Nayak Krishna S, Cunningham Charles H, Santos Juan M, Pauly John M
Department of Electrical Engineering, Stanford University, Stanford, California, USA.
Magn Reson Med. 2004 Apr;51(4):655-60. doi: 10.1002/mrm.20053.
Real-time cardiac and coronary MRI at 1.5T is relatively "signal starved" and the 3T platform is attractive for its immediate factor of two increase in magnetization. Cardiac imaging at 3T, however, is both subtly and significantly different from imaging at 1.5T because of increased susceptibility artifacts, differences in tissue relaxation, and RF homogeneity issues. New RF excitation and pulse sequence designs are presented which deal with the fat-suppression requirements and off-resonance issues at 3T. Real-time cardiac imaging at 3T is demonstrated with high blood SNR, blood-myocardium CNR, resolution, and image quality, using new spectral-spatial RF pulses and fast spiral gradient echo pulse sequences. The proposed sequence achieves 1.5 mm in-plane resolution over a 20 cm FOV, with a 5.52 mm measured slice thickness and 32 dB of lipid suppression. Complete images are acquired every 120 ms and are reconstructed and displayed at 24 frames/sec using a sliding window. Results from healthy volunteers show improved image quality, a 53% improvement in blood SNR efficiency, and a 232% improvement in blood-myocardium CNR efficiency compared to 1.5T.
1.5T的实时心脏和冠状动脉磁共振成像相对“信号匮乏”，而3T平台因其能使磁化强度即刻提高两倍这一因素而颇具吸引力。然而，由于敏感性伪影增加、组织弛豫差异以及射频均匀性问题，3T的心脏成像与1.5T的成像在细微和显著方面都有所不同。本文提出了新的射频激发和脉冲序列设计，以应对3T时的脂肪抑制要求和失谐问题。利用新的频谱空间射频脉冲和快速螺旋梯度回波脉冲序列，展示了3T下具有高血液信噪比、血液 - 心肌对比噪声比、分辨率和图像质量的实时心脏成像。所提出的序列在20 cm视野范围内实现了1.5 mm的平面分辨率，测量切片厚度为5.52 mm，脂质抑制达32 dB。每120 ms采集完整图像，并使用滑动窗口以24帧/秒的速度进行重建和显示。与1.5T相比，健康志愿者的结果显示图像质量得到改善，血液信噪比效率提高了53%，血液 - 心肌对比噪声比效率提高了232%。
