Relationship of subjective ratings of image quality and observer performance

The relationship between radiologists' perception of image quality and their actual performance was assessed. If the two variables are strongly correlated, the easier obtained perception of quality index might be used as a prerequisite test to determine if a ROC study is justified. One-hundred seventy cases were evaluated for the presence or absence of interstitial disease and nodules by nine readers using seven display modes. Each reader also assigned each image a mode- specific perceived quality rating using a 5-category ordinal scale. Average perceived quality was highest for conventional film. It was slightly poorer for the subsets of cases with interstitial disease and for cases classified independently as 'subtle.' Trend tests indicated a relationship between area under the ROC curves (A_z) and perceived image quality for nodules. For interstitial disease, the relationship was weaker and of borderline statistical significance. The subjective image quality index was related to the area under the ROC curve, but the average difference between pairs of display modes was not a good predictor of difference in actual observer performances. A subjective quality index may have limited usefulness in screening differences between modalities prior to the performance of a ROC study.