Glucose determination based on near-IR spectroscopy is investigated for reflectance and transmittance measurement. A wavelength range is 1100 to 2500 nm, which includes both the combination and overtone bands of glucose absorption. Intralipid solutions are used as samples, where glucose concentrations vary between 0 and 1000 mg/dl. Sample thickness for reflectance is 10 cm and 1- and 2-mm-thick samples are used for transmission. Partial least-squares regression (PLSR) analyses are performed to predict glucose concentrations. The standard errors of calibration are comparable between reflectance and 2-mm-thick transmittance. The reflectance method is inferior to the transmittance method in terms of the standard errors of prediction. Loading vector analysis for reflectance does not show glucose absorption features. Reflected light may not have enough information of glucose since a major portion of detected light has a short optical path length. In addition, prediction becomes more dependent on medium scattering rather than glucose, compared with transmission measurement. Loading vectors obtained from a PLSR transmittance analysis have glucose absorption profiles. The 1-mm-thick samples give better results than the 2-mm-thick samples for both calibration and prediction models. The transmittance setup is recommended for noninvasive glucose monitoring.
For noninvasive measurement of bio-fluid substances in human body based on optical spectroscopy, optical measurement system is one of the most important parts. We studied glucose specificities by analyzing the factors in the partial least squares regression models for the two cases of reflectance and transmittance measurements. Glucose -intralipid solutions were used as the samples whose scatterer's concentrations were varied. We used intralipid concentrations of 4%, 4.08% and 4.16% in the solution and these values were comparable to tissue scattering. Temperature was maintained at 30°C during measurement. Factor analysis for reflectance data didn't show glucose absorption feature and the factors were very noisy particularly in the combination band. It is speculated that light does not have enough information of glucose since the pathlength in reflectance is very short. On the other hand, the factors obtained from the PLS analysis of transmittance revealed glucose signatures. We suggest that transmittance measurement is preferred for in vivo glucose monitoring than reflectance measurement.
Photo-plethysmography measure pulsatile blood flow in real-time and non-invasively.One of widely known application of PPG is a measurement of saturated oxygen in arterial blood (SpO2). In our work , using several wave length more than those used in a pulse oximeter, an algorithm and instrument have been developed to measure hematocrit, saturated oxygen pulse and respiratory rates simultaneously.To predict hemotocrit, a dedicated algorithm is developed based on scattering of RBC and a protocall for detecting outlier signal is used to increase accuracy and reliability.Digital filtering techniques are used to exart respiratory rate signal. Utilization of wave length under 1000nm and a multi-wavelength LED array chip and digital-oriented electronic enable us to make a compact device. Our preliminary clinical trails shown that the achived percent errors are±8.2% for hematocrit when tested with 594 person ,r2 for SpO fitting is 0.99985 when tested with a Bi-Tek pulse oximeter simulator and the SPO2 error for in vivo test is ±2.5% over the range of 75~100%. The error of pulse rates is less than ±5%. We obtained a positive predictive value of 96% for respiratory rates in qualitative analysis.
The method and device for non-invasive measurement of blood glucose concentration based on the diffuse reflectance from the transcutaneous layers is proposed. Original normalizing ratio algorithm permitting to separate glucose absorption from absorption of other blood components is suggested. It was shown that the influence of water and some other components such as hemoglobin, albumin, globulin's and cholesterol concentration variations to the estimation of the glucose concentration can be compensated using spectral analysis of the reflection on several specially selected wavelengths and proposed algorithm. Device with optical geometry minimizing the effects of changes in the scattering background of biological tissues was developed. NIR spectral range 800 - 1800 nm was used because of its good transparency for biological tissue and presence of glucose absorption band. We used two kinds of light sources, namely LED array and Xe flash lamp. Tissue phantoms (different glucose concentration (0 - 1000 mg/dl) solutions with polystyrene beads or with milk) were used as samples. Scattering and absorption contribution to the dependence of diffuse reflection on glucose concentration was experimentally verified.
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