title: The challenge of bias-free coil combination for quantitative susceptibility mapping at ultra-high field.
abstract: OBJECTIVE
  Quantitative susceptibility mapping is a technique to estimate the magnetic property of tissue with particularly high sensitivity at ultra-high field. However, a key challenge at ultra-high field is the combination of phase data acquired using phased array receive coils. Several methods for combining phase data have been proposed, but the influence of coil combination choices on susceptibility quantitation has not been studied systematically.
  
  
  METHODS
  We combined phase data using COMPOSER (COMbining Phase data using a Short Echo-time Reference scan) and a reference-free channel-by-channel method. We investigated the effect of the chosen combination method on susceptibility results in a group of 28 participants at 7 Tesla.
  
  
  RESULTS
  Our results show that reference scans can bias susceptibility values. Although the proposed reference-free channel-by-channel method cannot remove transmit field phase, it shows comparable results to the COMPOSER method in which a high-resolution ultrashort echo-time reference scan was used.
  
  
  CONCLUSIONS
  We conclude that ultrashort echo-time reference scans reduce quantitation bias and remove the transmit field phase when using COMPOSER to combine phase data, and not combining the phase data before susceptibility processing avoids this bias, resulting in comparable results. Magn Reson Med 79:97-107, 2018. © 2017 InternationalSociety for Magnetic Resonance in Medicine.
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Steffen
authors.initials: S
authors.lastname: Bollmann
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Simon Daniel
authors.initials: SD
authors.lastname: Robinson
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.|Siemens Healthcare Pty Ltd, Brisbane, Queensland, Australia.
authors.forename: Kieran
authors.initials: K
authors.lastname: O'Brien
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Viktor
authors.initials: V
authors.lastname: Vegh
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Andrew
authors.initials: A
authors.lastname: Janke
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Lars
authors.initials: L
authors.lastname: Marstaller
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Reutens
authors.affiliation: Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Markus
authors.initials: M
authors.lastname: Barth
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging*; D001931:Brain Mapping / Q000379:methods; D017352:Echo-Planar Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008280:Magnetics; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: 3D EPI; COMPOSER; PETRA; QSM; atlas-based segmentation; ultra-high field