title: MR relaxation times in human brain: measurement at 4 T.
abstract: OBJECTIVE
  To determine the values for relaxation times in human brain for magnetic resonance (MR) imaging at 4 T.
  
  
  METHODS
  T1 measurements were made with a progressive saturation sequence, an implementation of the Look-Locker sequence, and an inversion-recovery (IR) interleaved echo-planar imaging (IEPI) sequence. T2 measurements were made with a standard spin-echo (SE) sequence and an SE IEPI sequence.
  
  
  RESULTS
  The T1 measurements yielded values of 1,724 msec +/- 51 for gray matter, 1,043 msec +/- 27 for white matter, and 4,550 msec +/- 800 msec for cerebrospinal fluid. The deep gray matter regions had T1 values of 1,458 +/- 38 (caudate nucleus) and 1,372 +/- 60 (putamen). The T2 measurements yielded results of 63 msec +/- 6.2 for gray matter and 49.8 msec +/- 2.2 for white matter.
  
  
  CONCLUSIONS
  The T1 values measured at 4 T show a higher value than predicted from extrapolation at lower field strengths. The T2 measurements showed a slight decrease in values over those measured at lower-field strength. The gain in signal-to-noise ratio from the higher field strength may be substantially offset by these altered relaxation time values to a degree that is sequence dependent.
authors.affiliation: Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1061, USA.
authors.forename: P
authors.initials: P
authors.lastname: Jezzard
authors.forename: S
authors.initials: S
authors.lastname: Duewell
authors.forename: R S
authors.initials: RS
authors.lastname: Balaban
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013997:Time Factors