Yablonskiy D A, Reinus W R, Stark H, Haacke E M
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Magn Reson Med. 1997 Feb;37(2):214-21. doi: 10.1002/mrm.1910370213.
In this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model; a phantom of parallel polyethylene filaments was scanned every 15 degrees between 0 degrees and 90 degrees with respect to the system's main magnetic field (B0). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel-wise fashion into R2 and R2' maps. As predicted, R2' relaxation showed anisotropic behavior and changed according to sin2 (theta), confirming that columnar structures parallel with B0 will cause no MR susceptibility effects. Scans of the distal radius showed that R2' relaxation was twice as great with the forearm perpendicular to B0 as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R2 relaxation was isotropic and did not change with object orientation.
在本文中，作者对单轴小梁骨模型中磁化率效应的各向异性进行了定量分析，并展示了其与临床磁共振骨矿物质密度测量的相关性。描述了一个物理模型，该模型对单轴小梁骨的各向异性磁共振行为进行了定量分析。为了测试该模型，相对于系统主磁场（B0），在0度至90度之间每隔15度对平行聚乙烯细丝的模型进行扫描。对一名健康女性志愿者的桡骨远端干骺端进行正交投影扫描。将每个模型图像和每个桡骨图像的信号以逐像素方式分离为R2和R2'图。正如所预测的，R2'弛豫表现出各向异性行为，并根据sin2（θ）发生变化，证实与B0平行的柱状结构不会产生磁共振磁化率效应。桡骨远端扫描显示，当前臂垂直于B0时，R2'弛豫是平行于B0时的两倍，表明支柱和柱状结构的贡献不同。对于模型和桡骨扫描，R2弛豫是各向同性的，并且不会随物体方向而变化。
