View box luminance measurements and their effect on reader performance

Rationale and Objectives, The purpose of this study was to investigate the importance of view box luminance and viewing conditions on low-contrast det ection by readers. Materials and Methods. Radiographs of a mammographic contrast-detail phanto m were examined on 632 view box panels. The luminance of these panels was o btained by using a calibrated meter and ranged from 860 to 3,300 nit. Twelv e radiologists reported the number of contrast-detail disks for each size ( diameter, 0.3-7.0 mm) I deemed to be visible on films with optical densitie s of 1.00-2.60. Radiologist performance in reading low-contrast phantom ima ges was also studied as a function of room illuminance and image masking. Results. Median luminance was 1,700 nit, with 25- and 75-percentile Values of 1,450 and 2,150 nit, respectively. : Low-contrast visibility generally w as independent of view box luminance, regardless of film density or disk di ameter. Low-contrast visibility deteriorated when masking around the image was removed and at normal room illuminance. The greatest deterioration in p erformance occurred at the highest film densities and with the smallest siz e disks. Conclusion. Detection of low-contrast features on radiographs is relatively independent of view box luminance, but it is degraded by the presence of s tray light and by increased room illuminance.