Iterative reconstruction scheme for optical tomography based on the equation of radiative transfer

We report on the development of an iterative image reconstruction scheme fo r optical tomography that is based on the equation of radiative transfer. U nlike the commonly applied diffusion approximation, the equation of radiati ve transfer accurately describes the photon propagation in turbid media wit hout any limiting assumptions regarding the optical properties. The reconst ruction scheme consists of three major parts: (1) a forward model that pred icts the detector readings based on solutions of the time-independent radia tive transfer equation, (2) an objective function that provides a measure o f the differences between the detected and the predicted data, and (3) an u pdating scheme that uses the gradient of the objective function to perform a line minimization to get new guesses of the optical properties. The gradi ent is obtained by employing an adjoint differentiation scheme, which makes use of the structure of the finite-difference discrete-ordinate formulatio n of the transport forward model. Based on the new guess of the optical pro perties a new forward calculation is performed to get new detector predicti ons. The reconstruction process is completed when the minimum of the object ive function is found within a defined error. To illustrate the performance of the code we present initial reconstruction results based on simulated d ata. (C) 1999 American Association of Physicists, in Medicine. [S0094-2405( 99)01208-0].