| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 95 === Issues related to generation of tissue harmonic signal are discussed in this study. Tissue harmonic signal is produced due to finite amplitude distortion when sound wave propagates through the body. Intensity of tissue harmonic is generally low and thus the sensitivity and penetration in tissue harmonic imaging is limited. In contrast harmonic imaging, however, suppression of tissue harmonic is beneficial because tissue harmonic may reduce image contrast between contrast agents and surrounding tissues. In the study we propose a new approach, third harmonic transmit phasing , which is based on phasing the frequency-sum and frequency-difference components of tissue harmonic signal to enhance or to suppress tissue harmonic signal. The proposed method doesn’t decrease contrast resolution when the tissue harmonic is enhanced. Though suppression of tissue harmonic is achieved at the cost of elevated sidelobes, improvement of image contrast in contrast harmonic imaging is not affected.
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