Dual-Energy Contrast Enhanced Digital Breast Tomosynthesis (DE-CE-DBT) has the potential to deliver diagnostic
information for vascularized breast pathology beyond that available from screening DBT. DE-CE-DBT involves a
contrast (iodine) injection followed by a low energy (LE) and a high energy (HE) acquisitions. These undergo weighted
subtraction then a reconstruction that ideally shows only the iodinated signal. Scatter in the projection data leads to
“cupping” artifacts that can reduce the visibility and quantitative accuracy of the iodinated signal. The use of filtered
backprojection (FBP) reconstruction ameliorates these types of artifacts, but the use of FBP precludes the advantages of
iterative reconstructions. This motivates an effective and clinically practical scatter correction (SC) method for the
projection data. We propose a simple SC method, applied at each acquisition angle. It uses scatter-only data at the edge
of the image to interpolate a scatter estimate within the breast region. The interpolation has an approximately correct
spatial profile but is quantitatively inaccurate. We further correct the interpolated scatter data with the aid of easily
obtainable knowledge of SPR (scatter-to-primary ratio) at a single reference point. We validated the SC method using a
CIRS breast phantom with iodine inserts. We evaluated its efficacy in terms of SDNR and iodine quantitative accuracy.
We also applied our SC method to a patient DE-CE-DBT study and showed that the SC allowed detection of a
previously confirmed tumor at the edge of the breast. The SC method is quick to use and may be useful in a clinical
We are investigating human-observer models that perform clinically realistic detection and localization tasks as a
means of making reliable assessments of digital breast tomosynthesis images. The channelized non-prewhitening
(CNPW) observer uses the background known exactly task for localization and detection. Visual-search observer
models attempt to replicate the search patterns of trained radiologists. The visual-search observer described in
this paper utilizes a two-phase approach, with an initial holistic search followed by directed analysis and decision
making. Gradient template matching is used for the holistic search, and the CNPW observer is used for analysis
and decision making. Spherical masses were embedded into anthropomorphic breast phantoms, and simulated
projections were made using ray-tracing and a serial cascade model. A localization ROC study was performed
on these images using the visual-search model observer and the CNPW observer. Observer performance from
the two computer observers was compared to human observer performance. The visual-search observer was able
to produce area under the LROC curve values similar to those from human observers; however, more research is
needed to increase the robustness of the algorithm.
X-ray scatter leads to erroneous calculations of dual-energy digital mammography (DEDM). The purpose of this work is
to design an algorithmic method for scatter correction in DEDM without extra exposures or lead sheet. The method was
developed based on the knowledge that scatter radiation in mammograms varies slowly spatially and most pixels in
mammograms are non-calcification pixels, and implemented on a commercial full-field digital mammography system
with a phantom of breast tissue equivalent material. The
pinhole-array interpolation scatter correction method was also
implemented on the system. We compared the background dual-energy (DE) calcification signals in the DE calcification
images. Results show that the background signal in the DE calcification image can be reduced. The rms of background
DE calcification image signal of 1105μm with scatter-uncorrected data was reduced to 187μm and 253μm after scatter
correction, using our algorithmic method and pinhole-array interpolation method, respectively. The range of background
DE calcification signals using scatter-uncorrected data was reduced by ~80% with scatter-corrected data using
algorithmic method. The proposed algorithmic scatter correction method is effective; it has similar or even better
performance than pinhole-array interpolation method in scatter correction for DEDM.
Normal mammographic backgrounds have power spectra that can be described using a power law
P(f) = c/fβ, where β ranges from 1.5 to 4.5. Anatomic noise can be the dominant noise source
in a radiograph. Many researchers are characterizing anatomic noise by β, which can be measured
from an image. We investigated the effect of sampling distance, offset, and region of interest (ROI)
size on β. We calculated β for tomosynthesis projection view and reconstructed images, and we
found that ROI size affects the value of β. We evaluated four different square ROI sizes (1.28, 2.56,
3.2, and 5.12 cm), and we found that the larger ROI sizes yielded larger β values in the projection
The β values change rapidly across a single projection view; however, despite the variation
across the breast, different sampling schemes (which include a variety of sampling distances and
offsets) produced average β values with less than 5% variation. The particular location and number
of samples used to calculate β does not matter as long as the whole image is covered, but the size
of the ROI must be chosen carefully.
We have investigated the effect of non-isotropic blur in an indirect x-ray conversion screen in tomosynthesis
imaging. To study this effect, we have implemented a screen model for angle-dependent x-ray incidence, and
have validated the model using experimental as well as Monte-Carlo simulations reported in the literature.
We investigated detector characteristics such as MTF, NPS and DQE, and we estimated system performance
in a signal-known exactly detection task.
We found that for such a screen, the frequency dependence of the MTF varies with x-ray source angle, while
the frequency dependence of the NPS does not. Furthermore, as the x-ray source angle is increased, the DQE
becomes more narrow and DQE(f=0) grows. We found that for a tomosynthesis scan angle of 90 degrees and a
conversion screen thickness of 130 microns, detectability for small signals (radius=0.125 mm) was decreased by
13%, compared to signal radii above 0.5 mm.
The magnitude of the degradation is expected to vary for different tomosynthesis configurations, such as scan
angle and conversion screen thickness.
Microcalcifications (MCs) are an important early sign of breast cancer. In conventional mammography, MC
detectability is limited primarily due to quantum noise. In tomosynthesis, a dose comparable to that delivered in
one projection mammogram is divided across a number of projection views (typically ranging between 10 and 30).
This potentially will reduce the detectability of MCs, if detector noise is not very low. The purpose of this study
is to explore the relationship between MC detectability in the projection views and in the reconstructed image.
The effect of angular range and number of angles on detectability will also be evaluated for an ideal detector.
Microcalcification detectability is shown to be greater in the sinogram than in the reconstructed images. Further,
the detectability is reduced when the MC is located far from the center of the breast. Also, the detectability in
the projection images is dependent on the projection angle.