Study of full-field optical coherence tomography

光學同調斷層掃描術為現今重要的生醫造影技術之一，其縱向解析度受到光源的中心波長及頻寬所影響。針對此點，本實驗室自行生長了中心波長及頻寬分別為560 nm及95 nm的單纖衣摻鈰釔鋁石榴石晶體光纖，並以此光源架設了一套全域式光學同調斷層掃瞄系統，經實驗可得極高的解析度，縱向及橫向分別為1.47 μm及1.28 μm，可清楚解析多數生物樣本的細微結構。 本論文中，探討了橫向優先與縱向優先之影像運算法，並於橫向優先法中討論濾波頻帶對解析度之影響，得到頻帶上邊界應大於橫向解析頻率，而下邊界只需濾除直流成份之結論。在此情況下，兩運算法有著相近的解析能力，因此在橫向優先法之運算下，可望提升系統呈現影像之即時性。 利用本系統量測單顆細胞樣本，藉由改變參考光強及分析干涉效率之變化，歸納出細胞量測時合適的參考鏡反射率約為6%。接著，為了進行較深處的樣本量測，我們設計一個可調式元件來補償色散效應，同時建立其數學模型並由實驗結果得到了驗證。最後實際量測330 μm深度下的單顆細胞，結果顯示此元件的補償確實提升了解析度及訊噪比，使樣本深處的細胞更為清晰，展示了此系統的實際應用性。Optical coherence tomography (OCT) has become one of the most important techniques in biomedical imaging realm. Its axial resolution is determined by central wavelength and bandwidth of the light source. Due to this reason, we made the Ce3+:YAG single-cladding crystal fiber, which generate amplified spontaneous emission centered at 560 nm with bandwidth of 95 nm. And we use it as the light source to demonstrate a full-field OCT with axial resolution of 1.468 μm and lateral resolution of 1.28 μm. In this thesis, we discuss about axial-first and lateral-first image processing method. In the section of lateral-first method, we further discuss the influence on resolution when tuning the range of band-pass filter. Then we give a conclusion that the upper limit of filter should be higher than the maximum spatial frequency sampled by lateral resolution, and the lower limit of filter only need to filter out the DC component. In this condition, both processing methods perform comparable resolution. Therefore, the instantaneity of OCT images could be improved in lateral-first image processing method. We use full-field OCT to scan the single cell specimen and find out that the most suitable reflectivity of reference mirror is about 6%. In order to measure the deeper region of specimen, we design a component to compensate dispersion effect named adjustable dispersion compensator (ADC). We also build a mathematical model to describe the operation of ADC and successfully verify its validity from experimental result. Finally, we demonstrate that the quality of 330-μm-deep single cell OCT image can be improved by the help of ADC and shows the application potential of this homemade component.誌謝 i 中文摘要 ii Abstract iii 目 錄 iv 圖目錄 vi 表目錄 x 第一章 緒論 1 第二章 光學同調斷層掃描術 3 2.1 低同調干涉術理論 3 2.2 基本架構及解析度 8 2.3 全域式光學同調斷層掃描術 11 第三章 系統架構及設計 13 3.1 系統光源 13 3.2 光學系統 18 3.3 壓電致動器之校正 21 3.4 系統測試 26 第四章 單顆細胞掃描 31 4.1 樣本介紹及製備 31 4.2 細胞影像 34 4.3 細胞量測之干涉效率分析 38 第五章 縱向優先與橫向優先之影像運算法比較 49 5.1 動機 49 5.2 縱向優先影像運算法 51 5.3 橫向優先影像運算法 54 5.4 解析度比較 62 第六章 可調式色散補償 76 6.1 色散之影響 76 6.2 可調式色散補償元件 82 6.2.1 元件設計 82 6.2.2 數學描述 84 6.2.3 補償機制 89 6.2.4 元件製備 96 6.2.5 驗證方法 99 第七章 結論與未來展望 105 參考文獻 10