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螺旋磁共振成像中k空间轨迹的估计

Estimation of k-space trajectories in spiral MRI.

作者信息

Tan Hao, Meyer Craig H

机构信息

Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22908, USA.

出版信息

Magn Reson Med. 2009 Jun;61(6):1396-404. doi: 10.1002/mrm.21813.

Abstract

For non-Cartesian data acquisition in MRI, k-space trajectory infidelity due to eddy current effects and other hardware imperfections will blur and distort the reconstructed images. Even with the shielded gradients and eddy current compensation techniques of current scanners, the deviation between the actual k-space trajectory and the requested trajectory remains a major reason for image artifacts in non-Cartesian MRI. It is often not practical to measure the k-space trajectory for each imaging slice. It has been reported that better image quality is achieved in radial scanning by correcting anisotropic delays on different physical gradient axes. In this article the delay model is applied in spiral k-space trajectory estimation to reduce image artifacts. Then a novel estimation method combining the anisotropic delay model and a simple convolution eddy current model further reduces the artifact level in spiral image reconstruction. The root mean square error and peak error in both phantom and in vivo images reconstructed using the estimated trajectories are reduced substantially compared to the results achieved by only tuning delays. After a one-time calibration, it is thus possible to get an accurate estimate of the spiral trajectory and a high-quality image reconstruction for an arbitrary scan plane.

摘要

对于MRI中的非笛卡尔数据采集,由于涡流效应和其他硬件缺陷导致的k空间轨迹失准会使重建图像模糊和失真。即使采用当前扫描仪的屏蔽梯度和涡流补偿技术,实际k空间轨迹与所需轨迹之间的偏差仍然是非笛卡尔MRI中图像伪影的主要原因。对每个成像切片测量k空间轨迹通常并不实际。据报道,通过校正不同物理梯度轴上的各向异性延迟,在径向扫描中可获得更好的图像质量。在本文中,延迟模型应用于螺旋k空间轨迹估计以减少图像伪影。然后,一种结合各向异性延迟模型和简单卷积涡流模型的新型估计方法进一步降低了螺旋图像重建中的伪影水平。与仅调整延迟所获得的结果相比,使用估计轨迹重建的体模图像和活体图像中的均方根误差和峰值误差都大幅降低。经过一次校准后,因此有可能获得螺旋轨迹的准确估计以及针对任意扫描平面的高质量图像重建。

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本文引用的文献

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Improvements in spiral MR imaging.螺旋磁共振成像的改进。
MAGMA. 1999 Oct;9(1-2):29-41. doi: 10.1007/BF02634590.
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Magn Reson Med. 1999 Jan;41(1):103-12. doi: 10.1002/(sici)1522-2594(199901)41:1<103::aid-mrm15>3.0.co;2-m.
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Magn Reson Med. 1998 Apr;39(4):606-14. doi: 10.1002/mrm.1910390414.

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