光學同調斷層掃瞄技術研究及應用

Abstract

光學同調斷層掃瞄可提供生物之二維到三維影像，在臨床診斷上應用頗廣。光學同調斷層掃瞄的基本架構為一干涉儀，其深度解析度由系統所使用的光源頻譜寬度所決定，使用頻譜較寬的光源可以獲得比較高的深度解析度。另外，掃瞄速度的提升也是另一個光學同調斷層掃瞄重要的課題。相位延遲調變掃瞄器和頻譜域光學同調斷層掃瞄都是可以提昇掃瞄速度的技術。高解析度以及快速掃瞄都是光學同調斷層掃瞄系統重要的發展方向，然而，同時保持高解析度及高掃瞄速度相當困難。 在這篇論文中，我們研究方目標為發展高解析度且高速掃瞄的光學同調斷層掃瞄系統。首先，我們提出了一個軟體色散補償的技術，利用結合多次掃描來達到動態的色散補償以配合不同的應用。第二，我們提出了一個提升光學同調斷層掃瞄解析度的技術，此技術的原理是結合不同相位調變速度的掃描，來達到提升解析度的效果。第三，我們設計並製作一套高解析度的頻譜域光學同調斷層掃瞄的系統。頻譜域光學同調斷層掃瞄有較高的掃瞄速度，在這個研究中，我們利用非線性光學去加大光源的頻寬以達到高解析度且高掃瞄速度的目標。最後，我們使用頻譜解析頻譜域光學同調斷層掃瞄量測血氧飽和濃度，藉由比較波長大於以及小於800奈米的深度背向散射強度變化的差異，渴求出血氧飽和濃度的變化。頻譜解析頻譜域光學同調斷層掃瞄，因為它可以提供特定位置的血氧飽和濃度資訊，比一般商用的近紅外光譜血氧量測儀較為優越。

Optical coherence tomography (OCT) is one of the widely used biomedical imaging techniques, which can provide two-dimensional cross-section images for many clinical applications. An OCT system is based on an optical interferometer. The longitudinal resolution depends on the bandwidth of the light source used in the OCT system. Use of a broadband light source can lead to the longitudinal resolution down to a few microns. The scanning speed of OCT system is another advantageous issue for its application. The development of the technique of spectral–domain OCT improves significantly the OCT scanning speed. In this dissertation, we first propose a software dispersion compensation method to eliminate the dispersion mismatch in an OCT system. By combining the multiple scans, dispersion mismatch can be dynamically adjusted for different applications. Second, we demonstrate a method for improving the OCT resolution. The resolution enhancement originates from the superposition of several longitudinal scans with different phase modulation speeds. Third, a high-resolution spectral-domain OCT system is demonstrated. In the spectral-domain OCT system, the resolution is improved by using a broadband light source generate from the nonlinear optics effects in a high numerical-aperture fiber. By fast sweeping the spectrum, a fast-scanning and high-resolution OCT system can be achieved. Next, the hemoglobin oxygen saturation level is measured by a spectroscopic spectral-domain OCT system. Hemoglobin oxygen saturation level can be obtained by comparing the A-mode scan profiles between the wavelength ranges shorter and longer than 800 nm. This technique has the potential for high-resolution in vivo haemoglobin oxygen saturation level monitoring.