Acoustoelastic Full-Waveform Inversion For Transcranial Ultrasound Computed Tomography

Full-waveform inversion applied to ultrasound computed tomography is a promising technique to provide high-resolution quantitative images of soft human tissues, which are otherwise difficult to illuminate by conventional ultrasound imaging. A particular challenge which arises within transcranial ultrasound is the imprint of the solid skull on the measured wavefield. We present an acoustoelastic approach to full-waveform inversion for transcranial ultrasound computed tomography that accurately accounts for the solid-fluid interactions along the skull-tissue interfaces. Using the spectral-element method on cubical meshes, we obtain a scalable and performant method to resolve such a coupled physical system. Moreover, since the volume of the skull is small compared to the entire simulation domain, solving a coupled system of the acoustoelastic wave equation increases the computational cost only by a small margin compared to the acoustic approximation. We perform an in silico forward and inverse modeling study that reveals significant coupling effects at the skull-tissue interfaces when considering the skull as an elastic medium as opposed to an acoustic medium. Applying full-waveform inversion to a set of synthetically generated acoustoelastic forward data allows for favorable reconstructions to be achieved when considering an acoustoelastic prior model of the skull.