Sparse reconstruction for fluorescence molecular tomography via a fast iterative algorithm

Fluorescence molecular tomography(FMT)is a fast-developing optical imaging modalitythat has great potential in early diagnosis of disease and drugs development.However,recon-struction algorithms have to address a highly ill-posed problem to fulfll 3D reconstruction inFMT.In this contribution,we propose an efficient iterative algorithm to solve the large-scalereconstruction problem,in which the sparsity of fluorescent targets is taken as useful a prioriinformation in designing the reconstruction algorithm.In the implementation,a fast sparseapproximation scheme combined with a stage-wise learning strategy enable the algorithm to dealwith the ill-posed inverse problem at reduced computational costs.We validate the proposed fastiterative method with numerical simulation on a digital mouse model.Experimental results demonstrate that our method is robust for different finite element meshes and different Poissonnoise levels.

A SIMULATION STUDY ON DYNAMIC-SAMPLING-MODE FOR FLUORESCENCE MOLECULAR TOMOGRAPHY

Fluorescence tomography can obtain a sufficient dataset and optimal three-dimensional imageswhen projections are captured over 360◦ by CCD camera. Herein a non-stop dynamic samplingmode for fluorescence tomography is proposed in an attempt to improve the optical measurementspeed of the traditional imaging system and stability of the object to be imaged. A series ofsimulations are carried out to evaluate the accuracy of dataset acquired from the dynamicsampling mode. Reconstruction with the corresponding data obtained in the dynamic-modeprocess is also performed with the phantom. The results demonstrate the feasibility of suchan imaging mode when the angular velocity is set to the appropriate value, thus laying thefoundation for real experiments to verify the superiority in performance of this new imagingmode over the traditional one.

Recent methodology advances in fluorescence molecular tomography

Molecular imaging(MI)is a novel imaging discipline that has been continuously developed in recent years.It combines biochemistry,multimodal imaging,biomathematics,bioinformatics,cell&molecular physiology,biophysics,and pharmacology,and it provides a new technology platform for the early diagnosis and quantitative analysis of diseases,treatment monitoring and evaluation,and the development of comprehensive physiology.Fluorescence Molecular Tomography(FMT)is a type of optical imaging modality in MI that captures the three-dimensional distribution of fluorescence within a biological tissue generated by a specific molecule of fluorescent material within a biological tissue.Compared with other optical molecular imaging methods,FMT has the characteristics of high sensitivity,low cost,and safety and reliability.It has become the research frontier and research hotspot of optical molecular imaging technology.This paper took an overview of the recent methodology advances in FMT,mainly focused on the photon propagation model of FMT based on the radiative transfer equation(RTE),and the reconstruction problem solution consist of forward problem and inverse problem.We introduce the detailed technologies utilized in reconstruction of FMT.Finally,the challenges in FMT were discussed.This survey aims at summarizing current research hotspots in methodology of FMT,fromwhich future research may benefit.

IN VIVO VALIDATION OF DUAL-MODALITY SYSTEM FOR SIMULTANEOUS POSITRON EMISSION TOMOGRAPHY AND OPTICAL TOMOGRAPHIC IMAGING

We report on tests of combined positron emission tomography(PET)andfluorescence molecular tomography(FMT)imaging system for in vivo investigation on small animals.A nude mouse was inoculated with MD-MB-231 breast cancer cells which expressed redfluorescent protein(RFP).For FMT system,reflective illumination mode was adopted with full-angle data acquisition.[18F]-Fluorodeoxyglucose([18F]-FDG)was used as radioactive tracer for PET.Both data were acquired simultaneously and then reconstructed separately before fusion.Fluorescent tomography results showed exactly where the tumor was located while PET results offered more metabolic information.Results confirmed feasibility for tumor detection and showed superiority to single modality imaging.

A strategy for enhanced tumor targeting of photodynamic therapy based on Escherichia coli-driven drug delivery system

Escherichia coli(E. coli) DH5α has been recognized as a non-pathogenic bacterial strain with tumor colonization ability. However, whether such a bacteria-driven drug-delivery system can improve the targeting of tumor therapy or not remains essentially untouched. Herein, a series of zinc phthalocyanine(ZnPc) photosensitizers with different numbers of charges were prepared and their electrostatic adhesion properties on E. coli were investigated via measuring their fluorescence intensities by flow cytometer. Among these ZnPc photosensitizers investigated, the ZnPc conjugate with four positive charges(named ZnPc-IR710) exhibited the highest loading capacity and the best fluorescence imaging performance of E. coli. With the help of E. coli, E. coli@ZnPcIR710 presented a significantly enhanced cytotoxicity on human breast cancer MCF-7 cells compared with ZnPc-IR710(survival rate of tumor cells was 39% vs. 57% at a concentration of 50 nmol L-1). Moreover, in vivo study showed that E. coli@ZnPc-IR710 remarkably inhibited the tumor growth and resulted in a complete tumor growth suppress in subcutaneous mouse 4T1 breast tumor model. These results demonstrated the great promise of bacterial-guided photodynamic therapy(PDT) in the treatment of solid tumors, and provide a unique strategy to enhance the antitumor efficacy of PDT by utilizing bacterial vectors in tumors.