超音波發射端對於諧波格雷編碼需要四分之一相位偏移，然而低階脈衝產生器因為只能發射三階振幅的方波，導致無法完全的產生位移90°的方波，因此所產生的諧波格雷編碼不能完整轉換出正確的反相編碼”1”與”-1”，此編碼錯誤的問題造成了明顯的軸向旁瓣在匹配解碼後。本論文利用相位任意波形發射的脈衝寬度調變(pulse-width-modulation, PWM)在匹配格雷編碼上去抑制旁瓣峰值程度(peak range side lobe, PRSL)，其結果顯示在三階振幅的波形中，擁有高取樣率如100倍中心頻率的PWM發射波形提供的PRSL最低，然而當取樣率下降PRSL則會快速的上升。對比一般方波發射，PWM發射波形的PRSL可能會更高假如其取樣率低於20倍中心頻率。本論文提出一個新穎的正交格雷解碼技術，使用兩組互相正交的格雷發射波形去消除在格雷編碼中因為其相位未完全反相的編碼錯誤，此結果指出正交格雷解碼可以改善B-mode影像9.5dB的對比度藉由移除在無回聲cyst區域中的旁瓣假影，對比一般傳統的匹配濾波解碼。

Quadrature phase shift is required in the ultrasound transmit end for harmonic Golay encoding. Nonetheless, typical 3-level square transmit waveform fails to reproduce the 90° phase shift and thus the resultant harmonic code is not exactly encoded as the phased-inverted symbols of +1 and -1. This introduces coding error and subsequent range side lobe artifacts after complementary decoding. In this work, pulse-width-modulation (PWM) of phased arbitrary transmit waveforms is applied for complementary Golay encoding to suppress peak range side lobe level (PRSL). Results show that, among 3-level waveforms, PWM transmit with high sampling rate (fs = 100f0) provides the lowest PRSL but the PRSL increases rapidly when the sampling rate decreases. Compared to the typical square wave, the PRSL of PWM transmit could be even higher if the sampling rate is lower than 20 times f0. A novel orthogonal Golay decoding technique is also developed by using two mutually orthogonal Golay transmit pairs to eliminate the coding error from incomplete phase inversion in Golay encoding. Results indicate that the orthogonal decoding can improve the B-mode image contrast by 9.5 dB by removing side lobe artifacts in the anechoic cyst region, compared to the conventional matched decoding.

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