Reeder S B, Atalar E, Faranesh A Z, McVeigh E R
Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Magn Reson Med. 1999 Feb;41(2):375-85. doi: 10.1002/(sici)1522-2594(199902)41:2<375::aid-mrm23>3.0.co;2-z.
Cardiac magnetic resonance imaging requires high temporal resolution to resolve motion and contrast uptake with low total scan times to avoid breathing artifacts. While spoiled gradient echo (SPGR) imaging is robust and reproducible, it is relatively inefficient and requires long breath-holds to acquire high time resolution movies of the heart. Echo planar imaging (EPI) is highly efficient with excellent signal-to-noise ratio (SNR) behavior; however, it is particularly difficult to use in the heart because of its sensitivity to chemical shift, susceptibility, and motion. EPI may also require reference scans, which are used to measure hardware delays and phase offsets that cause ghosting artifacts; these reference scans are more difficult and less reliable in the heart. Consequently, a hybrid EPI/SPGR sequence is proposed for application to rapid cardiac imaging. A detailed optimization of SNR and echo train length for multi-echo sequences is presented. It is shown that significant reductions in total scan time are possible while maintaining good image quality. This will allow complete motion sampling of the entire heart in one to three breath-holds, necessary for MR cardiac dobutamine stress testing. Improved speed performance also permits sampling of three to six slices every heartbeat for bolus injection perfusion studies.
心脏磁共振成像需要高时间分辨率来分辨心脏运动和对比剂摄取情况，同时总扫描时间要短，以避免呼吸伪影。虽然扰相梯度回波（SPGR）成像稳健且可重复，但效率相对较低，需要长时间屏气才能获取心脏的高时间分辨率电影。回波平面成像（EPI）效率很高，具有出色的信噪比（SNR）表现；然而，由于其对化学位移、敏感性和运动敏感，在心脏成像中使用特别困难。EPI还可能需要参考扫描，用于测量导致鬼影伪影的硬件延迟和相位偏移；这些参考扫描在心脏成像中更困难且可靠性更低。因此，提出了一种混合EPI/SPGR序列用于快速心脏成像。本文给出了多回波序列的SNR和回波链长度的详细优化。结果表明，在保持良好图像质量的同时，总扫描时间有可能显著缩短。这将允许在一到三次屏气内对整个心脏进行完整的运动采样，这对于磁共振心脏多巴酚丁胺负荷试验是必要的。提高的速度性能还允许在每次心跳时对三到六个层面进行采样，用于团注灌注研究。
