Parker Dennis L, Payne Allison, Todd Nick, Hadley J Rock
Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA.
Magn Reson Med. 2014 Aug;72(2):563-9. doi: 10.1002/mrm.24932. Epub 2013 Sep 4.
This study develops a method to obtain optimal estimates of absolute magnetization phase from multiple-coil MRI data.
The element-specific phases of a multi-element receiver coil array are accounted for by using the phase of a real or virtual reference coil that is sensitive over the entire imaged volume. The virtual-reference coil is generated as a weighted combination of measurements from all receiver coils. The phase-corrected multiple coil complex images are combined using the inverse covariance matrix. These methods are tested on images of an agar phantom, an in vivo breast, and an anesthetized rabbit obtained using combinations of four, nine, and three receiver channels, respectively.
The four- and three-channel acquisitions require formation of a virtual-reference receiver coil while one channel of the nine-channel receive array has a sensitivity profile covering the entire imaged volume. Referencing to a real or virtual coil gives receiver phases that are essentially identical except for the individual receiver channel noise. The resulting combined images, which account for receiver channel noise covariance, show the expected reduction in phase variance.
The proposed virtual reference coil method determines a phase distribution for each coil from which an optimal phase map can be obtained.
本研究开发一种从多线圈磁共振成像（MRI）数据中获取绝对磁化相位最优估计值的方法。
通过使用在整个成像体积上敏感的真实或虚拟参考线圈的相位来考虑多元素接收线圈阵列中特定元素的相位。虚拟参考线圈作为所有接收线圈测量值的加权组合生成。经相位校正的多线圈复数图像使用逆协方差矩阵进行组合。这些方法分别在使用四个、九个和三个接收通道组合获取的琼脂模型、活体乳房和麻醉兔的图像上进行了测试。
四通道和三通道采集需要形成虚拟参考接收线圈，而九通道接收阵列的一个通道具有覆盖整个成像体积的灵敏度分布。参考真实或虚拟线圈得到的接收相位基本相同，只是存在各个接收通道的噪声。考虑了接收通道噪声协方差的最终组合图像显示出预期的相位方差降低。
所提出的虚拟参考线圈方法确定每个线圈的相位分布，从中可获得最优相位图。
