研究生: |
彭俊凱 Chun-kai Peng |
---|---|
論文名稱: |
雙頻諧波影像之軸向旁瓣消除與正交編碼波形 Range Side Lobe Inversion and Orthogonal-Encoded Golay for Dual Frequency Harmonic Imaging |
指導教授: |
沈哲州
Che-Chou Shen |
口試委員: |
李百祺
none 鄭耿璽 none 廖愛禾 Ai-Ho Liao |
學位類別: |
碩士 Master |
系所名稱: |
電資學院 - 電機工程系 Department of Electrical Engineering |
論文出版年: | 2014 |
畢業學年度: | 102 |
語文別: | 中文 |
論文頁數: | 93 |
中文關鍵詞: | 雙頻 、編碼波形 、啾聲編碼 、格雷編碼 、正交編碼 、組織諧波影像 、旁瓣信號 |
外文關鍵詞: | Dual-frequency, excitation code, chirp encode, golay encode, orthogonal code, tissue harmonic image, range side lobe |
相關次數: | 點閱:471 下載:4 |
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雙頻諧波影像(dual-frequency harmonic imaging)同時發射中心頻率為f0 與2f0 之雙頻組合波形並接收其產生的二次諧波(second harmonic)與互調變諧波(inter-modulation harmonic)進行成像,故在發射端與接收端均可完整利用探頭頻寬,但雙頻諧波信號的低訊雜比(signal-to-noise ratio, SNR)仍為其成像品質的主要限制。前期研究中發展了一特殊啾聲編碼波形(chirp)用以改善雙頻諧波影像之訊雜比,但該波形經脈衝壓縮後仍會因影像頻帶之間的互干擾而殘留軸向旁瓣訊號(range side-lobe)。本研究中提出軸向旁瓣反相消除法(range side-lobe inversion, RSI)以抑制該啾聲編碼波形之軸向旁瓣,藉由設計編碼波形的發射相位來達到軸向旁瓣反相效果,再與原編碼波形進行結合以消除雙頻啾聲編碼之軸向旁瓣訊號。我們進一步探討格雷編碼中影像頻帶互干擾問題,並與具備正交特性之高位元格雷編碼進行比較。實驗結果顯示啾聲編碼波形在使用軸向旁瓣反相技術後可以提供較佳之壓縮品質與旁瓣抑制效果,而格雷編碼應用方面效果亦然,並且高位元正交格雷編碼驗證其成像品質也得到有效的提升。
Dual-frequency (DF) tissue harmonic imaging effectively utilizes the system bandwidth for frequency compounding and has been proposed to detect the harmonic signal at two independent frequencies. In DF harmonic imaging, the second harmonic signal at second harmonic (2f0) frequency and the inter-modulation harmonic signal at fundamental (f0) frequency are simultaneously generated for imaging. Therefore, the signal bandwidths are determined by the pulse length of the components respectively for the DF harmonic signal two spectral peaks with center frequencies at f0 and 2f0. Though particular chirp-encoded excitation can achieve high signal-to-noise ratio (SNR) for penetration together with wide signal bandwidth for resolution, it suffers from the range side lobes cause by the mutual interference between two imaging bands. In this study, range side lobe inversion method (RSI) is to fire an auxiliary chirp to change the polarity of the range side lobes, the range side lobes can be suppressed in the combination of the original chirp and the auxiliary chirp. The advantage of the phase encoding of complementary Golay pairs was taken to alleviate the mutual interference, and a new orthogonal encoded method for multi-bits Golay code has been developed to further suppress the range side lobes interference from the incorrect coded Golay pairs. The experiment result shows that, with the RSI method, the quality of pulse compression in DF harmonic imaging improves. And the comparison between multi-bits Golay code shows that orthogonal encoded method can avoid interference between two imaging bands.
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