Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Switzerland.
J Magn Reson Imaging. 2009 Nov;30(5):1171-8. doi: 10.1002/jmri.21951.
To improve the traditional Nyquist ghost correction approach in echo planar imaging (EPI) at high fields, via schemes based on the reversal of the EPI readout gradient polarity for every other volume throughout a functional magnetic resonance imaging (fMRI) acquisition train.
An EPI sequence in which the readout gradient was inverted every other volume was implemented on two ultrahigh-field systems. Phantom images and fMRI data were acquired to evaluate ghost intensities and the presence of false-positive blood oxygenation level-dependent (BOLD) signal with and without ghost correction. Three different algorithms for ghost correction of alternating readout EPI were compared.
Irrespective of the chosen processing approach, ghosting was significantly reduced (up to 70% lower intensity) in both rat brain images acquired on a 9.4T animal scanner and human brain images acquired at 7T, resulting in a reduction of sources of false-positive activation in fMRI data.
It is concluded that at high B(0) fields, substantial gains in Nyquist ghost correction of echo planar time series are possible by alternating the readout gradient every other volume.
通过在功能磁共振成像（fMRI）采集过程中对每一卷的回波平面成像（EPI）读出梯度极性进行反转的方案，改进传统的高场 EPI 中的奈奎斯特鬼校正方法。
在两个超高场系统上实现了每隔一卷反转读出梯度的 EPI 序列。采集了幻影图像和 fMRI 数据，以评估有无鬼校正时的鬼像强度和假阳性血氧水平依赖（BOLD）信号的存在。比较了三种交替读出 EPI 鬼校正的不同算法。
无论选择哪种处理方法，在 9.4T 动物扫描仪上采集的大鼠脑图像和在 7T 上采集的人脑图像中，鬼像都得到了显著的减少（强度降低高达 70%），从而减少了 fMRI 数据中假阳性激活的来源。
在高 B（0）场中，通过每隔一卷交替读出梯度，可以对回波平面时间序列的奈奎斯特鬼校正获得实质性的增益。
