title: Gradient-echo magnetic resonance signal decay in a porcine vertebral body model: influence of chemical shift.
abstract: OBJECTIVE
  This study investigates how magnetic resonance (MR) signal and T2* of trabecular bone are affected by chemical shift.
  
  
  METHODS
  Five pigs were sacrificed, and 150 gradient-echo MR images with increasing echo times (TEs) were obtained of the lumbar spine. Two vertebrae were excised, defatted, and imaged. Commercial fat-protein emulsions with 40%, 27%, and 15% concentrations of fat were studied. Regions of interest in subcutaneous fat (n = 3), bladder (n = 4), vertebral body (n = 10), and defatted vertebral body (n = 10) were used to study decay of signal intensity.
  
  
  RESULTS
  MR signal intensity of the vertebrae decreased with a superimposed modulation. The periodicity was 4.65 msec (range, 4.60-4.68 msec). At a TE of 0 msec, a phase shift of 24 degrees (range, 14 degrees-37 degrees), which corresponds to a shift in TE of 0.31 msec at 1.5 T, was present. In the fat-protein emulsions, the amplitude of the modulation increased with the amount of fat.
  
  
  CONCLUSIONS
  Chemical shift and the amount of fat affects T2* measurements.
authors.affiliation: MR Research Centre, Karolinska Institute, Sweden.
authors.forename: T B
authors.initials: TB
authors.lastname: Brismar
authors.forename: H
authors.initials: H
authors.lastname: Ringertz
mesh_terms: D000273:Adipose Tissue / Q000737:chemistry; D000818:Animals; D001834:Body Water / Q000737:chemistry; D001853:Bone Marrow / Q000737:chemistry; D008159:Lumbar Vertebrae / Q000737:chemistry*; D008279:Magnetic Resonance Imaging; D010507:Periodicity; D013552:Swine