  It has previously been shown that 2D spectral mammography can be used to
discriminate between (likely benign) cystic and (potentially malignant) solid
lesions in order to reduce unnecessary recalls in mammography. One limitation
of the technique is, however, that the composition of overlapping tissue needs
to be interpolated from a region surrounding the lesion. The purpose of this
investigation was to demonstrate that lesion characterization can be done with
spectral tomosynthesis, and to investigate whether the 3D information available
in tomosynthesis can reduce the uncertainty from the interpolation of
surrounding tissue. A phantom experiment was designed to simulate a cyst and a
tumor, where the tumor was overlaid with a structure that made it mimic a cyst.
In 2D, the two targets appeared similar in composition, whereas spectral
tomosynthesis revealed the exact compositional difference. However, the loss of
discrimination signal due to spread from the plane of interest was of the same
strength as the reduction of anatomical noise. Results from a preliminary
investigation on clinical tomosynthesis images of solid lesions yielded results
that were consistent with the phantom experiments, but were still to some
extent inconclusive. We conclude that lesion characterization is feasible in
spectral tomosynthesis, but more data, as well as refinement of the calibration
and discrimination algorithms, are needed to draw final conclusions about the
benefit compared to 2D.
