A deformable finite element model of the breast for predicting mechanical deformations under external perturbations

Rationale and Objectives. Live guidance during needle breast procedures is not currently possible with high-field-strength (1.5-T), superconducting ma gnetic resonance (MR) imaging. The physician can calculate only the approxi mate location and extent of a tumor in the compressed patient breast before inserting the needle, and the tissue specimen removed at biopsy may not ac tually belong to the lesion of interest. The authors developed a virtual re ality system for guiding breast biopsy with MR imaging, which uses a deform able finite element model of the breast. Materials and Methods. The geometry of the model is constructed from MR dat a, and its mechanical properties are modeled by using a nonlinear material model. This method allows the breast to be imaged with or without mild comp ression before the procedure. The breast is then compressed, and the finite element model is used to predict the position of the tumor during the proc edure. Three breasts of patients with cancer were imaged with and without c ompression. Deformable models of these breasts were built, virtually compre ssed, and used to predict tumor positions in the real compressed breasts. T he models were also used to register MR data sets of the same patient breas t imaged with different amounts of compression. Results. The model is shown to predict reasonably well the displacement by plate compression of breast lesions 5 mm or larger. Conclusion. A deformable model of the breast based on finite elements with nonlinear material properties can help in modeling and predicting breast de formation. The entire procedure lasts less than half an hour, making it cli nically practical.