| Summary: | 碩士 === 國立成功大學 === 生物醫學工程學系 === 101 === High frequency ultrasound imaging system has non-invasive and real-time characteristics, so it is widely used in medical diagnosis. High frequency ultrasound system with high resolution has been widely studied in recent years. It is able to observe superficial object such as blood vessels, eyes, skin and small animal tissues. The resolution of high frequency ultrasound system is highly dependent on ultrasound pulser. Recently, the commercial available ultrasound pulser is very expensive with low bandwidth. It is unipolar (negative) pulse and the frequency of pulse cannot be adjustable. The center frequency of pulser does not obtain the center frequency of 50 MHz transducer, reducing the image resolution. This study developed a novel bipolar pulse generator that has small size, low cost, high voltage and low noise, it can adjust the frequency of the pulse, the pulse repetition frequency and can select high voltage ±50 V ＆ ±100 V. The results of test are compared with commercial instrument 5900PR. The center frequency of bipolar pulse is close to the center frequency of 50 MHz transducer. The image of lateral resolution improved from 100 μm to 60 μm. The quality of image was improved in the B-mode and C-mode image, its sharpness and clarity has noticeably improved. In the vascular image of hand, we measured the vascular changes at different temperatures. It showed that normal subject and diabetes patient have significant difference and can reflect the diabetes patient's condition. The resolution of high frequency ultrasound imaging system improved, it can provide more useful information in the biological research and medical diagnosis.
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