Ladd M E, Bock M
Erwin L. Hahn Institute for Magnetic Resonance Imaging, Institut für Diagnostische und Interventionelle Radiologie und Neuroradiologie, Universität Duisburg-Essen, Universitätsklinikum Essen, Arendahls Wiese 199, 45141, Essen, Deutschland.
Radiologe. 2013 May;53(5):401-10. doi: 10.1007/s00117-012-2344-x.
CLINICAL/METHODICAL ISSUE: The spatial, temporal and spectral resolution in magnetic resonance imaging (MRI) is in many cases currently not sufficient to detect submillimeter lesions or to image the dynamics of the beating heart.
At present MRI systems at 1.5 T and 3 T are the standard units for clinical imaging.
The use of ultrahigh magnetic fields of 7 T and higher increases the signal-to-noise ratio, which holds promise for a significant improvement of the spatial and/or temporal resolution as well as for new contrast mechanisms.
With 7 T MRI, images of the brain have been acquired routinely with a spatial resolution of 0.3 mm. The theoretical improvement of the signal-to-noise ratio is often not fully realized due to B1 inhomogeneities and contrast variations.
With MRI at 7 T a notable increase in spatial resolution can be achieved. Methods such as time-of-flight MR angiography and susceptibility-weighted imaging (e.g. neurofunctional MRI, fMRI) profit especially from the higher field strengths. Transmission field inhomogeneities are still a major challenge for ultrahigh field (UHF) MRI and are also a partially unsolved safety problem.
The use of UHF MRI is currently limited to special applications and the expected gain of the high field must be weighed against technical limitations in both image acquisition and interpretation.
临床/方法学问题：在许多情况下，磁共振成像（MRI）的空间、时间和频谱分辨率目前不足以检测亚毫米级病变或对跳动心脏的动态进行成像。
目前，1.5T和3T的MRI系统是临床成像的标准设备。
使用7T及更高的超高磁场可提高信噪比，有望显著提高空间和/或时间分辨率以及产生新的对比机制。
使用7T MRI，已常规获取空间分辨率为0.3mm的脑部图像。由于B1不均匀性和对比度变化，信噪比的理论提升往往无法完全实现。
使用7T MRI可显著提高空间分辨率。诸如飞行时间磁共振血管造影和磁化率加权成像（如神经功能MRI，fMRI）等方法尤其受益于更高的场强。传输场不均匀性仍然是超高场（UHF）MRI的主要挑战，也是一个部分未解决的安全问题。
目前，UHF MRI的使用仅限于特殊应用，必须在图像采集和解读中的技术限制与高场预期收益之间进行权衡。
