Mesoscopic Fluorescence Molecular Tomography: A Numerical Study of the Optical Clearing Effect

The paper is devoted to the study of the tissue optical clearing effect through numerical experiment on the reconstruction of a phantom with a fluorophore with the use of mesoscopic fluorescence molecular tomography (MFMT). This is the first attempt to answer the question of whether it is possible to improve the accuracy of reconstructing spatial structures and the sensitivity of MFMT to the structure reproduction depth by optically clearing the superficial tissue layers. The reconstruction region is a cube 10x10x10 mm3 in size. The fluorophore is specified as two nested cylindrical shells 1 mm thick at a distance of 1 mm between them. This allows us to estimate the modulation transfer coefficient for structures 1 mm in size for the entire depth of the object. Fluorescence signals and spatial sensitivity functions are modeled in reflectance geometry by the Monte Carlo method with the TurbidMC code. The inverse problem is solved using the algebraic reconstruction technique with fast iterative shrinkage thresholding and total variation regularization. Reconstruction results and their quantitative analysis using the modulation transfer coefficient show that optical clearing makes it possible to increase the depth at which fluorescent structures can be accurately reproduced—from 5.5 to 9 mm.