An evaluation of the use of pectoral muscle to nipple level as a component to assess the quality of the medio-lateral oblique mammogram

Abstract

Objective: The national breast screening quality assurance (QA) guidelines state that medio-lateral oblique mammograms (MLO) should achieve the pectoral muscle to nipple level in 75% of cases using a line parallel to the horizontal edge of the film (PL). An alternative method would be to use a line at 90 degrees to the tangent of the breast at the point of the nipple (TM). The aim of this study was to evaluate these methods. Method: Questionnaires were sent to all breast screening units requesting that 50 randomly selected technically adequate MLOs be evaluated using the PL and TM. Results: From 54 replies (52%) the mean percentage for the PL was 40.5% (range 19–89). Only one unit achieved the QA objective. The mean percentage for the TM was 93% (range 83–100). P<0.001. Conclusion: The PL method for assessing the pectoral muscle to nipple level is reproducible but cannot be achieved in the majority of cases. The QA guidelines' target would be achievable if the TM was used to assess the pectoral muscle to nipple level. However some doubts have been raised as to the reproducibility of this method. As all the mammograms were deemed technically adequate the indication is that the QA guidelines are unachievable rather than there being a short fall in the quality of the mammograms.