4.5 Article

Phase-sensitive B1 mapping: Effects of relaxation and RF spoiling

Journal

MAGNETIC RESONANCE IN MEDICINE
Volume 80, Issue 1, Pages 101-111

Publisher

WILEY
DOI: 10.1002/mrm.27009

Keywords

MRI; B-1 mapping; RF spoiling; flip angle mapping; frequency shifts

Funding

  1. NIA NIH HHS [R01 AG054513] Funding Source: Medline
  2. NINDS NIH HHS [R01 NS055963] Funding Source: Medline

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PurposeTo develop a phase-based B-1 mapping technique accounting for the effects of imperfect RF spoiling and magnetization relaxation. Theory and MethodsThe technique is based on a multi-gradient-echo sequence with 2 successive orthogonal radiofrequency (RF) excitation pulses followed by the train of gradient echoes measurements. We have derived a theoretical expression relating the MR signal phase produced by the 2 successive RF pulses to the B-1 field and B-0-related frequency shift. The expression takes into account effects of imperfections of RF spoiling and T-1 and T2* relaxations. ResultsOur computer simulations and experiments revealed that imperfections of RF spoiling cause significant errors in B-1 mapping if not accounted for. By accounting for these effects along with effects of magnetization relaxation and frequency shift, we demonstrated the high accuracy of our approach. The technique has been tested on spherical phantoms and a healthy volunteer. ConclusionIn this paper, we have proposed, implemented, and demonstrated the accuracy of a new phase-based technique for fast and robust B-1 mapping based on the measured MR signal phase, frequency, and relaxation. Because imperfect RF spoiling effects are accounted for, this technique can be applied with short TRs and therefore substantially reduces the scan time. Magn Reson Med 80:101-111, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.

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