Using a human visual system model to optimize soft-copy mammography display: Influence of display phosphor

Rationale and Objectives. The authors developed an efficient method for optimizing cathode ray tube performance for soft-copy digital mammography displays, based on correlation between the performance of human observers and the performance of a mathematical computer model of the human visual system. The authors measured radiologist performance on soft-copy display monitors with different phosphors and used these results to validate the human visual performance model. Materials and Methods. Six radiologists viewed a series of 250 mammographic images with microcalcifications of different contrast levels. They viewed images on two soft-copy display monitors with phosphor luminescence-one with P45 and the other with P104. The same images were analyzed with the JNDmetrix Visual Discrimination Model, which is based on psychophysical just-noticeable difference measurement principles and on frequency-channel vision-modeling principles. Receiver operating characteristic curves were generated for the human and model observers' performances, and results were compared statistically. Results. Both human and model performance (area under the receiver operating characteristic curve) was better overall with the P45 than with the P104 monitor, especially for microcalcifications in the midlevel contrast range. There was high correlation between the human and model observers. Conclusion. The results indicate that the type of phosphor in a display monitor can influence observer performance significantly and that a model based on characteristics of the human visual system can be used to predict human observer performance accurately.