Evaluation of the spatial resolution of a dedicated breast CT system using computer simulation

Abstract

Spatial resolution is one of the most crucial parameters for an imaging system. The modulation transfer function (MTF) was physically measured using wire images on a prototype breast CT scanner previously¹. In this study, the effects on MTF from different components in the imaging chain, including the x-ray focal spot distribution, detector lag, and x-ray detector MTF were physically measured. The contributions of these three factors and gantry motion affecting CT system resolution were studied using computer simulation. The CT system MTF was computed and the role of each factor was studied independently. The simulated MTF results demonstrated that the x-ray focal spot size and detector MTF have an effect on the system resolution, while the scanner motion degrades only the azimuthal MTF, with greater degradation occurring further from isocenter where greater rotational velocities occur. The azimuthal MTF of this system has a cutoff frequency of 2.0 cycles/mm at the isocenter but degrades to 1.0 cycles/mm at the periphery. The radial MTF has a cutoff frequency of 2.0 cycles/mm, at both the isocenter and periphery. The comparison between the computer simulated and physically measured MTF values demonstrates reasonable accuracy in the simulation process. The results from computer simulation also suggest ways in which the spatial resolution can be improved by system modification.