Flexible ultrasound array for subcortical brain stimulation in humans: a simulation study

Transcranial focused ultrasound (tFUS) is a non-invasive neuromodulatory tool that holds promise for various neuropsychiatric disorders. While it offers several distinct advantages, it also faces notable technical challenges. The irregular shape and inhomogeneous acoustic properties of the human skull impede efficient acoustic energy transmission through the skull. So far, clinical semi-spherical (hemispherical) arrays still suffer from strong wave reflection and refraction at the skull interface, especially with steering. We propose a flexible ultrasound array that conforms to individual skull shapes and can be optimized to target vertex-accessible subcortical regions. The impact of flexible array configuration was investigated by comparing the flexible array with a semi-spherical array commonly used in the clinical setting. Numerical results show that the random-patterned flexible array reduces the z-axis -6 dB full width at half maximum (FWHM) by 29.4% and enhances the focal peak pressure by 44.4% when compared to the semi-spherical array without steering. In addition, it achieves a wide steering range over a 30 × 20 mm² region while maintaining the focusing performance. We expect that our proposed tFUS stimulation with a flexible array may provide a theoretical framework for improving the therapeutic efficiency for various neuropsychiatric conditions.