ENTROPY BASED NON-INTERACTIVE NYQUIST GHOST CORRECTION ALGORITHM

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。介绍。在EPI中，奈奎斯特重影是由于奇偶回波的不对准造成的。出于这个原因，临床EPI扫描通常在预扫描过程中合并参考扫描，从中可以使用相位信息来纠正鬼影错误。对于多镜头、多线圈和多层采集，这种额外的扫描通常可以超过一分钟，这在急性中风的情况下可能是至关重要的。参考扫描的另一种有趣的替代方法是不需要额外信息的后处理方法。其中一种方法(1)通过迭代细化相位参数来最小化在鬼影区域中选择的ROI中的强度。但是，通常情况下，这种方法需要用户交互。另一种优雅的方法(2)使用总图像熵作为迭代优化的成本函数，并且不假设被成像物体的形状或大小。然而，据报道，校正64层128¿128 4枪数据集的计算时间为2.5分钟(2)。为了使该方法成为临床参考扫描的可靠替代品，无论选择的采集参数、感兴趣的解剖结构以及系统校准的好坏，它都可能永远不会失败。在这里，我们提出了一种强大的迭代熵最小化实现，用于去除鬼影，我们现在通常将其作为临床单次和多次扫描、grappa加速DWI和PWI EPI检查的参考扫描的替代品。

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. Nyquist ghosting occurs in EPI due to misalignment between odd and even echoes. For this reason, clinical EPI scans are commonly performed with a reference scan incorporated into the prescan process from which phase information can be used to correct ghosting errors. For multi-shot, multi-coil and multi-slice acquisitions, this additional scan can often exceed a minute, which may be crucial in cases of acute stroke, for example. An interesting alternative to reference scans are post-processing methods that require no additional information. One such method (1) minimizes the intensity in a ROI selected in the ghost area by iteratively refining phase parameters. In general, however, this method requires user interaction. Another elegant method (2) uses the total image entropy as a cost function for iterative optimization and makes no assumptions about the shape or size of the object being imaged. However, the computation time to correct a 64-slice 128¿128 4-shot data set has been reported to be 2.5 min (2). For this method to be a dependable replacement for the reference scan in the clinic it may never fail, regardless of acquisition parameters chosen, anatomy of interest and how well the system is calibrated. Here we present a robust iterative entropy minimization implementation for ghost removal that we now use routinely as a replacement for reference scanning in clinical single- and multi-shot, GRAPPA-accelerated DWI and PWI EPI exams.