研發應用於攝護腺腫瘤熱消融之聚焦超音波換能器

Abstract

超音波具有良好穿透軟組織的能力，藉由高強度聚焦超音波換能器將聲波的能量匯集在聚焦區內，在短時間內使位於焦區內的組織產生急遽的溫度上升，焦區內的高溫使組織產生凝固性壞死，達到熱消融病變組織的療效，屬於非侵入性的治療。本研究之目的為研發攝護腺腫瘤熱消容灣用之高強度聚焦超音波換能器。 本研究設計兩種幾何形狀的聚焦超音波換能器：橢圓形及長方形。使用套裝軟體MATLAB_2017a模擬換能器的聲場及聚焦區域大小，換能器的初步設計參數為中心頻率3.5 MHz、寬為22 mm、長為45 mm、曲率半徑為45 mm。換能器乃由1-3壓電複合材料所組成，主動材料為壓電陶瓷，被動材料為環氧樹脂。換能器特性化測試結果顯示中心頻率3.3 MHz、頻寬為0.9 MHz、轉換效率為12.45%、寬為25 mm、長為50 mm、曲率半徑為45 mm、聚焦區域大小為2x1.6x4.2mm3。已經藉由溫感水膠燒灼實驗驗證換能器的加熱效果及聚焦特性。

Ultrasound has a good ability to penetrate soft tissue. High-intensity focused ultrasound (HIFU) transducers are capable of concentrating acoustic power to generate a steep temperature elevation in the focal zone, causing thermally coagulative necrosis of tumor. The purpose of this work was to develop HIFU transducers dedicated for the non-invasive treatment of prostate cancer. Transducers with elliptic or rectangular aperture were designed in this study. Acoustic fields of transducers were calculated based on Rayleigh-Sommerfeld Diffraction Integral and the size of focal zone was analyzed. MATLAB 2017a (The MathWorks, Inc., Natick, MA) was used in the numerical simulation. The initial design of the transducer was 22 mm in width and 45 mm in height, a radius of curvature of 45 mm, and the center frequency of 3.5 MHz. The transducers were made of 1-3 piezoelectric composites, where PZT 8 was the active material and epoxy was the passive material. The center frequency of the transducer prototype was 3.8 MHz with the -6 dB bandwidth of 0.45 MHz. Moreover, the electro-acoustic efficiency and focal zone were measured to be 12.45% and 2x1.6x4.2 mm3. Experimental results of ablating thermo-sensitive phantoms verified the feasibility of the developed transducer.