Title : CAD in mammography : lesion - level vs . case - level analysis of the effects

Title: CAD in mammography: lesion-level vs. case-level analysis of the effects of prompts on human decisions Abstract OBJECT: To understand decision processes in CAD-supported breast screening by analysing how prompts affect readers' judgements of individual mammographic features (lesions). To this end we analysed hitherto unexamined details of reports completed by mammogram readers in an earlier evaluation of a CAD tool. Assessments of lesions were extracted from 2889 reports for 59 cancer cases. Statistical analyses of these data focused on what features readers considered when recalling a cancer case and how readers reacted to CAD prompts. RESULTS: 13.5% of recall decisions were found to be caused by responses to features other than those indicating actual cancer. Effects of CAD: lesions were more likely to be examined if prompted; the presence of a prompt on a cancer increased the probability of both detection and recall especially for less accurate readers in more subtle cases; lack of prompts made cancer features less likely to be detected; false prompts made non-cancer features more likely to be classified as cancer. The apparent lack of impact reported for CAD in some studies is plausibly due to CAD systematically affecting readers' identification of individual features, in a beneficial way for certain combinations of readers and features and a damaging way for others. Mammogram readers do not ignore prompts. Methodologically, assessing CAD by numbers of recalled cancer cases may be misleading.