KEYWORDS: Absorption, Tissues, Scattering, Signal attenuation, Temperature metrology, Skin, In vivo imaging, Monte Carlo methods, Optical fibers, Tissue optics
We present a scattering-independent measurement to monitor the pure near-infrared light absorption variation for scattering media, especially for in vivo tissue. We found a scattering variation independent source-detector separation (SVI-SDS), where the diffuse light intensity only varies with tissue absorption change but does not vary with scattering change. We applied the SVI-SDS setup to monitor the tissue spectra with a temperature modulation. We also proposed a method to simplify the measurement by using two fixed SDSs for all wavelengths. It makes the detection device easy to design and fit to the required SVI-SDSs. Monte Carlo simulation and experiments on intralipid solutions and in vitro pig skin samples are performed to test the method. The temperature absorption spectra were acquired, and the temperature insensitive wavelengths of the tissue are discussed. We believe this new method will guide many potential applications for the absorption-based tissue spectroscopy.
In the non-invasive blood glucose measurement based on near-infrared spectroscopy, the glucose signal is very weak and easy to be disturbed. Tissue temperature fluctuation is a primary disturbance source, since it would greatly affect the accuracy of blood glucose concentration results. We present a method called differential diffuse reflection spectroscopy, which makes a differential processing on the data from multiple source-detector distances (SDDs), and it can directly estimate the change in effective attenuation coefficient (EAC) of tissue. Using EAC spectra, we investigated the influence of temperature on the tissue spectra and then used a multivariable analysis of external parameters orthogonalization (EPO) to calibrate the spectra. The spectra of 1000-1800 nm caused by temperature and glucose are compared. Theoretical computing, Monte Carlo simulations and experiments were used to test this method. In conclusion, this proposed method using EAC spectrum to monitor the tissue change shows a promising application potential in non-invasive blood glucose measurement.
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