Near-Infrared Diffuse Reflectance Measurement Method Based on Temperature-Insensitive Radial Distance

The variation of temperature is one of the main interference factors that affect the detection accuracy of near-infrared (NIR) diffuse reflectance. In this paper, a measurement method based on temperature-insensitive radial distance was proposed, and its feasibility and effectiveness were verified in Intralipid solutions. First, the possibility of temperature-insensitive radial distance was deduced based on the analytic solution of the steady-state diffusion equation in an infinite media, and the temperature-insensitive radial distances of 3% Intralipid solution in the wavelength range of 1000-1600nm was calculated. Second, a detection system was designed to measure the diffuse reflectance of 3% Intralipid solutions at multiple radial distances with different glucose concentration (0-100mM) and different temperatures (35-40?). Both theoretical calculations and experimental results demonstrated the existence of temperature-insensitive radial distances in the range of 1000-1340nm and 1440-1600nm, and the distances were hardly affected by glucose variations. Finally, the glucose information extracted from the diffuse reflectance of Intralipid solutions at different radial distances under random temperature variations and constant temperature were compared. The result showed that the correlation between the glucose concentration and the diffuse reflectance obtained at the temperature-insensitive radial distance was significantly better than that of other radial distances, which was almost close to the situation of constant temperature. Therefore, the measurement method based on temperature-insensitive radial distance can effectively reduce the influence of temperature variations on NIR diffuse reflectance, and it is expected to improve the accuracy of diffuse reflectance in human body components detection and industrial field analysis.