以時域有限差分法模擬分析光學同調掃描術量測數據建構細胞模型

論文摘要利用光學同調掃描術 (Optical Coherence Tomography 即 OCT) 產生的影像可以看到相對應解析度的細胞影像，但是最原始的資料 (raw data)所隱含的訊息並沒有被完全的分析。本篇論文就是針對OCT原始的資料，利用時域有限差分法 (Finite-Difference Time-Domain即FDTD) 來協助比對分析，將隱含在原始資料裡的訊息解讀出來，本論文的目標就是將實驗數據分析，重建樣本的結構和折射率。光學同調掃描術的原理是利用光的反射對樣本進行軸向 (Z direction) 的探測，藉由麥克森干涉儀 (Michelson interferometer) 將從參考臂 (reference arm) 反射的光和從樣本反射的光做干涉來重新建構樣本的結構。從樣本反射的光是由於光受到樣本在軸向折射率變化而產生反射，而反射的比例是依照菲涅耳方程式 (Fresnel’s equation)來計算。由於生物細胞結構複雜，折射率分布也非均值，因此先藉由FDTD初步模擬均勻結構的細胞及組織在OCT的原始資料形態，再進行較複雜結構的模擬與探討。模擬結果顯示，FDTD可以協助觀察OCT的訊號，在影像部分，相較於OCT光源解析度下的細微結構，會有微弱的反射訊號並不會大大的影響OCT成像，但是卻使得折射率計算難度增加。實驗數據部分，重建的結果為等效折射率，細微結構的訊號會使誤差增加。

關鍵字

光學同調掃描術；麥克森干涉儀；時域有限差分法；菲涅耳方程式；折射率

並列摘要

ABSTRACT Optical Coherence Tomography (OCT) imaging can be performed by processing the raw data, the information such as refractive indices contained in the carrier raw data is completely neglected. The goal of this thesis is to analyze the carrier raw data generated by OCT via Finite-Difference Time-Domain method (FDTD) and to reconstruct the refractive indices from the carrier raw data. OCT imaging is performed by Michelson interferometer. Light reflected from sample arm coupling with light reflected from reference arm forms interferometry and then is detected by charge-coupled device (CCD), which is how the OCT performs imaging. The mechanism of the reflection of light follows the Fresnel’s equation. The simulation results indicate that when the sample is homogeneous and simple structure, the interferometry shows up at the boundary of the sample, while the finer structures show reflections but hard to specify the exact boundary. The cell model, tissue model, and epidermis tissue model are shown respectively in our simulation. The relative error of the calculated refractive indices is mainly from the fine structures. It is shown how the fine structure of the sample would affect the reflected signals and reconstruction. Results show that the noise signals would blur the OCT images, which also affect the calculation of refractive indices.

並列關鍵字

Optical Coherence Tomography ； Michelson interferometry ； Finite-Difference Time-Domain method ； Fresnel’s equation ； refractive index

參考文獻

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國際替代計量

以時域有限差分法模擬分析光學同調掃描術量測數據建構細胞模型

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