臺灣博碩士論文加值系統

超音波諧波影像可用以提升微氣泡對比劑的偵測能力，但諧波影像一般為了提升影像的軸向解析度，常會使用較短的發射脈衝而出現諧波溢漏信號(harmonic leakage)，此外組織諧波信號的產生也會使得影像的CTR值(contrast-to-tissue ratio)下降。本文主要探討當對比劑諧波影像中有諧波溢漏信號存在時，如何利用組織諧波與溢漏諧波之間的相位關係來將背景組織區域的諧波信號抑制，以提升影像的CTR值。我們提出利用改變基頻發射信號的相位來調整組織諧波與溢漏諧波之間的相位差，當兩者反相時便可降低背景組織區域的諧波信號強度，在實驗與模擬驗證中可發現本技術確實可以抑制背景組織的諧波信號，而對比劑諧波信號則較不受基頻發射相位影響，因此整個諧波影像的CTR值可被提升達5dB左右。

Ultrasonic harmonic imaging provides superior image quality than linear imaging and has become an important diagnostic tool in many clinical applications. Nevertheless, the contrast-to-tissue ratio (CTR) in harmonic imaging is generally limited by tissue background signal comprising both the leakage harmonic signal and the tissue harmonic signal. Harmonic leakage generally occurs when a wideband transmit pulse is utilized for better axial resolution. In addition, generation of tissue harmonic signal during acoustic propagation also decreases the CTR. In this paper, suppression of tissue background signal in harmonic imaging is studied by selecting an optimal phase of the transmit signal to achieve destructive cancellation between the tissue harmonic signal and the leakage harmonic signal. With the optimal suppression phase, our results indicate that the tissue signal can be significantly reduced at second harmonic band while the harmonic amplitude from contrast agents shows negligible change with the selection of transmit phase. Consequently, about 5-dB CTR improvement can be achieved from effective reduction of tissue background amplitude in optimal transmit phasing.

摘要
Abstract
致謝
目錄
圖目錄
表目錄
第一章 緒論
1-1 醫用超音波影像的基本原理與特性
1-2 超音波對比劑簡介
1-3 超音波對比劑之諧波影像
1-4 組織諧波與溢漏諧波
1-5 諧波抑制的相關文獻
1-6 研究動機與目標
1-7 論文架構
第二章 改變發射波形的基頻相位法原理
2-1 發射連續波(Continuous Wave)情形
2-2 發射脈衝波(Pulse Wave)情形
第三章 研究方法
3-1 模擬方法
3-1-1 組織諧波信號的模擬
3-1-2 對比劑諧波信號的模擬
3-2 實驗方法與系統架構
3-2-1 諧波信號的量測
3-2-2 仿體影像的組成
第四章 模擬與實驗結果
4-1 模擬結果
4-1-1 組織諧波信號
4-1-2 對比劑諧波信號
4-2 實驗結果
4-2-1 組織諧波信號
4-2-2 對比劑諧波信號
4-2-3 仿體影像
第五章 討論、結論與未來工作
5-1 討論
5-2 結論
5-3 未來工作
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