Mohamed F B, Vinitski S, Faro S H, Ortega H V, Enochs S
Department of Radiological Sciences, MCP/Hahnemann University, Philadelphia, PA 19129, USA.
J Comput Assist Tomogr. 1999 Nov-Dec;23(6):1008-12. doi: 10.1097/00004728-199911000-00035.
One of the major sources of image nonuniformity in the high field MR scanners is the radiofrequency (RF) coil inhomogeneity. It degrades conspicuity of lesion(s) in the MR images of the brain and surrounding tissues and reduces accuracy of image postprocessing particularly at the edges of the coil. In this investigation, we have devised and tested a simple method to correct for nonuniformity of MR images of the brain at the edges of the RF head coil. Initially, a cylindrical oil phantom, which fit exactly in the head coil, was scanned on a 1.5 T imager. Then, a correction algorithm identified a reference pixel value in the phantom at the most homogeneous region of the RF coil. Next, every pixel inside the phantom was normalized relative to this reference value. The resulting set of coefficients or "correction matrices" was obtained for different types of MR contrast agent. Finally, brain MR images of normal subjects and multiple sclerosis patients were acquired and processed by the corresponding correction matrices obtained with different pulse sequences. Application of correction matrices to brain MR images showed a gain in pixel intensity particularly in the slices at the edge of the coil.
高场强磁共振成像仪中图像不均匀性的主要来源之一是射频（RF）线圈的不均匀性。它会降低脑部及周围组织磁共振图像中病变的可见度，并降低图像后处理的准确性，尤其是在线圈边缘处。在本研究中，我们设计并测试了一种简单的方法来校正射频头部线圈边缘处脑部磁共振图像的不均匀性。首先，在1.5T成像仪上扫描一个恰好能放入头部线圈的圆柱形油模体。然后，一种校正算法在射频线圈最均匀区域的模体中确定一个参考像素值。接下来，模体内的每个像素相对于该参考值进行归一化。针对不同类型的磁共振造影剂获得了相应的系数集或“校正矩阵”。最后，获取正常受试者和多发性硬化症患者的脑部磁共振图像，并使用通过不同脉冲序列获得的相应校正矩阵进行处理。将校正矩阵应用于脑部磁共振图像显示像素强度有所增加，尤其是在线圈边缘的切片中。
