Study On Theories And Experiments Of Signal Acquisition For Non-Invasive Blood Glucose Sensing With Near-Infrared Spectroscopy

Diabetes and its complications are major threats to human beings. Since thenoninvasive blood glucose detecting technique has many advantages such as freefrom pain and no risk of infection, it brings great improvements in pain relief andthus glucose-concentration monitoring in real time. This research focuses onnon-invasive blood glucose concentration sensing with near-infrared diffusereflectance spectroscopy.Based on the properties of glucose distribution for layered skin tissue, amethod of glucose concentration measurement using dermal diffuse reflectancespectroscopy is proposed in this paper. By solving the static diffuse equation forsemi-infinite medium, this research analyzes the mechanism of glucoseconcentration influencing the spectral energy by absorbing and scattering effects.On the basis of this analysis, an approximate relationship between the diffusereflection energy and glucose concentration is established. Moreover, a mechanicalsystem is built up to measure the diffuse reflection spectra from palm with thismethod.An efficient scheme is proposed to obtain the spectra diffusion-reflected bythe dermal layer of palm. By the Monte Carlo modeling, the radial distribution,penetration depth and transmission path length of the diffuse photons are analyzed.Considering the influence of photon quantity and the effective path length on theinformation quantity from the dermal layer, the distribution curve between dermalinformation quantity and radial detecting distance is established. According to thedistribution properties of peak values in the curve, the material structureparameters of the optical probe are determined. In this paper, we study the mechanism of contact pressure acting on diffusereflectance spectra. Based on the definition of particle's scattering section andabsorption section, the expressions between tissue thickness and optical propertyparameters such as scattering and absorption coefficient are obtained. A finiteelement model is introduced to calculate the tissue thickness under certain contactpressures, and then the relationship between contact pressure and optical propertyparameters such as scattering and absorption coefficient is established. Accordingto this relationship, theoretical formula between the diffuse reflectance and contactpressure is deduced.The solution is then developed to minimize the influences of contact pressureon in-vivo diffuse reflectance measurements. The experimental results reveal theinfluence of contact pressure on the diffuse reflectance and the variation trend ofdiffuse reflectance with contact time. Based on these results, the optimal contactstate and optimal measuring time for measuring diffuse reflectance spectra are firstpresented in this paper. As a result, the stability of spectra is improved greatly.Finally, the clinical investigation on detecting non-invasive blood glucoseconcentration within human bodies is carried out. The improved OGTT (OralGlucose Tolerance Test) method is used to collect the sample data for calibrationset, and the PLS (Partial Least Squares) algorithm is applied to build calibrationmodels for the sample data collected in each OGTT experiment. The results of 50OGTT experiments established by full cross validation method show that the rangeof root mean square error of prediction (RMSEP) is 0.6773±0.0886mmol/l. Theclinical results prove the credibility of such NIR diffuse reflection measuringsystem.