MULTI-ECHO WATER-FAT SEPARATION

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 目的：该项目旨在使用多回波序列实现快速有效的扫描，并实现稳健的水脂分离。为了实现这一目标，需要一个强大的场图估计和成像技术的结合，与新的多回波序列。 研究方法：我们已经开发了一种多分辨率场图估计方法，该方法直接以粗略的分辨率定位可能的场图值，然后逐步将场图估计细化到全分辨率。为了提高成像效率和减少运动引起的伪影，我们实现了双极多回波序列， 使用交替读出梯度在不同回波时间采集图像，以最大化扫描效率。 对于实际应用，必须解决由交替读出梯度引起的问题，包括k空间回波未对准、场不均匀性引起的未对准和化学位移引起的未对准。 总结：所开发的技术和序列提供了许多优点，例如高SNR效率、与标准多回波序列相比减少的回波间隔、减少的运动诱导伪影以及可靠的场图估计和水-脂肪分离。

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. Purpose: This project aims to enable fast and efficient scanning with robust water-fat separation using multi-echo sequences. To achieve this aim, requires a combination of robust field-map estimation and imaging techniques that work with novel multi-echo sequences. Methods: We have developed a multi-resolution field map estimation method that directly locates possible field map values at a coarse resolution and then progressively refines field map estimation to full resolution. To improve imaging efficiency and reduce motion induced artifacts, we have implemented a bipolar multi-echo sequence that acquires images at different echo times using alternating readout gradients to maximize scan efficiency. For practical use, the problems caused by the alternating readout gradients, including k-space echo misalignment, field-inhomogeneity induced misregistration, and chemical-shift induced misregistration must be addressed. Summary: The developed techniques and sequences offer many advantages such as high SNR efficiency, reduced echo-spacing compared to standard multi-echo sequences, reduced motion induced artifacts, and reliable field-map estimation and water-fat separation.