Near infrared spectroscopy is an optical imaging technique which offers a non-invasive, portable, and low-cost method for continuously measuring the oxygenation of tissues. In particular, it can provide the brain activation through measuring the blood oxygenation and blood volume in the cortex. Understanding and then improving the spatial and depth sensitivity of near infrared spectroscopy measurements to brain tissue are essential for designing experiments as well as interpreting research findings. In this study, we investigate the effect of applying two common light beam profiles including Uniform and Gaussian on the penetration depth of an LED-based near infrared spectroscopy. In this regard, two Gaussian profiles were produced by adjusting plano-convex and bi-convex lenses and the Uniform profile was provided by applying a flat lens. Two experiments were conducted in this study. First, a simulation experiment was carried out based on scanning the intra space of a liquid phantom by using static and pulsating absorbers to compare the penetration depth of the configurations applied on the LED-based near infrared spectroscopy with that of a laser-based near infrared spectroscopy. Second, to show the feasibility of the best proposed configuration applied, an in vivo experiment of stress assessment has been performed and its results have been compared with that results obtained by laser one. The results showed that the LED-based near infrared spectroscopy equipped with bi-convex lens provides a penetration depth and hence quality measurements of near infrared spectroscopy and its extracted heart rate variability signals as well as laser-based near infrared spectroscopy especially in the application of stress assessment.

中文翻译：

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LED-NIR 高斯光束轮廓的模拟和体内研究

近红外光谱是一种光学成像技术，它为连续测量组织的氧合提供了一种非侵入性、便携和低成本的方法。特别是，它可以通过测量皮层的血氧和血容量来提供大脑激活。了解并提高近红外光谱测量对脑组织的空间和深度灵敏度对于设计实验以及解释研究结果至关重要。在这项研究中，我们研究了应用包括均匀和高斯在内的两种常见光束轮廓对基于 LED 的近红外光谱的穿透深度的影响。在这方面，通过调整平凸透镜和双凸透镜产生两个高斯轮廓，并通过应用平面透镜提供均匀轮廓。本研究进行了两个实验。首先，通过使用静态和脉动吸收器扫描液体体模内部空间进行模拟实验，比较应用于基于 LED 的近红外光谱和基于激光的近红外光谱的配置的穿透深度。光谱学。其次，为了显示所应用的最佳建议配置的可行性，进行了应力评估的体内实验，并将其结果与激光获得的结果进行了比较。