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    Method to reduce eddy current effects in diffusion-weighted echo planar imaging
    1.
    发明授权
    Method to reduce eddy current effects in diffusion-weighted echo planar imaging 失效
    减少扩散加权回波平面成像中涡流效应的方法

    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。

    Method and apparatus for producing diffusion weighted MR images
    2.
    发明授权
    Method and apparatus for producing diffusion weighted MR images 有权
    用于产生扩散加权MR图像的方法和装置

    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。

    Method and apparatus to reduce the effects of maxwell terms and other perturbation magnetic fields in MR images
    3.
    发明授权
    Method and apparatus to reduce the effects of maxwell terms and other perturbation magnetic fields in MR images 失效
    减少麦克斯韦术语和其他扰动磁场对MR图像影响的方法和装置

    公开(公告)号：US06528998B1

    公开(公告)日：2003-03-04

    申请号：US09540768

    申请日：2000-03-31

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

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

    IPC分类号： G01V300

    CPC分类号： G01R33/56581

    摘要： A method and apparatus for correcting ghosting artifacts that are related to Maxwell fields and/or other perturbation magnetic fields is disclosed. The method and apparatus includes acquiring MR image n-space data and an MR reference scan, each having perturbation field effects therein. After determining phase correction values from the MR reference scan and reconstructing an MR image using the phase correction values, a projection phase error is calculated from the reconstructed MR image and then subtracted from the reference scan, the result of which is used to determine a new set of phase correction values. The new set of phase correction values is applied to the acquired MR image data to reconstruct a new image. The reconstructed new image can then be reused to calculate a new projection phase error, which again is subtracted from the reference scan data and the process is repeated until an image of desired ghost artifact reduction is achieved.

    摘要翻译： 公开了一种用于校正与麦克斯韦尔场和/或其他扰动磁场相关的重影伪像的方法和装置。 该方法和装置包括获取每个在其中具有扰动场效应的MR图像n空间数据和MR参考扫描。 在从MR参考扫描确定相位校正值并使用相位校正值重建MR图像之后，从重建的MR图像计算投影相位误差，然后从参考扫描中减去其结果，其结果用于确定新的 一组相位校正值。 将新的相位校正值集合应用于所获取的MR图像数据以重构新图像。 然后可以重新构建重建的新图像以计算新的投影相位误差，其再次从参考扫描数据中减去，并且重复该过程，直到实现期望的鬼影伪像减少的图像。

    Method and apparatus to reduce perturbation field effects in MR images by restricting the region of interest
    4.
    发明授权
    Method and apparatus to reduce perturbation field effects in MR images by restricting the region of interest 失效
    通过限制感兴趣区域来减少MR图像的扰动场效应的方法和装置

    公开(公告)号：US06469505B1

    公开(公告)日：2002-10-22

    申请号：US09540687

    申请日：2000-03-31

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

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

    IPC分类号： G01V300

    CPC分类号： G01R33/56563 ,  G01R33/5604 ,  G01R33/56518

    摘要： A method and apparatus for correcting ghost artifacts that are related to orthogonal perturbation magnetic fields is disclosed. The technique includes acquiring MR data and an MR reference scan, each in the presence of orthogonal perturbation magnetic fields. However, the region of interest for the MR reference scan is limited to a relatively narrow band within the imaging subject. Preferably, the narrow band is selected in the vicinity of the magnet iso-center and parallel to the readout direction. Alternatively, the narrow band can also be selected in the limited region where the orthogonal perturbation fields are either minimal or constant along the phase encoding direction, and parallel to the readout direction. The selection of the relatively narrow band is accomplished by either spatially saturating surrounding regions, or using a two-dimensional spatially selective RF pulse. Phase correction values can then be calculated from a more accurately defined slope and intercept of the phase of the MR reference scan and used to correct the MR data. A reconstructed MR image using this technique has reduced ghost artifacts otherwise caused by the adverse effects of the orthogonal perturbation fields in the phase correction process.

    摘要翻译： 公开了一种用于校正与正交扰动磁场相关的重影伪影的方法和装置。 该技术包括获取MR数据和MR参考扫描，每个在存在正交扰动磁场的情况下。 然而，用于MR参考扫描的感兴趣区域被限制在成像对象内的相对较窄的频带。 优选地，在磁体等中心附近并且平行于读出方向选择窄带。 或者，也可以在有限区域选择窄带，其中正交扰动场沿相位编码方向为最小或恒定，并且平行于读出方向。 通过空间饱和的周围区域或使用二维空间选择性RF脉冲来实现相对窄带的选择。 然后可以从更准确地定义的MR参考扫描的相位的斜率和截距来计算相位校正值，并用于校正MR数据。 使用该技术的重构MR图像减少了由相位校正处理中的正交扰动场的不利影响引起的鬼影。

    Reduction of Nyquist ghost artifacts in oblique echo planar imaging
    5.
    发明授权
    Reduction of Nyquist ghost artifacts in oblique echo planar imaging 失效
    在倾斜回波平面成像中减少奈奎斯特幻影

