Newitt D C, Majumdar S, Jergas M D, Genant H K
Department of Radiology, University of California, San Francisco 94143-1290, USA.
Magn Reson Med. 1996 Jun;35(6):921-7. doi: 10.1002/mrm.1910350622.
In this study, we examine MRI T2' decay characteristics for bone marrow in trabecular bone networks, using an asymmetric spin-echo sequence to isolate the inhomogeneous decay due to susceptibility variations between bone and marrow or water. In in vitro measurements on trabecular bone specimens from human vertebral bodies, tibia, and radii, we find significant deviations from a monoexponential signal decay. The initial decay is seen to have a Gaussian decay character, switching to a primarily exponential decay at later decay times. A similar trend is observed in in vivo measurements in the distal radius. Unlike an exponential decay, which may be characterized by a single decay rate, this is indicative of a significant variation in the decay rate with time. The deviations from exponential decay are seen to be orientation dependent, being most significant when the primary trabecular orientation is perpendicular to the static magnetic field.
在本研究中，我们使用非对称自旋回波序列来分离由于骨与骨髓或水之间的磁化率差异导致的不均匀衰减，从而研究小梁骨网络中骨髓的MRI T2'衰减特性。在对来自人体椎体、胫骨和桡骨的小梁骨标本进行的体外测量中，我们发现信号衰减明显偏离单指数衰减。初始衰减呈现高斯衰减特征，在较晚的衰减时间切换为主要的指数衰减。在桡骨远端的体内测量中也观察到类似趋势。与可能由单一衰减率表征的指数衰减不同，这表明衰减率随时间有显著变化。指数衰减的偏差被认为与方向有关，当主要小梁方向垂直于静磁场时最为显著。
