Finite element modelling of breast biomechanics: directly calculating the reference state

Patient-specific models of the biomechanics of the breast based on finite deformation theory is potentially a valuable tool to assist clinicians in assimilating and assessing information obtained from different views of the breast, under different loading conditions and using different imaging modalities. It is anticipated that a computational model of the large deformation mechanics of the breast will also improve the accuracy of non-rigid registration techniques by restricting the deformations imposed by the algorithm to be those which are physically plausible. Accurate registration will assist clinicians in tracking suspicious regions of tissue across multiple views of the breast, which are typically taken by applying different loads on the breast during imaging. For instance, a model that can predict deformations during mammography would help to track a region of tissue between a cranio-caudal (CC) view and a medio-lateral oblique (MLO) view. Due to the nonlinear deformations imposed on the breast during different imaging techniques, the finite element reference geometry from which deformations are predicted is important. Gravity loads act on the breast during all imaging modalities. In this paper, we describe a novel modification to solving the finite element implementation of finite deformation theory, which can predict the reference state of the breast from a deformed configuration that has been derived from images of a patient placed in a single known orientation with respect to the direction of gravity.