Rapid B1 field mapping at 3 T using the 180° signal null method with extended flip angle

Abinand C Rejimon; Diana Y Lee; Christopher M Bergeron; You Zhuo; Wenshu Qian; Richard G Spencer; Mustapha Bouhrara

doi:10.1016/j.mri.2018.06.010

Rapid B₁ field mapping at 3 T using the 180° signal null method with extended flip angle

Magn Reson Imaging. 2018 Nov:53:173-179. doi: 10.1016/j.mri.2018.06.010. Epub 2018 Jun 26.

Authors

Abinand C Rejimon¹, Diana Y Lee², Christopher M Bergeron³, You Zhuo⁴, Wenshu Qian⁵, Richard G Spencer⁶, Mustapha Bouhrara⁷

Affiliations

¹ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: abinand.rejimon@nih.gov.
² Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: diana.lee5@nih.gov.
³ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: christopher.bergeron@nih.gov.
⁴ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: joy.zhou@nih.gov.
⁵ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: qian.wenshu@nih.gov.
⁶ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: spencerri@mail.nih.gov.
⁷ Laboratory of Clinical Investigation, National Institute on Aging, NIH, 251 Bayview Boulevard, Baltimore, MD 21224, USA. Electronic address: bouhraram@mail.nih.gov.

Abstract

Purpose: To extend the null signal method (NSM) for B₁ mapping to 3 T magnetic resonance imaging (MRI).

Background: The NSM operates in the steady state regime and exploits the linearity of the spoiled gradient recalled echo (SPGR) signal around the 180° flip angle (FA). Using linear regression, B₁ maps are derived from three SPGR images acquired at different FAs with a short repetition time. While the conventional NSM allows accurate mapping of B₁ for moderate B₁ variation, we observed that this method fails for the larger B₁ variations typical of high-field MRI.

Methods: We analyzed the effect of the FA range of the acquired SPGR images on B₁ determination using the NSM for 3 T MRI through extensive numerical and in vivo analyses. B₁ maps derived from the extended angle-range NSM (EA-NSM) were calculated and compared to those derived from the conventional, more restricted angle range, NSM, and to those derived from the reference, but much more time-consuming, double angle method (DAM). Furthermore, we investigated the compatibility of EA-NSM B₁ mapping and the half-scan and SENSE reconstruction methods for accelerating acquisition time.

Results: Our results show that the use of the conventional FA range leads to substantial inaccuracies in B₁ determination. Both numerical and in vivo analyses demonstrate that expanding the FA range of the acquired SPGR images substantially improves the accuracy of B₁ maps. Furthermore, B₁ maps derived from EA-NSM were demonstrated to be quantitatively comparable to those derived from the lengthy DAM protocol. We also found that B₁ maps derived from SPGR images using the EA-NSM and imaging acceleration methods were comparable to those derived from images acquired without acceleration. Finally, the use of half scanning combined with SENSE reconstruction permits whole-brain B₁ mapping in ~1 min.

Conclusions: The EA-NSM permits accurate, fast, and practical B₁ mapping in a 3 T clinical setting.

Keywords: B(1) mapping; Null signal method; Spoiled gradient recalled echo.

Published by Elsevier Inc.

Publication types

Research Support, N.I.H., Intramural

MeSH terms

Adult
Aged
Algorithms
Brain / diagnostic imaging*
Computer Simulation
Female
Humans
Image Enhancement
Image Processing, Computer-Assisted / methods*
Linear Models
Magnetic Resonance Imaging / methods*
Male
Middle Aged
Phantoms, Imaging

Grants and funding

Z99 AG999999/Intramural NIH HHS/United States