Quality Control in Mammography

Abstract

In those countries that have acquired considerable experience in the field of breast cancer screening by mammography, it is now generally acknowledged that a comprehensive system of quality assurance is a fundamental requirement. The reason for this is that mammography is a far from ideal screening test in that it requires a very high level of performance in the production and interpretation of the images to perform the function of a screening test successfully. In this context it is perhaps relevant to contrast mammography with a simple chest X-ray as a screening test. To produce a satisfactory chest X-ray, any standard films with moderate performance can be used: the performance of the intensifying screens is likewise uncritical, there is no need for a moving grid, exposure control is simple with considerable latitude, and the equipment required to produce the image can be very basic. There are no particular problems when processing the exposed film and the variations in normal appearances are considerably less than is the case in mammography. A satisfactory screening mammogram, on the other hand, requires a very high quality dedicated film-screen combination whose performance needs constant checking. The mammography unit required to produce the mammogram is necessarily dedicated and is subject to a detailed high specification in all aspects of its operation which again need constant monitoring. Positioning of the patient for the examination is a highly skilled operation and requires considerable training and experience. The processing of mammograms is a specialised process and dedicated processing facilities are needed. As with all other aspects of image production, the performance of the processing unit should be closely monitored. Sensitometric testing of the processor is necessary daily and sometimes more frequently. Finally, a high level of training and experience is needed to enable a radiologist to read screening mammograms successfully and reliably. For the process of screening by mammography to be successful, all elements in the chain must operate at an optimal level or the number of cancers missed by the process inevitably rises. Thus, mammography can only be an efficient screening test if strict quality-assurance guidelines exist for all aspects of any screening programme.