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1. 发明授权

US6150815A Method of correcting for magnetic field inhomogeneity in magnetic resonance imaging 失效
标题翻译：磁共振成像磁场不均匀性校正方法
公开(公告)号：US6150815A
公开(公告)日：2000-11-21
申请号：US58272
申请日：1998-04-09
申请人： Dennis Lyle Janzen , Douglas George Connell , Alexander Lloyd MacKay , Qing-San Xiang
发明人： Dennis Lyle Janzen , Douglas George Connell , Alexander Lloyd MacKay , Qing-San Xiang
IPC分类号： A61B5/055 , G01R33/09 , G01R33/565 , G01V3/00
CPC分类号： B82Y25/00 , G01R33/093 , G01R33/56563
摘要： A method of correcting for magnetic field inhomogeneity caused by various factors, such as implanted metal and air/tissue interfaces, in magnetic resonance imaging (MRI) is provided. Geometric distortion due to inhomogeneity in a static magnetic field B.sub.0 is corrected for by addition of a compensation gradient. The compensation gradient is applied in the slice selection direction Z, has a timing substantially identical to the standard frequency encoding gradient G.sub.x, and has an amplitude identical to the slice selection gradient G.sub.z that is applied during the initial RF excitation. Inhomogeneity in an RF field B.sub.1 is compensated for by utilizing an RF coil that is large enough in size as compared with a metal implant to make the volumetric percentage of the metal in the coil insignificant. Inhomogeneity in a gradient field G=(G.sub.x, G.sub.y, G.sub.z) is corrected for by a treatment of the most significant error factor G.sub.z that causes slice thickness error. Specifically, the method acquires two images with complementary slice thickness error by using two pulse sequences with flipped slice selection gradients G.sub.z ; combination of the two images successfully cancels the effect of the slice thickness error. Local dephasive MRI signal loss due to magnetic field inhomogeneity is corrected for by acquisition of two images with positive and negative offset G.sub.z gradient lobes, respectively. The pair of images are combined to cancel the effect of local signal loss error.
摘要翻译：提供了一种在磁共振成像（MRI）中校正由诸如植入的金属和空气/组织界面等各种因素引起的磁场不均匀性的方法。通过添加补偿梯度来校正由静态磁场B0中的不均匀性引起的几何畸变。在切片选择方向Z上施加补偿梯度，具有与标准频率编码梯度Gx基本相同的定时，并且具有与在初始RF激励期间施加的切片选择梯度Gz相同的振幅。通过利用与金属植入物相比尺寸足够大的RF线圈来补偿RF场B1中的不均匀性，使得线圈中的金属的体积百分比不显着。通过处理导致切片厚度误差的最显着误差因子Gz来校正梯度场G =（Gx，Gy，Gz）中的不均匀性。具体地说，该方法通过使用具有翻转切片选择梯度Gz的两个脉冲序列获得具有互补切片厚度误差的两个图像; 两个图像的组合成功地消除了切片厚度误差的影响。通过获取具有正和负偏移Gz梯度波瓣的两个图像来校正由于磁场不均匀性引起的局部剥夺性MRI信号损失。这对图像被组合以消除本地信号丢失误差的影响。

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