A LINEAR-ARRAY SILICON PIXEL DETECTOR - IMAGES OF A MAMMOGRAPHIC TESTOBJECT AND EVALUATION OF DELIVERED DOSES

We present images of a mammographic test object obtained using a linea r array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 mu m(2) and images were acquired by scanning the test object between the laminar detector and the x-ray so urce with a scanning step of 100 mu m. A molybdenum anode tube was use d with two different filtrations: 2 mm aluminium and 25 mu m molybdenu m. Conventional film-screen images were also obtained in order to comp are spatial and contrast resolution. In our digital images it is possi ble to recognize low-contrast details having dimensions smaller than o r equal to the dimensions of details visible by means of a clinical ma mmographic unit. The detection of microcalcifications smaller than 150 mu m was possible only when using the Mo filtration. However a copper wire of 50 mu m diameter was detectable when embedded in a simulated tissue.We discuss in detail the mean glandular doses (MGDs) delivered during the image acquisition. The MGDs necessary to obtain good-qualit y images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x-ray spectrum, the dose reduction becomes la rger when the applied spectrum is harder than in film-screen acquisiti on (Al filtration and 35 kVp).