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Time Course of Perception and Decision Making During Mammographic Interpretation

Calvin F. Nodine1, Claudia Mello-Thoms2, Harold L. Kundel1 and Susan P. Weinstein1

1 Department of Radiology, University of Pennsylvania Health Care System, 3600 Market St., Ste. 370, Philadelphia, PA 19104-2644.
2 Department of Radiology, Imaging Division, University of Pittsburgh, 300 Halkert St., Ste. 4200, Pittsburgh, PA 15213-3180.



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  		Fig. 1. —Graph shows mean cumulative number of case decision outcomes as function of time to decision for mammographers for final-decision phase. Most true-positive responses ([UNK]) were made within 40 sec. These responses were offset by false-positive responses for cases with normal findings ({blacktriangledown}) and false-positive responses for cases with abnormal findings ({circ}) that began to influence performance at 20 sec. False-positive responses for normal cases continued to influence performance throughout time course of viewing, but false-positive responses for abnormal cases leveled off at approximately 40 sec, and true-positive responses continued to outweigh false-positive responses for both normal and abnormal cases throughout time of viewing.

 


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  		Fig. 2. —Graph shows mean cumulative number of case decision outcomes as function of time to decision for trainees for final-decision phase. As was seen with mammographers, most true-positive responses ([UNK]) were made within 40 sec, but performance of trainees was approximately half that of mammographers. False-positive responses on cases with abnormal findings ({circ}) and false-positive responses on cases with normal findings ({blacktriangledown}) began to affect performance at 15 sec. At 35 sec, false-positive responses for normal cases plus false-positive responses for abnormal cases started to overtake true-positive responses, and performance continued to deteriorate as decision time increased.

 


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  		Fig. 3. —Graph shows positive predictive value for mammographers ([UNK]) and trainees ({blacktriangledown}). Positive predictive value is function of time to decision for final-decision phase and takes into account both true-positive responses (TP) and false-positive responses for cases with normal findings (FPn). Positive predictive value is calculated as [TP / (TP + FPn)]. False-positive responses for abnormal cases were not included, which is common usage. Positive predictive value performance begins high and levels off for both mammographers and trainees. Each set of positive predictive value data are fit by two linear-regression lines. These lines cross at approximately 25 sec for mammographers and at approximately 40 sec for trainees. These lines divide performance over time course of viewing into what Christensen et al. [1] labeled rapid phase and slow phase. We hypothesize that rapid phase reflects global discovery of lesions by Gestalt process and that slow phase reflects detection of lesions by focal search process.

 


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  		Fig. 4A. —56-year-old woman with microcalcifications in right breast. Two mammograms obtained in craniocaudal (left) and mediolateral oblique (right) views that served as one of 40 test cases. Microcalcifications are present on both mammograms.

 


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  		Fig. 4B. —56-year-old woman with microcalcifications in right breast. Eye-fixation record of trainee scanning mammograms shown in A. Total search time was 28 sec. Lesion area is indicated by large circle (radius = 1.65 cm) with thin line in each image. Areas of fixation are indicated by small circles that are connected by lines to show path of trainee's eyes. Clusters of areas of fixation within radius of 1.65 cm that had combined dwell time of more than 1000 msec are represented by large circles with thick lines. Note that trainee did not fixate on true lesion in either image. Rather, trainee focused attention on subareolar region, indicated by three fixation clusters (large circles with thick lines) of 1000 msec in two images. Trainee reported lesion in this area and interpreted it as architectural distortion at end of search.

 


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  		Fig. 4C. —56-year-old woman with microcalcifications in right breast. Eye-fixation record of experienced mammographer scanning A. Total search time was 34 sec. Lesion area is again shown by large circle with thin lines. Mammographer focused attention on true lesion, cluster of microcalcifications. Attention was fixated on craniocaudal view almost immediately on presentation. Mammographer crossed over to mediolateral oblique view and fixated lesion within 16 sec. During entire search, mammographer fixated lesion in both images for dwell times greater than 1000 msec, indicated by thick-line fixation-cluster circles overlapping thin-line lesion circles. Mammographer also fixated same subareolar region in lateral breast on craniocaudal view that trainee fixated for 1000 msec, but mammographer did not report abnormal finding for this location. True lesion, however, was reported as microcalcification cluster at end of search.

 


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  		Fig. 5. —Graph shows localization receiver operating characteristic curves (LROC) for mammographers ([UNK]) and trainees ([UNK]). Measure of performance is area under LROC curve. Area under curve for mammographers was 0.66. Area under curve for trainees was 0.47. These areas are significantly different.

 

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