  Our interest has been to study the effect that scattered radiation has on
contrast, signal-to-noise ratio and thickness reconstruction in digital
mammographies. Using the GEANT code we have performed Monte-Carlo simulations
of 25 kVp Mo/Mo photons, through a breast phantom which contains a 0.2-1.0 mm
thick microcalcifications incident on a 20x106 $mm^{2}$ pixelized detector. The
data have been analyzed assuming 6 different shapes of the incident beam: a
0.2x0.2 $mm^{2}$ ``narrow'' beam, 4 different 20 mm long scanning beams of
various widths, and a 20x100 $mm^{2}$ beam with no scatter reduction mechanisms
(NSR) . Since the image of a point depends on scattered photons which passed up
to 2 cm away from the object (for 4 cm thick phantom), we identify the
background definition as a main source of systematic uncertainty in the image
quality analysis. We propose the use of two dimensional functions (a polynomial
for the background and Gaussians for the signal) for total photon transmission
description. Our main results indicate the possible calcification thickness
reconstruction with an accuracy of the order of 6% using 3 mm wide scanning
beam. Signal-to-noise ratio with the 3 mm wide beam gets improved by 20% with
respect to NSR, a figure similar to that obtained with the narrow beam.
Thickness reconstruction is shown to be an alternative to signal-to-noise ratio
for microcalcification detection.
