Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
Magn Reson Med. 2013 Dec;70(6):1567-79. doi: 10.1002/mrm.24606. Epub 2013 Feb 6.
To analyze and correct for eddy current-induced phase imperfections in cardiac cine balanced steady-state free precession (bSSFP) imaging.
Eddy current-induced phase offsets were measured for different phase-encoding schemes using a higher order dynamic field camera. Based on these measurements, offset phases were corrected for in postprocessing and by run-time phase compensation applying radiofrequency phase increments and additional compensatory gradient areas. The findings were validated using numerical simulations, phantom experiments, and in vivo cardiac scans.
Depending on the phase-encoding scheme, significant eddy current-induced phase offsets were detected. Time-varying phase offsets were observed at subsequent excitations leading to steady-state distortions and hence to profile-dependent amplitude modulations in k-space. Taking into account measured k-space trajectories algebraic image reconstruction allowed compensating imperfect spatial encoding. Correction of amplitude modulations was successfully accomplished by run-time phase compensation.
Using magnetic field monitoring, artifacts in cine balanced steady-state free precession caused by uncompensated eddy current fields can be significantly reduced.
分析和校正心脏电影双稳态自由进动（bSSFP）成象中涡流引起的相位误差。
使用高阶动态磁场相机测量了不同相位编码方案的涡流引起的相位偏移。基于这些测量结果，通过后处理和实时相位补偿，应用射频相位增量和附加补偿梯度区域，对偏移相位进行校正。通过数值模拟、体模实验和活体心脏扫描验证了这些发现。
根据相位编码方案的不同，检测到了明显的涡流引起的相位偏移。在随后的激发中观察到时变的相位偏移，导致稳态失真，从而导致 k 空间中与轮廓相关的幅度调制。考虑到测量的 k 空间轨迹，代数图像重建可以补偿不完全的空间编码。通过实时相位补偿成功地实现了对幅度调制的校正。
通过磁场监测，可以显著减少未补偿涡流场引起的电影双稳态自由进动的伪影。
