An element-wise approach for simulating transcranial MRI-guided focused ultrasound thermal ablation

TL;DR

This paper presents an element-wise simulation method for transcranial MRI-guided focused ultrasound, enabling rapid and accurate modeling of thermal ablation in neurosurgery with potential for optimization and improved treatment planning.

Contribution

The study introduces an element-wise approach that allows parallel computation of ultrasound pressure fields, improving simulation speed and accuracy for TcMRgFUS treatments.

Findings

Predicted and measured heating showed strong correlation (R2 > 0.7).

The approach enables rapid 3D temperature mapping for different phase settings.

Optimizing skull density relationships improves simulation accuracy.

Abstract

This work explored an element-wise approach to model transcranial MRI-guided focused ultrasound (TcMRgFUS) thermal ablation, a noninvasive approach to neurosurgery. Each element of the phased array transducer was simulated individually and could be simultaneously loaded into computer memory, allowing for rapid calculation of the pressure field for different phase offsets used for beam steering and aberration correction. We simulated the pressure distribution for 431 sonications in 32 patients, applied the phase and magnitude values used during treatment, and estimated the resulting temperature rise. We systematically varied the relationship between CT-derived skull density and the acoustic attenuation and sound speed to obtain the best agreement between the predictions and MR temperature imaging (MRTI). The optimization was validated with simulations of 396 sonications from 40 additional treatments. After optimization, the predicted and measured heating agreed well (R2: 0.74 patients 1-32; 0.71 patients 33-72). The dimensions and obliquity of the heating in the simulated temperature maps correlated well with the MRTI (R2: 0.62, 0.74 respectively), but the measured heating was more spatially diffuse. The energy needed to achieve ablation varied by an order of magnitude (3.3-36.1 kJ). While this element-wise approach requires more computation time up front, it can be performed in parallel. It allows for rapid calculation of the three-dimensional heating at the focus for different phase and magnitude values on the array. We also show how this approach can be used to optimize the relationship between CT-derived skull density and acoustic properties. While the relationships found here need further validation in a larger patient population, these results demonstrate the promise of this approach to model TcMRgFUS.