臺灣博碩士論文加值系統

超音波影像是一種常用的醫學影像工具，而高頻超音波特有良好的解析度特性，可應用在許多如細微組織的診斷及基因研究上。本論文整合各種硬體和多種信號處理方法建立一套具有多種影像格式的高頻超音波影像系統，以期望應用在眼科及皮膚科的臨床診斷、應用小動物之藥物開發、癌症及基因研究上。
現有的高頻超音波影像系統受限於穿透深度較淺和無法動態聚焦的限制，本論文中藉由編碼波形提升發射信號的平均功率提升信號的穿透深度，整合各項高速硬體、配合脈衝壓縮濾波器以增加系統的訊雜比與軸向解析度，並提出以最小均方差(LMSE)為設計原則的最佳化濾波器，結合多重深度掃瞄技術以提升非聚焦區域的橫向解析度並解決無法動態聚焦的問題。
從實驗結果證明，本論文中所建立的50 MHz高頻超音波影像系統，具有55 dB 的訊雜比和100 mm 以下的影像解析度。並且利用模擬結果討論最佳化濾波器於單一探頭系統中所遭遇的問題。在未來相關高頻超音波的研究中，可參考本論文中所提出的系統架構及方法，將可針對後續如高頻組織諧波影像、微灌流的計算、高頻對比劑的特性、甚至與其他醫學影像合作等相關領域更進一步地研究，以期對臨床及生物醫學的研究有所貢獻。

Ultrasound imaging is a well-established imaging modality that provides diagnostic information in the form of cross-sectional images of soft tissue. However, for many clinical applications involving subtle tissue structure, the resolution of the conventional ultrasound imaging system that operates between 2 and 10 MHz is inadequate. Recent developments have taken advantage of the fact that resolution increases linearly with frequency. In this paper, a high frequency ultrasonic imaging system with high resolution and multi-format imaging has been developed for noninvasive imaging of small scale superficial structures such as the skin, the anterior chamber of the eye, and mouse embryos for studies in developmental biology.
The major design problem concerning medical high frequency ultrasonic imaging systems is caused by the strong attenuation of the tissue, which limits the maximum depth of penetration and the achievable signal to noise ratio (SNR). In this paper, the coded excitation and pulse compression techniques, which can increase the average transmitted power, are utilized to increase both the depth of penetration and SNR. In addition, since array transducers with dynamic focusing are not available for high frequency system, the image quality is significantly deteriorated in the out-of-focused region. Hence, a filter-based synthetic aperture focusing technique is employed here to improve the degraded beam quality. Such a filter is designed in the LMSE sense and is also known as the optimal filter. Moreover, depth scan technique is also applied to increase the depth of field for this high frequency system.
The experimental results demonstrate that the 50 MHz ultrasonic imaging system developed in this paper has resolution on the order of 100 mm and a 55-dB SNR. Implementation issues of optimal filter to increase the depth of field for a single crystal transducer system are also discussed. Based on the high frequency ultrasonic imaging system constructed in this paper, advanced high frequency ultrasound research on high frequency tissue harmonics, perfusion blood estimation and contrast agent characteristics could be performed. In addition, combined with other medical imaging systems, this system might be able to provide much more valuable information on clinical diagnostics and biomedical research in the future.

第一章 緒論 1
1.1 高頻超音波影像簡介 1
1.1.1 高頻超音波影像簡史 1
1.1.2 高頻超音波影像應用 2
1.2 研究動機與目標 8
1.3 論文架構 10
第二章 高頻超音波影像特性 11
2.1 聲波頻譜 11
2.2 超音波成像原理 12
2.3 組織衰減效應 15
2.4 常見影像格式 18
第三章 高頻影像技術 21
3.1 編碼發射信號 21
3.2 脈衝壓縮技術 25
3.2.1 匹配濾波器 26
3.2.2 最佳化濾波器設計 26
3.3 橫向濾波器 28
3.4 馬達掃瞄技術 31
3.4.1 多重深度掃瞄 31
3.4.2 固定深度影像 33
第四章 實驗系統設計 34
4.1 實驗系統架構與介面 34
4.2 雜訊量測與消除系統 38
4.3 影像仿體製作 40
4.3.1 線仿體 40
4.3.2 組織仿體 40
4.3.2 in-vitro眼睛仿體 42
第五章 結果分析與討論 43
5.1 頻率響應 43
5.2 雜訊抑制 45
5.2.1 熱雜訊 45
5.2.2 量化雜訊分析 46
5.2.3 電磁保護屏蔽 47
5.2.4 信號平均 48
5.2.5 編碼波形及脈衝壓縮 50
5.3 影像解析度 52
5.3.1 評估解析度方法 52
5.3.2 脈衝壓縮技術 52
5.3.3 橫向濾波器 55
5.3.3.1 觸發信號錯誤 56
5.3.3.2 馬達位移錯誤 57
5.3.3.3 探頭角度錯誤 58
5.4 穿透深度 60
5.4.1 評估穿透深度方法 60
5.4.2 衰減係數 61
5.4.3 編碼波形及脈衝壓縮 61
5.5馬達掃瞄技術與其他影像格式 63
5.5.1 多重深度掃瞄 63
5.5.2 固定深度掃瞄 65
5.5.3 三維影像重建 67
5.6 in-vitro影像 69
5.7組織諧波影像 71
5.8 結論 73
5.9 未來工作 74
第六章 參考文獻 76

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