INFLUENCE OF VISUAL DISTRACTORS ON DETECTABILITY OF LIVER NODULES ON CONTRAST-ENHANCED SPIRAL COMPUTED-TOMOGRAPHY SCANS

Rationale and Objectives. The authors evaluated the ability of observe rs to identify simulated nodules placed electronically on normal contr ast material-enhanced computed tomography (CT) scans of the liver to a ssess the effect of nodule size and polarity on detection and localiza tion. Methods. Seven readers evaluated two sets of CT scans that conta ined 80 stimuli each. The simulated nodules were either darker or brig hter than the contrast-enhanced liver and were 5.6-8.0 mm in diameter. Readers were asked to fmd the most suspicious-looking nodule on each section and rate the likelihood that the chosen location actually cont ained a nodule. Results. The fraction of nodules found by each observe r was substantially greater for dark nodules than for bright ones (0.6 79 +/- 0.03 vs 0.345 +/- 0.045, respectively [mean +/- standard error] ). This difference was consistent for all nodule sizes. Additional ana lyses (including receiver operating characteristic curves of condition al responses) suggested that the presence of bright blood vessels dist racted the readers and decreased their ability to find bright nodules. Conclusion. Normal vascular structures on contrast-enhanced CT scans of the liver impair an observer's ability to detect bright Liver nodul es.