Chen N K, Wyrwicz A M
Center for MR Research, ENH Research Institute, Northwestern University, Evanston, Illinois 60201, USA.
Magn Reson Med. 2001 Mar;45(3):525-8. doi: 10.1002/1522-2594(200103)45:3<525::aid-mrm1070>3.0.co;2-s.
A new phase-shifted EPI pulse sequence is described that encodes EPI phase errors due to all off-resonance factors, including B(o) field inhomogeneity, eddy current effects, and gradient waveform imperfections. Combined with the previously proposed multichannel modulation postprocessing algorithm (Chen and Wyrwicz, MRM 1999;41:1206-1213), the encoded phase error information can be used to effectively remove geometric distortions in subsequent EPI scans. The proposed EPI distortion correction technique has been shown to be effective in removing distortions due to gradient waveform imperfections and phase gradient-induced eddy current effects. In addition, this new method retains advantages of the earlier method, such as simultaneous correction of different off-resonance factors without use of a complicated phase unwrapping procedure. The effectiveness of this technique is illustrated with EPI studies on phantoms and animal subjects. Implementation to different versions of EPI sequences is also described. Magn Reson Med 45:525-528, 2001.
本文描述了一种新的相移EPI脉冲序列，该序列对所有失谐因素引起的EPI相位误差进行编码，这些因素包括主磁场（B₀）不均匀性、涡流效应和梯度波形缺陷。结合先前提出的多通道调制后处理算法（Chen和Wyrwicz，《磁共振医学》1999年；41:1206 - 1213），编码后的相位误差信息可用于在后续EPI扫描中有效消除几何失真。所提出的EPI失真校正技术已被证明在消除由梯度波形缺陷和相位梯度引起的涡流效应导致的失真方面是有效的。此外，这种新方法保留了早期方法的优点，例如无需复杂的相位解缠程序即可同时校正不同的失谐因素。通过对体模和动物受试者的EPI研究说明了该技术的有效性。还描述了该技术在不同版本EPI序列中的实现。《磁共振医学》45:525 - 528，2001年。
