van der Zwaag Wietske, Francis Susan, Bowtell Richard
Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
Magn Reson Med. 2006 Dec;56(6):1320-7. doi: 10.1002/mrm.21080.
Echo volumar imaging (EVI) is a 3D modification of echo-planar imaging (EPI) that allows data from an entire volume to be acquired following a single RF excitation. EVI provides a high rate of volumar data acquisition, which is advantageous for functional MRI (fMRI). However, few studies to date have applied EVI to fMRI, since because of gradient hardware limitations EVI generally has to be used with long sampling times, resulting in high sensitivity to susceptibility-induced distortions. In this study we modified the EVI sequence to improve its suitability for fMRI. The sampling time is reduced by the use of a high gradient-switching frequency, a small number of echoes, and outer volume suppression (OVS); rewind gradients ameliorate Nyquist ghosting; and phase correction via a calibration scan reduces ghosting and distortion. It is shown that the modified EVI sequence allows fMRI data to be acquired with a temporal resolution of 167 ms.
回波容积成像（EVI）是回波平面成像（EPI）的一种三维改进技术，它允许在单次射频激发后采集来自整个容积的数据。EVI提供了高速的容积数据采集速率，这对功能磁共振成像（fMRI）有利。然而，由于梯度硬件的限制，EVI通常必须使用较长的采样时间，导致对磁化率诱导失真的高敏感性，因此迄今为止很少有研究将EVI应用于fMRI。在本研究中，我们对EVI序列进行了修改，以提高其对fMRI的适用性。通过使用高梯度切换频率、少量回波和外容积抑制（OVS）来减少采样时间；重绕梯度改善奈奎斯特鬼影；通过校准扫描进行相位校正可减少鬼影和失真。结果表明，改进后的EVI序列能够以167毫秒的时间分辨率采集fMRI数据。
