Babcock E E, Brateman L, Weinreb J C, Horner S D, Nunnally R L
J Comput Assist Tomogr. 1985 Mar-Apr;9(2):252-7. doi: 10.1097/00004728-198503000-00004.
The boundaries of some organs as seen in clinical magnetic resonance images appear to be asymmetric. This effect is caused by chemical shift differences between the resonant frequencies of the hydrogen nuclei of water and fat. The zeugmatographic technique maps resonant frequencies to unique spatial locations. These differences in resonant frequencies can appear as artifactual misplacement of information as this one-to-one correspondence is lost. Various phantoms are used to demonstrate that the boundary artifact appears only in the direction of the read (frequency-encoding) gradient when media of two different chemical shifts are separated by an interface. When the relative shift is less than the width of the interface, the boundary appears to be asymmetric; when the relative shift is greater than the width of the interface, a bright band is seen along one edge with a dark band along the other. This artifact is more pronounced in low resolution images than in high resolution images, and these effects are seen even when the relative chemical shift is smaller than a pixel bandwidth. These effects are explained both conceptually and analytically. The clinician should be aware of the potential presence of this artifact at boundary interfaces that bear diagnostic significance.
在临床磁共振图像中，一些器官的边界看起来是不对称的。这种效应是由水和脂肪中氢原子核共振频率之间的化学位移差异引起的。磁共振成像技术将共振频率映射到独特的空间位置。当这种一一对应关系丧失时，共振频率的这些差异可能表现为信息的人为错位。使用各种体模来证明，当两种具有不同化学位移的介质被一个界面分开时，边界伪影仅出现在读出（频率编码）梯度的方向上。当相对位移小于界面宽度时，边界看起来是不对称的；当相对位移大于界面宽度时，在一条边缘处会看到一条亮带，而在另一条边缘处会看到一条暗带。这种伪影在低分辨率图像中比在高分辨率图像中更明显，并且即使相对化学位移小于像素带宽，也会出现这些效应。从概念和分析两个方面对这些效应进行了解释。临床医生应该意识到在具有诊断意义的边界界面处可能存在这种伪影。
