基於生物樣本上之應用改良單輸入偏振靈敏光學同調斷層掃描系統與演算法

Abstract

偏振靈敏光學同調斷層掃描術 (Polarization-sensitive optical coherence tomography, PS-OCT) 能夠針對樣本組織進行非侵入式掃描，並提供二維或三維的樣本斷層影像，除了這些一般光學同調斷層掃描術 (Optical Coherence Tomography, OCT) 也能提供的資訊外，PS-OCT 更針對偏振光 (Polarized light) 的偏振態 (Polarization state) 對於樣本組織的變化做進一步分析，得到如光偏振態、相位延遲 (Phase retardation)、光軸方向 (Optic axis orientation)、去偏振性 (Depolarization) 以及其它樣本與光偏振性相關的性質，將這些性質進行量化並以數值變化方式呈現在結果影像上，讓使用者能夠從斷層掃描的結構影像上得到其它額外資訊。 本篇論文針對實驗室中現有的單輸入偏振靈敏光學同調斷層掃描系統 (Single-Input PS-OCT) 進行復原並改良。由於大多數生物樣本的可量測深度都大於系統原本的影像深度，因此在系統硬體方面，針對用於同步光源掃頻與數位訊號擷取的光學時脈訊號 (Optical k-clock signal)，加上額外的光學時脈頻率倍增模組 (Optical clock frequency doubling circuit module) 以提升取樣頻率，使得系統的影像深度提升為原本的兩倍。除此之外，在 PS-OCT理論方面提供了更加詳細的理論推導，也額外提供更多對於光學時脈頻率倍增模組應用在 OCT 系統上的分析演算法，並套用在實際樣本應用上。最後在實驗結果的部分，將利用量測系統的相關參數來驗證光學時脈頻率倍增模組於該 PS-OCT 系統上之可行性，並針對各式離體生物組織以及活體鼠眼睛視網膜樣本來進行量測，從 PS-OCT 的特殊結構影像來觀察這些樣本對於偏振光的特性。

Polarization-sensitive optical coherence tomography (PS-OCT) enables non-invasive imaging of biological tissues, yielding two-dimensional or three-dimensional cross-sectional images. In addition to the structural information provided by conventional optical coherence tomography (OCT), PS-OCT enables further analysis of changes in the polarization state of polarized light upon interaction with biological tissues. This enables the extraction of polarization-related properties, including polarization state, optic axis orientation, depolarization, and other polarization-associated characteristics. These properties are quantified and visualized in the resulting images, offering additional contrast and complementary information beyond structural features. This study focuses on restoring and enhancing an existing single-input PS-OCT system previously developed in the laboratory. Because the imaging depth of the original system was insufficient for most biological samples, a hardware modification was implemented to extend its axial imaging range. Specifically, an optical clock frequency doubling circuit module was integrated into the system to increase the sampling rate by doubling the frequency of the optical k-clock signal, which synchronizes the wavelength sweep of the light source with digital data acquisition. This enhancement successfully extended the imaging depth of the system by a factor of two. In addition to the hardware upgrade, this study presents a more detailed theoretical derivation of the PS-OCT system, along with analytical algorithms tailored for integrating the optical clock frequency doubling circuit module in OCT systems. These improvements were tested on real sample measurements. Finally, experimental validation was performed to demonstrate the feasibility of integrating the optical clock frequency doubling circuit module into the PS-OCT system. Measurements were performed on various ex vivo biological tissues as well as in vivo mouse retinal samples. The polarization-sensitive contrasts provided by PS-OCT reveal valuable insights into the polarization-related properties of these tissues.