Infrared Optical Imaging Based On Frequency-domain Radiative Transfer

Since the world’s first laser emerged in1960, it caused wide attention ofresearchers, and has been constantly evolving. So far, laser has been widely used innational defense, atmospheric remote sensing, bio-medical, laser communications,information processing, industrial processing, testing diagnostics, optical coherencetomography, photodynamic therapy and some other fields. In the laser family, theultrashort pulse lasers born in1970s shares a wide use as its femtosecond short laserbeam. The paper mainly studies the applications of ultrashort pulse laser in the field ofmedical science as Biomedical Photonic Imaging. This technology uses characteristicsof near-infrared laser which has better penetration and no damage on biological tissue.Then simulate physical parameters distribution of biological tissue depend on the signaldetected on the surface of biological tissue, so as to achieve the early detection ofhuman diseases. Theories of optical imaging can be concluded into three kinds:continuous wave technology, time domain methods and frequency domain methods.Time domain and frequency domain methods can both be used to reconstruct absorptionand scattering coefficients. However, the means of frequency domain shares a greateradvantage in optical imaging and enjoys wide use recent years.This paper focuses on parameters reconstruction of participatory media. Analyzethe transfer process of radiation in the media and methods for solving the inverseproblem relied on the information detected to derive internal optical parameters of themedia. The main contents of this paper can be summarized as the following aspects:Deduce the radiative transfer equation of frequency domain by the FourierTransform. Use finite volume method for solving the frequency domain equation.Simulate transmission process of ultrashort pulse laser in the participatory media.Gather transmitted radiation signals on the edge of the media. After all of these steps,finish the study of optical imaging.Analyze different methods for solving the inverse problem. According to theiradvantages and disadvantages, select the conjugate gradient method. Derivate andimprove adjoint differentiation algorithm for optical imaging.Simulate physical properties of biological tissue to build the model oftwo-dimensional inhomogeneous medium. Analyze results of different models, choosethe appropriate way of irradiation and add regularization information to reconstructionresults. Based on the information above, reconstruct parameters of inhomogeneousmedium with inclusions which have different sizes, different locations, different shapesand different physical properties. At last, analyze the minimum size of imaging.