Skull Acoustic System Modeling for Optimizing Transcranial Ultrasound Focusing

Transcranial focused ultrasound (tFUS) is an emerging noninvasive neuromodulation technique, but efficient acoustic energy delivery through the skull remains a major challenge due to skull-induced attenuation and distortion. In this study, we systematically characterized the frequency-dependent transmission efficiency of human skulls using both experimental measurements and acoustic simulations. By conducting frequency sweeps across different skull thicknesses and locations, we identified significant spectral variability and site-specific optimal transmission frequencies. Spatial field mapping further confirmed that transmission dips not only reduce energy delivery but also lead to severe focal distortion. To address this, we proposed a frequency-optimized ultrasound array design by selecting the optimal frequency for each element based on local transmission properties. Results demonstrated that the optimized-frequency array significantly improved the focal pressure amplitude and spatial confinement compared to conventional uniform-frequency arrays.