THE FORWARD AND INVERSE MODELS IN TIME-RESOLVED OPTICAL TOMOGRAPHY IMAGING AND THEIR FINITE-ELEMENT METHOD SOLUTIONS

Time-resolved optical computerized tomographic imaging has gained wide spread attention in biomedical research recently because of its non-in vasiveness and non-destructiveness to biological and several attempts, aimed at implementing a practical system, have been made for eliminat ing the obstacles arising from multiple light scattering of biological tissue. In this paper the basic principle of time-resolved optical ab sorption and scattering tomography is first presented. The diffusion a pproximation-based photon transport model in a highly scattering tissu e, which offers an advantage in speed in comparison vath other stochas tic models, and the procedure for solving this forward model by using the finite-element method (FEM) are then accessed. Theoretically, a co mmonly used iterative steepest descent algorithm for solving the inver se problem is introduced based on the FEM solution of Jacobian of the forward operator. Owing to the ill-posed Jacobian matrix of the forwar d operator caused by scatter-dominated photon propagation and unavoida ble influence of the noise from the measurement process, a Tikhonov-Mi ller regularization method is applied to the inverse problem in order to provide an acceptable approximation to its solution. A universal st rategy for the FEM solution to the optical tomography problem several numerically simulated images of absorbers and scatters embedded in a h omogeneous tissue sample are reconstructed from either mean-time-of-fl ight or integrated intensity data for the verification of the approach . (C) 1998 Elsevier Science B.V. All rights reserved.