應用於乳癌治療之磁振相容半環形相位調控超音波換能器之研發

Abstract

本研究的目的是針對乳房腫瘤，開發半環形相位聚焦式超音波換能器來做熱治療。利用高強度聚焦式超音波，其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，達到以高熱殺死細胞的效果；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。 使用純壓電陶瓷，對其作切割並填入樹脂，成為壓電複合材料。換能器由16個獨立單元的壓電複合材料組成，驅動頻率為2.5MHz，大小為直徑20公分、曲率半徑10公分、高2.5公分。換能器使用多通道高功率驅動器系統作驅動，超音波能量藉由壓電複合材料的壓電效應產生。利用史密斯圖製作匹配電路，藉由微量力實驗測量電聲轉換效率與使壓電片連續工作15分鐘來確認換能器聲功率輸出的穩定性，並採用溫度感應型水膠，觀察其變色反應，驗證換能器加熱效果。另外將換能器放置於MRI環境中，證明其具有磁振相容性。 實驗結果顯示，各單元壓電片可輸出功率為30W，電聲轉換效率為30%。超音波換能器在連續15分鐘的工作期間，依然能夠穩定的將電能轉換為超音波，但由於受到電源供應器的限制、電聲轉換效率的不足，以及聚焦區域過大的問題，所以無法有效使溫感型水膠變色。 本研究完成了半環形相位調控超音波換能器的開發，確定壓電複合材料的製程以及其工作的穩定性，並驗證換能器所使用的材料具有相當程度的磁振相容性。

In this study,a C-shaped phase-array focused ultrasound transducer for breast tumor treatment was developed. High-intensity focused ultrasound (HIFU) has the ability to concentratepower to generate a steep temperature elevation at the target to kill the cells. In addition, ultrasound has a great ability of soft tissue penetration and can be appliedfor non-invasive treatments. Piezoelectric ceramics was cut with designed dimension and then filled withepoxy to made it become piezoelectric-composite. Thepiezoelectric-composite was then used to make a C-shaped ultrasound transducer with a diameter of 20cm,a radius of curvature of 10cm and a height of 2.5cm. The transducer consisted of 16 separated elements and operated at a frequency of 2.5MHz. We used a multi-channel power system to drive the transducer. The piezoelectric-composite elements generated the ultrasound power by piezoelectric effect. We madematching circuit for each element based onSmith Chart. The electro-acoustic transfer ratio was measured by radiation force test and the transducer has been working for 15 minutes continuously to confirm thestability of acoustic output power. We used thermo-sensitive phantom to observe the heating effect. The transducer was placed in an MRI environment to demonstrate its MR compatibility. The results showed that the output power of each element could reach 30 Watt, and the electro-acoustic transfer ratio was about 30%. During a 15-min working time, the transducer could transfer the acoustic power stably. Due to the limitation of power supply, low electro-acoustic efficiency, and a large focal zone, the transducer could not reach the requirement for changing phantom’s color. In this study, we developed a C-shaped phase-array focused ultrasound transducer for breast tumor thermal therapy. The manufacturing process of piezoelectric-composite material and the stability of transducer were confirmed. Theultrasound transducer had a certain degree of MR compatibility.