IMAGE QUALITY OF GRAPPA ACCELERATED EPI IMAGE QUALITY

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。导言。GRAPPA1和SENSE2已被证明是非常有效的方法来减少回声平面成像(EPI)3、4中的几何失真和图像模糊。这在提高图像质量和总体病变显着性方面具有巨大的潜力，具有广泛的临床应用前景。EPI中图像的进一步退化是由于奇偶回波之间的轻微不平衡导致回波未对准，从而导致FOV/2重影。这项研究的目的是表明，对于一种自校准的并行成像重建方法，即使是EPI相位校正中的微小误差也会导致相当大的重建误差。材料和方法梯度不平衡、滤波延迟和涡流等几个因素是导致EPI中奇偶回波之间误差的原因。这些误差通常会导致k空间中的相位误差和回波不对准，从而导致单次激发EPI扫描中的FOV/2重影；交错EPI出现较高空间周期性的重影。在参考扫描的基础上，通常在网格化之前对图像域中的数据进行零阶和一阶相位校正，以避免这些重影。在这里，我们证明了EPI相位校正中的不准确可能导致出乎意料的高图像退化，即使在原始b=0数据中重影看起来很小。虽然任何使重影伪影最小化的重影校正方案都应该适用，但我们使用了实验室最近开发的一种无参考方法。该相位校正是基于基于图像的熵来确定适当的一阶和零阶相位项，从而以快速可靠的方式最小化FOV/2重影的量。参考资料。1Griswold，M.等人。MRM 47：1202-10,2002；2 Pruessmann，K.等人。MRM 42：952-62,1999；3Bammer，R.等人。MRM 46：548-54,2001；4 Heidemann，R.等人。ISMRM第9届年会，苏格兰格拉斯哥，2001年，第169页。5斯凯尔、S等人。ISMRM DWI研讨会，路易斯湖：第16页：2005认可。这项工作得到了美国国立卫生研究院(1R01EB002771)、斯坦福高级磁共振技术中心(P41RR09784)、卢卡斯基金会和橡树基金会的部分支持。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction. It has been demonstrated that GRAPPA1 and SENSE2 are extremely powerful methods to reduce geometric distortions and image blurring in echo planar imaging (EPI) 3, 4. This bears great potential to improve image quality and overall lesion conspicuity for numerous clinical applications. Further image degradation in EPI is due to slight imbalances between odd and even echoes that lead to echo misalignment and hence FOV/2 ghosts. The objective of this study is to show that for a self-calibrated parallel imaging reconstruction approach even slight inaccuracies in EPI phase correction can lead to substantial reconstruction errors. Materials and Methods. Several factors, such as gradient imbalances, filter delays, and eddy currents, are causative for errors between odd and even echoes in EPI. These errors typically cause phase errors and echo misalignment in k-space and therefore result in FOV/2 ghosts in single-shot EPI scans; ghosts of higher spatial periodicity occur for interleaved EPI. Based on a reference scan, zero and first order phase correction is usually applied to the data in the image domain prior to gridding to avoid these ghosts. Here, we demonstrate that inaccuracies in EPI phase correction can lead to unexpectedly high image degradation even if the ghosts appear to minor in the original b=0 data. Although any ghost correction scheme that minimizes the ghosting artifacts should be applicable, we have used a referenceless method that was recently developed in our lab. This phase correction is based on image based entropy to determine the appropriate first and zero order phase terms to minimize the amount of FOV/2 ghosting in a rapid and reliable fashion. References. 1Griswold, M. et al. MRM 47: 1202-10, 2002; 2Pruessmann, K. et al. MRM 42: 952-62, 1999; 3Bammer, R. et al. MRM 46: 548-54, 2001; 4Heidemann, R. et al. 9th Annual Meeting of the ISMRM, Glasgow, Scotland, 2001, p 169. 5Skare, S et al. ISMRM DWI workshop, Lake Louise: p 16:2005 Acknowledgements. This work was supported in part by the NIH (1R01EB002771), the Center of Advanced MR Technology at Stanford (P41RR09784), Lucas Foundation, and Oak Foundation.