應用於陣列式超音波探頭之多通道高功率驅動器系統開發

Abstract

本研究目的是研發一套多通道應用於高強度聚焦式超音波(High Intensity Focused Ultrasound，HIFU)來進行熱治療。 系統架構中應用了PSoC (Programmable System-on-Chip)、FPGA(Field Programmable Gate Array) 、LabVIEW做為中樞控制系統，半橋式功率放大器為驅動電路。首先PSoC微處理器(MCU)作為應用控制單元、FPGA進行相位控制切割，使在通道輸出時達到6 bit相位解析度，最小相位解析度5.625⁰。LabVIEW圖形化控制介面並結合功率放大器電路，達到以2.5MHz為基頻且頻率可調、高功率的輸出。使用者可透過LabVIEW圖形化軟體控制介面調整此功率放大器之頻率、相位、輸出功率等，進而控制、監控超音波探頭之功率大小。 實驗結果顯示各通道均可達30W以上，並且在頻率2.0MHz~2.7MHz皆有良好的放大倍率及輸出波形，其最佳工作頻率為2.3MHz~2.5MHz；在FPGA相位切割下，各通道具有5.625⁰的相位精準度，其誤差值在±0.2⁰內。 此系統與超音波探頭結合時，初步測試發現高功率時放大器的穩定性、匹配電路等皆是影響其系統輸出功率之因素；功率量測也因雜訊而使其量測數據受到干擾，導致誤差值存在；故高頻元件的選擇、系統穩定性優化、電路的校正和雜訊的抑制等皆是未來系統改善方向。

The purpose of this study is to develop a multi-channel high-intensity focused ultrasound driving system applied to phased-array ultrasound transducers for tumor therapy with hyperthermia or thermal surgery. The architecture of developed system includes PSoC (Programmable System-on-Chip), FPGA(Field Programmable Gate Array) and LabVIEW as central control units, and the system uses half-bridge power amplifier as a driving circuit. First PSoC microcontroller (MCU) is used as an applicable control unit. Phase is segmented by FPGA, which provides 6-bit phase resolution for the output of each channel with a minimum resolution of 5.625⁰. Finally, LabVIEW-designed graphic control interface (GUI)was combined with the power amplifier circuit to achieve a fundamental frequency of 2.5MHz with high power output and adjustable frequency. Users can adjust and monitor the system’s working frequency, phase delay, and output power through this interface. Experimental results showed that the output power of each channel can reach higher than 30 Watt. When the frequency is between 2.0and 2.7MHz, the system has good amplifying rates and waveform, and the optimal working frequency is from 2.3to 2.5MHz.Segmented by FPGA, the minimum resolution is 5.625⁰ and the error range is within ±0.2⁰. In the preliminary tests with ultrasound transducers, the results indicated that stability of high output power and matching circuits are the factors influencing the output power. Besides, the output power of the amplifier we measured is not very accurate because of noises. For a better system, some improvement must be made including selection of high-frequency components, system stability optimization, circuit calibration, and noise reduction.