title: The myth of the 50-50 breast.
abstract: OBJECTIVE
  For dosimetry and for work in optimization of x-ray imaging of the breast, it is commonly assumed that the breast is composed of 50% fibroglandular tissue and 50% fat. The purpose of this study was to assess whether this assumption was realistic.
  
  
  METHODS
  First, data obtained from an experimental breast CT scanner were used to validate an algorithm that measures breast density from digitized film mammograms. Density results obtained from a total of 2831 women, including 191 women receiving CT and from mammograms of 2640 women from three other groups, were then used to estimate breast compositions.
  
  
  RESULTS
  Mean compositions, expressed as percent fibroglandular tissue (including the skin), varied from 13.7% to 25.6% among the groups with an overall mean of 19.3%. The mean compressed breast thickness for the mammograms was 5.9 cm (sigma = 1.6 cm). 80% of the women in our study had volumetric breast density less than 27% and 95% were below 45%.
  
  
  CONCLUSIONS
  Based on the results obtained from the four groups of women in our study, the "50-50" breast is not a representative model of the breast composition.
authors.affiliation: Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario M4N 3M5, Canada. martin.yaffe@swri.ca
authors.forename: M J
authors.initials: MJ
authors.lastname: Yaffe
authors.forename: J M
authors.initials: JM
authors.lastname: Boone
authors.forename: N
authors.initials: N
authors.lastname: Packard
authors.forename: O
authors.initials: O
authors.lastname: Alonzo-Proulx
authors.forename: S Y
authors.initials: SY
authors.lastname: Huang
authors.forename: C L
authors.initials: CL
authors.lastname: Peressotti
authors.forename: A
authors.initials: A
authors.lastname: Al-Mayah
authors.forename: K
authors.initials: K
authors.lastname: Brock
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000000981:diagnostic imaging; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001940:Breast / Q000166:cytology*; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D008954:Models, Biological