A linear array silicon pixel detector: Images of a mammographic test object and evaluation of delivered doses

We present images of a mammographic test object obtained using a linear array silicon pixel detector capable of single-photon counting. The detector pixel size was 200 x 300 μm2 and images were acquired by scanning the test object between the laminar detector and the x-ray source with a scanning step of 100μm. A molybdenum anode tube was used with two different filtrations: 2 mm aluminium and 25 μm molybdenum. Conventional film-screen images were also obtained in order to compare spatial and contrast resolution. In our digital images it is possible to recognize low-contrast details having dimensions smaller than or equal to the dimensions of details visible by means of a clinical mammographic unit. The detection of microcalcifications smaller than 150 μm was possible only when using the Mo filtration. However a copper wire of 50 μm 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-quality images are always smaller than at a conventional mammographic unit. Since MGDs depend on the x- ray spectrum, the dose reduction becomes larger when the applied spectrum is harder than in film-screen acquisition (Al filtration and 35 kVp).