Lesion detectability in 2D-mammography and digital breast tomosynthesis using different targets and observers

Abstract

This work investigates the detection performance of specialist and non-specialist observers for different targets in 2D-mammography and digital breast tomosynthesis (DBT) using the OPTIMAM virtual clinical trials (VCT) Toolbox and a 4-alternative forced choice (4AFC) assessment paradigm. Using 2D-mammography and DBT images of virtual breast phantoms, we compare the detection limits of simple uniform spherical targets and irregular solid masses. Target diameters of 4 mm and 6 mm have been chosen to represent target sizes close to the minimum detectable size found in breast screening, across a range of controlled contrast levels. The images were viewed by a set of specialist observers (five medical physicists and six experienced clinical readers) and five non-specialists. Combined results from both observer groups indicate that DBT has a significantly lower detectable threshold contrast than 2D-mammography for small masses (4 mm: 2.1% [DBT] versus 6.9% [2D]; 6 mm: 0.7% [DBT] versus 3.9% [2D]) and spheres (4 mm: 2.9% [DBT] versus 5.3% [2D]; 6 mm: 0.3% [DBT] versus 2.2% [2D]) (p < 0.0001). Both observer groups found spheres significantly easier to detect than irregular solid masses for both sizes and modalities (p < 0.0001) (except 4 mm DBT). The detection performances of specialist and non-specialist observers were generally found to be comparable, where each group marginally outperformed the other in particular detection tasks. Within the specialist group, the clinical readers performed better than the medical physicists with irregular masses (p < 0.0001). The results indicate that using spherical targets in such studies may produce over-optimistic detection thresholds compared to more complex masses, and that the superiority of DBT for detecting masses over 2D-mammography has been quantified. The results also suggest specialist observers may be supplemented by non-specialist observers (with training) in some types of 4AFC studies.

The threshold detectable mass diameter for 2D-mammography and digital breast tomosynthesis

“…DBT was found to have a lower threshold detectable mass diameter than 2D-mammography (p-value of < 0.0001), whichever choice of PC was made; 90.7% or 62.5%, although the threshold values are higher for the higher PC choice. The order of performance of the systems agrees with a previous 4AFC observer study [20], carried out using methods similar to those used in the current study, but which used Hologic reconstruction software instead of Briona reconstruction software, and which evaluated the signal contrast needed to correctly identify a mass, instead of the threshold detectable mass diameter. Elangovan et al [20] showed that observers needed over three times the signal contrast to correctly identify a mass in 2D-mammography compared with DBT (narrow angle).…”

“…The order of performance of the systems agrees with a previous 4AFC observer study [20], carried out using methods similar to those used in the current study, but which used Hologic reconstruction software instead of Briona reconstruction software, and which evaluated the signal contrast needed to correctly identify a mass, instead of the threshold detectable mass diameter. Elangovan et al [20] showed that observers needed over three times the signal contrast to correctly identify a mass in 2D-mammography compared with DBT (narrow angle). The work by Mackenzie et al [19] used similar methods to quantify the minimum detectable mass diameter for 2D-mammography and DBT for the Siemens Inspiration system (which has the wide-angle geometry used in this study).…”

“…As this was a forced choice study and does not include the effect of 'searching' or interpretation, non-radiologists as observers were acceptable. Elangovan et al [20] found that although radiologists had a slightly better detection rate in 4-AFC studies than non-radiologists, there were no differences in the overall conclusions about the effect of differences in technology. An in-house Java-based plug-in (ImageJ 1.50i, NIH, USA) was used to run the 4AFC study (Fig.…”

“…Alternatively, simulation methods are sensitive and useful for investigating the imaging technology. Observer studies with lesions inserted into physical phantoms (anthropomorphic or structured) [15,16] or fully simulated breast images [17][18][19][20] have yielded useful results, while image metrics such as contrast-to-noise ratio (CNR), CNR/ASF (artefact spread function) [21][22][23] have also been used successfully.…”

“…Simulation studies have shown that masses were visible at a lower contrast than with 2D-mammography in comparison to DBT [17,20]. In the recent work of Hadjipanteli et al [18] three commercially-implemented geometries (2D-mammography, narrow angle (15°/15 projections) and wide angle (50°/25 projections)) were compared.…”