Breast density is the fractional measurement of glandular tissue versus that of adipose and connective tissue in the breast. This value is often determined from the subjective interpretation of a mammography image by a radiologist. Because this may vary significantly between interpretations, a more formal measure is required to describe a breast density in terms of it's radiographic characteristics, and can be clearly understood and communicated. Geant4 Monte-Carlo package was used to develop a simulation

Geant4 Monte-Carlo package was used to develop a simulation of the mammography imaging process that included relevant geometries specific to a GE Senograph Essential mammography unit. Filter transmission data was collected for filter materials molybdenum, rhodium and aluminium with anode materials molybdenum, rhodium and tungsten over energy ranges 24- 36kV with 2kV increments. Subsequent breast transmission data was col- lected for selected beam parameters using polymethyl methacrylate(PMMA) and water as breast materials.

From this transmission data a water equivalent thickness was able to be calculated with the aid of Dance, Skinner, Young, Beckett, and Kotre (2000) equivalent breast thickness calculations, as well as an associated breast den- sity, or glandularity. It was found that the mean simulated breast trans- mission uncertainty was ±4.8%, and mean GE Senograph Essential breast transmission uncertainty was ±5.2%. This meant the majority of trans- mission curves fell within each others error bars as the mean transmission difference was 8.6%. Ultimately a water equivalent thickness was calculated to within a mean accuracy of ±7.0%.