Motion-robust cardiac B1+ mapping at 3T using interleaved bloch-siegert shifts.
To develop and evaluate a robust motion-insensitive Bloch-Siegert shift based B1+ mapping method in the heart.



Cardiac Bloch-Siegert B1+ mapping was performed with interleaved positive and negative off-resonance shifts and diastolic spoiled gradient echo imaging in 12 heartbeats. Numerical simulations were performed to study the impact of respiratory motion. The method was compared with three-dimensional (3D) actual flip angle imaging (AFI) and two-dimensional (2D) saturated double angle method (SDAM) in phantom scans. Cardiac B1+ maps of three different views were acquired in six healthy volunteers using Bloch-Siegert and SDAM during breath-hold and free breathing. In vivo maps were evaluated for inter-view consistency using the correlation coefficients of the B1+ profiles along the lines of intersection between the views.



For the Bloch-Siegert sequence, numerical simulations indicated high similarity between breath-hold and free breathing scans, and phantom results indicated low deviation from the 3D AFI reference (normalized root mean square error [NRMSE] = 2.0%). Increased deviation was observed with 2D SDAM (NRMSE = 5.0%) due to underestimation caused by imperfect excitation slice profiles. Breath-hold and free breathing Bloch-Siegert in vivo B1+ maps were visually comparable with no significant difference in the inter-view consistency (P > 0.36). SDAM showed strongly impaired B1+ map quality during free breathing. Inter-view consistency was significantly lower than with the Bloch-Siegert method (breath-hold: P = 0.014, free breathing: P < 0.0001).



The proposed interleaved Bloch-Siegert sequence enables cardiac B1+ mapping with improved inter-view consistency and high resilience to respiratory motion. Magn Reson Med 78:670-677, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, USA.|Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.|Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
Sebastian
S
Weingärtner
Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University, Mannheim, Germany.
Fabian
F
Zimmer
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Gregory J
GJ
Metzger
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Kâmil
K
Uğurbil
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Pierre-Francois
PF
Van de Moortele
Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, USA.|Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Mehmet
M
Akçakaya
D000293:Adolescent; D000328:Adult; D057791:Cardiac Imaging Techniques / Q000379:methods*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D055815:Young Adult

B1+ mapping; Bloch-Siegert shift; motion robustness; abdominal imaging; cardiac imaging