Blaimer Martin, Jakob Peter M, Breuer Felix A
Research Center Magnetic-Resonance-Bavaria (MRB), Würzburg, Germany.
Magn Reson Med. 2014 Jul;72(1):166-71. doi: 10.1002/mrm.24896. Epub 2013 Jul 31.
To implement a regularization method for the phase-constrained generalized partially parallel acquisitions (GRAPPA) algorithm to reduce image artifacts caused by data inconsistencies.
Phase-constrained GRAPPA reconstructions are implemented through the use of virtual coils. To that end, synthetic virtual coils are generated by using complex conjugate symmetric signals from the actual coils. Regularization is achieved by applying coefficient-based penalty factors during the GRAPPA calibration procedure. Different penalizing factors are applied for the actual and virtual coils. The method is tested in vivo using T2-weighted turbo spin echo (TSE) images.
T2 signal decay perturbs conjugate k-space symmetry and produces artifacts in phase-constrained parallel MRI reconstructions of T2-weighted TSE images. Using the proposed regularization method, artifacts are suppressed at the cost of noise amplification. However, there is still a significant SNR gain compared with conventional GRAPPA.
The proposed regularization method is an efficient approach for artifact suppression and maintains the SNR benefit of phase-constrained parallel MRI over conventional parallel MRI.
为相位约束广义部分并行采集（GRAPPA）算法实施一种正则化方法，以减少由数据不一致引起的图像伪影。
通过使用虚拟线圈实现相位约束GRAPPA重建。为此，利用来自实际线圈的复共轭对称信号生成合成虚拟线圈。在GRAPPA校准过程中应用基于系数的惩罚因子来实现正则化。对实际线圈和虚拟线圈应用不同的惩罚因子。该方法在体内使用T2加权快速自旋回波（TSE）图像进行测试。
T2信号衰减扰乱共轭k空间对称性，并在T2加权TSE图像的相位约束并行MRI重建中产生伪影。使用所提出的正则化方法，以噪声放大为代价抑制了伪影。然而，与传统GRAPPA相比，仍有显著的信噪比增益。
所提出的正则化方法是一种有效的伪影抑制方法，并保持了相位约束并行MRI相对于传统并行MRI的信噪比优势。
