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. 2018 Jan;5(1):015501.
doi: 10.1117/1.JMI.5.1.015501. Epub 2018 Jan 17.

Virtual assessment of stereoscopic viewing of digital breast tomosynthesis projection images

Affiliations

Virtual assessment of stereoscopic viewing of digital breast tomosynthesis projection images

Gezheng Wen et al. J Med Imaging (Bellingham). 2018 Jan.

Abstract

Digital breast tomosynthesis (DBT) acquires a series of projection images from different angles as an x-ray source rotates around the breast. Such imaging geometry lends DBT naturally to stereoscopic viewing as two projection images with a reasonable separation angle can easily form a stereo pair. This simulation study assessed the efficacy of stereo viewing of DBT projection images. Three-dimensional computational breast phantoms with realistically shaped synthetic lesions were scanned by three simulated DBT systems. The projection images were combined into a sequence of stereo pairs and presented to a stereomatching-based model observer for deciding lesion presence. Signal-to-noise ratio was estimated, and the detection performance with stack viewing of reconstructed slices was the benchmark. We have shown that: (1) stereo viewing of projection images may underperform stack viewing of reconstructed slices for current DBT geometries; (2) DBT geometries may impact the efficacy of the two viewing modes differently: narrow-arc and wide-arc geometries may be better for stereo viewing and stack viewing, respectively; (3) the efficacy of stereo viewing may be more robust than stack viewing to reductions in dose. While in principle stereo viewing is potentially effective for visualizing DBT data, effective stereo viewing may require specifically optimized DBT image acquisition.

Keywords: digital breast tomosynthesis; disparity; model observer; reconstruction; stereo matching; stereoscopic viewing.

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Figures

Fig. 1
Fig. 1
(a) Coronal view of two example breast phantoms with 7 cm compressed thickness. The two phantoms had different spatial distributions of segmented breast tissue classes. (b) Example synthetic breast lesion to be detected. The central mass contained some surface irregularities.
Fig. 2
Fig. 2
Schematic of the three DBT system geometries that differ in the angular span and the number of projections per scan. (a) and (b) used narrow-arc geometries with 16 deg of angular span, whereas (c) used a wide-arc geometry with 48 deg of angular span. The angular interval between two consecutive projections (e.g., red dotted line and black dash line) indicates the angular increment of the geometry. (a) used 1 deg of angular increment, whereas (b) and (c) used 2 deg of angular increment.
Fig. 3
Fig. 3
(a, b) An example of a stereo pair with a separation angle of 8 deg. (c) The corresponding cyclopean view constructed from the stereo pair in (a) and (b). (d) An example FBP reconstructed slice. The red boxes in (a)–(d) indicate the locations of the three ROIs on projections, cyclopean view, and reconstructed slices, respectively. (e)–(f) Example ROI 1 extracted from the cyclopean view in (c) and from the reconstructed slice in (d), respectively. The ROIs were of size 25  mm×25  mm around the center of the lesions.
Fig. 4
Fig. 4
Example of five PLS channels [first (left) to fifth (right) channel] for: (a) the sequence of cyclopean ROIs; (b) the reconstructed ROIs. Results with ROI 3 from the geometry of 16 deg angular span and 17 projections per scan are shown here. PLS channels captured lesion characteristics and local anatomical background.
Fig. 5
Fig. 5
The SNRs achieved at the three ROIs using stereo viewing of projection images (blue), and that using stack viewing of FBP reconstructed slices (red). Results with the DBT geometry of 16 deg angular span and 17 projections per scan are shown here. The SNRs for stereo viewing (blue) were statistically lower than those for stack viewing (red). The SNRs for both stereo viewing and stack viewing were different across the three ROIs.
Fig. 6
Fig. 6
Difference in the SNRs achieved with the geometries (16 deg of angular span, 17 projections per scan) and (48 deg of angular span, 25 projections per scan). Results with ROI 3 and FBP reconstruction are shown here. ΔSNR with stereo viewing (blue) was significantly higher than zero, but ΔSNR with reconstructed slices (red) was significantly lower than zero. Narrow-arc geometries may be better for stereo viewing, while wide-arc geometries may be better for stack viewing.
Fig. 7
Fig. 7
Difference in the SNRs achieved with the geometries “half-dose” and “full-dose” (16 deg of angular span, nine projections per scan). Results with ROI 3 are shown here. ΔSNR with stereo viewing of projection images (blue), and with stack viewing of MLEM reconstructed slices (red) was statistically equivalent to zero, while ΔSNR with stack viewing of FBP and SART reconstructed slices (red) was significantly lower than zero. If a DBT geometry could be specifically optimized for stereo viewing, it may be possible to reduce the dose required for DBT image acquisition.

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