Numerical Evaluation of the Human Skull with Focused Ultrasound Stimulation

Transcranial focused ultrasound stimulation is a promising brain stimulation technique for its noninvasiveness and higher spatial resolutions and is used for various neuromodulation applications. As the skull is the primary barrier to delivering ultrasound to the deep brain region, it induces unpredictable ultrasound exposure. The objective of the study is to design customised transducers and assess the effects of the skull on ultrasound wave propagation. Computational skull models were constructed using computerised tomography scans. A full-wave finite-difference time-domain simulation platform, Sim4Life, was then used to design and simulate ultrasound wave propagation. In addition, the impacts of the skull were assessed through sensitivity analysis in the intracranial intensity, pressure, full width at half maximum, and energy deposition. Compared to the intracranial intensity distribution when the transducer is placed over the top area of the skull, the peak intensity increased by 23.4% for transmission through the temporal window. The temporal window, the thinnest part of the skull, provides a site for intracranial peak intensity and optimal focal spot area using focused ultrasound. The numerical investigation in this study provided a guideline for targeting and dosing, accounting for and lessening variability in studies addressing transcranial focused ultrasound applications.