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系統識別號 U0026-2608201415593400
論文名稱(中文) 利用換能器的聲束特性修正合成孔徑聚焦技術以改善超音波影像
論文名稱(英文) A Modified Synthetic Aperture Focusing Technique Utilizing Beam Characteristics of Transducer for Ultrasound Image Improvement
校院名稱 成功大學
系所名稱(中) 醫學資訊研究所
系所名稱(英) Institute of Medical Informatics
學年度 102
學期 2
出版年 103
研究生(中文) 何嘉哲
研究生(英文) Chia-Che Ho
學號 Q56011029
學位類別 碩士
語文別 英文
論文頁數 90頁
口試委員 指導教授-王士豪
口試委員-廖峻德
口試委員-黃執中
口試委員-林奕勳
中文關鍵字 超音波  修正合成孔徑聚焦技術  虛擬緣  聲場與換能器特性 
英文關鍵字 ultrasound  synthetic aperture focusing technique  virtual source  beam width and transducer characteristics 
學科別分類
中文摘要 合成孔徑聚焦技術已證實可以提升遠離探頭聚焦區超音波影像的側向解析度。然而,在虛擬緣的觀念下掃描線有限的點數,其經過合成孔徑聚焦技術修正後的影像會在聚焦區附近產生黑色假影的問題。此假影問題可藉由使用時間增益補償方式調整影像的亮度,然而此方法會因主觀意識不同而有不同的結果。為了改善此問題,此實驗將使用超音波換能器的聲場特性結合現在的合成孔徑聚焦技術來改善黑色假影問題。在實驗中,將使用不同頻率單陣元探頭來掃描。一開始,先由B-mode線假體影像來估計聲場,其中將使用-3dB到-20dB來估計聲束寬。由於時間延遲經由幾合運算會出現估計錯誤的問題,因此再將由B-mode線假體影像來計算時間延遲。結果顯示在結合量測聲場的合成孔徑聚焦技術不僅可以保持原本合成孔徑聚焦技術的優點並可以達到去除黑色假影的問題。在不同頻率的換能器中,結合-9dB聲場的合成孔徑聚焦技術將更適用於影像修正。結果顯示修正後的合成孔徑聚焦技術將能提升超音波的影像品質,並可以用於未來的臨床應用。
英文摘要 Synthetic aperture focusing technique (SAFT) has been proposed to improve the lateral resolution of ultrasound image outside the focal region of the transducer. However, SAFT would result an unexpected artifact image at the region near the focal point of transducer; which is due to the use of a virtue source concept associated with limited numbers of scan lines. The artifact image could be eliminated by using an appropriate time gain compensation (TGC). However, TGC is subjective to users’ settings. To further improve this issue, the present study incorporated the transducer’s depth-dependency beam characteristics into SAFT imaging procedure. Ultrasound images were acquired using different frequency of single element transducers. Initially, the beam widths of transducer were estimated from B-mode wire images using from -3 to -20dB width. Due to the erroneous time delay in accompanying with geometric calculation, the time delay was also estimated from those B-mode wire images. The -20dB beam width of transducer as a function of axial depth were measured for better estimating the time delay of each scanning point. The modified SAFT were verified by means of self-made phantoms with wire targets and contrast targets and in-vivo images. With the experiments, the modified SAFT images with the correction of beam width of the transducer may not only retain the advantages of original SAFT but also improve the artifact image near the focal region. The beam widths of transducer estimated from B-mode wire images using from -6 to -20dB width could be incorporated into SAFT imaging procedure and the modified SAFT was adaptive to different frequency of single element transducers. These results show that current modified SAFT-based imaging may greatly enhance ultrasound image quality for further clinical applications.
論文目次 摘要 I
ABSTRACT II
致謝 IV
CONTENTS V
LIST OF TABLES VI
LIST OF FIGURES VII
CHAPTER 1:INTRODUCTION 1
1.1 GENERAL 1
1.2 SYNTHETIC APERTURE FOCUSING TECHNIQUE 2
1.3 RESEARCH OBJECTIVES 6
CHAPTER 2:BACKGROUND 8
2.1 FUNDAMENTALS OF ACOUSTIC WAVE PROPAGATION 8
2.2 REFLECTION AND REFRACTION 11
2.3 ULTRASONIC ATTENUATION AND SCATTERING 13
2.4 SAFT WITH VIRTUAL SOURCE CONCEPT 19
CHAPTER 3:MATERIALS AND METHODS 24
3.1 MODIFIED SYNTHETIC APERTURE FOCUSING TECHNIQUE 24
3.2 ULTRASOUND IMAGING SYSTEM 28
3.3 EXPERIMENT ON PHANTOMS 34
CHAPTER 4:RESULTS AND DISCUSSIONS 36
4.1 THE MODIFIED SAFT FOR LOW-FREQUENCY TRANSDUCER 36
4.1.1 3.5 MHz single element transducer 36
4.1.2 7.5 MHz single element transducer 43
4.1.3 10 MHz single element transducer 50
4.1.4 15 MHz single element transducer 57
4.2 THE MODIFIED SAFT FOR HIGH-FREQUENCY TRANSDUCER 64
4.2.1 30 MHz single element transducer 64
4.2.2 40 MHz single element transducer 71
4.3 THE MODIFIED SAFT EXPERIMENTED ON BLOOD VESSELS 78
CHAPTER 5:CONCLUSIONS AND FUTURE WORKS 87
5.1 CONCLUSIONS 87
5.2 FUTURE WORKS 87
REFERENCE 89
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