title: A method for determining skeletal lengths from DXA images.
abstract: BACKGROUND
  Skeletal ratios and bone lengths are widely used in anthropology and forensic pathology and hip axis length is a useful predictor of fracture. The aim of this study was to show that skeletal ratios, such as length of femur to height, could be accurately measured from a DXA (dual energy X-ray absorptiometry) image.
  
  
  METHODS
  90 normal Caucasian females, 18-80 years old, with whole body DXA data were used as subjects. Two methods, linear pixel count (LPC) and reticule and ruler (RET) were used to measure skeletal sizes on DXA images and compared with real clinical measures from 20 subjects and 20 x-rays of the femur and tibia taken in 2003.
  
  
  RESULTS
  Although both methods were highly correlated, the LPC inter- and intra-observer error was lower at 1.6% compared to that of RET at 2.3%. Both methods correlated positively with real clinical measures, with LPC having a marginally stronger correlation coefficient (r2 = 0.94; r2 = 0.84; average r2 = 0.89) than RET (r2 = 0.86; r2 = 0.84; average r2 = 0.85) with X-rays and real measures respectively. Also, the time taken to use LPC was half that of RET at 5 minutes per scan.
  
  
  CONCLUSIONS
  Skeletal ratios can be accurately and precisely measured from DXA total body scan images. The LPC method is easy to use and relatively rapid. This new phenotype will be useful for osteoporosis research for individuals or large-scale epidemiological or genetic studies.
authors.affiliation: King's College London, St Thomas' Hospital Campus, Twin Research & Genetic Epidemiology Unit, Lambeth Palace Road, London, SE1 7EH, UK. usha.chinappen@kcl.ac.uk
authors.forename: Usha
authors.initials: U
authors.lastname: Chinappen-Horsley
authors.forename: Glen M
authors.initials: GM
authors.lastname: Blake
authors.forename: Ignac
authors.initials: I
authors.lastname: Fogelman
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods* / Q000592:standards* / Q000706:statistics & numerical data; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry / Q000379:methods*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012863:Skeleton; D013977:Tibia / Q000000981:diagnostic imaging