Optimally Enhanced Heating for Focused Ultrasound Surgery with Split Foci, Dual-Frequency, or Multi Foci

摘要

To substantially enhance heating in HIFU treatment, several methods such as split foci, multi foci, and dual-frequency modes are used. The enhanced-cavitation heating protocols are implemented experimentally in BSA gel-phantom using four-element split-focus array. Using dual frequency of 1.2 and 2.4 MHz, the superimposing of two frequency pressures at confocal region can enhance nucleation cavitation and inertial cavitation activity. When using 135° phase shift combined with dual frequency of 1.2 and 2.4 MHz, the peak negative pressure reach maximum due to peak-negative pressures of two frequencies occur at same time, resulting strong cavitation activities. When using dual frequency of 1.2 and 2.4 MHz, 25-Hz pulse-repetition frequency (PRF), both 135° and 180° phase shift protocols, the experiment results show the largest lesion size of 10.5 x 10.5 x 11 mm~3, quickest lesion inception time of less than 0.2 s, therefore, both 135° and 180° phase shift protocols are most efficient in enhanced-cavitation heating. The filtered-PCD mean square waveforms reveal that the strong inertial-cavitation activities involve in those two treatments. The lesion size of four foci of 180° phase shift, single frequency, 25 Hz PRF, is 2 times that of 0° phase shift, single frequency even if the peak intensity of 180° case is half less than that of 0° phase shift case. When arrange multi foci using phased array in a style of a wavelength distance between neighbor foci in focal plane, the result is the same as that using split foci of 180° phase shift and single frequency.