Tomosynthesis imaging in chest radiography provides volumetric information with the potential for improved diagnostic
value when compared to the standard AP or LAT projections. In this paper we explore the image quality benefits of 2D
scanning trajectories when coupled with advanced image reconstruction approaches. It is intuitively clear that 2D
trajectories provide projection data that is more complete in terms of Radon space filling, when compared with
conventional tomosynthesis using a linearly scanned source. Incorporating this additional information for obtaining
improved image quality is, however, not a straightforward problem. The typical tomosynthesis reconstruction algorithms
are based on direct inversion methods e.g. Filtered Backprojection (FBP) or iterative algorithms that are variants of the
Algebraic Reconstruction Technique (ART). The FBP approach is fast and provides high frequency details in the image
but at the same time introduces streaking artifacts degrading the image quality. The iterative methods can reduce the
image artifacts by using image priors but suffer from a slow convergence rate, thereby producing images lacking high
frequency details. In this paper we propose using a fast converging optimal gradient iterative scheme that has advantages
of both the FBP and iterative methods in that it produces images with high frequency details while reducing the image
artifacts. We show that using favorable 2D scanning trajectories along with the proposed reconstruction method has the
advantage of providing improved depth information for structures such as the spine and potentially producing images
with more isotropic resolution.
We are investigating factors affecting the detection of microcalcifications in digital breast tomography (DBT). In this
study, we analyzed the effects of projection-view (PV) distribution on spatial blurring of calcifications on the tomosynthesized slices (X-Y plane) and along the depth (Z) direction. DBT scans of a breast phantom with simulated microcalcifications were acquired with a GE prototype system at 21 angles in 3° increments over a ±30° range. Six
subsets of 11 PVs were selected from the full set to simulate DBT of different angular ranges and angular increments.
SART was applied to each subset to reconstruct the DBT slices. The FWHMs of the line profiles of calcifications within
their in-focus DBT slices and FWHMs of the inter-plane artifact spread function (ASF) in the Z-direction for the
different PV distributions were compared. The results indicate that DBT acquired with a large angular range or a
reasonable number of PVs at large angles yield superior ASF with smaller FWHM in the Z-direction. PV distributions
with a narrow angular range have stronger inter-plane artifacts. In the X-Y focal planes, the effect of PV distributions on
spatial blurring depends on the directions. The normalized line profiles of the calcifications reconstructed with the
different PV distributions are similar in the X-direction. The differences in the FWHMs between the different PV distributions are less than half a pixel. In the Y-(x-ray tube motion) direction, the normalized line profiles of the calcifications reconstructed with DBT acquired with a narrow angular range or a reasonable number of PVs at small angles have less blurring in terms of smaller FWHMs of the line profiles. PV distributions with a wide angular range have stronger in-plane artifacts in the Y-direction. Further study is underway to compare different reconstruction techniques and parameters. The information will be useful for optimization of DBT for detection of microcalcifications.
We report on the design of a neutron detector using industry standard 3He tubes to count delayed neutrons during the
interrogation of cargo containers for the presence of Special Nuclear Material (SNM). Simulations of the detector
design were run for delayed neutron spectra for a variety of cargos containing SNM using the Monte Carlo computer
code COG. The simulations identified parameters crucial to optimize the detector design. These choices include
moderating material type and thickness, tube spacing, tube pressure and number of tubes. An experimental prototype
was also constructed based on the simulated design specifications. This paper discusses the parameters that lead up to
the optimized detector design. It also compares the performance of the Monte Carlo simulated design and the
experimental detector when exposed to a 239Pu-Be source.
