| Popis: |
The testing of a mammographic AEC system involves the insertion of suitable phantoms to take the place of the varying thicknesses and composition of the breasts encountered clinically. In this paper we examine the usefulness of mixed-material phantoms, as compared to the single material phantoms recommended by the ACR and the British authorities. The combinations of material are chosen, for each test thickness in the range 2 to 8.5 cm, to closely simulate actual breast composition. It is quite possible, using single-material phantoms, to set up operating conditions and a technique chart for a mammographic unit that will yield images of reproducible optical density within 0.15 OD. While these data will satisfy the regulatory requirements, they are unlikely to meet this object in practice, since breasts are variable in their composition. We have used various combinations of four readily available phantom materials to simulate the adipose and glandular composition of breasts of thicknesses from 2 to 8 cm. From our data, a technique chart was developed that has been found to produce superior clinical images while meeting the ACR optical density requirements. |
