Papadakis N G, Martin K M, Pickard J D, Hall L D, Carpenter T A, Huang C L
Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, UK.
Magn Reson Med. 2000 Oct;44(4):616-24. doi: 10.1002/1522-2594(200010)44:4<616::aid-mrm16>3.0.co;2-t.
This article describes a method which enables fast and objective pulse-sequence-specific preemphasis calibration, using standard pulse sequences and system hardware. The method is based on a k-space measurement technique, and has been applied to single-shot, diffusion-weighted, spin-echo, echo-planar imaging (DW-SE-EPI), which is particularly sensitive to eddy-current-induced image distortions. The efficiency of the technique was demonstrated not only by the reduction of eddy-current fields to a negligible level using full preemphasis compensation, but also by the fact that adjustment of the slow time-base alone sufficed for the practical elimination of image distortions in the DW-SE-EPI images and the subsequent diffusion tensor maps (in a phantom and a human brain). By seeking to eliminate directly the effect of eddy-current-induced phase shifts during the EPI data collection, the method is free of the complications and restrictions associated with other eddy-current correction techniques for DW-SE-EPI (such as acquisition of additional calibration scans, intense postprocessing, extensive pulse-sequence modifications), making their use redundant.
本文介绍了一种方法，该方法利用标准脉冲序列和系统硬件，能够实现快速、客观的特定脉冲序列预加重校准。该方法基于一种k空间测量技术，并已应用于单次激发、扩散加权、自旋回波、回波平面成像（DW-SE-EPI），这种成像对涡流引起的图像失真特别敏感。该技术的有效性不仅体现在通过完全预加重补偿将涡流场降低到可忽略不计的水平，还体现在仅调整慢时基就足以在实际中消除DW-SE-EPI图像及后续扩散张量图（在体模和人脑成像中）中的图像失真。通过在EPI数据采集过程中直接消除涡流引起的相移的影响，该方法没有与DW-SE-EPI的其他涡流校正技术相关的复杂性和限制（如采集额外的校准扫描、大量的后处理、广泛的脉冲序列修改），从而使这些技术变得多余。
