Technische Universität München, Munich, Germany.
GE Global Research Europe, Munich, Germany.
J Magn Reson Imaging. 2019 Feb;49(2):499-507. doi: 10.1002/jmri.26234. Epub 2018 Nov 15.
Field inhomogeneities in MRI caused by interactions between the radiofrequency field and the patient anatomy can lead to artifacts and contrast variations, consequently degrading the overall image quality and thereby compromising diagnostic value of the images.
To develop an efficient free-breathing and motion-robust mapping method that allows for the investigation of spatial homogeneity of the transmitted radiofrequency field in the myocardium at 3.0T. Three joint approaches are used to adapt the dual refocusing echo acquisition mode (DREAM) sequence for cardiac applications: (1) electrocardiograph triggering; (2) a multi-snapshot undersampling scheme, which relies on the Golden Ratio, to accelerate the acquisition; and (3) motion-compensation based on low-resolution images acquired in each snapshot.
Prospective.
PHANTOM/SUBJECTS: Eurospin II T05 system, torso phantom, and five healthy volunteers.
FIELD STRENGTH/SEQUENCE: 3.0T/DREAM.
The proposed method was compared with the Bloch-Siegert shift (BSS) method and validated against the standard DREAM sequence. Cardiac maps were obtained in free-breathing and breath-hold as a proof of concept of the in vivo performance of the proposed method.
Mean and standard deviation (SD) values were analyzed for six standard regions of interest within the myocardium. Repeatability was assessed in terms of SD and coefficient of variation.
Phantom results indicated low deviation from the BSS method (mean difference = 3%). Equivalent distributions for free-breathing and breath-hold in vivo experiments demonstrated the motion robustness of this method with good repeatability (SD < 0.05). The amount of variations was found to be 26% over the myocardium within a short axis slice.
The feasibility of a cardiac mapping method with high spatial resolution in a reduced scan time per trigger was demonstrated. The free-breathing characteristic could be beneficial to determine shim components for multi-channel systems, currently limited to two for a single breath-hold.
1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:499-507.
磁共振成像中射频场与患者解剖结构之间的相互作用会导致伪影和对比度变化，从而降低整体图像质量，进而影响图像的诊断价值。
开发一种高效的自由呼吸和运动稳健的映射方法，以研究 3.0T 下心肌中发射射频场的空间均匀性。该方法采用三种联合方法来适应双重聚焦回波采集模式（DREAM）序列进行心脏应用：（1）心电图触发；（2）基于黄金比例的多快照欠采样方案，用于加速采集；（3）基于在每个快照中采集的低分辨率图像的运动补偿。
前瞻性。
体模/受试者：Eurospin II T05 系统、体模和五名健康志愿者。
磁场强度/序列：3.0T/DREAM。
将所提出的方法与 Bloch-Siegert 偏移（BSS）方法进行比较，并针对标准 DREAM 序列进行验证。获得了自由呼吸和屏气状态下的心脏图，以证明所提出方法的体内性能。
对心肌内的六个标准感兴趣区域进行了均值和标准差（SD）值分析。以 SD 和变异系数评估重复性。
体模结果表明与 BSS 方法的偏差较小（平均差异为 3%）。自由呼吸和体内实验的屏气实验的等效分布证明了该方法的运动稳健性，具有良好的重复性（SD<0.05）。在短轴切片内，心肌内的变化量约为 26%。
证明了一种具有高空间分辨率的心脏映射方法的可行性，该方法可在每个触发时减少扫描时间。自由呼吸的特点有利于确定多通道系统的补偿组件，目前该系统限制为单屏气一次两个。
1 技术功效：阶段 1 J. Magn. Reson. Imaging 2019;49:499-507.
