Improved detection: Digital breast tomosynthesis provides better contrast between dense and less dense components, such as fibroglandular tissue and fat, a feature that may reveal lesions not visible on digital mammography. Contrast between lesions and surrounding parenchyma is also increased on tomosynthesis.
FFDM AND TOMOSYNTHESIS
Some authors have reported a better conspicuity of cancers and a more appropriate BI-RADS categorization when tomosynthesis is added to standard digital mammography. In one such study, 98 women presenting with abnormal screening mammography underwent breast tomosynthesis with one to three views.7 The image quality of tomosynthesis was equivalent (n = 51) or superior (n = 37) to diagnostic mammography in 89% of cases (88/99). For masses, tomosynthesis image quality was rated as equivalent in 26% (five/19) or superior in 68% (13/19) of cases to diagnostic mammography. Masses constituted 19% (19/99) of findings detected on screening mammograms, but were 35% (13/37) of findings in which tomosynthesis had superior image quality.
In another study, breast cancer visibility on digital tomosynthesis was compared with one- and two-view digital mammography in a series of 36 patients. Subjects were selected on the basis of their digital mammograms showing only subtle signs of cancer.8 Forty breast cancers were found. Visualization of 22 lesions was better with tomosynthesis when compared with single-view mammography. The BI-RADS classification was upgraded in 58% of those cases. Visualization of 11 lesions was clearer with tomosynthesis when compared with two-view mammography. Thirty-three percent of these lesions were reclassified upward.
Tomosynthesis is making great strides, but still faces challenges.
Detection: Dense breast parenchyma that obscures the borders of masses limits the detection of breast lesions, even with tomosynthesis. Single-view tomosynthesis may fail to detect lesions located deep within the breast, in common with mammography.
Calcifications: Their small size makes the depiction and morphological characterization of breast microcalcifications challenging for breast tomosynthesis. Calcification clusters were well detected in our experience. The morphological features of microcalcifications were, however, altered due to geometric parameters. Chen et al showed that arc-shaped projections can distort the shape of microcalcifications in breast tomosynthesis.9 Using some digital breast tomosynthesis algorithms, such as the traditional “shift-and-add” algorithm, the appearance of calcifications may be blurred in the direction orthogonal to the tube motion. The spatial distribution of microcalcifications within the breast could be assessed, particularly when using MIP reconstructions. Significant artifacts caused by large calcifications can be recognized easily.
Further evaluation of digital breast tomosynthesis is needed. Should it be performed routinely or as an adjunct to mammography? Should it be used for screening or only in a diagnostic setting? These questions remain unanswered. The optimal number of tomosynthesis views (one? two? three?) has yet to be defined. The optimal acquisition geometry, that is, the tomographic angle and number of projection views, as well as the optimal acquisition parameters, such as target filter, tube voltage, and exposure, are still being investigated. Multiple reconstruction algorithms and acquisition protocols have been compared.10,11 Initial reports on the use of tomosynthesis, as well as on CAD, are promising.12,13 Larger clinical trials are needed before these techniques can be widely used, however.
The combination of the 3D exploration of breast volume provided by tomosynthesis with contrast administration may afford in a single examination a detailed assessment of breast cancer morphological features and vascular enhancement kinetics. The interest in this technique lies in its potentially lower cost and wider availability compared with MRI. Preliminary experience with contrast-enhanced tomosynthesis has shown dual-energy and temporal subtraction techniques are feasible.14,15
The 3D visualization of the breast from digital tomosynthesis provides useful information relative to standard mammography. The clinical efficacy of this technique, however, requires further clarification. Additional investigation that will help define the situations best served by this new tool is currently under way.