Nonlinear 3-D simulation of high-intensity focused ultrasound therapy in the kidney

TL;DR

This study uses nonlinear 3-D ultrasound simulations based on patient CT data to analyze how tissue properties affect high-intensity focused ultrasound therapy in the kidney, revealing significant intensity losses and focal shifts.

Contribution

It introduces a nonlinear simulation model incorporating tissue inhomogeneities, refraction, and reflection effects to better predict HIFU therapy outcomes in kidney treatment.

Findings

Attenuation and refraction cause an 11.0 dB drop in focal intensity.

Refraction effects shift the focal point by up to 2.6 mm.

Reflections at tissue interfaces have minimal impact (<0.1 dB).

Abstract

Kidney cancer is a severe disease which can be treated non-invasively using high-intensity focused ultrasound (HIFU) therapy. However, tissue in front of the transducer and the deep location of kidney can cause significant losses to the efficiency of the treatment. The effect of attenuation, refraction and reflection due to different tissue types on HIFU therapy of the kidney was studied using a nonlinear ultrasound simulation model. The geometry of the tissue was derived from a computed tomography (CT) dataset of a patient which had been segmented for water, bone, soft tissue, fat and kidney. The combined effect of inhomogeneous attenuation and sound-speed was found to result in an 11.0 dB drop in spatial peak-temporal average (SPTA) intensity in the kidney compared to pure water. The simulation without refraction effects showed a 6.3 dB decrease indicating that both attenuation and refraction contribute to the loss in focal intensity. The losses due to reflections at soft tissue interfaces were less than 0.1 dB. Focal point shifting due to refraction effects resulted in -1.3, 2.6 and 1.3 mm displacements in x-, y- and z-directions respectively. Furthermore, focal point splitting into several smaller subvolumes was observed. The total volume of the secondary focal points was approximately 46% of the largest primary focal point. This could potentially lead to undesired heating outside the target location and longer therapy times.