title: MR imaging contrast in human brain tissue: assessment and optimization at 4 T.
abstract: OBJECTIVE
  To evaluate multiple magnetic resonance (MR) imaging sequences for their ability to provide T1 and T2-weighted images at a field strength of 4 T, and to validate previously obtained relaxation time measurements.
  
  
  METHODS
  Different spin-echo, inversion-recovery (IR), gradient-recalled acquisition in the steady state (GRASS), and magnetization transfer contrast-enhanced GRASS sequences were evaluated in a single section, each in at least four volunteers. Also, interleaved echo-planar imaging (IEPI) and interleaved gradient-recalled echo (IGRE) sequences were analyzed and compared with standard sequences.
  
  
  RESULTS
  Predicted contrast behavior, according to MR relaxation time measurements, was found to agree well with that of the validation experiments. Fair T1 contrast can be achieved on MR images at 4 T, contrary to early predictions. Under other conditions, however, such as partially spin-density-weighted parameters, lower contrast is observed at the high field strength when compared with conventional field strengths.
  
  
  CONCLUSIONS
  The longer T1 values at higher field strengths have a substantial effect on image contrast. Depending on the sequence and parameters chosen, good image contrast can be realized at 4 T. IEPI and hybrid IR IGRE sequences are useful in shortening the prolonged examination times owing to the longer T1 values at higher field strengths.
authors.affiliation: Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1061, USA.
authors.forename: S
authors.initials: S
authors.lastname: Duewell
authors.forename: S D
authors.initials: SD
authors.lastname: Wolff
authors.forename: H
authors.initials: H
authors.lastname: Wen
authors.forename: R S
authors.initials: RS
authors.lastname: Balaban
authors.forename: P
authors.initials: P
authors.lastname: Jezzard
mesh_terms: D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D013997:Time Factors