Rapid fat suppression for three-dimensional echo planar imaging with minimized specific absorption rate

Authors

  • Rüdiger Stirnberg,

    Corresponding author
    1. Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH, Jülich, Germany
    2. German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany
    • Correspondence to: Rüdiger Stirnberg, Ph.D., Deutsches Zentrum für Neurodegenerative Erkrankungen e.V. (DZNE), Ernst-Robert-Curtius-Straße 12, 53117 Bonn, Germany. E-mail: ruediger.stirnberg@dzne.de

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  • Daniel Brenner,

    1. Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH, Jülich, Germany
    2. German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany
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  • Tony Stöcker,

    1. German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany
    2. Department of Physics and Astronomy, University of Bonn, Bonn, Germany
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  • N. Jon Shah

    1. Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH, Jülich, Germany
    2. Department of Neurology, Faculty of Medicine, RWTH Aachen University, JARA, Aachen, Germany
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Abstract

Purpose

To investigate a method for rapid water excitation with minimal radiofrequency power deposition for efficient functional MRI at ultrahigh fields.

Theory and Methods

The suitability of the spectral response of a single rectangular radiofrequency pulse (rect) as a replacement of conventional fat saturation in segmented three-dimensional (3D) echo planar imaging (EPI) is explored. A pulse duration formula for lipid signal nulling independent of the small-tip-angle approximation is derived and tested by means of simulations and experiments at 3 and 7 Tesla (T).

Results

Compared with conventional binomial-11 water excitation, the single rect method is more selective and less sensitive to shim imperfections. In functional MRI, a significant measurement speedup (25%) and specific absorption rate reduction (from 44% to 1% at 7T) compared with conventional fat saturation are achieved. Furthermore, magnetization transfer effects are reduced resulting in up to 25% higher brain tissue signal-to-noise ratio.

Conclusion

The proposed method is well suited for whole-brain functional MRI, not only at ultra-high fields, as it maximizes the sensitivity per unit time and at the same time minimizes radiofrequency power deposition. It requires little implementation effort and may thus be used in other spatially nonselective imaging methods that require fat suppression at minimal specific absorption rate and time requirements. Magn Reson Med 76:1517–1523, 2016. © 2015 International Society for Magnetic Resonance in Medicine

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