Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Magn Reson Med. 2009 Dec;62(6):1533-42. doi: 10.1002/mrm.22144.
Magnetic resonance elastography is a noninvasive imaging technique capable of quantifying and spatially resolving the shear stiffness of soft tissues by visualization of synchronized mechanical wave displacement fields. However, magnetic resonance elastography inversions generally assume that the measured tissue motion consists primarily of shear waves propagating in a uniform, infinite medium. This assumption is not valid in organs such as the heart, eye, bladder, skin, fascia, bone and spinal cord, in which the shear wavelength approaches the geometric dimensions of the object. The aim of this study was to develop and test mathematical inversion algorithms capable of resolving shear stiffness from displacement maps of flexural waves propagating in bounded media such as beams, plates, and spherical shells, using geometry-specific equations of motion. Magnetic resonance elastography and finite element modeling of beam, plate, and spherical shell phantoms of various geometries were performed. Mechanical testing of the phantoms agreed with the stiffness values obtained from finite element modeling and magnetic resonance elastography data, and a linear correlation of r(2) >or= 0.99 was observed between the stiffness values obtained using magnetic resonance elastography and finite element modeling data. In conclusion, we have demonstrated new inversion methods for calculating shear stiffness that may be more appropriate for waves propagating in bounded media.
磁共振弹性成像是一种非侵入性成像技术，通过可视化同步机械波位移场，能够定量和空间分辨软组织的剪切刚度。然而，磁共振弹性成像反演通常假设测量的组织运动主要由在均匀、无限介质中传播的剪切波组成。在心脏、眼睛、膀胱、皮肤、筋膜、骨骼和脊髓等器官中，这种假设是不成立的，因为剪切波的波长接近物体的几何尺寸。本研究的目的是开发和测试数学反演算法，这些算法能够从弯曲波的位移图中分辨出剪切刚度，弯曲波在梁、板和球壳等有界介质中传播，使用特定于几何形状的运动方程。对不同几何形状的梁、板和球壳模型进行了磁共振弹性成像和有限元模拟。对模型的力学测试与有限元建模和磁共振弹性成像数据得出的刚度值一致，并且使用磁共振弹性成像和有限元建模数据得出的刚度值之间观察到线性相关（r(2)≥0.99）。总之，我们已经证明了用于计算剪切刚度的新反演方法，这些方法可能更适用于在有界介质中传播的波。
