In this paper an attempt ofNIR analysis to measure the milk constituents is introduced. In milk, light is absorbed and scattered simultaneously. The concentrations of each component no longer have linear relationship to the absorbency, but proportional to the absorption coefficient and scattering coefficient. It is necessary to separate the effect of absorption and scattering. Compare with the widely used NIR method, we do not calibrate the prediction model by diffuse reflectance. The calibration is composed by two steps. Firstly, the optical parameters are measured by double integrating sphere; secondly, calibration is made by optical parameters. Concentration of protein and fat are within reasonable range. Fifty samples are acquired for calibration. The experimental result shows a higher prediction accuracy of protein than the intensity calibration method, and a comparable accuracy of fat.
Non-invasive glucose measurement by near-infrared spectroscopy is mainly based on the absorption of glucose. However, for non-invasive blood glucose measurement, the diffuse reflectance spectra are influenced not only by the absorption coefficient, but also by the scattering coefficient, anisotropy factor, and refractive index, which are normally nonlinear with the glucose concentrations. Furthermore, the variations of spectra depend on the relative changing direction of the absorption coefficient and scattering coefficient. In this paper, using the simulated samples of human tissues with different glucose concentrations in different conditions, we discussed the rules of how the glucose concentrations affected the absorption coefficient and scattering coefficient, respectively. The relations between the diffuse reflectance spectra and the absorption coefficient, as well as and the scattering coefficient were also investigated. Thus, we confirmed which of the optical parameters and measurement conditions would affect the diffuse reflectance spectra significantly. Based on the above results, proper methods could be selected to measure blood glucose concentration non-invasively according to different conditions, then the information of glucose absorption would be extracted more effectively, and higher measurement precision would be expected.
Concept of penetration depth of diffused photons migrating in turbid medium is introduced, and subsequently, distribution of penetration depth and mean penetration depth in three-layered media are investigated by using of Monte Carlo simulation technique. An optimal source-detector separation is derived from the mean penetration depth referring to monitoring the change of chromophore concentration of the sandwiched layer. In order to verify the separation, we perform Monte Carlo simulations 80 times with varied absorption coefficient of the sandwiched layer. All these diffuse reflectance of 80 times of Monte Carlo simulations are used to construct a calibration model with the method of PLS. High correlation coefficients and low RMSEP at the optimal separation have conformed correctness of the selection.
Accurate measurement of tissue optical properties is a key problem in study on optical distribution in tissue. Especially in near infrared range, it is still a hard problem because of affection of strong absorption of water. In this paper, P3 approximation for high absorption was applied theoretically, then device with high precision was designed experimentally for non-scattering transmission measurement and fluence rate measurement. SNR and measuring accuracy were improved by using dual-beam. With added absorber technique at both 632.8nm and 1064nm, optical parameters of 2% intralipid at 1064nm and 1% intralipid at 632.8nm wavelength were obtained. The radial distribution of light through application of Monte Carlo simulation agreed well with the experimental result, which indicated that the experiment system were accurate with root mean square (RMS) less than 8%, and that CuSO4 as added absorber at 1064nm and NIR was feasible. Optical parameters of turbid media can be measured in NIR.
Optical parameters of tissue have been measured for some biologic tissues ranging from visible wavelengths to near-infrared wavelengths through various measuring techniques up to now. Great differences exist in those measuring results due to difference in experimental methods and theories applied since obtaining of these parameters requires both several experiments and theoretical models for inversion. In this paper we measured optical parameters of tissue phantom through application of measurements of spatially-resolved diffuse-reflectance and transmission rate.