Premium
Motion‐robust cardiac B 1 + mapping at 3T using interleaved bloch‐siegert shifts
Author(s) -
Weingärtner Sebastian,
Zimmer Fabian,
Metzger Gregory J.,
Uğurbil Kâmil,
Van de Moortele PierreFrancois,
Akçakaya Mehmet
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26395
Subject(s) - flip angle , imaging phantom , bloch equations , breathing , mathematics , consistency (knowledge bases) , physics , nuclear magnetic resonance , standard deviation , magnetic resonance imaging , biomedical engineering , medicine , anatomy , optics , statistics , geometry , radiology
Purpose To develop and evaluate a robust motion‐insensitive Bloch‐Siegert shift basedB 1 +mapping method in the heart. Methods Cardiac Bloch‐SiegertB 1 +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. CardiacB 1 +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 theB 1 +profiles along the lines of intersection between the views. Results 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 vivoB 1 +maps were visually comparable with no significant difference in the inter‐view consistency ( P > 0.36). SDAM showed strongly impairedB 1 +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). Conclusion The proposed interleaved Bloch‐Siegert sequence enables cardiacB 1 +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