Spatial Frequency Domain Reconstruction Of Tissue Optical Property For In Vivo Assessment Of Photodynamic Therapy

Recently,photodynamic therapy has become a powerful tool for the treatment of cancer,port wine stain,etc.Nevertheless,there is a lack of an effective in vivo assessment method for personalized dosimetry.Among the numerous research on optical assessment,spatial frequency domain imaging has attracted more and more interests since it features wide-field imaging,non-contact detection and excellent specificity.This paper focuses on the reconstruction of optical property in spatial frequency domain for in vivo assessment of photodynamic therapy.In the field of spectroscopy: We establish a forward model for describing spatial frequency modulated light propagation in homogeneous medium in the 2nd chapter.The spatial frequency response of a medium to modulated lights is characterized by modulation transfer function.Based on the proposed forward model,we carry out the study of the reconstruction of absorption coefficient.To avoid the reference measurement that is required in traditional method,we develop a reference-free method for the recovery of tissue absorption coefficient based on spatial frequency domain characterization of modulation transfer function.Numerical simulations,phantom experiments and imaging of a small animal model are performed which demonstrate the effectiveness of the method as well as evaluate the precision.It shows that the proposed method will serve as a rapid,accurate and reference-free tool for spatial frequency domain determination of tissue absorption coefficient,and may facilitate the translation of spatial frequency domain measurement to clinical use.Moreover,existed method provides only 2-D topographic maps of optical property and suffers from burdensome process of measurement.To this end,we propose a novel approach for rapid detection and positioning of target using row-by-row & column-by-column analysis and multi-frequency synthesis.Phantom experiments are conducted and the results show that the proposed method is capable of achieving fast and precise 3-D positioning.The information acquired by this method may act as a priori-knowledge for improved 3-D tomography.In the field of tomography: To solve the problem of the spatial frequency modulated light propagation in heterogeneous medium,we develop a forward model based on our newly proposed spatial frequency domain phasor diffusion equation in Chapter 4.Compared with Monte Carlo simulation,the phasor diffusion equation is more flexible and computationally efficient,which conduces to our development of spatial frequency domain 3-D image reconstruction algorithms based on Born approximation and Rytov approximation,respectively.Nonlinear iterative reconstruction for spatial frequency domain diffuse optical tomography is achieved for the first time.Finally,simulations are conducted to evaluate the performance of the algorithm,and experiments on phantom and small animal model are performed to verify the effectiveness.The results validate the feasibility of the proposed reconstruction algorithm,and demonstrate that both the spatial resolution and the quantitation are improved compared with traditional ways.