Robinson Simon, Schödl Horst, Trattnig Siegfried
High Field MR Center of Excellence, Department of Radiology, Medical University of Vienna, Austria.
Magn Reson Med. 2014 Jul;72(1):80-92. doi: 10.1002/mrm.24897. Epub 2013 Jul 30.
To develop a method of unwrapping phase images from multi-echo scans that works even where there are several wraps between echoes, and which generates unwrapped phase images in addition to phase difference (PD) images.
The difference between the echo spacings in an acquisition with three unevenly spaced echoes (an imposed delay) can be selected such that the phase evolution in that time is in the range -π to +π in all voxels of interest. Under this condition, an image of the difference between the phase evolutions in the two inter-echo periods, an estimate of ΔB0 , is free of wraps. This ΔB0 estimate can be used to identify and remove receiver phase offsets and wraps in phase images.
The approach was tested on simulated data and high-resolution in vivo brain data acquired from six subjects at 7 Tesla.
The method generated wrap-free phase images. It was able to remove more wraps than is possible with PD imaging and was faster and more reliable than spatial unwrapping.
Unwrapping Multi-echo Phase Images with iRregular Echo spacings (UMPIRE) is conceptually simple, fast, reliable, and requires no fitting, thresholds, or operator intervention.
开发一种从多回波扫描中展开相位图像的方法，即使在回波之间存在多个包裹的情况下也能正常工作，并且除了相位差（PD）图像外还能生成展开的相位图像。
在具有三个不均匀间隔回波（施加延迟）的采集中，可以选择回波间隔之间的差异，使得在该时间段内所有感兴趣体素中的相位演变都在-π到+π的范围内。在这种情况下，两个回波间期内相位演变差异的图像（ΔB0的估计值）没有包裹。这个ΔB0估计值可用于识别和消除相位图像中的接收器相位偏移和包裹。
该方法在模拟数据和从6名受试者在7特斯拉下采集的高分辨率体内脑数据上进行了测试。
该方法生成了无包裹的相位图像。它能够比PD成像去除更多的包裹，并且比空间展开更快、更可靠。
具有不规则回波间隔的多回波相位图像展开（UMPIRE）在概念上简单、快速、可靠，并且不需要拟合、阈值或操作员干预。
