COMPARISON OF A CATHODE-RAY-TUBE AND FILM FOR DISPLAY OF COMPUTED RADIOGRAPHIC IMAGES

The goal of the study was to compare a cathode-ray-tube (CRT) digital display with film by using task-dependent image quality assessment met hods. Contrast-detail analysis was utilized. Human observers performed a simple detection task, specifically, detecting a pillbox target in a uniform Poisson field, using either film or a digital display that e mployed a CRT monitor. Observers performed equally well on both film a nd CRT when the window settings of the digital display were establishe d subjectively by a radiologist. Changing the window settings of the d igital display to match the average background luminance of a film-ill uminator combination decreased the luminance contrast of the targets a nd observer performance was reduced, though these effects were probabl y not linked. The ''gold standard'' film had lower luminance contrast than the CRT displayed images, yet observer performance was never lowe r for film than for the CRT. Therefore we concluded that luminance con trast was not a limiting factor for observer performance in this study . The CRT monitor changed fairly rapidly after it was calibrated. Duri ng a period of six months the gamma of the display increased from 1.82 to 2.42 and the maximum luminance decreased from 319 to 228 cd/m(2). Low luminance output demonstrated a larger percentage decrease (approx imate to 85%) than high luminance output (approximate to 29%) over the same time period. These observations suggest that standard window set tings should be reviewed from time to time to ensure that the display is used optimally. No special look-up table setup such as perceptual l inearization was used. (C) 1998 American Association of Physicists in Medicine.