As a countermeasure against rapidly expanding infectious diseases, it is becoming more important to obtain information on health conditions in a non-invasive, non-contact manner. Expectations are rising for health care devices that use optical technologies. Recent developments have lowered costs for light sources, image sensors, and photodetectors that support the visible, near-infrared, and mid-infrared regions as well as the development of low-cost high-precision bioanalysis systems based on light scattering and light absorption. This special issue introduces some health care devices that will imminently be put into practical use, those that have already been commercialized, and their social and technical backgrounds and measurement principles.

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We report the test results and technical details of a system we developed that improves the quality of telemedicine. The spread of COVID-19 has accelerated the need for telemedicine to more effectively prevent infections. However, in traditional Japanese (Kampo) medicine, where color is an important examination factor, accurate diagnoses cannot be made without adequate color reproduction. Since commercial smartphones are not capable of reproducing colors with the level of fidelity required for medical treatments, we created a color chart that includes the colors of the human skin and tongue that helps doctors identify their colors more accurately during a telemedicine examination. Using a mobile device, we also created a telemedicine system that includes automatic color correction with a color chart and non-contact heart rate measurements.

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A quantitative evaluation of peripheral hemodynamics is important to monitor tissue metabolism and health status. Optical spectroscopy provides functional and morphological information of living tissues based on optical absorption and scattering properties. Red-green-blue (RGB) camera-based diffuse reflectance imaging, which can be　achieved with a simple, robust optical system, has been widely applied to in vivo measurements and for imaging biological tissues. This article describes an RGB camera- based functional imaging technique and its applications to vital sign monitoring. The method estimated volume concentrations of oxygenated blood, deoxygenated blood, and melanin in skin tissue quantitatively based on a numerical simulation model for light transport in tissues. In vivo experiments with human subjects and rats demonstrate that the method has the ability to measure and visualize tissue oxygen saturation, plethysmogram, heart rate, peripheral vasomotion, and percutaneous arterial oxygen saturation.

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The non-invasive measurement of blood triglyceride concentrations has been attracting attention for the prevention of coronary artery disease. In particular, since postprandial hyperlipidemia is considered to be one of the main causes of coronary artery disease, routine non-invasive monitoring is highly desirable to check postprandial lipid metabolism. In this paper, we review various non-invasive optical measurement methods for blood components and introduce our proposed method that measures blood triglyceride concentrations using backscattered light. First, we describe its basic principle, which is based on spatially resolved measurement, and the technical issues for its quantification based on research trends. Then we discuss the development of marketable products and outline such business developments including the social implementation of products. Key Words: Triglyceride, Blood, Non-invasive,

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In recent years, noninvasive blood glucose measurement technologies have become more desirable. In this paper, we describe a method, which performs noninvasive blood glucose measurements, based on mid-infrared absorption spectroscopy, and uses only a few wavenumbers to unconditionally measure blood glucose levels in vivo. We identified the regression of blood glucose levels using only three wavenumbers, which were selected in a series cross validation technique. We demonstrated the performance of this model through correlations among different types of data and constructed an attenuated total reflection spectrometer with discrete fixed wavelengths using three distributed feedback quantum cascade lasers. To improve the accuracy of the glucose measurement, we examined the stabilization of the relative absorbance intensity between wavelengths by equalizing the illuminance distribution.

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We analyzed the absorption spectra of the skin surface taken by a mid-infrared, attenuated-total-reflection method for non-invasive measurements of blood lipid levels. The absorption spectra were acquired over several hours before and after meals and investigated the correlation with changes in blood lipid levels. The multivariate analysis results of the absorption spectra suggest the possibility of predicting concentrations of triglycerides and cholesterol in the blood. We predicted the concentration of low-density lipoprotein cholesterol from the absorption intensity at a single wavelength.

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One of the main missions of the Telescope Array (TA) project is to characterize Ultra-High Energy Cosmic Rays (UHECR) based on observations of atmospheric fluorescence, which is primarily emitted from nitrogen molecules excited by secondary particles of UHECR. The TA system is distributed over an area of 700 km 2 in the wilderness. The atmospheric fluorescence is detected at three measurement stations at the site using telescopes called Fluorescence Detectors (FDs). Ultraviolet (UV) lights from nitrogen fluorescence are absorbed by other atmospheric molecules and aerosols, affecting the measurement with FDs. Therefore, the transparency of the atmosphere for UV lights has been measured on site using a well-characterized Mie-LIDAR system. The main issue was that the Mie-LIDAR could provide an atmospheric transparency at one measurement station, which might not be the same as the one measured at the other stations, since they are apart from each other by several tens of kilometers. To address this issue, we installed a new UV laser system at the location equidistant from the three stations in order to measure atmospheric transparency at all stations at the same time. A parallel UV laser beam was emitted vertically from the ground to the sky, and the scattered light was measured with FDs at each station. After four years of measurements, we concluded that the atmospheric transparency at the three stations was equivalent with a 95% correlation

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