A Study On Reconstruction Of Tissue Optical Properties Based On Monte Carlo Propagation Model

Accurate measurement of tissue optical parameters is a very important field in tissue optics. Researches on the biological tissue optical properties are the precondition of light applications in the foundation research and clinical applications in medicalfields, which can ofer vital guidance to laser's clinic application. A method for rapid reconstruction of optical properties, such as the absorption and scattering properties of turbid media, is introduced in this dissertation. The main work includes choosing exact optical physical model of tissues, mathematics description and simulation analysis of photons propagation in tissue, exploiting a new algorithm to solve the inverse problem of estimating the tissue optical properties from the diffuse reflectance profiles, and experimental design and analysis to evaluating the validity of the inverse algorithm and measuring methods.The main content of the dissertation involves:1. Firstly, The theoretical framework of tissue optics was described completely and systematically. Then, the optical parameters describing the interaction between light and tissues are distinct explanated and deduced for definitions. Next, we introduced the theories of light transport in the tissues Monte Carlo simulations and diffusion approximation theory;2. Monte-Carlo (MC) method was chosen as the forward model to simulate the photon migration in the transport regime, for which diffusion approximation based approaches were not applicable. By using the Monte Carlo modeling for multi-layered tissues, the timing character and the statistical error of Monte Carlo simulation with different photon number was discussed.3. A flexible and fast perturbation model, purtubation Monte Carlo, has been developed for the rapid extraction of the information of photon migration the and the diffuse reflectance profile in tissue. With the derived information, photon migration inverse problem was solved by a combination algorithm of steepest descent and the Gauss-Newton method. The proposed method is valid for a wide range of optical properties and the related measurement can be simple and adaptable.4. We analyzed the unique corresponding relationship between the MC simulated diffuse reflectance data and the tissue optical properties. The reconstruction method was used to retrieve the tissue absorption and scattering coefficients in the single- and two-layered tissue models, from the steady-state spatially resolved diffuse reflectance profile.5. The method was demonstrated on a set of layered liquid-tissue phantoms having a wide range of absorptions coefficients and reduced scattering coefficients provided by Indian ink and Intralipid-10% in different concentration, respectively. As a reference, the absorption coefficient of Ink solution was measured with a spectrometer and the scattering coefficient of Intralid solution was calculated with Mie theory for the assumed particle size distribution in the corresponding concentration. CW measurements were carried out on the phantoms with different optode separations and the intensity decay of the diffuse reflectance corresponding to the incident light was recorded for extracting the optical properties. It shows that our results for optical parameters are creditable. The method has a higher accuracy and good real-time performance in the inverse problem of Tissue Optics field. Thus, the possibilities of estimating the tissue optical properties from the diffuse reflectance by using pMC reconstruction algorithm and steady-state measure technology were demonstrated.