本論文是對醫學超音波影像中的組織諧波信號相關問題進行討論。當聲波穿越人體時會因有限振幅失真現象使得組織諧波信號逐漸累積產生，組織諧波的特色是其信號強度微弱而影響影像的靈敏度以及穿透度﹔但對於對比劑諧波影像而言過強的組織諧波信號反而會影響微氣泡區域的影像對比，因此抑制組織諧波的技術也有其必要性。在本論文中我們提出＂三倍頻發射相位法＂以調整第二組織諧波信號的強度，其原理是藉由改變頻率合成分與頻率差成分之間的相位差以增強或者抑制組織諧波信號。由實驗與模擬的結果來看，利用三倍頻發射相位法來增強組織諧波可以有效提升諧波信號強度且不會造成對比解析度的下降，組織諧波的抑制方面雖然會使波束的旁瓣上升但並不會影響到對比劑諧波影像中因背景組織諧波強度下降所造成的的影像對比提升。

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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