Schenck J F
General Electric Corporate Research and Development Center, Schenectady, New York, 12309, USA.
Med Phys. 1996 Jun;23(6):815-50. doi: 10.1118/1.597854.
The concept of magnetic susceptibility is central to many current research and development activities in magnetic resonance imaging (MRI); for example, the development of MR-guided surgery has created a need for surgical instruments and other devices with susceptibility tailored to the MR environment; susceptibility effects can lead to position errors of up to several millimeters in MR-guided stereotactic surgery; and the variation of magnetic susceptibility on a microscopic scale within tissues contributes to MR contrast and is the basis of functional MRI. The magnetic aspects of MR compatibility are discussed in terms of two levels of acceptability: Materials with the first kind of magnetic field compatibility are such that magnetic forces and torques do not interfere significantly when the materials are used within the magnetic field of the scanner; materials with the second kind of magnetic field compatibility meet the more demanding requirement that they produce only negligible artifacts within the MR image and their effect on the positional accuracy of features within the image is negligible or can readily be corrected. Several materials exhibiting magnetic field compatibility of the second kind have been studied and a group of materials that produce essentially no image distortion, even when located directly within the imaging field of view, is identified. Because of demagnetizing effects, the shape and orientation, as well as the susceptibility, of objects within and adjacent to the imaging region is important in MRI. The quantitative use of susceptibility data is important to MRI, but the use of literature values for the susceptibility of materials is often difficult because of inconsistent traditions in the definitions and units used for magnetic parameters-particularly susceptibility. The uniform use of SI units for magnetic susceptibility and related quantities would help to achieve consistency and avoid confusion in MRI.
磁化率的概念是当前磁共振成像（MRI）许多研发活动的核心；例如，磁共振引导手术的发展使得需要具有适合磁共振环境的磁化率的手术器械和其他设备；在磁共振引导的立体定向手术中，磁化率效应可能导致高达几毫米的位置误差；组织内微观尺度上的磁化率变化有助于磁共振成像对比度，并且是功能磁共振成像的基础。磁共振兼容性的磁性方面根据两个可接受水平进行讨论：具有第一种磁场兼容性的材料，当在扫描仪的磁场中使用时，磁力和转矩不会产生显著干扰；具有第二种磁场兼容性的材料满足更严格的要求，即在磁共振图像中仅产生可忽略不计的伪影，并且它们对图像内特征位置精度的影响可忽略不计或可以很容易地校正。已经研究了几种表现出第二种磁场兼容性的材料，并确定了一组即使直接位于成像视野内也基本不会产生图像失真的材料。由于退磁效应，成像区域内和相邻区域的物体的形状、方向以及磁化率在磁共振成像中都很重要。磁化率数据的定量使用对磁共振成像很重要，但由于用于磁性参数（特别是磁化率）的定义和单位的传统不一致，使用材料磁化率的文献值往往很困难。统一使用国际单位制（SI）来表示磁化率和相关量将有助于在磁共振成像中实现一致性并避免混淆。
