公开(公告)号：US5864233A

公开(公告)日：1999-01-26

申请号：US803808

申请日：1997-02-22

申请人： Xiaohong Zhou ,  Joseph K. Maier ,  Hammond Glenn Reynolds

发明人： Xiaohong Zhou ,  Joseph K. Maier ,  Hammond Glenn Reynolds

IPC分类号： G01N27/90 ,  G01R33/563 ,  G01R33/565 ,  G01V3/00

CPC分类号： G01R33/56341 ,  G01R33/56518

摘要： An eddy current correction method is provided for use in an MR system disposed to generate difflusion-weighted echo planar images by employing a bipolar diffusion-weighting gradient as well as the nominal components in an echo planar imaging pulse sequence. The correction method comprises the steps of deriving eddy current parameters (i.e., amplitude and time constant) associated with each eddy-current-induced magnetic field component caused by the diffusion-weighting gradient, and generating a set of correction terms, each of the correction terms being a function of the parameters. The method includes the further steps of modifyg a set of ideal echo planar imaging gradients and the receiver phase and frequency to respectively offset the eddy current induced magnetic field gradient and the spatially independent B.sub.0 -magnetic field. The modification occurs in two stages. Prior to data acquisition, errors are exactly corrected by altering the pre-phasing and the slice-refocusing gradient areas as well as the initial receiver phase. During data acquisition, the eddy current induced errors are approximately compensated for by adding offset gradients and dynamically changing the receiver phase and frequency using either a piece-wise-constant approximation or a constant approximation. Using either method, artifacts in diffusion-weighted echo planar images can be significantly reduced.

摘要翻译： 提供涡流校正方法用于MR系统，其被布置为通过采用双极扩散加权梯度以及回波平面成像脉冲序列中的标称分量来产生散射加权回波平面图像。 校正方法包括以下步骤：导出与由扩散加权梯度引起的每个涡流感应磁场分量相关联的涡流参数（即振幅和时间常数），以及产生一组校正项，每个校正 术语是参数的函数。 该方法包括以下步骤：修改一组理想的回波平面成像梯度，以及接收器相位和频率以分别偏移涡流感应磁场梯度和空间上独立的B0磁场。 修改发生在两个阶段。 在数据采集之前，通过改变预定相和切片重新聚焦梯度区域以及初始接收器相位来精确地校正误差。 在数据采集过程中，通过增加偏移梯度和使用分段常数近似或恒定近似来动态地改变接收器相位和频率，近似补偿涡流感应误差。 使用任一种方法，扩散加权回波平面图像中的伪影可以显着减少。

公开(公告)号：US06323646B1

公开(公告)日：2001-11-27

申请号：US09316230

申请日：1999-05-21

申请人： Xiaohong Zhou ,  Joseph K. Maier ,  Steven J. Huff ,  Hammond Glenn Reynolds

发明人： Xiaohong Zhou ,  Joseph K. Maier ,  Steven J. Huff ,  Hammond Glenn Reynolds

IPC分类号： G01V300

CPC分类号： G01R33/56341

摘要： A technique is provided for generating images on an MRI system in which errors due to gradient pulses are compensated. The errors are identified in advance, such as in a calibration sequence performed on the MRI system. Receiver phase adjustment and logical gradient error values are derived from the identified error values. The calibration sequence may be a modified version of the MRI imaging sequence used to produce the images. The correction values may be based upon corrections at the center of k-space. The technique is particularly useful in compensating for effects of eddy currents in pulse sequences employing high slew rate gradient pulses, such as diffusion weighted echo planar imaging sequences.

摘要翻译： 提供了一种用于在MRI系统上生成图像的技术，其中补偿了由于梯度脉冲引起的误差。 错误是事先确定的，例如在MRI系统上执行的校准序列。 接收器相位调整和逻辑梯度误差值是从识别的误差值导出的。 校准序列可以是用于产生图像的MRI成像序列的修改版本。 校正值可以基于在k空间中心的校正。 该技术在补偿使用高压摆率梯度脉冲（例如扩散加权回波平面成像序列）的脉冲序列中对涡流的影响特别有用。