Time-domain Fluorescence Tomography Research Based On The Diffusion Approximation Theory

The birth of the world’s first laser device has been over half a century. In the past half century, Laser technology has rapidly developed and been widely used in many areas, such as communication, measurement technology, biological medicine, industrial material processing, national defense military, science and technology and many other fields. Optical imaging technology using near-infrared light to detect internal information of media has rapidly developed. Fluorescence diffuse optical imaging high because of it’s contrast ratio and strong selectivity. The measurement mode of fluorescent diffuse optical imaging technology mainly includes the steady state mode, the time domain mode and the frequency domain mode. Compared with the steady-state and frequency-domain fluorescence diffuse optical imaging technology, time-domain fluorescence diffuse optical imaging technology has unique advantages in the information data integrity, flexibility and stability of system, and has become the mainstream of current research.The main content of this paper is time-domain fluorescence diffuse optical imaging technology research based on the diffusion approximation. Specific work includes the following aspects:1. The direct model of fluorescence diffuse optical imaging technology was established to explain and simulate the transmission of the incident laser and excited fluorescence in the medium. The finite element method was applied to solve the coupled diffusion equations to obtain the emitted fluorescence analog signal on the edge of the medium. The effects of factors such as the incident laser pulse width, optical parameters of background medium, the size, location and optical parameters of the heterogeneity on the emitted fluorescence signal has been analyzed in detail.2. For the reverse question, the conjugate gradient method was selectedfor the inversion of fluorescence parameters insidethe medium. Fluorescent light diffusion imaging technology based on the steady-state coupled diffusion equations has been studied. The maximum posterior probability estimation method was introduced in the reconstruction process in conjunction with the generalized Gauss- Markov random field to improve the quality of the reconstructed image.In addition, theeffects of contrast ratio and measurement error on the reconstruction of fluorescence parameters have been studied.3. The fluorescent signal for two-dimensionalnon-uniform round media was simulated based in the time-domain coupled diffusion equations, then the conjugate gradient method was applied to derive the single and double fluorescence parameters within the media containing different number of fluorophors. In the inverse problem,the maximum posterior probability estimation methodwas introduced with the generalized Gauss – Markovrandom field to improve the quality of the reconstructed image.In addition, the effects of the contrast ratio and measurement error on the construction of fluorescent yield and lifetime distributions have been studied.