Research Centre for Biomedical Engineering (RCBE), City, University of London, London EC1V 0HB, UK.
Sensors (Basel). 2019 Feb 15;19(4):789. doi: 10.3390/s19040789.
Photoplethysmography (PPG) is a non-invasive photometric technique that measures the volume changes in arterial blood. Recent studies have reported limitations in developing and optimising PPG-based sensing technologies due to unavailability of the fundamental information such as PPG-pathlength and penetration depth in a certain region of interest (ROI) in the human body. In this paper, a robust computational model of a dual wavelength PPG system was developed using Monte Carlo technique. A three-dimensional heterogeneous volume of a specific ROI (i.e., human finger) was exposed at the red (660 nm) and infrared (940 nm) wavelengths in the reflectance and transmittance modalities of PPG. The optical interactions with the individual pulsatile and non-pulsatile tissue-components were demonstrated and the optical parameters (e.g., pathlength, penetration depth, absorbance, reflectance and transmittance) were investigated. Results optimised the source-detector separation for a reflectance finger-PPG sensor. The analysis with the recorded absorbance, reflectance and transmittance confirmed the maximum and minimum impact of the dermis and bone tissue-layers, respectively, in the formation of a PPG signal. The results presented in the paper provide the necessary information to develop PPG-based transcutaneous sensors and to understand the origin of the ac and dc components of the PPG signal.
光体积描记术（PPG）是一种非侵入性的光度测量技术，用于测量动脉血液的体积变化。最近的研究报告指出，由于缺乏人体特定感兴趣区域（ROI）中的基本信息，如 PPG 光程和穿透深度，因此在开发和优化基于 PPG 的传感技术方面存在局限性。在本文中，使用蒙特卡罗技术开发了一种双波长 PPG 系统的强大计算模型。在 PPG 的反射和透射模式下，特定 ROI（即人类手指）的三维异质体积暴露在红光（660nm）和红外光（940nm）波长下。演示了与单个脉动和非脉动组织成分的光学相互作用，并研究了光学参数（例如光程、穿透深度、吸收率、反射率和透射率）。结果优化了反射式手指 PPG 传感器的光源-探测器间距。对记录的吸收率、反射率和透射率的分析证实了真皮和骨组织层分别对 PPG 信号形成的最大和最小影响。本文中的结果提供了开发基于 PPG 的经皮传感器以及了解 PPG 信号的交流和直流分量的来源所需的信息。
