Abstract：In near-infrared spectroscopy (NIRS) is widely applied for the qualitative or quantitative component detection in foods, medicines, pollution and biological tissues as it can provide real-time, non-invasive and continuous measurement. In the quantitative analysis of components in scattering media based on NIRS, the attenuance of the media doesn’t exhibit linearity with the source-detector separation (SDS) due to light scattering. Then measurement models at different SDSs are difficult to be applied to each other. In this paper, we propose a signal processing method based on Diffusion Equation (DE) to acquire the linear attenuance and get a SDS-independent optical parameter, i. e. effective attenuation coefficient (EAC). The EAC spectrum can be used to detect the component since the spectrum shows a comprehensive absorption of it. We apply a differential measurement on the spectra from two arbitrary SDSs to get the EAC spectrum, which will be independent to the used SDSs as long as the SDSs are in a limited linear range. The SDSs also can be flexibly selected according the different wavebands. More over, the differential can greatly reduce the influence from light diffusing in medium, and then benefit the measurement model transferring for different scattering media. We tested the method on the turbid water solutions with high scattering property by using theoretical calculation, Monte Carlo (MC) simulation and experiment. The tested solutions’ scattering coefficients were in the range of 28.53～87.47 cm-1 and the waveband was 1 000～1 360 nm. The linear range of SDS for the attenuance was acquired. Taking the glucose measurement as an example, the EAC spectra of glucose in these media were tested. Using the SDSs from the linear range, we measured glucose’s EAC spectra. The experiment system was equipped with a SDS adjustable probe to get the diffuse light from different SDSs. The spectra of three typical media, which are 3%，5%，10% Intralipid solutions, were compared. These glucose spectra presented high similarity and could be linearly transferred to each other. Intralipid solutions are often used as biological tissue phantoms since their optical property covers most water rich materials. And the solutions can also be used to mimic water rich food like milk, juice etc. Therefore, our study would be widely beneficial to many cases. In summary, we proposed an effective method to extract linear attenuance for diffuse spectra in turbid scattering media. This method can well improve the real use of NIRS, since it not only helps flexibly select SDSs, but also presents a convenient and linear measurement model transferring for easy varying media, such as tissues, milk, and other foods.
Key words：Near infrared spectroscopy; Scattering medium; Diffusion equation; Monte Carlo simulation; Linear attenuance; Effective attenuation coefficient
曹海青，韩同帅，刘雪玉，刘 瑾. 浑浊散射介质中被测成分线性吸光度提取与模型转换研究[J]. 光谱学与光谱分析, 2019, 39(12): 3711-3717.
CAO Hai-qing, HAN Tong-shuai, LIU Xue-yu, LIU Jin. Extracting Linear Attenuance of Analyte in Turbid Scattering Media and Prediction Model Transfer Based Thereon. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(12): 3711-3717.
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