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3D T 2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems

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Abstract

Objectives

For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B +1 inhomogeneity. Previously, it was shown that a single kT-point pulse designed in the small tip-angle regime can replace all the pulses of the sequence (static kT-points). This work demonstrates that the B +1 dependence of T 2-weighted imaging can be further mitigated by designing a specific kT-point pulse for each pulse of a 3D TSE sequence (dynamic kT-points) even on single-channel transmit systems

Materials and methods

By combining the spatially resolved extended phase graph formalism (which calculates the echo signals throughout the sequence) with a gradient descent algorithm, dynamic kT-points were optimized such that the difference between the simulated signal and a target was minimized at each echo. Dynamic kT-points were inserted into the TSE sequence to acquire in vivo images at 7T.

Results

The improvement provided by the dynamic kT-points over the static kT-point design and conventional hard pulses was demonstrated via simulations. Images acquired with dynamic kT-points showed systematic improvement of signal and contrast at 7T over regular TSE—especially in cerebellar and temporal lobe regions without the need of parallel transmission.

Conclusion

Designing dynamic kT-points for a 3D TSE sequence allows the acquisition of T 2-weighted brain images on a single-transmit system at ultra-high field with reduced dropout and only mild residual effects due to the B +1 inhomogeneity.

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Acknowledgments

This work was supported by the Centre d’Imagerie BioMédicale (CIBM) of the University of Lausanne (UNIL), the Swiss Federal Institute of Technology Lausanne (EPFL), the University of Geneva (UniGe), the Centre Hospitalier Universitaire Vaudois (CHUV), the Hôpitaux Universitaires de Genève (HUG), and the Leenaards and Jeantet Foundations. The author would like to thank Wietske van der Zwaag for her help in the management of all the coregistered images present throughout the manuscript.

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Authors and Affiliations

  1. Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Station 6, 1015, Lausanne, Switzerland

    Florent Eggenschwiler, Daniel Gallichan & Rolf Gruetter

  2. Centre for Advanced Imaging, University of Queensland, Brisbane, Australia

    Kieran Robert O’Brien

  3. Siemens Healthcare Pty Ltd, Brisbane, QLD, Australia

    Kieran Robert O’Brien

  4. Department of Radiology, Universities of Lausanne and Geneva, Vaud, Switzerland

    Rolf Gruetter

  5. Donders Center for Cognitive Neuroimaging, Radboud University, Nijmegen, The Netherlands

    José Pedro Marques

Authors
  1. Florent Eggenschwiler
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  2. Kieran Robert O’Brien
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  3. Daniel Gallichan
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  4. Rolf Gruetter
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  5. José Pedro Marques
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Correspondence to Florent Eggenschwiler.

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The authors declare that they have no conflict of interest.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Informed consent was obtained from all individual participants included in the study.

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Eggenschwiler, F., O’Brien, K.R., Gallichan, D. et al. 3D T 2-weighted imaging at 7T using dynamic kT-points on single-transmit MRI systems. Magn Reson Mater Phy 29, 347–358 (2016). https://doi.org/10.1007/s10334-016-0545-4

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  • DOI: https://doi.org/10.1007/s10334-016-0545-4

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