MODFUS: A new in silico model to precisely design low-intensity focused ultrasound brain therapies.

Low-intensity focused ultrasound (FUS) is a novel therapeutic technology for treating several brain pathologies. Often, FUS studies rely on numerical simulations to perform targeting and evaluate the acoustic pressure (AP) deposited in the brain. However, such simulations only consider FUS attenuation in the skull, while brain tissue is modeled as fully homogeneous. We present MODFUS, a novel $in silico$ model suitable to precisely tune both the acoustic parameters and the position of several FUS probes before performing any FUS treatment. MODFUS simulates AP transmission throughout the brain in individual human head models based on CT+MRI fusion, hence considering the heterogeneously distributed acoustic properties across the brain. By using MODFUS, we demonstrate that the AP transmitted to the brain varies i) by more than $15%$ when considering realistic brain tissue models ii) up to $40%$ when the beam incidence angle changes slightly ($<10^{\circ}$) from an orthogonal configuration. These results confirm the need of a realistic tool for FUS treatment planning as well as the need for stereotaxic setups in neurological FUS applications.