Development of a test-object for an objective assessment of image quality in conventional or digital mammorgaphy

摘要

The assessment of image quality in mammography often relies on the subjective evaluation of films produced with test-objects containing structures such as masses, micro-calcifications and filaments. If the methodology is adequate to control the stability of a mammography unit, its use in a context of system optimization (from the x-ray spectrum to the detector response) is limited. Thus, a test-object which allows measurements of the detectability index d' from the non-prewhitening matched filter (NPWE) observer, was developed and tested. The test-object is 45 mm thick and allows the assessment of d' in areas of different glandular/fat compositions (i.e. image quality evaluation taking into account the dynamic range parameter). To simulate the absorption of the skin, a 100% fat equivalent tissue, with a thickness of 5 mm, is placed on each side of the test-object. On a conventional unit, it is possible to assess the image parameters at three optical density levels (i.e. 0.5-0.8; 1.6 - 1.6 and 2.3 - 2.6) in one exposure. The image of this test object on digital units has also been tested satisfactorily.