Emission Integral Effect on Non-Invasive Blood Glucose Measurements Made Using Mid-Infrared Passive Spectroscopic Imaging.

Living bodies emit mid-infrared light (wavelength band centered at approximately 10 µm) with a temperature-dependent intensity. Several studies have shown the possibility of measuring blood glucose levels using the mid-infrared emission of living bodies, and we have demonstrated non-invasive blood glucose measurements through distant wrist measurements (wavelength 8-14 µm) by mid-infrared passive spectroscopic imaging. However, it is not clear why blood glucose is detectable, as there is no formula that shows the effect of material thickness and concentration on emission intensity. In this study, we developed a principle for understanding glucose detection by proposing that an emission integral effect underpins the changes in emission intensity with substance thickness and absorption coefficient. We demonstrate the emission integral effect by measuring the spectral radiance of polypropylene with different thicknesses using mid-infrared passive spectroscopic imaging. The simulation results based on the emission integral effect indicate that in living bodies, dilute components such as glucose are easier to identify than components with high concentrations. Mid-infrared passive spectroscopic imaging offers potential innovative solutions for measuring various substances from a distance, with the emission integral effect acting as the basic working principle.