MAMMOGRAPHIC SCANNING EQUALIZATION RADIOGRAPHY

It is well recognized that variations in breast thickness and parenchy mal composition can produce a range of exposure which exceeds the lati tude of high contrast mammographic film/screen combinations. Optimal i maging of the dense breast is desired since 30%-60% of women present w ith dense breasts, and they are believed to be at the highest relative risk of developing breast cancer. The application of scanning equaliz ation radiography to mammography has been investigated through the con struction and characterization of a prototype mammographic scanning eq ualization radiography (MSER) system, designed to image mammographic p hantoms. The MSER system exposes a Min-R/MRH cassette by raster scanni ng a 2.0 X 1.6 cm beam of pulsed x-rays across the cassette. A scannin g detector behind the cassette measures the local x-ray transmission o f the breast. Feedback of the transmission information is used to modu late the duration of each x-ray pulse, to equalize the film exposure. The effective dynamic range of the MSER system is 25 times greater tha n that of conventional mammography. Artifact-free images of mammograph ic phantoms show that MSER effectively overcomes the latitude limitati ons of film/screen mammography, enabling high contrast imaging over a wide range of object x-ray transmission. Anthropomorphic phantom image s show,that MSER offers up to a sixfold increase in film contrast in t he normally underexposed regions of conventional mammograms. Character ization of the entrance exposure shows that there is not a significant difference in exposure between MSER and conventional mammographic tec hniques, suggesting that both would pose comparable risk to the patien t. Calculations show that the construction of a clinical multiple beam MSER system is feasible with minor changes to existing technology.