Quality assurance of mammograms in the Norwegian Breast Cancer Screening Program

This study compared the proportion of mammograms classified as perfect, good, moderately good or inadequate by a radiographer specially trained for doing such a classification at a breast centre (local-PGMI radiographer) with the proportion similarly assessed by an expert-PGMI radiographer. The results were compared with the recommendations given in the quality assurance manual of the Norwegian Breast Cancer Screening Programme. The reasons for classifying the mammograms into other than perfect, such as good, moderately good or inadequate were investigated.

The quality of the mammograms was measured by using the PGMI system, which is a quality-review model that classifies the images into the four categories according to positioning, compression, exposure, noise, artefacts, and movement. A total of 1280 mammograms from all 16 breast centres in the screening programme were classified.

The distribution of perfect, good, moderately good, and inadequate mammograms differed between the local-PGMI radiographers and the expert radiographer, for both the cranio-caudal (CC) and mediolateral–oblique (MLO) mammograms (P < 0.001 for both). The expert radiographer classified a higher proportion of both CC (28%) and MLO (14%) mammograms as inadequate than did the local-PGMI radiographers (7% and 3%, respectively; P < 0.001 for both). The guidelines recommend ≤3% of the mammograms to be inadequate. The reason given for the inadequate classifications by the expert radiographer was predominantly “parts of the breast missing” for both the CC and the MLO mammograms.

There is room to improve the quality of the mammograms in the screening programme in Norway. Attention should be given to positioning and the use of standardized terms in the PGMI classification.