• J Magn Reson Imaging · Dec 2017

    B1 mapping for bias-correction in quantitative T1 imaging of the brain at 3T using standard pulse sequences.

    • Mathieu Boudreau, Christine L Tardif, Nikola Stikov, John G Sled, Wayne Lee, and G Bruce Pike.
    • Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada.
    • J Magn Reson Imaging. 2017 Dec 1; 46 (6): 1673-1682.

    PurposeB1 mapping is important for many quantitative imaging protocols, particularly those that include whole-brain T1 mapping using the variable flip angle (VFA) technique. However, B1 mapping sequences are not typically available on many magnetic resonance imaging (MRI) scanners. The aim of this work was to demonstrate that B1 mapping implemented using standard scanner product pulse sequences can produce B1 (and VFA T1 ) maps comparable in quality and acquisition time to advanced techniques.Materials And MethodsSix healthy subjects were scanned at 3.0T. An interleaved multislice spin-echo echo planar imaging double-angle (EPI-DA) B1 mapping protocol, using a standard product pulse sequence, was compared to two alternative methods (actual flip angle imaging, AFI, and Bloch-Siegert shift, BS). Single-slice spin-echo DA B1 maps were used as a reference for comparison (Ref. DA). VFA flip angles were scaled using each B1 map prior to fitting T1 ; the nominal flip angle case was also compared.ResultsThe pooled-subject voxelwise correlation (ρ) for B1 maps (BS/AFI/EPI-DA) relative to the reference B1 scan (Ref. DA) were ρ = 0.92/0.95/0.98. VFA T1 correlations using these maps were ρ = 0.86/0.88/0.96, much better than without B1 correction (ρ = 0.53). The relative error for each B1 map (BS/AFI/EPI-DA/Nominal) had 95th percentiles of 5/4/3/13%.ConclusionOur findings show that B1 mapping implemented using product pulse sequences can provide excellent quality B1 (and VFA T1 ) maps, comparable to other custom techniques. This fast whole-brain measurement (∼2 min) can serve as an excellent alternative for researchers without access to advanced B1 pulse sequences.Level Of Evidence1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1673-1682.© 2017 International Society for Magnetic Resonance in Medicine.

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