環形相位陣列聚焦式超音波結合磁振造影系統應用於乳房腫瘤治療的研究

Abstract

由於高強度聚焦式超音波(HIFU)具有使能量集中的特性，能夠以極短時間在目標區域產生急遽的溫度上升，達到以高熱消滅細胞的效果；且超音波具有軟組織穿透能力，能以非侵入的方式進行治療，近年來已成為癌症治療的一種新方式。 本研究針對乳房腫瘤，開發環形相位聚焦式超音波換能器做為熱治療工具，換能器大小為直徑20公分、曲率半徑10公分、高2公分。本研究的環形換能器由16個獨立的壓電陶瓷組成，驅動頻率為1MHz，超音波能量藉由壓電陶瓷的壓電效應產生，並藉由實際測量壓電陶瓷的機電耦合係數和電聲轉換效率來確認換能器聲功率輸出的穩定性。 根據不同的臨床需求，可以利用調控輸出的聲波相位進行不同策略的熱治療。本研究藉由組織仿體和離體的里肌肉，針對腫瘤在乳房中心處進行不同相位模式的燒灼實驗，並搭配磁振造影系統觀察超音波聚焦區的溫度變化量和燒灼形態。由實驗結果可知，環形相位聚焦式換能器搭配不同相位的聚焦模式，產生足夠的加熱範圍，並確實有效使乳房中心位置的腫瘤產生足夠的溫度上升，使該處的組織變性而壞死，達到治療的目的。

High-intensity focused ultrasound (HIFU) has the characteristics of power concentration and can generate the steep temperature elevation at the target to kill the cells by hyperthermia. Because ultrasound has great ability of penetration to soft tissue and can apply non-invasive treatments, it becomes a new method for cancer therapies. In this study, we develop a ring-shaped phase-array focused ultrasound transducer for the breast tumor treatment. The transducer size is 20cm in diameter, with a radius of curvature of 10cm and a height of 2cm. The transducer consists of 16 separated piezoelectric ceramics, and operate at the frequency of 1MHz. Piezoelectric ceramics generate the ultrasound power by the piezoelectric effect of materials. We measure the electro-mechanical coupling constant and the electro-acoustic transverse ratio to confirm the acoustic output power stability of the transducer. According to different clinical requirements, we set different phase of output acoustic wave to form different heating results for the different thermal treatment strategies. We assume the tumor is located at the center of the breast, and use the breast phantom and pork sample in vitro to do the ablation experiments of different heating models. Furthermore, the ablation experiment apparatus is collocated with the MRI system to observe the heating patterns and the temperature change in the focal region. Experiment results show that the ring-shaped phase-array focused ultrasound transducer using different heating models can generate sufficient heating range and make the effective temperature rise at the tumor in the center of breast, achieve the treatment purpose of tissue denature and necrosis.