Modulation transfer functions for quality assurance of mammographic systems

A "quality relative index" for expressing radiographic system quality is described. The purpose of this investigation is to quantify MTF dependencies in order to establish criteria for assessing actual image quality in terms of relative sharpness, depending on the orientation and positioning of the object along the radiation field. A procedure is proposed in which numerical values are assigned to the MTF curves in order to inter-relate MTFs for different orientations in the field center for a given radiographic system. This procedure has been named the MTF Quality Relative Index, with a single number that defines how better or worse an MTF curve is for a given direction of a system in comparison to a different direction. From an equation using parameters extracted from the curves in the center, the procedure is extended to the whole field through analogy to the evaluation of 2-D MTFs calculated for the respective locations.