    公开(公告)号：US5672969A

    公开(公告)日：1997-09-30

    申请号：US637879

    申请日：1996-04-25

    申请人： Xiaohong Zhou ,  Joseph K. Maier ,  Frederick H. Epstein

    发明人： Xiaohong Zhou ,  Joseph K. Maier ,  Frederick H. Epstein

    IPC分类号： G01R33/54 ,  A61B5/055 ,  G01R33/561 ,  G01R33/565 ,  G01R33/20

    CPC分类号： G01R33/56572 ,  G01R33/5616

    摘要： In a magnetic resonance imaging (MRI) system, a method is provided for reducing oblique Nyquist ghost artifact in an image produced by an oblique EPI scan. Prior to commencing the EPI scan, referencing pre-scans are conducted to generate pre-scan echo trains respectively corresponding to the physical gradient axes. Distortion compensating parameters are derived from the pre-scan echo trains for reducing Nyquist ghost by alternatively modifying the data acquisitions stage of the oblique EPI scan, or the post-data acquisition image processing stage thereof. In one mode of operation, the pre-scan echo trains are generated while a subject is in the MRI system. In another mode of operation, pre-scan echo trains are generated while no subject is present in the MR system, so that the distortion compensating parameters represent characteristics of the MR system only, and thus may be used for EPI scans of different protocols. For such mode of operation the distortion compensating parameters may be computed as a function of readout gradient pulse spacing.

    摘要翻译： 在磁共振成像（MRI）系统中，提供了一种用于减少由倾斜EPI扫描产生的图像中的倾斜奈奎斯特幻影伪像的方法。 在开始EPI扫描之前，进行参考预扫描以产生分别对应于物理梯度轴的预扫描回波列。 通过交替地修改倾斜EPI扫描的数据采集阶段或其后数据采集图像处理阶段，从预扫描回波列导出失真补偿参数，以减少奈奎斯特重影。 在一种操作模式中，当受检者在MRI系统中时，产生预扫描回波列。 在另一种操作模式中，在MR系统中不存在主体的情况下产生预扫描回波串，使得失真补偿参数仅表示MR系统的特性，因此可用于不同协议的EPI扫描。 对于这种操作模式，失真补偿参数可以作为读出梯度脉冲间隔的函数来计算。

    Method and apparatus for identifying errors in magnetic resonance imaging examinations
    6.
    发明授权
    Method and apparatus for identifying errors in magnetic resonance imaging examinations 有权
    用于识别磁共振成像检查中的误差的方法和装置

    公开(公告)号：US06239599B1

    公开(公告)日：2001-05-29

    申请号：US09316344

    申请日：1999-05-21

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

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

    IPC分类号： G01V300

    CPC分类号： G01R33/58 ,  G01R33/56518 ,  G01R33/56554

    摘要： A technique is disclosed for determining errors in MRI sequences resulting from eddy currents generated by pulsed gradient fields. During a calibration sequence, with no phase-encoding, gradient pulses and readout sequences are applied along physical axes of a scanner and data sets are acquired for each combination. A reference data set is acquired with no gradient pulses applied. The resulting data sets are processed by one dimensional Fourier transformation, and the transformed data is analyzed to determine spatially invariant and linear gradient errors. The phase errors may be averaged for each physical axis. The technique is particularly useful in determining errors in diffusion weighted echo planar imaging sequences.

    摘要翻译： 公开了一种用于确定由脉冲梯度场产生的涡流产生的MRI序列中的误差的技术。 在校准序列期间，没有相位编码，沿着扫描仪的物理轴施加梯度脉冲和读出序列，并为每个组合采集数据集。 在不施加梯度脉冲的情况下获取参考数据集。 通过一维傅里叶变换处理所得到的数据集，并分析变换数据以确定空间不变和线性梯度误差。 每个物理轴可以对相位误差进行平均。 该技术在确定扩散加权回波平面成像序列中的误差方面特别有用。

    Correction of artifacts caused by maxwell terms in slice offset echo planar imaging
    8.
    发明授权
    Correction of artifacts caused by maxwell terms in slice offset echo planar imaging 有权
    校正由切片偏移回波平面成像中的maxwell项引起的假象

    公开(公告)号：US06064205A

    公开(公告)日：2000-05-16

    申请号：US265259

    申请日：1999-03-09

    申请人： Xiaohong Zhou ,  Yiping Du ,  Matthew A. Bernstein ,  Hammond G. Reynolds ,  Joseph K. Maier ,  Jason A. Polzin

    发明人： Xiaohong Zhou ,  Yiping Du ,  Matthew A. Bernstein ,  Hammond G. Reynolds ,  Joseph K. Maier ,  Jason A. Polzin

    IPC分类号： G01R33/32 ,  A61B5/055 ,  G01R33/54 ,  G01R33/561 ,  G01R33/565 ,  G01V3/00

    CPC分类号： G01R33/56581 ,  G01R33/56554

    摘要： Two methods are disclosed to remove the image artifacts produced by Maxwell terms arising from the imaging gradients in an echo planar imaging pulse sequence. In the first method, the frequency and phase errors caused by the Maxwell terms are calculated on an individual slice basis and subsequently compensated during data acquisition by dynamically adjusting the receiver frequency and phase. In the second method, two linear phase errors, one in the readout direction and the other in the phase-encoding direction, both of which arise from the Maxwell terms, are calculated on an individual-slice basis. These errors are compensated for in the k-space data after data acquisition.

    摘要翻译： 公开了两种方法来去除由回波平面成像脉冲序列中的成像梯度引起的由麦克斯韦尔产生的图像伪影。 在第一种方法中，由麦克斯韦尔项引起的频率和相位误差在单独的切片基础上计算，并随后通过动态调整接收机频率和相位在数据采集期间进行补偿。 在第二种方法中，以单个切片为基础计算两个线性相位误差，一个在读出方向上，另一个在相位编码方向上，两个来自麦克斯韦术语。 这些误差在数据采集后的k空间数据中得到补偿。