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Influence of display and observer responses in receiver operating characteristic (ROC) experiments

Medical image quality can be defined in terms of observer performances in detecting image abnormalities, since diagnosis is essentially based on visual inspection of medical images. There exists a large body of theoretical and experimental work specifying it in terms of signal to noise ratio, area under the ROC curve, and detectability index. However, the comparison between the theoretical and experimental figures of merit (FOMs) is made difficult because FOMs do operate on different signals and observers. In this paper we investigate the relationships between such signals, observers, and FOMs; the soundness of the underlying assumptions; and the possibility of optimizing image display. In section 2 we define three signal-observer pairs for which the main theoretical and experimental results are recalled. We also present the results obtained in our lab to show their consistency with results found in the literature. In section 3 we describe an experiment designed to evaluate the relationships between the three types of signal-observer pairs, and to assess the robustness of the model with respect to the assumptions. We also present in this section the results of this experiment. In section 4 these results and the relevance of FOMs are discussed.