Challenges and Opportunities of Ultra-High Field MRI
Magnetic resonance imaging (MRI) and spectroscopy (MRS) have contributed considerably to our understanding of the structure and function of the human brain, and are essential in modern radiological practice. The development and applications of MRI systems at fields of 7 Tesla and above provide many new opportunities and technical challenges. The increased signal strength at higher fields may be used to obtain higher resolution images, faster images and/or images with greater contrast to noise. These can be used to improve detection of lesions, for more accurate assessment of the structural anatomy of the brain (including higher resolution tractography of white matter), and improved sensitivity in functional MRI. However, high field MR imaging is also affected by macroscopic field variations caused by inhomogeneities of magnetic susceptibility within the body, and these can degrade spectra and introduce image distortions. Moreover, the performance of radiofrequency (RF) coils is also affected at higher fields, and it is more difficult to create uniform RF fields within large objects. These challenges are being met using various technical innovations such as dynamic shimming, the use of parallel arrays of coils, novel spectral-spatial excitation methods, novel pulse sequences and post-acquisition digital processing. In combination these efforts promise to allow ultra-high field imaging and spectroscopy to contribute significantly to our understanding of brain structure and function in various conditions.
KeywordsMRI MRS ultra-high field neuroimaging
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