Yousem D M, Janick P A, Atlas S W, Hackney D B, Glasser S A, Wehrli F W, Grossman R I
Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia 19104.
AJR Am J Roentgenol. 1990 May;154(5):1069-73. doi: 10.2214/ajr.154.5.2108544.
Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord.
在对颈椎轴位磁共振图像进行常规评估时（使用高强度脑脊液图像，即长TR/TE自旋回波或梯度回波图像），当将这些图像与相应的脊髓造影后CT扫描图像进行比较时，发现脊髓的前后径明显变窄。这种差异被认为是由于脑脊液-脊髓边界处的截断伪影所致。为了研究截断效应，我们比较了12例患者脊髓造影后CT扫描图像和磁共振图像中的脊髓直径，然后将其与正常志愿者以及琼脂-盐水脊柱模型的磁共振扫描结果进行比较。与患者的碘海醇CT扫描图像以及志愿者研究中256相位编码轴磁共振扫描图像中的脊髓直径相比，128×256矩阵磁共振扫描的128步相位编码轴上脊髓直径存在人为缩小。在脊柱模型研究中也发现了类似的差异，其中256步相位编码磁共振扫描、CT扫描以及直接测量得到的脊髓直径均超过了128步相位编码轴磁共振扫描中的脊髓直径。三项研究中测量值之间的差异范围分别高达2.3毫米（患者）、1.7毫米（志愿者）和1.8毫米（模型）。在所有三项研究中，改变摄影窗口宽度和水平会导致脊髓表观直径变化高达1.5毫米。为了消除这种影响，在相同的窗口水平下测量了模型和正常对照受试者的脊髓直径。截断伪影加上摄影中使用的标准窗口设置，可能会导致颈椎脊髓直径的显示不准确。
