Methodological Investigations On Time-domainDOT/FDOTBased On The Higher-ordersimplified Harmonics Approximation Of Radiative Transfer Equation

In recent years, a variety of imaging technologies play important roles in thestudies of small-animal imaging, and all these equipments provide powerful tools toscientific research. Diffuse optical tomography （DOT） and fluorescence diffuseoptical tomography （FDOT, the promotion of DOT） are two burgeoning non-invasiveoptical imaging technologies. At the present time, the diffusion equation, which isderived from the radiative transfer equation （RTE） by employing the P1approximation,is a widely accepted forward model in DOT/FDOT. But this methodology has severallimitations for small-animal applications, especially for small-geometry andhigh-absorption or low-scattering areas, e.g. liver, lung, blood vessel, etc. This thesisfocuses on developing a time-resolved DOT/FDOT scheme based on the high-orderapproximation to RTE to improve the quality of reconstructed image.In this paper, we derive the three-order spherical harmonic differential equations（P₃） with anisotropic factors. The results show that, compare with the solutions to thefirst-order diffusion equation and Monte-Carlo simulation, the developed P₃modelcould significantly and accurately describe the radiance distribution close to lightsource and strong absorption areas. We also develop a DOT image reconstructionmethod based on P₃approximation by using featured-data type from the GeneralizedPulse Spectrum Technique （GPST）, realizing simultaneous reconstruction ofabsorption coefficient and scattering coefficient.We employ third-order simplified spherical harmonics approximation （SP_N）suggested by Gelbafd, which can overcome the defect of great computation of P_Napproximation and meanwhile maintain its validity. Likewise, we present aDOT/FDOT image reconstruction algorithm based on the SP₃equation extended fromGPST.In view of the high detection sensitivity and reliable target localization of FDOT,we take the fluorescence message of the tumor location as prior information, andsegment the imaging area into destination and background region. Destination regionincludes the feature nodes selected from ROI and used to DOT reconstruction. Theprior information about tumor localization obtained from FDOT can significantlyreduce the dimensional number of variables involved in iteration process of DOTreconstruction, and improve the ill-posedness of the relevant inverse issue. The transmission-type cylindrical phantom experiment, implemented by thetime-correlated single photon counting system （TCSPC）, isconducted to test andverify the proposed2-D image reconstruction algorithm based on the differencemeasurement data. The experimental results demonstrate that the proposedmethodology is quite suitable for further application in DOT/FDOT.