A 4-Alternative Forced Choice (4-AFC) experimental paradigm was used to measure observer performance of lesion detection. Each 4-AFC experiment yields a lesion contrast that corresponds to a detection accuracy of 92%, I(92%). Experiments were performed to investigate how imaging performance varied with display level setting (window level) at a constant image contrast (window width). Three observers were used to investigate detection performance with window level using a high quality monitor calibrated three different ways (i.e., DICOM, gamma = 1.5, and gamma = 5.0). There were large inter-observer differences in absolute level of performance, with the detection threshold for the three readers varying by nearly a factor of two. For the DICOM display, the detection threshold was linearly related to image level setting. For one reader, detection performance was independent of level, whereas for the other two readers performance dropped by 30% and 11% over the range of level values investigated. Curves changed from linear for the DICOM display to curvilinear for two gamma monitor display settings. In addition, the absolute level of performance for each reader changed with monitor display setting. When the display gamma was 1.5, observer performance was generally reduced, whereas when the display gamma was 5.0, observer performance was generally better. Our data show that the choice of monitor display is an important parameter that significantly affects lesion detection performance. Adoption of the DICOM display standard will permit the direct inter-comparison of data acquired in different laboratories, as well as clinical practice.
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