A method for the comparison of biomechanical breast models

Biomechanical models of the breast are being developed for a wide range of applications including image alignment tasks to improve diagnosis and therapy monitoring, imaging related studies of the biomechanical properties of lesions, and image guided interventions. In this paper we present a method to evaluate the accuracy with which biomechanical breast models based on finite element methods (FEM) can predict the displacements of tissue within the breast. Our experimental data was obtained by compressing the breast of a volunteer in a controlled manner, and the acquisition of MR images of the breast before and after compression. Non-rigid registration of these two MR volumes together with interactive identification of corresponding landmarks provided an independent estimate of the displacements. In addition, the non-rigid registration provided estimates of the displacements of the surface points (skin points) of the breast. The accuracy of the FEM models was evaluated using all or a subset of these surface displacements as boundary conditions. The influence of pectoral muscle movement on the performance of the FEM models was also investigated. Our initial results indicate that the accurate setting of the boundary conditions is more important than the actual choice of elastic properties in these compression scenarios. With the complete boundary conditions, the displacements agreed to within 2.6mm for all FEM models on average. Assuming no movement at the posterior or the medial side of the breast, the accuracy of the FEM models deteriorated to worse than 4.6mm for all models.