Auditing the image quality of mammograms

A quantitative approach to assessing the image quality of mammograms at screening centres has been developed. In this study an expert radiologist made a subjective judgement of the overall film blackening for each mammogram taken on a sequential series of 100 women attending screening over a period of three days on a single screening system. To relate these subjective judgements to quantitative measurements each mammogram was digitised and the distribution of film densities analysed. Average film densities in the main breast area were found to vary from 1.2 to 2.4, with an average of 1.8 for oblique views and 1.7 for CC views. The densities measured on quality control films of 40 mm thick PMMA exposed at 28 kV and 30 kV, and processed at the same time as the clinical films, were 1.52 and 1.67 respectively. Mammograms were judged satisfactory when film densities in the main breast region were in the range 0.8 to 2.8 with average densities of about 1.6 to 2.0. The method described allows the ideal film blackening to be quantitatively assessed.