We report an evaluation of the effect of introducing 3D mammography (breast tomosynthesis) on acquisition time and reading time for screening mammography, finding that both measures were prolonged with integration of 3D imaging (adding 3D to conventional mammography). The study is based on a sufficient number of screening examinations to allow a reliable estimate of differences in (radiographer) acquisition time and in radiologists' reading time of combined 2D+3D compared with 2D mammography. It is reasonable to expect that adding (rather than substituting) further image acquisition and interpretation would increase workload (based on time measures). The primary intention of the study was therefore to establish the magnitude of effect on both acquisition and reading time, especially in the relatively early phase of implementation of 3D mammography in established screening services.
It could be argued that 3D mammography training of radiographers and radiologists, prior to conducting the study, was relatively brief. There is not an issue for radiographers' training, as the only difference between 2D and 2D+3D mammography is related to 3D image acquisition and reconstruction, which does not directly involve the radiographer (and hence does not require special training); radiographers' training essentially related to switching the machine from the 2D to the COMBO modality. Radiologists' training, however, was based on a minimum review of 100 3D images, so we cannot exclude that the reading time may improve (reduce) with longer experience in 3D interpretation. However, it has been our experience that long training is not needed for expert breast radiologists dedicated to mammography reading, and the learning curve may be expected to be modest for combined 2D/3D as it is a mammography-based
technology. We also examined (in a related evaluation of tomosynthesis) radiologists' reading time at 6 months further experience with 3D images and found minor changes (essentially slight reductions in average reading time for 2D+3D). Furthermore, the workstation software is simple and easy to manage: in the USA the manufacturer recommends 8 h of training before managing and reporting 3D images in practice, while in the present experience, training in managing and reporting 3D images was at least 10 times longer (based on training and several months application). Even if a learning curve in interpreting 3D reconstructed images to achieve optimal accuracy is assumed, this is likely to have less of an effect on reading time, as for 2D mammography, where reading time stabilises after a relatively short period, while individual differences in accuracy persist over a longer time [16
2D+3D mammography was associated with a modest (though statistically significant) increase in acquisition time. The study design considered only the crude patient positioning and image acquisition time, and the observed +26% excess for 2D+3D might be further reduced with respect to overall “door to door” time, including time for undressing/dressing, which is variable. Overall, time to perform 2D+3D mammography would be expected to exceed that of 2D mammography, and will vary with the mammography unit used—we had a relatively short acquisition time for 3D images (4 s per view, over a 15° angle). Acquisition time may be higher with other machines that use longer scanning time (up to 15 s per view).
When measuring radiologists' reading time we considered combined 2D+3D image reading relative to standard 2D mammography reading. We intentionally did not use 3D image reading alone because (based on current knowledge and screening practice) panoramic analysis of 2D images is essential prior to 3D image analysis. In our setting, radiologists are as yet developing expertise in 3D diagnostic pattern definition, and the superiority of 2D+3D imaging compared with 3D imaging alone has been reported [17
]; hence, we maintained the standard screen reading of 2D and evaluated the addition of 3D to 2D reading. It may be, nevertheless, that 3D-only mammography has a future role, possibly using a “synthetic” reconstruction as a 2D imaging surrogate, but this needs to be evaluated in appropriately designed trials, and needs to be supported by enhanced knowledge and consolidation of information from 3D diagnostic patterns. Deliberation over the almost double exposure dose delivered in the COMBO procedure (though still within acceptable exposure values), while not the purpose of the present study, is nonetheless a relevant issue that might prompt exploration of the use of 3D-only imaging in breast screening in future studies.
Our findings indicate that reading time is substantially different for 2D vs
2D+3D mammography. As pointed out earlier, this is not entirely surprising, as the time measured was for combined
2D+3D mammography, and because 3D images are reviewed by scrolling through different breast planes (similar to looking at a movie). This does not allow a panoramic view of the whole breast as with 2D mammography: 3D imaging requires separate analysis of different parts of each breast view (at least two segments), and this must be repeated for all four views. An increase in reading time for 2D+3D mammography has also been noted in other studies [19
]: based on the data reported in each of these studies, for Good et al [19
] we estimated a +172% incremental reading time, and for Gur et al [20
] we estimated +96% incremental reading time, and our data showed a relatively intermediate value (+133%) for incremental reading time for combined 2D+3D mammography. This aspect of 3D imaging is particularly unique to 3D mammography reading in screening practice, where the whole breast must be examined in search of abnormalities that may have been missed at 2D mammography. 3D mammography use for targeted analysis (for example, as a triage to further assessment where abnormalities have been identified at 2D mammography) is obviously less demanding in terms of reading time.
Based on present study findings, mammography screen reading using 2D+3D mammography more than doubled (on average) the reading time (see ), and the magnitude of the effect was similar for participating radiologists. In a 3D mammography screening scenario, even if only used for a subgroup of subjects (e.g.
with dense breast, therefore at higher risk of false-positives due to superimposition or masking), the radiologist's workload will be substantially increased with prolonged reading time. For the current population screening scenario (age 50–69 years), 2D+3D mammography screening of subjects with Breast Imaging-Reporting and Data System (BI-RADS) D3–D4 dense breast (around 25% of this population [21
]), assuming an incremental reading time of +100–200%, radiologists' reading time would be expected to increase by approximately 25–50%. Alternatively, extending 3D mammography screening to BI-RADS D2–4 subjects (around 70% of screening participants in targeted age group) will increase radiologists' reading time in the range of 70–140%. Although combined 2D+3D breast screening is not currently proposed, in the absence of high-level scientific evidence supporting its efficacy in screening, we recommend that future screening evaluations of 3D mammography consider the additional time demands in both feasibility and cost-effectiveness studies. In breast screening, computer-aided detection (CAD) may prove a useful complementary tool in the future; however, at this stage, development and application of 3D mammography CAD is still in its infancy.
We have pointed out that reader accuracy was not
a primary objective of this evaluation, but was integrated into the study as a measure of reader attention, and also provides an indication of relative
accuracy. It is therefore worth noting (but with cautious interpretation of these data, which have not excluded a learning effect from repeat reads) that an increased sensitivity was observed using 2D+3D mammography (relative to 2D alone), and this was associated with a substantial increase in specificity (reduction in recalls), also shown in other studies [8
]. The striking reduction in the numbers recalled for assessment based on 2D+3D, in particular, should be “tested” in large-scale studies, as this has the potential to reduce the burden of false-positive screens—an issue of considerable relevance to both screening participants and screening services.
We conclude that integrating 3D with 2D mammography in breast screening prolongs image acquisition and screen-reading times, relative to 2D mammography alone, and the effect is more marked for radiologists' reading time (at least in the implementation phase of this new technology). The prolonged reading time might reduce with further experience, and may be acceptable if associated with enhanced screening accuracy (yet to be demonstrated in large trials), particularly reduced recalls, and warrants evaluation in prospective trials of population breast screening.