Optimal patterns for sequentially multiple focusing in high intensity focused ultrasound and their application to thermal dose

Abstract

The purpose of this study is to propose a new method for multiple-focus generation to shorten overall treatment time as well as to avoid the formation of high intensity regions outside the target volume. A numerical simulation of the acoustic fields produced by a 1017-element spherical-section ultrasound phased array transducer operating at a frequency of 1.0MHz with 16 cm radius of curvature is performed for the proposed multiple-focus generation. The total foci are partitioned into the several patterns because multiple focusing generally gives rise to the grating lobes outside of the three dimensional region of interest even if applying the optimization of intensity gain in determining the phases and amplitudes of the excitation source vector. The optimization problem is repeatedly formulated in term of the focal points until the multiple-focus patterns cover all the focal points. Genetic algorithm is used for selecting the patterns without the grating lobes. The obtained set of multiple-focus patterns can sequentially be used to necrose a given volume in the short time as well as in the safe treatment. The proposed method might prove useful to improve the speed and safety of focused ultrasound thermal ablation. This strategy will also be effective for any transducers as well as for other cases of multiple-focus generation.