- 學位論文
微循環血流影像造影與分析系統
Microcirculation Blood Flow Imaging and Analysis System
摘要
微循環在微血管與組織中佔有相當重要的地位。氧氣與二氧化碳，以及養份廢物的交換，都是透過微循環的作用而完成。在病理上，許多重要病症常伴隨著局部的微循環障礙，如糖尿病、高血壓、心血管疾病等。因此，利用非侵入式微循環造影系統來觀測微循環所表現之生理訊號，將能提供活體微血管中的血流之生理訊息。本論文目的在於發展出一非侵入式表皮微循環造影系統，此系統乃基於正交極化頻譜(orthogonal polarization spectral)造影法，針對甲襞表皮微血管進行觀測。同時，亦完成血流速量測方法，可經由分析血流影片獲得微血管中的血流速訊息。 非侵入式表皮微循環造影系統包含以下幾個重要元件：20倍放大物鏡、照射光源與CCD(charge-coupled device)攝影機。為了決定此微循環造影系統之最佳光源，我們設計一光源實驗，分別以白光、藍光與綠光做為系統光源進行甲襞表皮微循環血流攝影。藍光與綠光的產生乃是分別將帶通濾波片放置於白光前(482±17.5 nm與556±10 nm)，爾後根據不同光源拍得之影像，分析其影像解析度與影像品質。首先，我們調整光源的強度，藉以觀察光源照度與影像品質之間的關係。另外，我們也改變皮膚溫度，希望了解在不同體表溫度下所形成的血流影像對影像品質的影響。因此，分別對正常體表溫度(33.09±0.75 ℃)與低溫(18.85±0.44 ℃)下之微循環進行攝影。由實驗結果得知，綠色光源為此造影系統之最佳光源。原因是，不論在常溫或低溫下，使用綠光皆可提供良好的影像解析度與最佳的對比度雜訊比率(contrast-to-noise ratio)。最後，相較於傳統式的垂直入射光於，傾斜角度之入射光設計，將可進一步提高影像品質。 在血流速量測方面，我們根據影像處理的方法，分析一條完整微血管的血流速度，能在微循環的尺度下提供正確的血流生理訊息。血流速量測系統的設計描述如下。影像對位功能是基於交互訊息法，用以解決攝影中手指或儀器的晃動問題。影像對位完成之後，使用細線化演算法可由原始之血管影像中獲得血管之完整骨幹，包含動脈端、靜脈端與轉彎處。血流速計算方法乃以光流(Optical flow)為主，同時以交互相關法(cross-correlation)與空間-時間圖解法(space-time diagram)為參考，進行血流速分析評估。流速實驗使用前之微循環造影系統，由三位受試者中錄製十二條血管之血流影片。每一位受試者錄製一段為時四十五秒的血流影片，期間血流將會經歷四個階段的變化。四個階段分別為：休息(resting, T1)、前阻塞(pre-occlusion, T2)、後阻塞(post-occlusion, T3)與釋放(release, T4)。由實驗結果得知，以光流估測法計算寫流速不但無須考慮血流方向，亦能正確計算出血球的位移量。血流速量測方法的驗證與比較實驗將針對正常血流速與前述四階段變化之血流速資料，分別利用光流法、交互相關法與空間-時間圖解法進行血流速結果之統計分析。結果顯示光流法可成為分析人體表皮微循環血流速之一項正確而重要的工具。
並列摘要
Microcirculation plays an important role between capillaries and biological tissues to supply oxygen and nutritive substances and to remove waste products. Diseases such as diabetes mellitus, hypertension and cardiac disease usually accompany some microcirculation lesions in a part of or the whole body. A non-invasive capillaroscopy imaging system for microcirculation has the potential to provide biological information of microvascular in vivo. This dissertation is aimed to develop a non-invasive cutaneous imaging system on the basis of orthogonal polarization spectral (OPS) imaging for observing capillaries in nail-fold. A new approach for the measurement of the red blood cell (RBC) velocity from capillary blood flow video is also proposed. The blood flow observation device consists of the following components: an objective lens with 20X magnification, a light source and a charge-coupled device (CCD) camera as an image recording device. A light source experiment was designed to decide the optimal light source specification of the imaging system. Videos of microcirculation in nail-fold were recorded by using a white light source with and without a color filter, respectively. Two bandpass filters with different wavelengths (i.e., 482±17.5 nm and 556±10 nm) were set in front of the light source to evaluate the image resolution and quality individually. First, we adjusted the power of light source to verify the relation between illumination and image quality. Second, we varied the skin temperature condition and compared the image quality at normal (33.09±0.75 ℃) and low (18.85±0.44 ℃) skin temperatures. The former experiment was to verify the relationship between illumination and image quality, while the latter was to check the temperature effect on image quality. As a result, the green light source was considered as the optimal choice because of its satisfying image resolution and higher contrast-to-noise ratio (CNR) at both normal and lower skin temperatures. Oblique angle lightening should also be applied because of its superior image quality. We also devised a RBC velocity measurement system that can provide complete velocity information for the whole vessel limb which demonstrates the advantage of measuring blood flow at the level of microcirculation accurately. An image registration function based on mutual information was used for stabilizing images in order to cope with slight finger movement during video acquisition. After image alignment, a skeleton extraction algorithm implemented by thinning was followed which enabled tracking blood flow entirely in arteriolar and venular limbs, and the curved segment as well. Optical flow, cross-correlation and space-time diagram approaches were applied individually for velocity estimation of twelve microcirculation videos acquired independently from three healthy volunteers. The RBC velocity of 12 vessels at three given measurement sites (arteriolar, curve and venular sites) in a 45-second period of occlusion-release condition of vessel were examined. There were four stages of flow conditions: resting (T1), pre-occlusion (T2), post-occlusion (T3) and release (T4). As results of RBC velocity studies, optical flow estimation is not only independent to the direction of flow, but also be able to calculate the intensity displacement of all pixels. Validation and comparison studies of applying optical flow to measure blood flow velocity in normal and variation conditions were performed. The results shown that optical flow estimation achieved to be a powerful technique that can be used to accurately measure RBC velocity of the human microcirculation in vivo.