Monte Carlo simulation studies of spatial resolution in magnification mammography using the edge method

Abstract

Small sized focal spots are very essential when magnification is performed in mammography, as they represent the only way to reduce the geometrical unsharpness. The effect of focal spot size on spatial resolution in contact mammography or under magnification has been experimentally investigated but, due to construction limitations, only a small range of focal spot sizes has been studied. In this study, a Monte Carlo simulation model is utilized in order to examine the effect of a wide range of focal spots on spatial resolution under magnification conditions. A thick sharp edge consisted of lead was imaged under various conditions and the corresponding spatial resolution was calculated through the Modulation Transfer Function. Results demonstrate that increasing the degree of magnification from 1.0 to 2.0 induces degradation on spatial resolution which varies from 49% for a 0.04 mm focal spot to 53.2% for a 0.14 mm one. Larger focal spots cause higher degradation even for low magnification. Focal spots larger than 0.10 mm are considered appropriate only for low degrees of magnification according to the IAEA regulations that designate spatial resolution for mammography higher than 12 lp/mm. However, for high degrees of magnification the focal spot size should be even smaller. The construction of a microfocus of 0.04 mm would result in acceptable values of spatial resolution even for degrees of magnification up to 1.9. © 2009 IOP Publishing Ltd and SISSA.