| Summary: | 碩士 === 長庚大學 === 電機工程研究所 === 95 === Abstract
Focused ultrasound technology has been examined to be capable of successfully performing noninvasively thermally ablate deep-seated biological tissues. When steering the focused energy at the specific target in biological tissues, the energy can steer concentrated energy to thermally ablate tissues, with the accumulated energy along the beam path is small and the unwanted damage in the intervening tissues can be avoid. To perform successful thermal ablations, temperature monitoring is essential to guarantee the treatment quality during the thermally ablative process. Two physical phenomena have been developed to be able to reflect temperature change: (1) Temperature induced backscattered signal amplitude change and (2) temperature- induced echo-time shifting effect. In the second approach, previous studies showed that the echo-time shift can be calculated by estimating the signal phase shifting based on cross-correlation analysis. However, the disadvantage of this approach is that cross-correlation is extremely time-consuming, which may degrade the future applicability in a commercialized ultrasonic imager. The purpose of this study is to propose a novel algorithm to perform the temperature estimation from ultrasonic echo by using the Hilbert transform rather than cross-correlation analysis. In the first part of experiment, a simple PC-controlled pulse/echo generator was used to synchronize with the focused ultrasound sonication, and then a single line data were analyzed to perform 1-D temperature estimation. In the second part of experiment, a commercialized ultrasound imager was employed to acquire multiple row data to perform 2-D temperature mapping. Phantom and ex-vivo tissue experiments were performed, and multiple point temperatures were measured from thermocouples to verify and calibrate the estimated data. Results showed that the proposed algorithm can extensively shorten the processing time (about 6~8 folds) without scarifying too much temperature estimation quality. This provides useful information for further temperature estimation form clinical ultrasonic imaging system.
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