Adiabatic RF pulse design for Bloch-Siegert B1+ mapping

Magn Reson Med. 2013 Sep;70(3):829-35. doi: 10.1002/mrm.24507. Epub 2012 Oct 5.

Abstract

The Bloch-Siegert (B-S) B1+ mapping method has been shown to be fast and accurate, yet it suffers from high Specific Absorption Rate (SAR) and moderately long echo time. An adiabatic RF pulse design is introduced here for optimizing the off-resonant B-S RF pulse to achieve more B-S B1+ measurement sensitivity for a given pulse width. The extra sensitivity can be used for higher angle-to-noise ratio B1+ maps or traded off for faster scans. Using numerical simulations and phantom experiments, it is shown that a numerically optimized 2-ms adiabatic B-S pulse is 2.5 times more efficient than a conventional 6-ms Fermi-shaped B-S pulse. The adiabatic B-S pulse performance is validated in a phantom, and in vivo brain B1+ mapping at 3T and 7T are shown.

Keywords: Bloch‐Siegert shift; adiabatic RF pulse design; flip angle; off resonance; parallel transmit.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Brain / anatomy & histology
  • Humans
  • Image Enhancement / methods
  • Image Interpretation, Computer-Assisted / methods
  • Magnetic Resonance Imaging / methods*
  • Phantoms, Imaging