Studies using simulated calcifications can be performed to measure the effect of different imaging factors on calcification detection in digital mammography. The simulated calcifications must be inserted into clinical images with realistic contrast and sharpness. MoCa is a program which modifies the contrast and sharpness of simulated calcification clusters extracted from images of mastectomy specimens acquired on a digital specimen cabinet at high magnification for insertion into clinical mammography images. This work determines whether the use of MoCa results in simulated calcifications with the correct contrast and sharpness. Aluminium foils (thickness 0.1-0.4 mm) and 1.60 µm thick gold discs (diameter 0.13-0.8 mm) on 0.5 mm aluminium were imaged with a range of thicknesses of polymethyl methacrylate (PMMA) using an amorphous selenium direct digital (DR) system and a powder phosphor computed radiography (CR) system (real images). Simulated images of the tests objects were also generated using MoCa. The contrast of the aluminium squares and the degradation of the contrast of the gold discs as a function of disc diameter were compared in the real and simulated images. The average ratios of the simulated-to-real aluminium contrasts over all aluminium and PMMA thicknesses were 1.03 ± 0.04 (two standard errors in the mean) and 0.99 ± 0.03 for the DR and CR systems, respectively. The ratio of the simulated-to-real degradations of contrast averaged over all disc diameters and PMMA thicknesses were 1.007 ± 0.008 and 1.002 ± 0.013 for DR and CR, respectively. The use of MoCa was accurate within the experimental errors.
Abstract. In mammography, the reduction of scattered X-rays is vital due to the low contrast or small dimension of the details that are searched for. The typical method of doing so in current conventional mammography is the anti-scatter grid. The disadvantage of this method is the absorption of a proportion of the primary beam and therefore an increase in dose is required to compensate for the loss of counts. An alternative method is proposed, using quasi-monochromatic beams and a pixellated spectroscopic detector. As Compton-scattered X-rays lose energy in the scattering process, they are detected at a lower energy in the spectrum. Therefore the spectrum can be windowed around the monochromatic energy peak, removing the scattered Xrays from the image. The work presented here shows contrast improvement of up to 50 % and contrast to noise ratio improvements of around 20 % for scatter free imaging in comparison to full spectrum imaging. Contrast improvements of around 45 % were found when comparing scatter free images to conventional polychromatic imaging for both the low contrast test object and the Rachel anthropomorphic breast phantom.
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