Investigations On Measurement Method And Experiment Of Tissue Optical Parameters At Continuous Wavelength Of Wide Spectrum Range

The measurement of tissue optical properties is a research hotspot in the field of biomedical photonics, which provides the basis for clinical applications like early diagnosis of disease, non-invasive detection of body composition and photodynamic therapy. In this paper, we investigated the measurement system in vitro based on double-integrating-spheres and the system in vivo based on diffuse reflectance spectroscopy according to the need of non-invasive blood glucose detection. On this basis, we analyzed the source of measurement error, and designed the correction algorithm, the forward model and inverse algorithm. Finally we measured the optical properties of scattering samples and different kinds of absorption samples. The results showed that the systems and algorithm in this paper can accurately measure the optical properties at continuous wavelength of wide spectrum range, providing a basis for the measurement of optical propeties in the non-invasive detection research.Firstly, this paper briefly introduced the basic theory of tissue optical properties measurements at continuous wavelength of wide spectrum range from the perspectives of tissue optical properties and the interaction between light and tissue. By comparing the advantages and disadvantages of different measurement methods, we introduced the measuring principle of DIS and the diffuse reflectance spectra under a single source-detect separation. The Monte-Carlo simulations, artificial neural network(ANN) algorithm and Levenberg-Marquardt algorithm, which are involved in the reconstructions are introduced.Secondly, we built the measurement system in vitro of wide spectrum range based on DIS, super continuum laser source and high precision spectrometer. The optimal measurement condition is determined by analyzing systematic error and measuring transfer functions, while the reconstruction method is based on BP-MCML forward model and L-M algorithm.Then, the measurement system of the diffuse reflectance spectra under a single source-detect separation was investigated by building the system, investigating the forward model and inverse algorithm of multi-dimensional unconstrained nonlinear optimization method and analyzing the factors that influence the measurement precision.Finally, different concentrations of Intralipid solution and mixed solution of Intralipid and blood are prepared, we measured the reflectance(R) and transmittance(T) of the sample in the wavelength range of 1100-1400 nm to determine the tissue optical properties, and verified the stability and accuracy of the DIS system. The results showed that at different wavelengths, the average measurement error of the absorption coefficient and reduced scattering coefficient are 8.2% and 3.4%, while the repeatability is 2.5%. A set of different concentrations of Intralipid mixed with blood and Evans Blue solution are prepared, we measured the optical properties of the solution with known main absorbing substance by using diffuse reflectance spectra, and the measurement error of the absorption coefficient and reduced scattering coefficient are around 10%.