Rational and Objectives
The objective of this study was to compare the stationary digital breast tomosynthesis (s-DBT) system to a conventional mammography system in a study of breast specimens. Radiologist evaluation of image quality was assessed in a reader study. This study represents the first human tissue imaging with the novel carbon nanotube–based s-DBT device.
Materials and Methods
Thirty-nine patients, with known breast lesions (Breast Imaging Reporting and Data System 4 or 5) by conventional mammography and scheduled for needle localization biopsy, were recruited under an institutional review board–approved protocol. Specimen images were obtained using a two-dimensional (2D) mammography system with a ×1.8 magnification factor and an s-DBT system without a high magnification factor. A reader study was performed with four breast fellowship-trained radiologists over two separate sessions. Malignancy scores were recorded for both masses and microcalcifications (MCs). Reader preference between the two modalities for MCs, masses, and surgical margins was recorded.
Results
The s-DBT system was found to be comparable to magnified 2D mammography for malignancy diagnosis. Readers preferred magnified 2D mammography for MC visualization ( P < .05). However, readers trended toward a preference for s-DBT with respect to masses and surgical margin assessment.
Conclusions
Here, we report on the first human data acquired using a stationary digital breast tomosynthesis system. The novel s-DBT system was found to be comparable to magnified 2D mammography imaging for malignancy diagnosis. Given the trend of preference for s-DBT over 2D mammography for both mass visibility and margin assessment, s-DBT could be a viable alternative to magnified 2D mammography for imaging breast specimens.
Malignant lesions in the breast can be difficult to visualize using full-field digital mammography (FFDM) when significant tissue overlap is present. Tissue overlap is most apparent in breast tissue that is thick and radiographically dense. Digital breast tomosynthesis (DBT) uses a small number of angular projections to reconstruct a pseudo–three-dimensional (3D)volume. Recent studies have shown an increase in the area under the curve (AUC) when using a combination of DBT and FFDM compared to FFDM alone . Recall rates for benign cases significantly decrease when using a combination of DBT and FFDM . However, for cases with microcalcifications (MCs), the use of DBT along with an FFDM image has shown no significant improvement in the AUC .
Current DBT systems use a single X-ray source which is translated over an angular span that typically covers between 15° and 50° . Larger angular spans sample more of the Fourier domain which reduces out-of-plane reconstruction artifacts. Translating a source over a larger angular span requires longer acquisition times, which leads to patient motion artifacts . These single-source systems also suffer from poor spatial resolution because of focal spot blurring from the tube motion . We have developed a stationary digital breast tomosynthesis (s-DBT) technology that uses a novel multiple focal-spot X-ray source array with carbon nanotubes (CNTs) as the field emission electron source . This stationary approach can increase acquisition speed and eliminate the focal spot motion. It has been shown that the s-DBT device offers significant improvement in image quality, including improved modulation transfer function (MTF) and lesion conspicuity in breast phantom studies .
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Materials and methods
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Results
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Table 1
Calculated Sensitivity and Specificity Values by Modality and Reader
Reader Sensitivity Specificity FFDM s-DBT FFDM s-DBT 1 24/24 (1.00) 23/25 (0.92) 4/14 (0.29) 2/13 (0.15) 2 21/25 (0.84) 19/25 (0.76) 5/14 (0.36) 7/14 (0.50) 3 24/25 (0.96) 25/25 (1.00) 0/13 (0.00) 0/13 (0.00) 4 23/25 (0.92) 25/25 (1.00) 4/14 (0.29) 2/14 (0.14)
FFDM, full-field digital mammography modality; s-DBT, stationary digital breast tomosynthesis.
Values were calculated from malignancy scores. Malignancy scores from 3 to 5 were considered positive for disease.
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Table 2
Results of McNemar Test for Discordance Between the Two Modalities for All Four Readers
Modality = FFDM Modality = s-DBT Negative Positive Subtotal Reader 1 ( P = .5637) Negative 1 1 2 Positive 2 32 34 Subtotal 3 33 36 Reader 2 ( P = .2482) Negative 5 4 9 Positive 8 22 30 Subtotal 13 26 39 Reader 3 ( P = NA) Negative 0 0 0 Positive 0 35 35 Subtotal 0 35 35 Reader 4 ( P = .0455) Negative 2 4 6 Positive 0 33 33 Subtotal 2 37 39
FFDM, full-field digital mammography modality; s-DBT, stationary digital breast tomosynthesis.
Insignificant discordance was found between the two modalities for readers 1, 2, and 3. In the case of reader 4, diagnostics based on two modalities are likely to be different.
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Table 3
Average Reader Preference for the Shape/Morphology of Masses, Microcalcification Assessment, and Margin Assessment
Reader Masses Microcalcifications Margins Mean SD_P_ Value Mean SD_P_ Value Mean SD_P_ Value 1 −1.02 1.40 <.05 −1.80 1.01 <.05 −0.44 1.35 <.05 2 0.18 1.20 .4094 −0.54 0.70 <.05 0.19 1.14 .2984 3 0.75 1.35 <.05 −0.20 0.98 .259 0.70 1.35 <.05 4 0.08 0.86 .5800 −0.62 0.52 <.05 0.21 0.72 .0743 Overall 0.07 1.34 — −0.70 0.95 — 0.16 1.22 —
SD, standard deviation.
Positive values represent a preference for stationary digital breast tomosynthesis compared to two-dimensional mammography.
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Table 4
Results of the Secondary Analysis Performed on the Preference Portion of the Reader Study
Grand Mean Estimate Standard Error Two-Sided P Value Shape/morphology 0.0598 0.1416 .6751 Microcalcifications −0.6718 0.1030 <.05 Margins 0.1586 0.1422 .2718
It was tested whether the mean preference was larger than zero using a linear mixed model with a random intercept effect and Wald test. Positive values represent a preference for stationary digital breast tomosynthesis compared to two-dimensional mammography.
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Discussion
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Acknowledgments
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