以掃頻式摻鈦藍寶石晶體光纖雷射為光源之血管內光學同調斷層掃描術的系統架設與分析

Design and Setup of Intravascular Optical Coherence Tomography with a Ti:Sapphire Crystal Fiber Based Wavelength-swept Laser

王俊凱(Chun-Kai Wang)

指導教授 ： 黃升龍

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103890

摘要

摻鈦藍寶石具有寬廣的放射頻譜，其螢光頻譜之半高寬可達180nm，對光學同調斷層掃描術(optical coherence tomography; OCT)而言，寬廣頻譜的輸出光源，可以獲得較高的縱向解析度；除此之外，摻鈦藍寶石之螢光中心波長為760nm，該波段對於組織散射損耗及水的吸收皆較小，此波段稱為診療視窗。然而摻鈦藍寶石本身因其短螢光生命週期和低吸收截面積，難達到低閥值的輸出，而本實驗室使用雷射加熱基座長晶法生長出纖心直徑為16μm且衰減係數僅為0.017cm^(-1)的玻璃纖衣波導結構，可建構出高效率，低雷射閥值的雷射輸出。
血管內之掃頻式光學同調斷層掃描術(intravascular swept-source OCT; IV-SSOCT)目前已被廣泛應用在醫界，透過非侵入式的掃描獲得血管的三維影像，如血管各層結構的厚度以及脂肪的堆積，可以幫助醫生對疾病做精確的判斷。
在本研究當中，以本實驗室研發之掃頻式摻鈦藍寶石晶體光纖雷射作為光源，最高掃描頻率可達100kHz，在雷射波長調整至782nm時，有最寬可調輸出頻寬達190.86nm，然而在對輸出頻譜進行分析後，本實驗以12kHz之掃描頻率進行OCT系統實驗，此外還以其他的掃頻雷射光源(BS-790-1-OEM)來進行比較與實驗，最後搭配OCT系統中光學、電子元件的審慎挑選，嘗試開發出較高縱向解析度(<5μm)的IV-SSOCT。
完成系統架設後，本實驗對不同的非生物以及生物檢體樣本進行掃描與形貌的分析，除了單一反射面的平面鏡樣本，還有可穿透的紙捲樣本，可量測得出紙捲厚度為150.4μm，最後是大鼠主動脈檢體影像，搭配H E染色的切片影像，可以大致了解血管的形貌以及厚度約為200μm，但是由於解析度以及光源強度不足導致內部的結構目前並不清晰。
未來，若能提高雷射功率與系統的可視深度，以及開發出針對中心波長780nm的可旋式掃描探頭，可期待獲得更清晰的三維影像。

關鍵字

摻鈦藍寶石 ； 晶體光纖 ； 掃頻式光學同調斷層掃描術 ； 血管內成像

並列摘要

Titanium (Ti): sapphire has the characteristic of broadband emission spectrum, 180-nm width of 3-dB bandwidth, which provide high axial resolution for optical coherence tomography (OCT). In addition, the center wavelength of fluorescence from Ti:sapphire is 760nm, a region known as therapeutic window, which has advantages such as low tissue scattering and water absorption. Nevertheless, result from short fluorescence lifetime and low absorption, Ti:sapphire laser has high threshold power as a defect. Therefore, based on the method of laser-heated growth, a glass-clad crystal fiber, 1.6-μm core diameter and 0.017-cm^(-1)attenuation coefficient, with high efficiency and low threshold power is applied in this research.
Recently, intravascular swept-source OCT (IV-SSOCT) has been widely utilized in medical profession by non-invasive scanning to acquire three-dimensional images of blood vessels with detailed information, e.g., the thickness of different layers and the accumulation of fat, which assist clinicians making a more precise diagnose.
In this study, a Ti:sapphire crystal fiber based wavelength-swept laser developed by our laboratory has been used as the light source with maximal sweep frequency, 100kHz, and the widest adjustable output bandwidth, 190.86nm, at 782-nm wavelength. After analyzing the output spectrum, 12-kHz sweep frequency is chosen in IV-SSOCT system experiment. Additionally, compared with other wavelength-swept laser (BS-790-1-OEM), optical and electronic components in the system are selected carefully to develop an IV-SSOCT with a higher axial resolution (<5μm).
After finishing the system setup, morphologies of several non-biological and biological samples have been scanned and analyzed, e.g., a flat mirror sample with one reflective surface and an experimental paper roll with 150.4-μm thickness, scanning result. Lastly, images of ex-vivo rat aorta from IV-SSOCT, combined with H E stained images that are utilized as reference, morphology and thickness, about 200μm, has been clarified. The internal structure is still not highly clear, because of the low resolution and low light source intensity.
In the future, either the power of laser and visible depth of images have improvement, or a rotatable scanning probe with 780-nm central wavelength has been developed and applied, higher quality three-dimensional images from IV-SSOCT may be expected.

並列關鍵字

Ti:sapphire ； crystal fiber ； swept source optical coherence tomography ； blood vessel imaging

參考文獻

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