Recovery of optical cross–section perturbations in dense–scattering media using transport–theory–based imaging operators and steady–state simulated data

J. Chang et al. (1996)


We present a useful strategy for imaging perturbations of the macroscopic absorption cross section of dense scattering media using steady–state light sources. A perturbation model based on transport theory is derived and the inverse problem is simplified to a system of linear equations, WΔμ = ΔR, where W is the weight matrix, Δμ is a vector of the unknown perturbations, and ΔR is the vector of detector readings. Monte Carlo simulations (MCS) compute the photon flux across the surfaces of phantoms containing simple or complex inhomogeneities. Calculation of the weight matrix is also based upon the results of MCS. Three reconstruction algorithms — conjugate gradient descent, projection onto convex sets and simultaneous algebraic reconstruction technique, with or without imposed positivity constraints — are used for image reconstruction. A rescaling technique that improves the conditioning of the weight matrix is also developed. Results show that the analysis of time–independent data using a perturbation model is capable of resolving the internal structure of a dense scattering medium. Imposition of positivity constraints improves image quality at the cost of a reduced convergence rate. Use of the rescaling technique increases the initial rate of convergence, resulting in accurate images in a smaller number of iterations.