This review illustrates current applications and possible future directions of 7 Tesla (7 T) Magnetic Resonance Imaging (MRI) in the field of brain MRI, in clinical studies as well as clinical practice. With its higher signal-to-noise (SNR) and contrast-to-noise ratio (CNR) compared to lower field strengths, high resolution, contrast-rich images can be obtained of diverse pathologies, like multiple sclerosis (MS), brain tumours, aging-related changes and cerebrovascular diseases. In some of these diseases, additional pathophysiological information can be gained compared to lower field strengths. Because of clear depiction of small anatomical details, and higher lesion conspicuousness, earlier diagnosis and start of treatment of brain diseases may become possible. Furthermore, additional insight into the pathogenesis of brain diseases obtained with 7 T MRI could be the basis for new treatment developments. However, imaging at high field comes with several limitations, like inhomogeneous transmit fields, a higher specific absorption rate (SAR) and, currently, extensive contraindications for patient scanning. Future studies will be aimed at assessing the advantages and disadvantages of 7 T MRI over lower field strengths in light of clinical applications, specifically the additional diagnostic and prognostic value of 7 T MRI.

The aim of the present study is to develop a submillimeter volumetric (three-dimensional) fluid-attenuated inversion recovery sequence at 7T. Implementation of the fluid-attenuated inversion recovery sequence is difficult as increased T 1 weighting from prolonged T 1 constants at 7T dominate the desired T 2 contrast and yield suboptimal signal-to-noise ratio. Magnetization preparation was used to reduce T 1 weighting and improve the T 2 weighting. Also, practical challenges limit the implementation. Long refocusing trains with low flip angles were used to mitigate the specific absorption rate constraints. This resulted in a three-dimensional magnetization preparation fluid-attenuated inversion recovery sequence with 0.8 3 0.8 3 0.8 5 0.5 mm 3 resolution in a clinically acceptable scan time. The contrast-to-noise ratio between gray matter and white matter (contrast-to-noise ratio 5 signal-to-noise ratio [gray matter] 2 signal-to-noise ratio [white matter]) increased from 12 6 9 without magnetization preparation to 28 6 8 with magnetization preparation (n 5 12). The signal-tonoise ratio increased for white matter by 13 6 6% and for gray matter by 48 6 15%. In conclusion, three-dimensional fluid-attenuated inversion recovery with high resolution and full brain coverage is feasible at 7T. Magnetization preparation reduces the T 1 weighting, thereby improving the T 2 weighted contrast and signal-to-noise ratio. Magn Reson Med 64:194-202, 2010. V C 2010 Wiley-Liss, Inc.Key words: magnetic resonance imaging; high field strength; 3D-FLAIR; high resolution; magnetization preparation Since its introduction in 1992, the fluid-attenuated inversion recovery (FLAIR) sequence (1) has become the key sequence for imaging pathologies in the central nervous system, including vascular diseases, multiple sclerosis, tumors, and degenerative diseases (2-4). The current drive toward detection of subcortical and intracortical lesions in multiple sclerosis and epilepsy requires images with submillimeter resolution in three dimensions, with high signal-to-noise ratio (SNR) and good contrast (5). The intrinsic high SNR and good parallel imaging (SENsitivity Encoding (SENSE)) properties of high-field (7T) MRI have the potential to fulfill these requirements (6).Whereas implementation of T* 2 -weighted gradient echo MRI at high field is relatively straightforward, obtaining high-resolution volumetric (three-dimensional [3D]) FLAIR images with good image quality, clinically acceptable scan time (for use in patients), and full brain coverage is difficult for several reasons. A fundamental problem is the lengthening of T 1 constants of gray and white matter (GM and WM) while the T 1 of cerebrospinal fluid (CSF) is relatively field independent (7). This has two detrimental effects. First, the desired T 2 contrast is compromised, as the prolonged T 1 times significantly increase T 1 weighting in FLAIR images. Second, the gain in SNR is suboptimal, as part of the gain in magnetization obtained by the increased field strength is lost by the reduced...

Background and Purpose-Conventional imaging methods cannot depict the vessel wall of intracranial arteries at sufficient resolutions. This hampers the evaluation of intracranial arterial disease. The aim of the present study was to develop a high-resolution MRI method to image intracranial vessel wall. Methods-We developed a volumetric (3-dimensional) turbo spin-echo (TSE) sequence for intracranial vessel wall imaging at 7.0-T MRI. Inversion recovery was used to null cerebrospinal fluid to increase contrast with the vessel wall.Magnetization preparation was applied before inversion to improve signal-to-noise ratio. Seven healthy volunteers and 35 patients with ischemic stroke or transient ischemic attack underwent imaging to test the magnetization preparation inversion recovery TSE sequence. Gadolinium-based contrast agent (Gadobutrol, 0.1 mL/kg) was administered to assess possible lesion enhancement in the patients. Results-The walls of intracranial arterial vessels could be visualized in all volunteers and patients with good contrast between wall, blood, and cerebrospinal fluid. The quality of the vessel wall depiction was independent of the vessel orientation relative to the plane of acquisition. In 21 of the 35 patients, a total number of 52 intracranial vessel wall lesions were identified. Eleven of the 52 lesions showed enhancement after contrast administration. Only 14 of the 52 lesions resulted in stenosis of the arterial lumen. Conclusions-Intracranial vessel wall and its pathology can be depicted with the magnetization preparation inversion recovery TSE sequence at 7.0 T. The magnetization preparation inversion recovery TSE sequence will make it possible to study the role of intracranial arterial wall pathology in ischemic stroke.

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Dedicated 7T breast MRI is technically feasible, can provide more SNR than at 3T, and has diagnostic potential.

The 7T MRI reveals increased numbers of VRS in MS. The finding that VRS are associated with supratentorial brain atrophy, but not with lesion count, suggests that VRS might rather serve as a neurodegenerative than an inflammatory marker in MS.

PurposeTo assess fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) at three field strengths, regarding signal-to-noise ratio (SNR), contrast and signal homogeneity, in order to determine the potential gain and current challenges of FLAIR at ultra-high field strength (7 T).MethodsFLAIR images of five healthy volunteers (age 24 ± 4 years, 4 male) were acquired at 1.5 T, 3 T and 7 T. Image homogeneity and visibility of normal brain structures were evaluated. SNR of grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF) were measured in regions not affected by transmit field heterogeneity.ResultsThe SNR (mean ± SD) at 7 T (GM 168 ± 15, WM 125 ± 11) increased slightly more than proportionally, compared with at 1.5 T (GM 30 ± 3, WM 22 ± 2) and 3 T (GM 62 ± 7, WM 44 ± 4). Relative contrast between GM and WM at 7 T (1.35 ± 0.07) was slightly less than at 3 T (1.42 ± 0.14) or 1.5 T (1.37 ± 0.07). Several major fibre bundles became visible at 7 T. One incidentally observed white matter lesion was well visible at all field strengths.ConclusionImage homogeneity remains challenging and should be improved by future technical developments. FLAIR imaging at 7 T yields a high SNR,with better contrast for WM substructures and the iron-bearing basal ganglia, and has potential for good conspicuity of WM lesions.

- Intracranial vessel wall imaging using MRI improves diagnosis of cerebrovascular diseases. - Conventional 7-T MRI sequences cannot image the whole cerebral arterial tree. - New whole-brain 7-T MRI sequences compare favourably with smaller-coverage sequences. - These whole-brain sequences can demonstrate the entire cerebral arterial tree. - These sequences should help in the diagnosis of vessel wall abnormalities.