation through the skull targeting the primary motor hand representation (M1) and the supplementary motor area (SMA). The optimal transducer positions were determined using our method (reflection coefficients were lowest), whereby the simulated magnitudes of the acoustic pressure values at the M1 and the SMA were respectively 91% and 92% greater than those when the reflection coefficients were greatest.