Anisotropic behaviour of breast tissue for large compressions

Several methods have been proposed to simulate large breast compressions such as those occurring during X-ray mammography. However evaluation of these methods against real data is rare. We acquired magnetic resonance images of eleven breasts before and after applying a relatively large in-vivo compression in the medial direction. Using non-rigid registration we observed an anisotropic deformation behaviour, with a reduced elongation in the anterior-posterior direction and an increased stretch in inferior-superior direction for all but one subject. Higher anisotropy was observed for larger compressions and in the central breast region. Using finite element simulations, we assessed the optimum performance of isotropic and transverse isotropic material models to predict the displacement of internal landmarks. We found that isotropic materials reduced the mean displacement error from 23.3 mm to 4.3 mm on average. Smaller errors were achieved with transverse isotropic materials (3.8 mm). For large compressions (>35%) the difference (5.2 mm vs. 4.1 mm) was statistically significant (p=0.04). Of the parameters varied, the amount of skin stiffness and anisotropy had the greatest influence on the results.