Scattered radiation plays a significant role in mammographic imaging, with scatter fractions over 50% for larger, denser
breasts. For screen-film systems, scatter primarily affects the image contrast, reducing the conspicuity of subtle lesions.
While digital systems can overcome contrast degradation, they remain susceptible to scatter's impact on the image
resolution and noise. To better understand this impact, we have created a Monte Carlo model of a mammographic
imaging system adaptable for different imaging situations. This model flags primary and scatter photons and therefore
can produce primary-only, scatter-only, or primary plus scatter images. Resolution was assessed using the edge
technique to compute the Modulation Transfer Function (MTF). The MTF of a selenium detector imaged with a 28 kVp
Mo/Mo beam filtered through a 6 cm heterogeneous breast was 0.81, 0.0002, and 0.65 at 5 mm-1 for the primary beam,
scatter-only, and primary plus scatter beam, respectively. Noise was measured from flat-field images via the noise
power spectrum (NNPS). The NNPS-exposure product using the same imaging conditions was 1.5 x 10-5 mm2x mR,
1.6 x 10-5 mm2x mR, and 1.9 x 10-5 mm2x mR at 5 mm-1 for the primary, scatter, and primary plus scatter beam, respectively.
The results show that scatter led to a notable low-frequency drop in the MTF and an increased magnitude of the NNPS-exposure
product. (This work was supported in part by USAMRMC W81XWH-04-1-0323.)