Determination of imaging performance of a digital mammography

Abstract

The method of calculating DQE of a general digital imaging system is proposed by IEC and it is coming to the stage of final draft. However, about digital mammography, nothing is decided yet. This research examines the evaluation method for image quality of a digital mammography with clinical equipment through physical evaluation of the mammographic computed radiography (CR) systems under clinical conditions. We used two CR systems. One consisted of a single plate image reader (FCR PROFECT CS, Fuji), which includes dual-side reading and 50-micron pixels. Other consisted of a single plate image reader (FCR 5000H, Fuji), which includes single-side reading and 100-micron pixels. Digital characteristic curves, presampling MTFs and digital Wiener spectra were measured as indices of image quality. Presampling MTFs were measured from slit and edge images at 28kV. Digital Wiener spectra were measured at 28kV with breast equivalent filter. Presampling MTFs with both readings were almost the same. Digital Wiener spectra with dual side reading were superior to those with single side reading. NEQ of CR system with dual side reading was superior to that with single side reading because of the good efficiency of light condensing. New mammographic CR systems with dual side readings should be a further powerful tool for detecting low-contrast lesions in breast. Wiener spectra need to determine exposure conditions, in order to perform comparison between institutions, since it is strongly influenced of beam quality and a dose. We also compared overall characteristic curves, overall MTFs and overall Wiener spectra of a new CR system with them of a screen-film system. Although MTF was calculated by the slit method, it is necessary to examine another method in quest of MTF including the effect of image processing of CR system.