Robert F. Wagner

The author traces some critical moments in the history of Image Science in the last half century from first-hand or once-removed experience. The Image Science used in the field of medical imaging today had its origins in the analysis of photon detection developed for modern television, conventional photography, and the human visual system. Almost all “model observers” used in image assessment today converge to the model originally used by Albert Rose in his analysis of those classic photo-detectors. A more general statistical analysis of the various “defects” of conventional and unconventional photon-imaging technologies was provided by Shaw. A number of investigators in medical imaging elaborated the work of these pioneers into a synthesis with the general theory of signal detectability and extended this work to the various forms of CT, energy-spectral-dependent imaging, and the further complication of anatomical-background-noise limited imaging. The author calls for further extensions of this work to the problem of under-sampled and thus artefact-limited imaging that will be important issues for high-speed CT and MRI.

The multiple-reader, multiple-case (MRMC) approach to receiver operating characteristic (ROC) analysis is becoming the dominant assessment paradigm in medical imaging. Its most common version involves having many readers read every patient case in the study, a critical feature since differences among competing imaging modalities are often dominated by differences in reader performance. The present authors have carried out MRMC ROC analysis on a uniquely large data set for mammography. The analysis quantifies the great range of observed reader skill in that data set. It also demonstrates that the sample sizes are sufficiently large that the conclusions generalize to the populations sampled here with little uncertainty from the finite sample size. A schematic approach to bracketing the utility matrix is then used to study trends in the resulting expected utility functions that correspond to the range of observed ROC curves. This is done for both the screening and the diagnostic context. The results raise 2 hypotheses for further investigation. First, it is possible that the present ambiguity surrounding the effectiveness of mammography is due in part to the observed range of reader skills and corresponding expected utility functions. Second, it is possible that computer-assisted modalities for mammography may lead to improvements in the expected utility function not only for screening but also in the diagnostic context, especially for the lower performing readers.