title: Incorporation of nonzero echo times in the SPGR and bSSFP signal models used in mcDESPOT.
abstract: OBJECTIVE
  To analyze the effect of neglecting nonzero echo times (TEs) in the conventional model of multicomponent driven equilibrium single pulse observation of T1 and T2 (mcDESPOT).
  
  
  METHODS
  Formulations of the two-component spoiled gradient recalled echo (SPGR) and balanced steady state free precession (bSSFP) models that incorporate nonzero TE effects are presented in the context of mcDESPOT and compared with the conventionally used SPGR and bSSFP models which ignore nonzero TEs. Relative errors in derived parameter estimates from conventional mcDESPOT, omitting TE effects, are assessed using simulations over a wide range of experimental and sample parameters.
  
  
  RESULTS
  The neglect of nonzero TE leads to an overestimate of the SPGR signal and an underestimate of the bSSFP signal. These effects can introduce large errors in parameter estimates derived from conventional mcDESPOT under realistic imaging conditions.
  
  
  CONCLUSIONS
  SPGR and bSSFP signal models accounting for nonzero TE effects should be incorporated into quantitative mcDESPOT analyses.
authors.affiliation: Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA.
authors.forename: Mustapha
authors.initials: M
authors.lastname: Bouhrara
authors.affiliation: Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Spencer
mesh_terms: D000465:Algorithms; D001921:Brain / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D012815:Signal Processing, Computer-Assisted
keywords: SPGR; bSSFP; mcDESPOT; quantitative MRI