title: Coil-to-coil physiological noise correlations and their impact on functional MRI time-series signal-to-noise ratio.
abstract: Physiological nuisance fluctuations ("physiological noise") are a major contribution to the time-series signal-to-noise ratio (tSNR) of functional imaging. While thermal noise correlations between array coil elements have a well-characterized effect on the image Signal to Noise Ratio (SNR0), the element-to-element covariance matrix of the time-series fluctuations has not yet been analyzed. We examine this effect with a goal of ultimately improving the combination of multichannel array data.
  
  
  
  We extend the theoretical relationship between tSNR and SNR0to include a time-series noise covariance matrix Ψt, distinct from the thermal noise covariance matrix Ψ0, and compare its structure to Ψ0and the signal coupling matrix SSHformed from the signal intensity vectors S.
  
  
  
  Inclusion of the measured time-series noise covariance matrix into the model relating tSNR and SNR0improves the fit of experimental multichannel data and is shown to be distinct from Ψ0or SSH.
  
  
  
  Time-series noise covariances in array coils are found to differ from Ψ0and more surprisingly, from the signal coupling matrix SSH. Correct characterization of the time-series noise has implications for the analysis of time-series data and for improving the coil element combination process. Magn Reson Med 76:1708-1719, 2016. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Siemens Healthcare GmbH, Erlangen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Triantafyllou
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Polimeni
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
authors.forename: Boris
authors.initials: B
authors.lastname: Keil
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts, USA.|Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
mesh_terms: D016477:Artifacts; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008959:Models, Neurological; D015233:Models, Statistical; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D013223:Statistics as Topic
keywords: 32Channel coil; 7T; SNR; array coils; fMRI; noise covariance; physiological noise