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Optimizing spherical navigator echoes for three-dimensional rigid-body motion detection.

Daniel W Petrie1, Andreu F Costa, Atsushi Takahashi

  • 1Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada.

Magnetic Resonance in Medicine
|April 22, 2005
PubMed
Summary
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Spherical navigator (SNAV) echoes effectively correct 3D motion. Optimal parameters for SNAV, including a variable-density trajectory, enhance accuracy for motion correction in MRI.

Area of Science:

  • Medical Imaging
  • Magnetic Resonance Imaging (MRI)
  • Biomedical Engineering

Background:

  • Three-dimensional rigid-body motion poses a significant challenge in MRI.
  • Spherical navigator (SNAV) echoes offer a promising solution for motion correction.

Purpose of the Study:

  • To investigate key design and performance parameters of the SNAV technique.
  • To introduce and evaluate a novel variable-sampling density (VSD) helical-spiral SNAV trajectory.

Main Methods:

  • Developed a VSD helical-spiral SNAV trajectory for comprehensive spherical shell data acquisition within scanner slew rate limits.
  • Verified VSD SNAV trajectory execution using a self-encoding technique for gradient waveform validation.
  • Conducted in vitro experiments to assess SNAV's ability to measure rotational and translational motion at varying k-space radii and sampling densities.

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Main Results:

  • The VSD SNAV trajectory successfully acquired data across the entire spherical shell.
  • Optimal accuracy for motion measurement was achieved with k-space radii of 1.4 and 1.6 cm⁻¹.
  • Acquiring 2400 to 4000 samples over the sphere yielded the best results.

Conclusions:

  • The VSD SNAV technique provides accurate measurement of rotational and translational motion.
  • Specific k-space radii and sampling densities are crucial for maximizing SNAV accuracy.
  • This optimized SNAV approach enhances motion correction capabilities in MRI.