功能性光學同調斷層掃瞄技術發展

Technology Development of Functional Optical Coherence Tomography

紀廷達(Ting-Ta Chi)

指導教授 ： 楊志忠

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.02917

摘要

這篇論文中首先我們展示了一個改良的血管照影術，雖然這方法與傳統的方法都是藉由分析空間頻率的高低來達到血管照影的目的，但相對於傳統的技術，此方法藉由改變x與k空間的運算次序，有效消地除掃瞄時樣品擾動所產生的相位雜訊。利用此法所得的血管分佈，可使傳統利用統計方式來消除相位雜訊的方法變得更有效率且能得到更正確的血流資訊。這方法還可運用於消除臨床探頭掃瞄時步進馬達所產生的相位雜訊。
接著我們利用空間局部軟體分析方法來降低雙參考面光學同調斷層掃瞄系統的架設難度並消除鏡像。傳統雙參考面光學同調斷層掃瞄系統必須嚴格的限制雙參考面之間的相位差為90度，所以必須精確地調整分光鏡的角度，但如果利用空間局部方法做運算只要兩參考面相位差大於30度就可以有效消除鏡像的問題，如此降低了分光鏡與整體雙參考面光學同調斷層掃瞄系統的架設難度。利用此方法得到高品質的全域光學都譜勒斷層掃瞄影像。
最後我們利用中心波長分別為800與1310奈米的光學同調斷層掃瞄系統與中心波長為1315奈米的強度調變激發雷射來觀察有無摻雜金奈米環洋菜凍樣品的光學同調斷層掃瞄影像與光熱光學同調斷層掃瞄影像。金奈米環表面電漿子共振波長約為1320奈米，因此利用中心波長為1310奈米的光學同調斷層掃瞄系統可觀察到背向散射的增強。而當使用強度調變的激發雷射時，兩光學系統都可得到清楚的光熱光學同調斷層掃瞄影像。由這些結果可以發現雖然中心波長為800奈米的光學系統所得的同調斷層掃瞄影像強度較弱，但還是可得到明顯的光熱光學同調斷層掃瞄影像，特別是在摻雜金奈米環洋菜凍樣品添加豆漿來增強背向散射時特別明顯。換言之，當光學同調斷層掃瞄系統的工作波長與表面電漿共子振波長不重疊時，增加背向散射的強度有助於增加光熱訊號的訊雜比。從追踪金奈米顆粒應用的角度看，同時得到清楚的光學同調斷層掃瞄影像與光熱光學同調斷層掃瞄影像將有助於精確標定金奈米顆粒的分佈。但為了達到這個目的，我們必須特別選擇金奈米顆粒使表面電漿子共振波長與光學同調斷層掃瞄系統的工作波長範圍重疊。

關鍵字

光學同調斷層掃瞄 ； 都普勒光學同調斷層掃瞄 ； 雙參考面光學同調斷層掃瞄

並列摘要

Abstract
First, an improved image processing procedure for suppressing the phase noise due to a motion artifact acquired during optical coherence tomography (OCT) scanning and effectively illustrating the blood vessel distribution in a living tissue is demonstrated. This new processing procedure and the widely used procedure for micro-angiography application are based on the selection of high-frequency components in the spatial frequency spectrum of B-mode scanning (x-space), which are contributed from the image portions of moving objects. However, by switching the processing order between the x-space and k-space, the new processing procedure shows the superior function of effectively suppressing the phase noise due to a motion artifact. After the blood vessel positions are precisely acquired based on the new processing procedure, the projected blood flow speed can be more accurately calibrated based on a previously reported method. The demonstrated new procedure is useful for clinical microangiography application, in which a stepping motor of generating motion artifacts is usually used in the scanning probe.
Secondary, the significantly less stringent operation of a two-reference swept-source OCT system for suppressing the mirror image is demonstrated based on the spatially localized image processing method. With this method, the phase difference between the two reference signals is not limited to 90 degrees. Based on the current experimental operation, the mirror image can be effectively suppressed as long as the phase difference is larger than 30 degrees. In other words, the adjustment of the beam splitter orientation for controlling the phase difference becomes much more flexible. Also, based on a phantom experiment, the combination the spatially localized mirror image suppression method with the two-reference OCT operation leads to the implementation of full-range optical Doppler tomography.
Finally, the intensity and photothermal images of OCT scanning of agar phantoms with and without the mixture of Au nanorings (NRIs) based on two OCT systems of different operation wavelengths are compared. The Au NRIs have the localized surface plasmon (LSP) resonance peak at ~1320 nm, leading to enhanced coherent scattering for producing clear OCT intensity images with the OCT system of 1310 nm in operation wavelength. Also, the LSP resonance induced absorption results in clear photothermal images through phase signal calibration of OCT scanning with the 1315-nm OCT system and another OCT system of 800 nm in central operation wavelength when a modulated excitation laser is applied. It is found that although the intensity image signal is weak with the 800-nm OCT system, its photothermal signal is quite strong, particularly when bean milk is mixed with agar for enhancing background scattering. The photothermal signal level increases with increasing background scattering when the OCT operation wavelength is located outside the spectral range of LSP resonance of Au NRI. In the viewpoint of practical application of Au nanoparticle (NP) tracking, simultaneous acquirement of clear OCT intensity and photothermal images can help in more precisely identifying the distribution of Au NPs. However, to this goal, the required matching of LSP resonance wavelength and OCT operation wavelength results in lower flexibility of choosing the used Au NP.

並列關鍵字

Optical Coherence Tomography (OCT) ； Optical Doppler Tomography (ODT) ； Two Reference OCT

參考文獻

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