Photon fluencies for diffuse optical tomography systems

Abstract

In this work, photon fluencies have been used to explore the depth of buried layers for diffuse optical tomography (DOT) systems. Back-reflected diffuse reflectance data were generated by Monte Carlo Modelling of Light Transport (MCMLT) simulations. Heterogeneous layers which have 1mm thickness were buried from 1mm to 8mm for 8 different simulations, consecutively. DOT systems are categorized based on the physical appearence as transmission through or back reflection geometry. Transmission through systems are more successful than back-reflected geometrical models from the view of the accuracy of the locations of the reconstructed images. On the other hand in the real world, back-reflection geometry is necessary for diagnostics and treatment purposes in the medical units and hospitals. DOT imaging systems basically use photon transport diffusion equation inside the turbid media. In literature, researchers and companies are using the linearized model of non-linear diffusion equation which is the first Taylor term of Rytov or Born approximation of radiative transport equation (RTE). The unknowns of the linearized equation system are differences of absorption coefficients over homogeneous background. After modeling of the linearized equation system, the next step is to solve the linearized equation system. Finally, researchers and company workers are using the forward model in different mathematical inverse problem solution algorithms which can be grouped as iterative, subspace, and regularization methods. Regularization methods are used very frequently hence the measurement system usually has noises and artifacts and the forward model transfer functions matrix is also not square. In this work a new method is presented for DOT imaging modalities without using any mathematical inverse problem solution algorithms. This new philosophy is using comparison of photon fluencies for different depth layers between homogeneous and heterogeneous tissue models. The new philosophical approach is being presented to explore the depth of the buried layers for DOT systems.