Effect of monitor luminance and ambient light on observer performance in soft-copy reading of digital chest radiographs

PURPOSE: To examine the combined effects of monitor luminance and ambient light on observer performance for detecting abnormalities in a soft-copy interpretation of digital chest radiographs. MATERIALS AND METHODS: A total of 254 digital chest radiographs were displayed on a high-resolution cathode ray tube monitor at three luminance levels (25, 50, and 100 foot-lamberts) under three ambient light levels (0, 50, and 460 lux). Six chest radiologists reviewed each image in nine modes of combined luminance and ambient light. The observers were allowed to adjust the window width and level of the soft-copy images. The abnormalities included nodule, pneumothorax, and interstitial disease. Observer performance was analyzed in terms of the receiver operating characteristics. The observers reported their subjective level of visual fatigue with each viewing mode. A statistical test was conducted for each of the abnormalities and for fatigue score by using repeated-measures two-way analysis of variance with an interaction. RESULTS: The detection of nodules was the only reading that was affected by the ambient light with a statistically significant difference (P < .05). Otherwise, observer performance for detecting a nodule, pneumothorax, and interstitial disease was not significantly different in the nine-mode comparison. There was no evidence that the luminance of the monitors was related to the ambient light for any of the abnormalities. The fatigue score showed a statistically significant difference due to both the luminance and ambient light. CONCLUSION: When adequate window width and level are applied to soft-copy images, the primary diagnosis with chest radiographs on the monitor is unlikely to be affected under low ambient light and a monitor luminance of 25 foot-lamberts or more. (C) RSNA, 2004.