PHYSICAL EVALUATION OF COMPUTED RADIOGRAPHY AS A MAMMOGRAPHIC X-RAY-IMAGING SYSTEM

The physical imaging properties of a computed radiography (CR) system operating under mammographic exposure conditions have been measured. T hese measurements include modulation transfer function (MTF), sensitom etric response and noise power spectrum (NPS). These figures were used to derive signal-to-noise ratio (SNR) descriptors of the system perfo rmance. The same measures were derived for a mammographic film-screen system. The SNR properties of the CR system indicate superior low freq uency performance over a wider dynamic range than the film-screen syst em. The spatial frequency dependent SNR properties of the CR system ar e, however, limited. The results of a psychophysical test support the results obtained from physical measurements. These results indicate th at despite its limited sharpness, details of dimensions relevant to di agnosis in mammography (circular details 0.25 mm diameter to represent microcalcifications and 3 mm diameter to represent small masses) are reproduced using CR with SNRs which are at least comparable with those of a mammographic film-screen system.