Use of a Breast Phantom to Improve Image Quality and Patient Exposure in Ontario Mammography Facilities

A survey of facilities performing mammography examinations in the Province of Ontario was carried out over the period from 1988 to 1991. Technical information was collected for a craniocaudal view of an average female patient. The image quality and patient skin entrance exposure were measured using an RMI mammography phantom and dosemeter for each facility. An image score and mean glandular breast dose were determined for each facility. Radiographic visualisation of specks as small as 0.54 mm, fibres as small as 0.75 mm and masses as small as 1.00 mm was considered the minimum acceptable level of performance and gave an image score of 10. Results of the initial 1988 survey identified a number of phantom mammograms (16 out of 53) with image scores of less than 10 or patient entrance exposure values greater than the Ontario legislated maximum value of 900 mR (232 µC.kg-1). Such information was used as a basis for consultation in order to improve image quality and patient entrance exposure in such facilities. Results of the 1990/91 survey indicated a substantial improvement with all facilities surveyed having an image quality score of 10 or greater and a patient skin exposure value less than the Ontario legislated maximum.