Breast Tomosynthesis: How I Read It

Twitter icon
Facebook icon
LinkedIn icon
e-mail icon
Google icon

laurie l. FajarDoliMin yangjeong Mi ParKNow that digital breast tomosynthesis (DBT) has gained FDA approval, many breast-imaging providers find themselves excited about the new technology, but facing uncertainty about reimbursement, implementation, and interpretation workflow. There remain a number of questions related to the display of (and approach to interpreting) DBT that need to be addressed if DBT is to be incorporated optimally into routine practice.

As they were for digital mammography (DM) in the recent past, the acquisition and dissemination of DBT technology will be marked by early and late adopters. Early adopters will be willing to work with uncertainty and develop the nuances of implementation and interpretation in their own unique environments; later adopters will pattern their practices on the reported experience of others. Clearly, those who determine how to interpret DBT exams best (and most efficiently) will influence its acceptance and clinical implementation.

The mechanism of DBT image acquisition has been well described. 1,2 Though standards from the industry and the Mammography Quality Standards Act (MQSA) do not yet exist for all aspects of this technology, practitioners are rapidly becoming knowledgeable and gaining experience in the nuances of best displaying and reviewing 3D DBT image datasets.

In general, DBT is displayed as 1-mm image slices that are reviewed using cine or manual scroll modes on dedicated soft-copy workstations. The first DBT image slice begins at the detector, for craniocaudal (CC) and mediolateral oblique (MLO) DBT projections. At the compression-plate aspect of the image set, five additional slices are included to ensure that all tissue is displayed.

Thus, one can estimate breast-compression thickness from the number of 1-mm BDT slices in the dataset by subtracting 5 mm from the total number of slices. Having location information readily available from DBT image slices makes evaluating masses, calcifications, or other findings related to the skin very straightforward on any routine screening exam, without the necessity for additional views to clarify that a mammographic finding is dermal in origin.

Currently, there are a few artifacts related to image reconstruction that radiologists need to understand and adapt to when interpreting DBT studies. Coarse calcifications (macrocalcifications), metallic (BB or scar) markers, postbiopsy clips, and other high-density objects within or applied to the breast create a coil-spring or slinky artifact (Figure 1). While these are initially distracting, many radiologists find that they are quickly able to read through these artifacts.

In the future, advanced reconstruction software might reduce or eliminate these artifacts, and many DBT users agree that the benefits of the technology outweigh its current limitations. Another concept to recognize is that, unlike 3D datasets acquired by breast-MRI volume acquisition techniques, the CC-DBT and MLO-DBT datasets cannot be cross-referenced with display software as, for example, a sagittal and axial breast-MRI imaging sequence. DBT CC and MLO projection data are acquired with nonisotropic voxels and with two separate breast positionings, rendering impossible the cross-referencing easily performed with breast MRI 3D datasets.

Currently, both a 2D standard DM image and a 3D DBT dataset are acquired with a single positioning and a single exposure for each of the standard screening views. This is commonly referred to as 2D/3D combo imaging and is performed with a total dose that is less than the maximum permitted by MQSA requirements.

Many radiologists learning to interpret DBT find that having the standard 2D to correlate with the 3D DBT images is of value in gaining confidence and reducing the learning curve. In addition, studies 3,4 have shown, based on screening ACR BI-RADS® ratings, that the combined use of DM and DBT was superior to DM alone in terms of significantly reducing recall rates for further diagnostic work-ups.

In the future, one of two scenarios might emerge. In the first, after a period of time when patients have undergone more than one DBT study, radiologists might be comfortable viewing only DBT images. In the second, the standard 2D DM images will be replaced by synthesized 2D images, created from the DBT dataset—which would reduce radiation dose.

A Dynamic Study

In general, the interpretation of a 2D/3D combo screening study begins with a review of the 2D images. After reviewing the four standard