title: Comparison of the effectiveness of 2 dual-energy X-ray absorptiometers with that of total body water and computed tomography in assessing changes in body composition during weight change.
abstract: BACKGROUND
  Little information is available on the assessment of changes in body composition as a function of weight change with the use of the fan beam of dual-energy X-ray absorptiometry (DXA).
  
  
  OBJECTIVE
  The objective was to determine the accuracy of the fan beam of the QDR 4500A densitometer and the pencil beam of the QDR 2000 densitometer in estimating changes in whole-body lean soft tissue mass (LSTM(DXA)) and fat mass (FM) with weight change.
  
  
  METHODS
  Thirty-seven subjects who lost 5.7 +/- 4.5 kg were measured before and after weight change. Using total body water and computed tomography (CT) of the midthigh, we compared changes in FFM(TBW) and LSTM(CT) with changes in LSTM(DXA).
  
  
  RESULTS
  Overall, compared with TBW, the fan beam gave a larger estimate of change (macro x +/- SD) in LSTM (fan beam - TBW: -0.7 +/- 1.6 kg) than did the pencil beam (pencil beam - TBW: -0.1 +/- 1.6 kg). When the change in LSTM obtained with the fan beam and pencil beam was regressed against the change in FFM(TBW), the slope of the line for the fan beam was 0.97 (r(2) = 0.61) and that for the pencil beam was 0.86 (r(2) = 0.61). Regression analysis showed that the results between the 2 units were not interchangeable. For the midthigh region, the change in LSTM(CT) was moderately correlated with the change in LSTM(DXA) with the fan beam and pencil beam.
  
  
  CONCLUSIONS
  The measurement of change in LSTM with the fan and pencil beams provides the same relation to changes in FFM assessed by TBW, but the 2 systems are not interchangeable.
authors.affiliation: Department of Preventive Medicine, University of Tennessee, Memphis, 38105, USA. tylavsky@physiol.utmem.edu
authors.forename: Frances A
authors.initials: FA
authors.lastname: Tylavsky
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Lohman
authors.forename: Maurice
authors.initials: M
authors.lastname: Dockrell
authors.forename: Thomas
authors.initials: T
authors.lastname: Lang
authors.forename: Dale A
authors.initials: DA
authors.lastname: Schoeller
authors.forename: Jim Y
authors.initials: JY
authors.lastname: Wan
authors.forename: Thomas
authors.initials: T
authors.lastname: Fuerst
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.forename: Michael
authors.initials: M
authors.lastname: Nevitt
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation / Q000379:methods*; D000273:Adipose Tissue / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D000293:Adolescent; D000328:Adult; D000368:Aged; D001823:Body Composition; D001834:Body Water / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013848:Thigh / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*; D015431:Weight Loss / Q000502:physiology*