Purpose: Automated breast ultrasound (ABUS) presents three-dimensional (3D) representations of the breast in the form of stacks of coronal and transverse plane images. ABUS is especially useful for the assessment of dense breasts. Here, we present the first eye tracking data showing how radiologists search and evaluate ABUS cases.Approach: Twelve readers evaluated single-breast cases in 20-min sessions. Positive findings were present in 56% of the evaluated cases. Eye position and the currently visible coronal and transverse slice were tracked, allowing for reconstruction of 3D “scanpaths.”Results: Individual readers had consistent search strategies. Most readers had strategies that involved examination of all available images. Overall accuracy was 0.74 (sensitivity = 0.66 and specificity = 0.84). The 20 false negative errors across all readers can be classified using Kundel’s (1978) taxonomy: 17 are “decision” errors (readers found the target but misclassified it as normal or benign). There was one recognition error and two “search” errors. This is an unusually high proportion of decision errors. Readers spent essentially the same proportion of time viewing coronal and transverse images, regardless of whether the case was positive or negative, correct or incorrect. Readers tended to use a “scanner” strategy when viewing coronal images and a “driller” strategy when viewing transverse images.Conclusions: These results suggest that ABUS errors are more likely to be errors of interpretation than of search. Further research could determine if readers’ exploration of all images is useful or if, in some negative cases, search of transverse images is redundant following a search of coronal images.
Purpose: Radiologists sometimes fail to report clearly visible, clinically significant findings. Eye tracking can provide insight into the causes of such errors.
Approach: We tracked eye movements of 17 radiologists, searching for masses in 80 mammograms (60 with masses).
Results: Errors were classified using the Kundel et al. (1978) taxonomy: search errors (target never fixated), recognition errors (fixated <500 ms), or decision errors (fixated >500 ms). Error proportions replicated Krupinski (1996): search 25%, recognition 25%, and decision 50%. Interestingly, we found few differences between experts and residents in accuracy or eye movement metrics. Error categorization depends on the definition of the useful field of view (UFOV) around fixation. We explored different UFOV definitions, based on targeting saccades and search saccades. Targeting saccades averaged slightly longer than search saccades. Of most interest, we found that the probability that the eyes would move to the target on the next saccade or even on one of the next three saccades was strikingly low (∼33 % , even when the eyes were <2 deg from the target). This makes it clear that observers do not fully process everything within a UFOV. Using a probabilistic UFOV, we find, unsurprisingly, that observers cover more of the image when no target is present than when it is found. Interestingly, we do not find evidence that observers cover too little of the image on trials when they miss the target.
Conclusions: These results indicate that many errors in mammography reflect failed deployment of attention; not failure to fixate clinically significant locations.
KEYWORDS: Digital breast tomosynthesis, Breast, Mammography, Signal detection, Cancer, Architectural distortion, Medical imaging, Pathology, Image processing, Lung
Evans et al. (2016) showed that radiologists can classify the mammograms as normal or abnormal at above-chance levels after a 250-ms exposure. Our study documents a similar gist signal in digital breast tomosynthesis (DBT) images. DBT is a relatively new technology that creates a three-dimensional image set of slices through the volume of the breast. It improves performance over two-dimensional (2-D) mammography but at a cost in reading time. In the experiment presented, radiologists (N = 16) viewed “movies” of DBT images from single breasts for an average of 1.5 s per case. Observers then marked the most likely lesion position on a blank outline and rated each case on a six-point scale from (1) certainly normal to (6) certainly recall. Results show that radiologists can discriminate normal from abnormal DBT cases at above-chance levels as in 2-D mammography. Ability was correlated with experience reading DBT. Observers performed at above-chance levels, even on those images where they could not localize the target, suggesting that this is a global signal that could prove valuable in the clinic.
Digital breast tomosynthesis (DBT) is beginning to be used more frequently alongside full-field digital mammography (DM) in routine breast cancer screening. However, little is known about radiologists’ search strategies reading DBT. This study aims to measure radiologists’ eye movements prior to testing search strategies intended to make DBT faster and/or more accurate. Twelve observers (board certified breast radiologists or current women’s imaging fellows) were instructed to search for lesions as they would report during normal clinical conditions. Observers were shown a single view of a single breast for each case and informed that this was an enriched study (10 positive cases out 20). Eye tracking used a SMI RED250mobile Eye Tracker sampling at 250Hz. Tracking error was below 0.5 deg. There was an increase in the detection rate/accuracy and decrease in false positives with DBT compared to DM. There was a longer search time in DBT compared to DM, with a shorter saccade length shown in DM. Different observers where shown to have differing search patterns however it was not possible to show any observer to have a true driller or scanner technique. Results generally replicated previous studies however; more work would be needed to obtain conclusions as to optimal search strategies.
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