開發高能聚焦超音波用之多通道相位調控功率放大器

Abstract

超音波具有非侵入性、穿透力深、無游離輻射等優點，近年來有許多腫瘤治療的研究已經或嘗試使用超音波來進行。其中已經應用於臨床的超音波治療技術為高能聚焦超音波（HIFU），其治療原理為超音波聚焦區內的腫瘤組織吸收HIFU後產生高溫，致使腫瘤細胞凝固性壞死。產生HIFU的元件稱之為HIFU換能器，而陣列式的換能器能夠透過相位調控達成動態聚焦或聚焦型態變化，有益於燒灼不同位置的腫瘤細胞。目前市售的HIFU換能器驅動器以單通道功率放大器為主，不適用於陣列式HIFU換能器。因此，本研究之目的在於開發一套多通道具備相位控制之功率放大器。 在本研究中使用套裝軟體LabVIEW進行使用者介面設計。硬體電路規劃為主板與子板，主板負責訊號控制與相位調控，使用FPGA來實現相位調控，子板電路負責驅動通道與功率回授監測。測試結果顯示這套開發系統為32通道且可提供兩種輸出頻率1 MHz及1.5 MHz，相位解析度最小可達到1.3度，每一通道的輸出阻抗為50歐姆，輸出波形與預期的相同。因此，經測試結果證實系統原型具備訊號產生、相位調控、功率放大與功率監測之功能。

Medical ultrasound has many advantages such as non-invasive operation, deep penetration, non-ionizing radiation. Recently, ultrasound has been used for treatment of the tumor. High-intensity focused ultrasound (HIFU) has been approved to ablate uterine fibroids, bone metastasis, prostate cancer, and essential tremor by the US FDA. The tumor absorbs HIFU at the focus and gets an abrupt rise in temperature, leading to thermally coagulative necrosis of the tumor cells. The device to produce HIFU is called HIFU transducer. The array transducer can perform dynamic focusing or form various focal patterns by tuning phase of each element which facilitates the ablation of the tumor at different sites. Typically, a commercial power amplifier has a single channel, two or four independent channels without the function of phase control. Therefore, the purpose of this study is to develop a multi-channel phase control power amplifier. In this study, we used LabVIEW software to design the user interface. The hardware circuitry was consisted of 1 motherboard and 8 daughterboards. The motherboard dominated signal control and phase control, where we used FPGA to fulfill phase control. The daughterboard was responsible for the channel drive circuit and power feedback. Preliminary results showed that the developed 32-channel amplifier could generate signals with the frequency at 1.0 MHz or 1.5 MHz. The minimum resolution of the phase was 1.3 degrees, and the output impedance of each channel was 50 Ohm.