title: Comparison of in-vivo body composition using two Lunar dual-energy X-ray absorptiometers.
abstract: OBJECTIVE
  To compare in-vivo composition analysis between two dual energy X-ray absorptiometers, a DPX and a DPX/L, from the same manufacturer (LUNAR), pre(Study A) and post(Study B) hardware changes on both absorptiometers.
  
  
  METHODS
  Comparison of (1) quality assurance (QA) data: air-counts low (38 keV), air-counts high (70 keV), air-counts ratio, percent spillover, R-delrin; and (2) total body compartments: total body tissue (TBTISS), total body fat (TBF), percent total body fat (%TBF), total body lean (TBLEAN), total body bone mineral content (TBBMC) and total body bone mineral density (TBBMD), between the two absorptiometers.
  
  
  METHODS
  Centre for Bone and Body Composition Research, University of Leeds.
  
  
  METHODS
  Study A, 14 normal subjects and Study B, a different cohort of 19 normal subjects, were scanned on both machines on the same day.
  
  
  RESULTS
  In Study A, large significant differences were observed in the QA parameters between the two machines. The DPX, air-counts low and air-counts high, being 25% and 22% lower than the DPX/L. The Bland Altman method of analysis indicated that the DPX was significantly higher for TBTISS (0.3 kg), %TBF (2%) and TBF ( 1.4 kg) and correspondingly lower for TBLEAN (-1.0 kg). No significant difference was observed in TBBMC. After the hardware changes (Study B) a marked reduction in the differences in QA air-counts was observed. The DPX air-counts low was now 1% higher and air-counts high 8% lower than the DPX/L. The DPX had now only small significant negative differences for %TBF (-0.6%) and TBF (-0.4 kg) and a small significant positive difference for TBLEAN (0.4 kg), compared to the DPX/L. TBBMC difference although slightly increased, was still non-significant.
  
  
  CONCLUSIONS
  The closer agreement observed in the QA parameters after the hardware changes was associated with a reduction in the mean differences, 95%CI of the mean differences and limits of agreement of the comparison of body composition analysis from the Lunar machines using the Bland-Altman method. The study indicates that the QA limits set for bone mineral analysis may require more stringent limits for body composition.
authors.affiliation: Centre for Bone and Body Composition Research, University of Leeds, The General Infirmary at Leeds, UK.
authors.forename: B
authors.initials: B
authors.lastname: Oldroyd
authors.forename: J G
authors.initials: JG
authors.lastname: Truscott
authors.forename: G
authors.initials: G
authors.lastname: Woodrow
authors.forename: R
authors.initials: R
authors.lastname: Milner
authors.forename: S P
authors.initials: SP
authors.lastname: Stewart
authors.forename: A H
authors.initials: AH
authors.lastname: Smith
authors.forename: C F
authors.initials: CF
authors.lastname: Westmacott
authors.forename: M A
authors.initials: MA
authors.lastname: Smith
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue; D000328:Adult; D000368:Aged; D001823:Body Composition; D015519:Bone Density; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011786:Quality Control; D012044:Regression Analysis