Exploring the Relationship between Hypodermis Thickness and Diffuse Reflectance Spectra in Different Age and Gender Groups

This study explores the use of spatially-resolved diffuse reflectance spectroscopy for non-invasive method for measuring subcutaneous fat layer thickness. We investigated the relationship between spectroscopic measurements and hypodermis thickness, particularly focusing on lipid absorption amplitudes at varying source-detector distances. Our results reveal that lipid absorption amplitude is directly proportional to hypodermis thickness for layers between 1 and 4 mm at a source-detector fiber distance of 14 mm. The lipid absorption amplitude plateaued beyond a thickness of 4 mm, limiting sensitivity for the thicker hypodermis layer. An exponential function was revealed to describe lipid absorption amplitude dependence on the fat thickness across different source-detector distances. Physiological factors, namely sex, was found to significantly influence absorption amplitudes, while age-related differences were not identified. A predictive model was developed, yielding moderate accuracy (RMSE = 1.56 mm) in estimating hypodermis thickness, which is limited by the reference method. The study concludes that spatially-resolved diffuse reflectance spectroscopy is a promising method for assessing subcutaneous fat thickness, benefiting from its non-invasive nature and immediate results. However, accuracy is influenced by physiological characteristics, including sex and age, thus requiring personalized calibration. Future research should aim to refine predictive models and assess the technique's applicability across various body sites and a wider range of hypodermis thicknesses.