title: Dixon-type and subtraction-type contrast-enhanced magnetic resonance angiography: A theoretical and experimental comparison of SNR and CNR.
abstract: OBJECTIVE
  The purpose of this work is to compare the behavior of the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in contrast-enhanced MR angiography with background suppression performed by either a Dixon-type or subtraction-type method.
  
  
  METHODS
  Theoretical expressions for the SNR and CNR for both background suppression techniques were derived. The theoretical Dixon:subtraction SNR and CNR ratios were compared to empirical ratios measured from phantom and in vivo studies for Dixon techniques utilizing one, two, and three echoes. Specifically, the SNR and CNR ratios were compared as the concentration of contrast material in the blood changed.
  
  
  RESULTS
  Empirical measurements of the SNR and CNR ratios compared favorably with the ratios predicted by theory. As the contrast concentration was reduced, the SNR advantage of the Dixon techniques increased asymptotically. In the ideal case, the SNR improvement over subtraction contrast-enhanced MR angiography was at least twofold for one- and two-echo Dixon techniques and at least a factor of 6 for the three-echo Dixon technique.
  
  
  CONCLUSIONS
  Expressions showing a contrast concentration-dependent SNR and CNR improvement of at least a factor of two when Dixon-type contrast-enhanced MR angiography is used in place of subtraction-type contrast-enhanced MR angiography were derived and validated with phantom and in vivo experiments. Magn Reson Med 74:81-92, 2015. © 2014 Wiley Periodicals, Inc.
authors.affiliation: Department of Radiology, Mayo Clinic, MR Research Laboratory, Rochester, Minnesota, USA.
authors.forename: Eric G
authors.initials: EG
authors.lastname: Stinson
authors.affiliation: Department of Radiology, Mayo Clinic, MR Research Laboratory, Rochester, Minnesota, USA.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Trzasko
authors.affiliation: Department of Radiology, Mayo Clinic, MR Research Laboratory, Rochester, Minnesota, USA.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Weavers
authors.affiliation: Department of Radiology, Mayo Clinic, MR Research Laboratory, Rochester, Minnesota, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Riederer
keywords: Dixon; contrast-enhanced MR angiography; contrast-to-noise ratio; fat-water; signal-to-noise ratio