Physics of bioluminescent light transport in tissue

Abstract

The main objectives of this thesis are to investigate and describe the physics of bioluminescent light transport in biological tissues, analyze the bioluminescence tomography (BLT) source reconstruction, and formulate the light intensity from tumor bioluminescence as a function of time. Chapter 1 gives some introductory information on history of medical imaging, bioluminescence phenomenon, bioluminescence imaging (BLI), and tissue optical properties in the sense of absorption and scattering. Chapter 2 introduces the Radiative Transfer Theory which is the most widely applied method for photon transport in biological tissues. In this chapter, you can find the derivation of the radiative transfer equation (RTE) in detail. We also derive the diffusion equation (DE) by making a diffusion approximation (DA) to the RTE. Chapter 3 analyzes the general mathematical framework for BLT: Forward and inverse problem, finite element method (FEM), the BLT source reconstruction method, least-squares minimization, Tikhonov regularization, and Newton-Raphson iteration method. In this chapter, we assume conventionally that the bioluminescent light intensity does not vary with respect to time, but varies with respect to position. However, in real measurements, the light intensity from luciferase activity naturally depends on luciferin concentration. For this aim, Chapter 4 includes a 2-Compartment pharmacokinetic model to formulate the light intensity from tumor bioluminescence with respect to time. We derive a formulation which relates luciferin concentration injected via intraperitoneally to a transgenic mouse and the light intensity produced from tumor bioluminescence within the mouse, which can be used on the tomographic source reconstruction.