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Spatial excitation using variable-density spiral trajectories.

Christoph Schröder1, Peter Börnert, Bernd Aldefeld

  • 1Philips Research Laboratories, Sector Technical Systems, Hamburg, Germany. christoph.schroeder@philips.com

Journal of Magnetic Resonance Imaging : JMRI
|June 20, 2003
PubMed
Summary

Variable-density k-space trajectories significantly reduce unwanted signal excitation outside the field of excitation (FOX) for multi-dimensional spatially selective radiofrequency (RF) pulses. This method maintains short pulse durations, enhancing spatial precision in MRI applications.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Radiofrequency (RF) Pulse Design
  • Spatial Selectivity

Background:

  • Designing multi-dimensional spatially selective RF pulses is crucial for precise MRI.
  • Minimizing signal excitation outside the nominal field of excitation (FOX) is a persistent challenge.
  • Traditional uniform k-space trajectories can lead to unwanted signal leakage.

Purpose of the Study:

  • To evaluate the efficacy of variable-density k-space trajectories for creating multi-dimensional spatially selective RF pulses.
  • To assess the impact of variable-density trajectories on signal excitation outside the FOX.
  • To determine if this approach can improve spatial selectivity without increasing RF pulse duration.

Main Methods:

  • Simulations, phantom studies, and in vivo experiments were conducted.

Related Experiment Videos

  • Two-dimensional spatially selective magnetization patterns were generated using variable-density spiral k-space trajectories.
  • Signal excitation outside the defined FOX was quantified and compared to uniform density trajectories.

    • Main Results:

    • Variable-density trajectories drastically reduced signal excitation outside the FOX compared to uniform density trajectories.
    • Short RF pulse durations were maintained.
    • The method demonstrated improved spatial selectivity.

    Conclusions:

    • Variable-density k-space trajectories offer a significant advantage by reducing unwanted signal excitation outside the FOX.
    • This reduction is achieved without substantially increasing RF excitation pulse duration.
    • The variable-density approach is beneficial for applications requiring well-defined spatial excitation profiles, including reduced field of view (FOV) imaging, spatial saturation, curved slice imaging, and MR spectroscopy.