供活體大鼠眼睛特性分析之全域式光學同調斷層掃描研究

Abstract

由於眼睛疾病的早期診斷治療是預防惡化的首要方法，近年光學同調斷層掃描(Optical coherence tomography; OCT)作為重要的生物影像工具，已被普遍應用於眼科臨床診斷，協助疾病確診及術後復原追蹤。全域式光學同調斷層掃描系統(Full-field optical coherence tomography; FF-OCT)之架構簡單，且掃描速度不亞於其他快速掃描的OCT技術，如掃頻雷射OCT (Sweep source OCT)。 本論文中展示兩套FF-OCT系統，皆使用實驗室自行生長的摻鈦藍寶石(Ti:sapphire)晶體光纖放大自發輻(Amplified spontaneous emission; ASE)作為光源。第一套系統為架設Michelson-based FF-OCT，是文獻中首套應用於活體大鼠視網膜及脈絡膜量測的FF-OCT系統。其光源中心波長為 769.7 nm，頻寬為 163.5 nm。由於OCT 系統之縱向解析度與光源的中心波長以及頻寬有關，上述的光源特性使OCT系統在空氣中縱向解析度達到2.1 μm，在視網膜組之中為 1.58 μm。此系統呈現了5層視網膜影像、視網膜厚度(~250 μm)、RPE層細胞大小(15-20 μm)、清晰的脈絡膜結構及厚度(20-42 μm) ，皆符合文獻記載。 第二套系統為應用實驗室現有的Mirau-based FF-OCT系統進行活體大鼠角膜量測。其光源中心波長為 769.9 nm，頻寬為 163.8 nm，使系統縱向解析度達到1.67 μm，在角膜組織中為1.21 μm，而橫向解析度為1.12 μm。可得到清晰且完整的4層角膜結構及厚度(~160 μm)，並經影像處理及分析後，能辨別表皮細胞層厚度(20-30 μm)及細胞位置、內皮細胞層厚度(~1.4 μm)及細胞密度(2,998-3,217 μm)，並且皆與文獻記載之數值相符。 本論文展現FF-OCT系統應用於活體眼睛量測之潛力，可協助學術研究，進一步開發更期能應用於人體眼睛疾病診斷。

Early stage diagnosis has been shown to be an efficient way to prevent the deterioration of eye diseases. In recent years, optical coherence tomography (OCT), as an important clinical imaging modality, has been widely used in clinical diagnosis in ophthalmology, helping follow the diseases progression and monitor response to therapy. Full-field optical coherence tomography (FF-OCT), a branch of OCT, has a simple setup, and its scanning speed is comparable to other fast-scanning OCT configuration, like sweep source OCT. In this work, two FF-OCT systems which both adopted amplified spontaneous emission (ASE) generated from the homemade Ti:sapphire crystal fiber as light source were demonstrated. The first system of this work is a Michelson-based FF-OCT system, which is the first FF-OCT system applied to in-vivo rat retinal and choroidal measurements in literature. The central wavelength of the light source of this system is 769.7 nm, and the 3-dB bandwidth is 163.5 nm, as a result, the system has an axial resolution of 2.1 μm in air and 1.58 μm in retinal tissue. The system revealed 5 layers of retinal image and the exquisite structure of choroid. It was found that the retinal thickness is about 250 μm, the cell size of retinal pigment epithelium is between 15 to 20 μm, and choroidal thickness is between 20 to 42 μm, and these results are consistent with these in literature. The second system employs a homemade Mirau-based FF-OCT to conduct in-vivo rat cornea measurement. The central wavelength of the system light source of is 769.9 nm, and the 3-dB bandwidth is 163.8 nm, giving the system 1.67-μm axial resolution in air and 1.21 μm in corneal tissue, and the lateral resolution is 1.12 μm. With the system, a clear corneal image with 4-layer structure can be obtained. After image processing and analysis, the corneal thickness (~160 μm), the thickness of corneal epithelium (20-30 μm), the location of the cell, the thickness of corneal endothelium (~1.4 μm) and endothelial cell density (2,998-3,217 μm) can also be calculated, and the results are consistent with these in literature. This work shows the potential of applying FF-OCT to in-vivo eye measurement. These FF-OCT systems can help academic research in current stage, and with further development, they are expected to be introduced to human trials.