title: T2* Measurement bias due to concomitant gradient fields.
abstract: To demonstrate that concomitant magnetic fields can cause significant spatially dependent biases in T2* relaxometry measurements with implications for clinical applications such as BOLD and dynamic susceptibility contrast-enhanced MRI.
  
  
  
  After developing a theoretical framework for intravoxel dephasing and signal loss from concomitant magnetic fields, this framework and the effect of concomitant fields on T2* are validated with phantom experiments and numerical simulation. In lower leg and renal T2* mapping, we quantify measurement bias for imaging protocols with high gradient amplitude multiecho readouts, comparable to those used in clinical applications.
  
  
  
  Concordance between phantom experiment and numerical simulation validate the theoretical framework. Changes in T2* measured in the lower leg and kidney varied by up to 15% and 35%, respectively, as a result of concomitant gradient effects when compared with the control measurements.
  
  
  
  Concomitant magnetic fields produced by imaging gradient coils can cause clinically significant T2* mapping errors when high amplitude, long duration gradient waveforms are used. While we have shown that measurement biases can be quite large, modification of imaging parameters can potentially reduce concomitant field-induced measurement errors to acceptable levels. Magn Reson Med 77:1562-1572, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Lorne W
authors.identifier: 0000-0003-0041-6711
authors.initials: LW
authors.lastname: Hofstetter
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Glen
authors.initials: G
authors.lastname: Morrell
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.|Department of Radiology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Joshua
authors.initials: J
authors.lastname: Kaggie
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.|Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Kristi
authors.initials: K
authors.lastname: Carlston
authors.affiliation: Department of Radiology, University of Utah, Salt Lake City, Utah, USA.
authors.forename: Vivian S
authors.initials: VS
authors.lastname: Lee
mesh_terms: D016477:Artifacts; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: BOLD; T2*; concomitant gradient fields; iron quantification; renal-BOLD