Duerst Yolanda, Wilm Bertram J, Dietrich Benjamin E, Vannesjo S Johanna, Barmet Christoph, Schmid Thomas, Brunner David O, Pruessmann Klaas P
Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Switzerland.
Magn Reson Med. 2015 Feb;73(2):884-93. doi: 10.1002/mrm.25167. Epub 2014 Mar 13.
MR imaging and spectroscopy require a highly stable, uniform background field. The field stability is typically limited by hardware imperfections, external perturbations, or field fluctuations of physiological origin. The purpose of the present work is to address these issues by introducing spatiotemporal field stabilization based on real-time sensing and feedback control.
An array of NMR field probes is used to sense the field evolution in a whole-body MR system concurrently with regular system operation. The field observations serve as inputs to a proportional-integral controller that governs correction currents in gradient and higher-order shim coils such as to keep the field stable in a volume of interest.
The feedback system was successfully set up, currently reaching a minimum latency of 20 ms. Its utility is first demonstrated by countering thermal field drift during an EPI protocol. It is then used to address respiratory field fluctuations in a T2 *-weighted brain exam, resulting in substantially improved image quality.
Feedback field control is an effective means of eliminating dynamic field distortions in MR systems. Third-order spatial control at an update time of 100 ms has proven sufficient to largely eliminate thermal and breathing effects in brain imaging at 7 Tesla.
磁共振成像和波谱分析需要高度稳定、均匀的背景场。场稳定性通常受硬件缺陷、外部干扰或生理源性场波动的限制。本研究的目的是通过引入基于实时传感和反馈控制的时空场稳定技术来解决这些问题。
在全身磁共振系统正常运行的同时，使用一组核磁共振场探头来感知场的变化。场观测结果作为比例积分控制器的输入，该控制器控制梯度线圈和高阶匀场线圈中的校正电流，从而在感兴趣的体积内保持场的稳定。
反馈系统成功建立，目前最小延迟达到20毫秒。首先通过在回波平面成像协议期间对抗热场漂移来证明其效用。然后将其用于解决T2 *加权脑成像检查中的呼吸场波动问题，从而显著提高图像质量。
反馈场控制是消除磁共振系统中动态场畸变的有效手段。已证明在100毫秒的更新时间进行三阶空间控制足以在很大程度上消除7特斯拉脑成像中的热效应和呼吸效应。
