Full-Wave Modeling of Transcranial Ultrasound using Volume-Surface Integral Equations and CT-Derived Heterogeneous Skull Data

TL;DR

This paper introduces a computational method using volume-surface integral equations to accurately model full-wave transcranial ultrasound propagation through heterogeneous skulls derived from CT data, even with coarse voxel resolution.

Contribution

The paper presents a novel efficient numerical approach for full-wave ultrasound modeling through heterogeneous skulls using CT data and integral equations, overcoming resolution limitations.

Findings

Effective simulation of ultrasound beam distortion caused by skull heterogeneity.

Validation against high-resolution models shows high accuracy.

Significant beam distortion of 7.8 mm due to skull properties.

Abstract

Transcranial ultrasound therapy uses focused acoustic energy to induce therapeutic bioeffects in the brain. Ultrasound must be transmitted through the skull, which is highly attenuating and heterogeneous, causing beam distortion, reducing focal pressure, and shifting the target location. Computational models are frequently used to predict beam aberration, assess cranial heating, and correct the phase of ultrasound transducers. These models often rely on computed tomography (CT) images to build patient-specific geometries and estimate skull acoustic properties. However, the coarse voxel resolution of CT limits accuracy for differential equation solvers at ultrasound frequencies. This paper presents an efficient numerical method based on volume-surface integral equations to model full-wave acoustic propagation through heterogeneous skull bone. We show that our approach effectively simulates transcranial ultrasound, even when using the original CT voxels as the computational mesh, where the 0.5 mm voxel length is relatively coarse compared to the shortest wavelength of 3 mm. The method is validated against a high-resolution boundary element model using an averaged skull representation. Simulations using a CT-based skull model and a bowl transducer reveal significant beam distortion of 7.8 mm attributed to the skull's heterogeneous acoustical properties.