title: Effects of signal-to-noise ratio on the accuracy and reproducibility of diffusion tensor imaging-derived fractional anisotropy, mean diffusivity, and principal eigenvector measurements at 1.5 T.
abstract: OBJECTIVE
  To develop an experimental protocol to calculate the precision and accuracy of fractional anisotropy (FA), mean diffusivity (MD), and the orientation of the principal eigenvector (PEV) as a function of the signal-to-noise ratio (SNR) in vivo.
  
  
  METHODS
  A healthy male volunteer was scanned in three separate scanning sessions, yielding a total of 45 diffusion tensor imaging (DTI) scans. To provide FA, MD, and PEV as a function of SNR, sequential scans from a scan session were grouped into nonintersecting sets. Analysis of the accuracy and precision of the DTI-derived contrasts was done in both a voxel-wise and region of interest (ROI)-based manner.
  
  
  RESULTS
  An upward bias of FA and no significant bias in MD were present as SNR decreased, confirming results from simulation-based studies. Notably, while the precision of the PEV became worse at low SNR, no bias in the PEV orientation was observed. Overall, an accurate and precise quantification of FA values in GM requires substantially more SNR than the quantification of white matter (WM) FA values
  
  
  CONCLUSIONS
  This study provides guidance for FA, MD, and PEV quantification and a means to investigate the minimal detectable differences within and across scan sessions as a function of SNR.
authors.affiliation: F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Jonathan A D
authors.initials: JA
authors.lastname: Farrell
authors.forename: Bennett A
authors.initials: BA
authors.lastname: Landman
authors.forename: Craig K
authors.initials: CK
authors.lastname: Jones
authors.forename: Seth A
authors.initials: SA
authors.lastname: Smith
authors.forename: Jerry L
authors.initials: JL
authors.lastname: Prince
authors.forename: Peter C M
authors.initials: PC
authors.lastname: van Zijl
authors.forename: Susumu
authors.initials: S
authors.lastname: Mori
mesh_terms: D000328:Adult; D016880:Anisotropy; D016477:Artifacts; D002138:Calibration; D003198:Computer Simulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D015233:Models, Statistical; D015337:Multicenter Studies as Topic; D015203:Reproducibility of Results; D013997:Time Factors