Procedure for quantitatively assessing automatic exposure control in mammography: a study of the GE Senographe 600 TS
S Meeson1, KC Young1, PB Hollaway2 and MG Wallis3
1National Co-ordinating Centre for the Physics of Mammography, Department of Medical Physics, St. Luke’s Wing, Royal Surrey County Hospital, Guildford GU2 7XX, 2Regional Radiation Protection Service, Department of Medical Physics, St. Luke’s Wing, Royal Surrey County Hospital, Guildford GU2 7XX, and 3Warwickshire, Solihull & Coventry Breast Screening Centre, Coventry and Warwickshire Hospital, Stoney Stanton Road, Coventry CV1 4FH, UK
The correct operation of a mammography system's automatic exposurecontrol system (AEC) is essential if mammograms are to be producedwith a suitable film exposure. A methodology has been developedthat allows the performance of the AEC to be assessed quantitativelyusing clinical films. By digitizing mammograms, the mean opticaldensity (OD) in the main breast region and in a region of interestcorresponding to the position of the AEC detector are evaluatedfor each film, together with the area of the main breast. Usingthese data it is possible to determine the relationships betweenthe mean OD, breast size and AEC detector position. The performanceof the AEC on a GE Senographe 600 TS system was investigated.The study found that there is a tendency to underexpose smallerbreasts, i.e. with an area less than approximately 4000 mm2.This is equivalent to a compressed tissue width of approximately60-80 mm. The difference in mean OD between the mammogramsof small and large breasts was up to 0.7 OD. Provided thesensitive area of the AEC detector is known, this method ofassessing AEC performance can be used with any mammography system.
Last modified 17th August 2001
Stuart Meeson
