title: Rapid determination of vertebral fat fraction over a large range of vertebral bodies.
abstract: BACKGROUND
  Vertebral body fat fraction (FF) has been found to vary between lumbar vertebrae using magnetic resonance spectroscopy (MRS). We aim to more quickly assess a larger number of adjacent vertebrae using a single T2-weighted iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) sequence.
  
  
  METHODS
  Five men had dual-energy X-ray absorptometry (DEXA) and 1.5-T MR scans performed. MRS was performed at L3, and a sagittal IDEAL sequence was also performed, resulting in separate fat-only and water-only readings from T10 to S2. For the IDEAL measurements, two independent observers followed a set reading protocol, with five observations each per vertebra. Intra- and interobserver variability were assessed as deviations from the mean within and between observers, respectively.
  
  
  RESULTS
  For FF measurements there was limited intra-observer variation, with observers being on average within 3.4% of the pooled mean value. Similarly, there was good interobserver agreement, with an average variation of 2.1%. All men showed a reduction in FF of 1.6-7% between L5 and S1. Otherwise, there was a trend of increasing FF moving inferiorly from T10 to S2. This averaged 2.7% per vertebra (range 1.1-3.8%) and may not have been dependent on MRS-measured FF at the L3 level. There was poor correlation between MRS-measured FF at L2-4 and bone mineral density measured using DEXA (R(2)  = 0.06).
  
  
  CONCLUSIONS
  IDEAL measurements are generally reproducible between observers following a set protocol. There appears to be a gradient in FF moving from T10 to S2, with S1 showing a consistent decrease. This variation may better describe overall marrow function than a single-vertebra reading.
authors.affiliation: Calvary Mater Newcastle, Newcastle, New South Wales, Australia; School of Medicine, University of Queensland, Toowoomba, Queensland, Australia; Centre for Advanced Imaging, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Jarad
authors.initials: J
authors.lastname: Martin
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Nicholson
authors.forename: Gary
authors.initials: G
authors.lastname: Cowin
authors.forename: Clare
authors.initials: C
authors.lastname: Ilente
authors.forename: Winnie
authors.initials: W
authors.lastname: Wong
authors.forename: Dominic
authors.initials: D
authors.lastname: Kennedy
mesh_terms: D050154:Adiposity / Q000502:physiology*; D000368:Aged; D000465:Algorithms; D001834:Body Water / Q000737:chemistry*; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000737:chemistry* / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D008055:Lipids
keywords: bone marrow; fat fraction; fat imaging; magnetic resonance imaging; magnetic resonance spectroscopy; osteoporosis