title: Comparison of a new and existing method of mammographic density measurement: intramethod reliability and associations with known risk factors.
abstract: BACKGROUND
  Mammographic density is one of the strongest risk factors for breast cancer. It is commonly measured by an interactive threshold method that does not fully use information contained in a mammogram. An alternative fully automated standard mammogram form (SMF) method measures density using a volumetric approach.
  
  
  METHODS
  We examined between-breast and between-view agreement, reliability, and associations of breast cancer risk factors with the threshold and SMF measures of breast density on the same set of 1,000 digitized films from 250 women who attended routine breast cancer screening by two-view mammography in 2004 at a London population-based screening center. Data were analyzed using random-effects models on transformed percent density.
  
  
  RESULTS
  Median (interquartile range) percent densities were 12.8% (5.0-22.3) and 21.8% (18.4-26.6) in the threshold and SMF methods, respectively. There was no evidence of systematic differences between left-right breasts or between views in either method. Reliability of a single measurement was lower in the SMF than in the threshold method (0.77 versus 0.92 for craniocaudal and 0.68 versus 0.89 for mediolateral oblique views). Increasing body mass index and parity were associated with reduced density in both methods; however, an increase in density with hormone replacement therapy use was found only with the threshold method.
  
  
  CONCLUSIONS
  Established properties of mammographic density were observed for SMF percent density; however, this method had poorer left-right reliability than the threshold method and has yet to be shown to be a predictor of breast cancer risk.
authors.affiliation: Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, Wellington, New Zealand. valerie.mccormack@lshtm.ac.uk
authors.forename: Valerie A
authors.initials: VA
authors.lastname: McCormack
authors.forename: Ralph
authors.initials: R
authors.lastname: Highnam
authors.forename: Nicholas
authors.initials: N
authors.lastname: Perry
authors.forename: Isabel
authors.initials: I
authors.lastname: dos Santos Silva
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008327:Mammography / Q000379:methods*; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012307:Risk Factors