Performance characteristic of imaging systems in mammography: A comparative ROC analysis

A testobject containing simulated microcalcifications was imaged by five film-screen combinations suitable for use in mammography, firstly in scatter-free condition, secondly with the addition of tissue equivalent scattering material, and thirdly with further addition of a grid to reduce radiation scatter. The ability of the systems to resolve microparticles of known size was assessed using the technique of signal detection theory. The empirical Receiver-Operating-Characteristic (ROC) curves were generated for each system, and a quantitative comparison was carried out using the area A underneath the ROC curve as a measure of accuracy. By means of this accuracy index and by application of rank order statistics the imaging systems have been separated into three major groups. Firstly a super high resolution system requiring the highest radiation dose and another system producing almost equal resolution at a medium dose level. Secondly a group with intermediate results at a medium radiation dose, and thirdly a mediocre imaging system at a low dose level. The ability to image small particles does not increase linearly with radiation dose. It can be concluded that the application of a grid in mammography in combination with a suitable film-screen combination is a most efficient tool to improve image quality at acceptable radiation dose. (orig.)