On Absorption Parameter In Tissue Optical Imaging

In past decades, tissue optical imaging has attracted a great deal attention,since the biotissues to light (especially near infrared light) always presents characteristics of strongly scattering and low absorption. The photons propagating in biotissues can provide many kinds of information of physiology, and light of low power is non-ionising radiation and harmless to patients or doctors. Because of these advantages, light exhibits abroad applications on continuous and non-invasive continuous monitoring as well as tissue optical imaging. This dissertation presents the study on absorption coefficient in tissue optical imaging in two ways as following: one is for optically thick tissue imaging, including numerical algorithms for forward problem and reconstruction algorithms for inverse problem in diffuse optical tomography. The other is for optically thin tissue imaging, the effects of tissue absorption on laser speckle imaging are studied experimentally and theoretically for the first time. The main contents and conclusions are listed as following: (1)The finite difference method is applied to solute the fixed problem of time-dependent photon diffusion equation, the implicit formats of Crank-Nicholson method and alternating direction implicit method are derived, and applied to homogeneous and heterogeneous tissues. For improving computing efficiency, we used successive over relaxation method and Tri-diagonal Matrix method. Numerical comparisons with analytical solution and the results of Monte Carlo simulation are achieved. Numerical results show that two methods can achieve high accuracy and good stability. (2) Tikhonov regularization method is proposed to study the inverse problem about the reconstruction of absorption coefficient in diffuse optical tomography. Based the perturbation theory, we have derived transfer matrix and object function of inverse problem. Finally, we have accomplished numerical simulation of the reconstruction of absorption coefficient. (3) The effects of tissue light absorption on characteristic of images of laser biospeckles are detailedly studied with experiments. Based on conventional speckle theory, some relevant formulae including light absorption parameters are derived theoretically, and the result compared with experiment shows that the theory proposed in this thesis accords with the experiments.