Akisik Fatih M, Sandrasegaran Kumaresan, Aisen Alex M, Lin Chen, Lall Chandana
Department of Radiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Radiographics. 2007 Sep-Oct;27(5):1433-44; discussion 1462-4. doi: 10.1148/rg.275075023.
Magnetic resonance (MR) imaging at 3.0 T offers an improved signal-to-noise ratio compared with that at 1.5 T. However, the physics of high field strength also brings disadvantages, such as increases in the specific absorption rate, in magnetic field inhomogeneity effects, and in susceptibility artifacts. The use of 3.0-T MR imaging for abdominal evaluations, in particular, has lagged behind that for other applications because of the difficulty of imaging a large volume while compensating for respiratory motion. At a minimum, abdominal MR imaging at 3.0 T requires modifications in the pulse sequences used at 1.5 T. Such modifications may include a decrease in the flip angle used for refocusing pulses and an increase in the repetition time for T1-weighted acquisitions. In addition, parallel imaging and other techniques (hyper-echo sequences, transition between pseudo steady states) may be used to maintain a high signal-to-noise ratio while decreasing acquisition time and minimizing the occurrence of artifacts on abdominal MR images.
与1.5T磁共振成像相比，3.0T磁共振成像具有更高的信噪比。然而，高场强的物理特性也带来了一些缺点，比如比吸收率增加、磁场不均匀性效应增加以及磁化率伪影增加。特别是，由于在补偿呼吸运动的同时对大体积进行成像存在困难，3.0T磁共振成像在腹部评估方面的应用落后于其他应用。至少，3.0T腹部磁共振成像需要对1.5T时使用的脉冲序列进行修改。这些修改可能包括用于重聚焦脉冲的翻转角减小以及T1加权采集的重复时间增加。此外，并行成像和其他技术（超回波序列、伪稳态之间的转换）可用于在减少采集时间并使腹部磁共振图像上的伪影出现频率最小化的同时保持高信噪比。
