Sensitivity of the Distorted Born Iterative Method to the Initial Guess in Microwave Breast Imaging

The distorted Born iterative method (DBIM) has been explored recently for microwave breast imaging. DBIM is an iterative method; thus, it requires an initial guess of the dielectric properties of the breast. In this paper, we study the sensitivity of DBIM imaging accuracy and convergence speed to the properties of a homogeneous initial guess. We conduct this investigation for a multifrequency formulation of DBIM, wherein the dispersive breast tissue properties are described with a Debye model. The parameters of the Debye model for the initial guess are linearly linked to reflect typical breast tissue dielectric properties. The static permittivity characterizing the properties is swept over an appropriate range of initial guesses and DBIM is used to obtain imaging results for each guess. Image quality and the number of iterations required for convergence is evaluated using three-dimensional (3-D) anatomically realistic numerical breast phantoms. This investigation not only vividly illustrates the sensitivity of DBIM to the initial guess but also definitively demonstrates that the use of initial values close to the average properties of the breast yields near-optimal performance. Finally, we present and evaluate a practical algorithm for estimating the average properties to be used as the initial guess.