Centre of Medical Image Computing, UCL, London WC1E 6BT, United Kingdom.
Med Phys. 2011 Feb;38(2):682-90. doi: 10.1118/1.3525837.
Several methods have been proposed to simulate large breast compressions such as those occurring during x-ray mammography. However, the evaluation of these methods against real data is rare. The aim of this study is to learn more about the deformation behavior of breasts and to assess a simulation method.
Magnetic resonance (MR) images of 11 breasts before and after applying a relatively large in vivo compression in the medial direction were acquired. Nonrigid registration was employed to study the deformation behavior. Optimal material properties for finite element modeling were determined and their prediction performance was assessed. The realism of simulated compressions was evaluated by comparing the breast shapes on simulated and real mammograms.
Following image registration, 19 breast compressions from 8 women were studied. An anisotropic deformation behavior, with a reduced elongation in the anterior-posterior direction and an increased stretch in the inferior-superior direction was observed. Using finite element simulations, the performance of isotropic and transverse isotropic material models to predict the displacement of internal landmarks was compared. Isotropic materials reduced the mean displacement error of the landmarks from 23.3 to 4.7 mm, on average, after optimizing material properties with respect to breast surface alignment and image similarity. Statistically significantly smaller errors were achieved with transverse isotropic materials (4.1 mm, P=0.0045). Homogeneous material models performed substantially worse (transverse isotropic: 5.5 mm; isotropic: 6.7 mm). Of the parameters varied, the amount of anisotropy had the greatest influence on the results. Optimal material properties varied less when grouped by patient rather than by compression magnitude (mean: 0.72 vs. 1.44). Employing these optimal materials for simulating mammograms from ten MR breast images of a different cohort resulted in more realistic breast shapes than when using established material models.
Breasts in the prone position exhibited an anisotropic compression behavior. Transverse isotropic materials with an increased stiffness in the anterior-posterior direction improved the prediction of these deformations and produced more realistic mammogram simulations from MR images.
已经提出了几种模拟大乳房压缩的方法，例如在 X 射线乳房摄影术中发生的压缩。然而，针对这些方法对真实数据的评估却很少。本研究的目的是更多地了解乳房的变形行为并评估一种模拟方法。
对 11 例乳房在向内侧施加相对较大的体内压缩前后的磁共振（MR）图像进行采集。采用非刚性配准来研究变形行为。确定用于有限元建模的最佳材料特性，并评估其预测性能。通过比较模拟和真实乳房 X 光片上的乳房形状来评估模拟压缩的逼真度。
对图像配准后，研究了来自 8 位女性的 19 次乳房压缩。观察到各向异性变形行为，在前-后方向的伸长率降低，在下-上方向的拉伸率增加。使用有限元模拟，比较了各向同性和横向各向同性材料模型预测内部标志点位移的性能。通过针对乳房表面对准和图像相似性来优化材料特性，各向同性材料将标志点的平均位移误差从 23.3 减少到 4.7mm，平均减少了 23.3 到 4.7mm。使用横向各向同性材料可实现显著更小的误差（4.1mm，P=0.0045）。均匀材料模型的性能要差得多（横向各向同性：5.5mm；各向同性：6.7mm）。在所研究的参数中，各向异性的程度对结果的影响最大。当按患者分组而不是按压缩幅度分组时，最优材料特性的变化较小（平均值：0.72 比 1.44）。在对来自不同队列的十个 MR 乳房图像进行模拟乳房 X 光片时，使用这些最佳材料可产生比使用既定材料模型更逼真的乳房形状。
俯卧位乳房表现出各向异性的压缩行为。在前-后方向增加刚度的横向各向同性材料可改善这些变形的预测，并从 MR 图像生成更逼真的乳房 X 光片模拟。
