Magnetic Resonance in Medicine

Cover image for Vol. 71 Issue 4

Edited By: Matt A. Bernstein

Online ISSN: 1522-2594

Associated Title(s): Journal of Magnetic Resonance Imaging

Virtual Issue: Ultra High Field MRI


Ultra high field MRI, i.e., 7 tesla and beyond, is becoming progressively more available for fundamental and clinical research involving human subjects. With proven increases to the signal to noise ratio, as well as spatial and spectral resolution, ultra high field has shown to provide a significant gain in image quality for many applications. Particularly for the human brain, where several methods for correcting B0 and B1 distortion in vivo have been demonstrated, fundamental research has begun to be translated to clinical research, which shows promising improvements in clinical diagnostics compared to lower field MRI. For instance, more lesions can be detected with 7T MRI in multiple sclerosis and traumatic brain injury compared to 3T, and the vascular system can be imaged with higher spatial resolution and contrast benefitting characterization of tumours, trauma, and stroke. Likewise, magnetic susceptibility-related contrast variation due to iron and myelin orientation and related mechanisms provide intriguing insights into Alzheimer’s and neuro-degenerative diseases. In fundamental work to unravel brain morphology and function [i.e., 5, 16, 17], a new level of research is possible with ultra high field, as the spatial resolution enables layer- specific morphology and the resolution of functional MRI meets the functional columnar architecture of activations [i.e., 3, 9]. Consequently, ultra high field is in full bloom, considering applications in the human brain.

But there is more. The technical challenges related to non-uniformities in B0 [i.e., 4] and B1 have translated to opportunities for boosting spatial and temporal resolution even further, and also exploring relatively new contrast mechanisms in chemical exchange [i.e., 12, 18], MR spectroscopy [i.e. 6, 15] and conductivity and permittivity mapping. Not only does the increased B1 non uniformity lead to better B1 encoding for improved image acceleration (like SENSE), also the non uniformities in transmit can be used for zoomed imaging, particularly when using multiple transmit channels [i.e., 7, 10, 11, 13, 14]. Steering B1 with multiple antennas provides additional degrees of freedom for reducing local RF power deposition, hence increasing imaging efficiency even further [i.e., 8]. Particularly when combined with dynamic steering and monitoring of B0 magnetic field non uniformities, artefact levels can be reduced, opening the way for improved body imaging with ultra high field. While still sprouting, clinical potentials of body imaging at ultra high field have been shown in prostate and breast cancer, liver, cardiovascular and musculoskeletal diseases [i.e., 1,2].

In conclusion, ultra high field has become attractive for fundamental and clinical research in humans. Currently, there are more than 40 sites around the world that have a 7T+ (i.e., 7T or stronger) facility for MRI on human subjects, and they are actively conducting research as demonstrated by the substantial number of Magnetic Resonance in Medicine papers that have been published in the last two years (1-18, keywords: “7T” or “9.4T”, excluding research of non-human subjects).

References

1. Comparing localized and nonlocalized dynamic 31P magnetic resonance spectroscopy in exercising muscle at 7T
Meyerspeer, Martin; Robinson, Simon; Nabuurs, Christine I.; et al.

2. Rapid 3D-imaging of phosphocreatine recovery kinetics in the human lower leg muscles with compressed sensing
Parasoglou, Prodromos; Feng, Li; Xia, Ding; et al.

3. Isotropic submillimeter fMRI in the human brain at 7 T: Combining reduced field-of-view imaging and partially parallel acquisitions
Heidemann, Robin M.; Ivanov, Dimo; Trampel, Robert; et al.

4. Role of very high order and degree B0 shimming for spectroscopic imaging of the human brain at 7 tesla
Pan, Jullie W.; Lo, Kai-Ming; Hetherington, Hoby P.

5. Diffusion-prepared fast imaging with steady-state free precession (DP-FISP): A rapid diffusion MRI technique at 7 T
Lu, Lan; Erokwu, Bernadette; Lee, Gregory; et al.

6. Increase in SNR for 31P MR spectroscopy by combining polarization transfer with a direct detection sequence
van der Kemp, W. J. M.; Boer, V. O.; Luijten, P. R.; et al.

7. Parallel Traveling-Wave MRI: A Feasibility Study
Pang, Yong; Vigneron, Daniel B.; Zhang, Xiaoliang

8. Fast design of local N-gram-specific absorption rate-optimized radiofrequency pulses for parallel transmit systems
Sbrizzi, Alessandro; Hoogduin, Hans; Lagendijk, Jan J.; et al.

9. Temporal SNR characteristics in segmented 3D-EPI at 7T
van der Zwaag, W.; Marques, J. P.; Kober, T.; et al.

10. k(T)-points: Short three-dimensional tailored RF pulses for flip-angle homogenization over an extended volume
Cloos, M. A.; Boulant, N.; Luong, M.; et al.

11. Improved Large Tip Angle Parallel Transmission Pulse Design Through a Perturbation Analysis of the Bloch Equation
Zheng, Hai; Zhao, Tiejun; Qian, Yongxian; et al.

12. Development of Chemical Exchange Saturation Transfer at 7T
Dula, Adrienne N.; Asche, Elizabeth M.; Landman, Bennett A.; et al.

13. Transmit B-1-Field Correction at 7T Using Actively Tuned Coupled Inner Elements
Merkle, Hellmut; Murphy-Boesch, Joseph; van Gelderen, Peter; et al.

14. Traveling-Wave RF Shimming and Parallel MRI
Brunner, David O.; Paska, Jan; Froehlich, Juerg; et al.

15. Semi-LASER Localized Dynamic P-31 Magnetic Resonance Spectroscopy in Exercising Muscle at Ultra-High Magnetic Field
Meyerspeer, Martin; Scheenen, Tom; Schmid, Albrecht Ingo; et al.

16. Nonexponential T2* decay in white matter
Zwart, Jongho Lee, Pascal Sati, Daniel S. Reich and Jeff H. Duyn

17. Human imaging at 9.4 T using T2*-, phase-, and susceptibility-weighted contrast
Juliane Budde, G. Shajan, Jens Hoffmann, Kâmil Uğurbil and Rolf Pohmann

18. CEST-FISP: A Novel Technique for Rapid Chemical Exchange Saturation Transfer MRI at 7 T
Shah, T.; Lu, L.; Dell, K. M.; et al.

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