Rationale and Objectives
The aim of this study was to retrospectively compare the interpretive performance of synthetically reconstructed two-dimensional images in combination with digital breast tomosynthesis (DBT) versus full-field digital mammography (FFDM) plus DBT.
Materials and Methods
Ten radiologists trained in reading tomosynthesis examinations interpreted retrospectively, under two modes, 114 mammograms. One mode included the directly acquired full-field digital mammograms combined with DBT, and the other included synthetically reconstructed projection images combined with DBT. The reconstructed images do not require additional radiation exposure. The two modes were compared with respect to sensitivity, namely, recommendation to recall a breast with either a pathology-proven cancer ( n = 48) or a high-risk lesion ( n = 6), and specificity, namely, no recommendation to recall a breast not depicting an abnormality ( n = 144) or depicting only benign abnormalities ( n = 30).
Results
The average sensitivity for FFDM with DBT was 0.826, compared to 0.772 for synthetic FFDM with DBT (difference, 0.054; P = .017 and P = .053 for fixed and random reader effects, respectively). The proportions of breasts with no or benign abnormalities recommended to be recalled were virtually the same: 0.298 and 0.297 for the two modalities, respectively (95% confidence intervals for the difference, −0.028 to 0.036 and −0.070 to 0.066 for fixed and random reader effects, respectively). Sixteen additional clusters of microcalcifications (“positive” breasts) were missed by all readers combined when interpreting the mode with synthesized images versus FFDM.
Conclusions
Lower sensitivity with comparable specificity was observed with the tested version of synthetically generated images compared to FFDM, both combined with DBT. Improved synthesized images with experimentally verified acceptable diagnostic quality will be needed to eliminate double exposure during DBT-based screening.
Digital breast tomosynthesis (DBT) has been investigated for several years for the possible use of this technology, among other applications, in screening for the early detection of breast cancer . The largest benefit demonstrated to date in this context is the possibility of significantly reducing recall rates, with some indications that observer performance in detecting specific “masslike” abnormalities could also be improved, albeit to a lesser extent . Recently, the US Food and Drug Administration approved the use of tomosynthesis in breast cancer screening . However, DBT in combination with full-field digital mammography (FFDM), which is the considered practice as presented to and approved by the Food and Drug Administration, requires approximately doubling the radiation dose to the breast being imaged. The primary reason for the practice of this combined procedure is the concern that some abnormalities, in particular microcalcification clusters, will not be as readily and as easily detected and/or correctly interpreted on the tomosynthesis image sets as on conventional projection images on FFDM . With the knowledge that there are reasonably simple ways to reconstruct two-dimensional (2D) projection images, as well as three-dimensional (3D) image series, from the information acquired during a DBT data acquisition procedure, double exposure could potentially be eliminated during the combined procedure if it can be demonstrated that the 2D images reconstructed from DBT data sets result in satisfactory image quality. As a result, radiation dose would be reduced by approximately 50%, to a comparable level commonly used in 2D-only mammographic procedures. Before “double-dose” DBT is unilaterally and widely implemented in the screening environment, it is necessary to assess the possible use of synthetically reconstructed 2D images during the interpretation. Therefore, we performed a preliminary retrospective observer performance study as described herein for this purpose.
Materials and methods
A group of full-field digital mammographic and DBT examinations performed in 2008 and 2009 on 118 women ranging in age from 36 to 77 years (mean age, 51 ± 8.7 years) were specifically selected for this study. Selection was based on the availability of a matched 2D (FFDM) and 3D (DBT) image set and a predefined set of findings as a result of the final interpretation and follow-up status verification. Examinations were excluded when the findings of interest were judged to be quite obvious to detect and interpret regardless of the viewing mode. Images were acquired with a combination protocol in which conventional FFDM is acquired first, followed by a tomosynthesis acquisition technique. During the combined full-field digital mammographic and DBT acquisition, the breast is compressed in a conventional manner and a full-field digital mammographic image is obtained, and then the x-ray tube moves along a limited arc allowing 15 low-dose images (“frames”) to be acquired rather than the single image acquired during the full-field digital acquisition. After acquisition, the data from the frames are used to reconstruct 1-mm-thick slices, the number of which varies depending on the thickness of the compressed breast. The radiation dose associated with the series of low-dose projection images is approximately the same as that of a projection mammogram with average midbreast dose of approximately 2 mGy per view. All women were recruited under institutional review board–approved protocols with written informed consent when they arrived at our breast imaging facility for screening, diagnostic workup, or biopsy procedures.
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Description of the Data Set
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Table 1
Distribution of Breasts with Verified Positive, Benign, and Negative Findings
Outcome Finding Number of Breasts Cancer IDC only 8 IDC and DCIS 15 IDC and ILC 1 IDC, DCIS, and HR 4 IDC and metaplastic carcinoma 1 IDC and HR 3 DCIS only 6 DCIS and HR 7 ILC only 3 HR ADH 1 ADH and LCIS 1 Papilloma 2 ALH 2 Verified benign 30 Negative 144 Total 228
ADH, atypical ductal hyperplasia; ALH, atypical lobular hyperplasia; DCIS, ductal carcinoma in situ; HR, high risk; IDC, invasive ductal carcinoma; ILC, infiltrating lobular carcinoma; LCIS, lobular carcinoma in situ.
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Data Analysis
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Results
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Table 2
Breast-based Recommendations (BI-RADS) for Recalling Positive and Negative Breasts for Additional Workup
Reader Actually Acquired FFDM + DBT Synthetically Reconstructed FFDM + DBT Breasts with No or Only Benign Abnormalities Breasts with Cancer or High-risk Abnormalities Breasts with No or Only Benign Abnormalities Breasts with Cancer or High-risk Abnormalities Recall Rate_n_ Recall Rate_n_ Recall Rate_n_ Recall Rate_n_ 1 35.1 174 85.2 54 23.6 174 81.5 54 2 21.8 174 75.9 54 22.4 174 70.4 54 3 19.0 174 81.5 54 26.4 174 77.8 54 4 36.2 174 92.6 54 37.9 174 81.5 54 5 52.3 174 92.6 54 40.8 174 85.2 54 6 24.1 174 79.6 54 21.3 174 70.4 54 7 23.6 174 81.5 54 46.0 174 77.8 54 8 36.2 174 74.1 54 41.4 174 79.6 54 9 27.6 174 81.5 54 19.0 174 74.1 54 10 22.4 174 81.5 54 17.8 174 74.1 54 Average 29.8 82.6 29.7 77.2
BI-RADS, Breast Imaging Reporting and Data System; DBT, digital breast tomosynthesis; FFDM, full-field digital mammogram.
Recall rates are percentages.
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Discussion
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Conclusions
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References
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