CHICAGO — The addition of digital breast tomosynthesis to digital mammography at screening could improve diagnostic accuracy and reduce recall rates by about 40%, according to results of a multicenter study.
Tomosynthesis creates a single three-dimensional image of the breast by combining data from 11 projection two-dimensional radiographs acquired during a single sweep of the x-ray tube around the patient.
The technique improves breast visualization by reducing the overlap of normal breast structures, Dr. Elizabeth Rafferty reported during a late-breaking session at the annual meeting of the Radiological Society of North America. The total radiation dose of 1.5 mGy is about half that of a single mammographic exposure.
The technique is neither clinically available nor approved by the Food and Drug Administration, but based on findings from a data set of 316 women, Hologic Inc. (Bedford, Mass.) has petitioned the FDA for approval of the combined modality of tomosynthesis and digital mammography.
The data set was derived from a study in which 1,083 women, age 18 years or more, underwent two-view, full-field digital mammogram (FFDM) and digital tomosynthesis exams at five U.S. centers. The 316 women in the study included 100 women who presented for diagnostic examinations and 216 women who presented for screening exams, of whom 141 were recalled for additional imaging and 75 had normal exams. In all, 96 women underwent biopsy; 48 lesions were benign, and 48 were malignant.
Twelve board-certified radiologists trained on 200 tomosynthesis imaging cases scored the digital mammography images as Breast Imaging Reporting and Data System (BIRADS) 0, 1, and 2. For the cases scored as a BIRADS 0, the radiologists were asked to give a forced BIRADS score of 1–5 showing the likelihood of disease in that patient and assign a probability of malignancy score rating from 1 to 100.
The combination of FFDM and tomosynthesis resulted in highly significant improvements in the radiologists' performance, as shown by receiver-operator curve analyses, said Dr. Rafferty of the radiology department at Harvard University Medical School in Boston. The performance benefits were seen primarily in the analysis of masses, architectural distortion, and focal asymmetries. A receiver-operator analysis showed that for all the readers, the combined modality of tomosynthesis and FFDM was superior to FFDM alone when using the forced BIRADS score and the probability of malignancy scale.
Using multicase and multireader analyses, the diagnostic accuracy (area under the curve) improved significantly for the forced BIRADS score from 0.83 with FFDM alone to 0.90 with FFDM plus tomosynthesis, with 0.5 representing a worthless diagnostic test and 1 a perfect test. The area under the curve for the probability of malignancy scale also significantly improved from 0.82 to 0.89 with the combined modality.
The investigators hypothesized that tomosynthesis would provide little gain in the assessment of clustered breast calcifications because calcifications are well seen on traditional mammography and aren't typically obscured by surrounding tissue. The data bore out this hypothesis, with only a slight, nonsignificant improvement from 0.80 to 0.84 observed in the area under the curve.
In noncalcified cases, the difference in the area under the curve for FFDM versus the combined modality was highly significant (0.82 vs. 0.92), representing good versus excellent dignostic accuracy. Dr. Rafferty has received research support from Hologic, the study sponsor.
Architectural distortion is clearer in tomosynthesis slices (right) than on digital mammography (left).
A spiculated cancer is better seen in the tomosynthesis slice (right) than on digital mammography (left).
Spiculated cancer with microcalcification is more apparent in the tomosynthesis slice (right) than on digital mammography image (left). HOLOGIC, INC.