Application of the limited-memory quasi-Newton algorithm for multi-dimensional, large flip-angle RF pulses at 7T

Mads S Vinding, Daniel Brenner, Desmond H Y Tse, Sebastian Vellmer, Thomas Vosegaard, Dieter Suter, Tony Stöcker, Ivan I Maximov

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)

Abstract

OBJECTIVE: Ultrahigh field MRI provides great opportunities for medical diagnostics and research. However, ultrahigh field MRI also brings challenges, such as larger magnetic susceptibility induced field changes. Parallel-transmit radio-frequency pulses can ameliorate these complications while performing advanced tasks in routine applications. To address one class of such pulses, we propose an optimal-control algorithm as a tool for designing advanced multi-dimensional, large flip-angle, radio-frequency pulses. We contrast initial conditions, constraints, and field correction abilities against increasing pulse trajectory acceleration factors.

MATERIALS AND METHODS: On an 8-channel 7T system, we demonstrate the quasi-Newton algorithm with pulse designs for reduced field-of-view imaging with an oil phantom and in vivo with scans of the human brain stem. We used echo-planar imaging with 2D spatial-selective pulses. Pulses are computed sufficiently rapid for routine applications.

RESULTS: Our dataset was quantitatively analyzed with the conventional mean-square-error metric and the structural-similarity index from image processing. Analysis of both full and reduced field-of-view scans benefit from utilizing both complementary measures.

CONCLUSION: We obtained excellent outer-volume suppression with our proposed method, thus enabling reduced field-of-view imaging using pulse trajectory acceleration factors up to 4.

Original languageEnglish
Pages (from-to)29-39
Number of pages11
JournalMagnetic Resonance Materials in Physics Biology and Medicine
Volume30
Issue number1
DOIs
Publication statusPublished - Feb 2017

Keywords

  • MRI
  • RF pulse design
  • Parallel transmit
  • Ultrahigh field MRI
  • DESIGN
  • EXCITATION
  • TRANSMISSION
  • TRAJECTORIES
  • MULTISLICE
  • DREAM

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