Tomosynthesis is emerging as a promising modality for breast imaging. Several manufacturers have developed prototype
units and have acquired clinical and phantom data. Scanning configurations of these prototypes vary. So far, studies
relating scanning configuration to image quality have been limited to those geometries that could be implemented on a
particular prototype. To overcome this limitation, we are developing a model of breast tomosynthesis image acquisition
system, which models the formation of the x-ray image and x-ray detector.
The x-ray image of an object is computed analytically for a polychromatic x-ray beam. Objects consist of volumetric
regions that are bounded by either a planar, ellipsoidal, cylindrical or conical surface, allowing for a variety of objects. xray
scatter is computed by convolving the image with a scatter point-spread function. Poisson noise according to the
entrance exposure is added to the image.
The x-ray detector in this model is composed of a phosphor screen followed by a detector array. X-ray interactions in the
screen are modeled as depth-dependent. The optical output of the screen is converted into digital units using a gain factor
which was assumed to be Gaussian distributed.
To validate this data model, we acquired images of a contrast-detail phantom on a stereotactic biopsy unit. The x-ray
source is mounted on an arm that pivots in a plane about the detector center. The x-ray detector consists of a Min-R type
screen fiber-optically coupled to a CCD camera.
To compare actual and simulated data, we compared line profiles as well as several automatically extracted image
features such as contrast-to-noise ratio, contrast, area and radial gradient index. Good agreement was found between
simulation and physical data, indicating that we can now use this model to explore image quality for various
tomosynthesis scanning configurations.