New phase-based B1 mapping method using two-dimensional spin-echo imaging with hyperbolic secant pulses

Yoojin Lee, Yeji Han, Hyunwook Park, Hidehiro Watanabe, Michael Garwood, Jang Yeon Park

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Purpose: To propose a new phase-based B1-mapping method that exploits phase information created by hyperbolic secant (HS) pulses in conventional 2D spin-echo imaging.

Methods: In this B1-mapping method, HS pulses are used to accomplish π/2 excitation and π refocusing in standard multislice spin-echo imaging. When setting the ratio of pulse lengths of the π/2 and π HS pulses to 2:1, the spin-echo phase is independent of offset frequency and varies as a function of B1 strength. To eliminate undesired phase accumulations induced by unknown factors other than the B1 strength, two spin-echo images are acquired using HS pulses applied with opposite frequency-sweep directions, and the resulting phase images are subtracted from each other. To demonstrate the performance of the proposed method, phantom and in vivo experiments were performed using a surface coil and a volume coil.

Results: The B1 maps obtained by using the proposed method were in accordance with the B1 maps obtained using previous methods in both phantom and in vivo experiments.

Conclusion: The proposed method is easy to implement without any sequence modification, is insensitive to B0 inhomogeneity and chemical shift, and is robust in a reasonably wide range of B1 field strength.

Original languageEnglish (US)
Pages (from-to)170-181
Number of pages12
JournalMagnetic resonance in medicine
Volume73
Issue number1
DOIs
StatePublished - Jan 1 2015

Keywords

  • B mapping
  • Flip-Angle mapping
  • Frequencymodulation pulse
  • Hyperbolic secant pulse
  • RF field mapping
  • Spin-echo imaging

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