內頸靜脈血氧儀之最佳光源-偵測器距離探討與潛在影響因子分析

Abstract

本研究目的為探討影響「定量內頸靜脈血氧飽和度之最佳光源-偵測器距離(Source-Detector Separation, SDS)」的潛在因子，並評估實驗過程中可能的噪聲大小與來源，最後嘗試運用訊噪比(Signal-to-noise ratio, SNR)的概念計算內頸靜脈光感測敏感度相對於噪聲的比例，觀察不同的活體受試者是否存在不同的最佳SDS。

方法上，本研究透過建立三維蒙地卡羅組織模型，從組織的幾何參數與光學參數著手，分析哪些潛在因子可能影響光對於內頸靜脈的感測敏感度，並影響最佳SDS的位置。另外，本研究也設計實驗，分析定量內頸靜脈血氧飽和度的光學系統在真實環境量測過程中的噪聲來源，並建立合理的噪聲估算模型，如此能夠評估不同受試者各SDS的訊噪比，以找到最佳SDS的位置。

模擬結果顯示，幾何參數中，內頸靜脈上緣至皮膚表面的距離是主要影響內頸靜脈感測敏感度峰值位置的因子，而光學參數中，由不同波長帶來的小範圍光學參數變化並不太會影響內頸靜脈感測敏感度的峰值位置，但從文獻整理而得的大範圍光學參數變化卻會影響，其中吸收係數(Absorption coefficient, µa)的影響較散射係數(Scattering coefficient, µs)大，若以不同組織而言，肌肉光學參數變化對內頸靜脈感測敏感度的影響是最大的。

活體結果中，本研究首先透過比對量測的內頸靜脈感測敏感度數據與模擬數據，驗證所使用的蒙地卡羅組織模型是可靠的。接著從活體實驗數據分析出量測過程中的噪聲來源可分為受試者生理擾動產生的噪聲與系統偵測光子產生的噪聲，以這兩個成份為基礎，能夠建立出噪聲估算模型。而透過訊噪比找出受試者最佳SDS的結果裡，本研究成功從3位受試者的實驗數據中，確認各自皆有唯一的最佳SDS，且不同受試者的位置不同，此顯示本研究的方法有效。另外也發現，多個實驗心跳訊號的平均能為訊號提高訊噪比，此結果對於評估系統需要的訊噪比十分重要。

This study aims to investigate factors affecting the "optimal source-detector separation (SDS) for quantification of internal jugular venous blood oxygen saturation " and use the internal jugular vein sensing sensitivity-to-noise ratio to determine the optimal SDS for different subjects.

Methodologically, we employed a three-dimensional Monte Carlo tissue model and started from tissue geometric and optical parameters to analyze factors influencing light sensing sensitivity on the internal jugular vein. Additionally, we conducted experiments to analyze noise sources in our practical optical system. We ultimately established a noise model to evaluate noise across different SDS values in different subjects, calculating signal-to-noise ratios to determine optimal SDS.

Results indicated that among geometric parameters, the distance from the upper edge of the internal jugular vein to the skin surface predominantly influenced the sensing sensitivity peak position. Regarding optical parameters, small-range wavelength-dependent changes had minimal impact, while wide-ranging optical parameter variations from literatures significantly affected the peak position. Among these, the absorption coefficient had a more significant effect than the scattering coefficient, with muscle optical parameters having the greatest influence among different tissues.

In vivo experiments validated the Monte Carlo tissue model by comparing measured internal jugular vein sensing sensitivity data with simulated results. In analyzing potential noise sources during experiments, we identified physiological disturbances and photon detection in system as key contributors. Evaluating the optimal SDS revealed subject-specific optimal SDS values, with varying positions among subjects. Additionally, noise reduction in the experimental signal altered the SNR in each SDS, highlighting the importance of noise evaluation in determining the optimal SDS.