A new mammography tomosynthesis prototype system that acquires 21 projection images over a 60 degree angular range in approximately 8 seconds has been developed and characterized. Fast imaging sequences are facilitated by a high power tube and generator for faster delivery of the x-ray exposure and a high speed detector read-out. An enhanced a-Si/CsI flat panel digital detector provides greater DQE at low exposure, enabling tomo image sequence acquisitions at total patient dose levels between 150% and 200% of the dose of a standard mammographic view. For clinical scenarios where a single MLO tomographic acquisition per breast may replace the standard CC and MLO views, total tomosynthesis breast dose is comparable to or below the dose in standard mammography. The system supports co-registered acquisition of x-ray tomosynthesis and 3-D ultrasound data sets by incorporating an ultrasound transducer scanning system that flips into position above the compression paddle for the ultrasound exam. Initial images acquired with the system are presented.
Two mechanisms for MTF dependence on incident x-ray angle are demonstrated by an experimental technique that separates the two phenomena. The dominant effect is that travel of x-ray photons through the scintillator at non-normal incidence involves an in-plane component. This mechanism leads to a significant but deterministic blurring of the incident image, but has no effect on the noise transfer characteristics of the detector. A secondary effect is that at large angles to the surface normal, x-ray-to-optical conversion occurs at positions in the scintillator further away from the photodiode surface. This leads to a small net decrease in MTF and NPS at angles above 60 degrees. The deterministic character of the angular dependence of gain, MTF and NPS leads to the conclusion that sufficient angular range can be supported by this detector construction. Excellent functionality in the context of tomography is expected.
Digital tomosynthesis mammography is an advanced x-ray application that can provide detailed 3D information about the imaged breast. We introduce a novel reconstruction method based on simple backprojection, which yields high contrast reconstructions with reduced artifacts at a relatively low computational complexity. The first step in the proposed reconstruction method is a simple backprojection with an order statistics-based operator (e.g., minimum) used for combining the backprojected images into a reconstructed slice. Accordingly, a given pixel value does generally not contribute to all slices. The percentage of slices where a given pixel value does not contribute, as well as the associated reconstructed values, are collected. Using a form of re-projection consistency constraint, one now updates the projection images, and repeats the order statistics backprojection reconstruction step, but now using the enhanced projection images calculated in the first step. In our digital mammography application, this new approach enhances the contrast of structures in the reconstruction, and allows in particular to recover the loss in signal level due to reduced tissue thickness near the skinline, while keeping artifacts to a minimum. We present results obtained with the algorithm for phantom images.
The objective of this work was to acquire co-registered digital tomosynthesis mammograms and 3-D breast ultrasound images of breast phantoms. A prototype mammography compression paddle was built for this application and installed on an x-ray tomosynthesis prototype system (GE). Following x-ray exposure, an automated two-dimensional ultrasound probe mover assembly is precisely positioned above the compression plate, and an attached high-frequency ultrasound transducer is scanned over the acoustically coupled phantom or localized region of interest within the phantom through computerized control. The co-ordinate system of one of the two data sets is then transformed into that of the other, and matching regions of interest on either image set can be simultaneously viewed on the x-ray and ultrasound images thus enhancing qualitative visualization, localization and characterization of regions of interest. The potentials of structured noise reduction, cyst versus solid mass differentiation and full 3-D visualization of multi-modality registered data sets in a single automated combined examination are realized for the first time. Elements of system design and required image correction algorithms will be described and phantom studies with this prototype, automated system on an anthropomorphic breast phantom will be presented.
We have implemented a scatter-correction algorithm (SCA) for digital mammography based on an iterative restoration filter. The scatter contribution to the image is modeled by an additive component that is proportional to the filtered unattenuated x-ray photon signal and dependent on the characteristics of the imaged object. The SCA's result is closer to the scatter-free signal than when a scatter grid is used. Presently, the SCA shows improved contrast-to-noise performance relative to the scatter grid for a breast thickness up to 3.6 cm, with potential for better performance up to 6 cm. We investigated the efficacy of our scatter-correction method on a series of x-ray images of anthropomorphic breast phantoms with maximum thicknesses ranging from 3.0 cm to 6.0 cm. A comparison of the scatter-corrected images with the scatter-free signal acquired using a slit collimator shows average deviations of 3 percent or less, even in the edge region of the phantoms. These results indicate that the SCA is superior to a scatter grid for 2D quantitative mammography applications, and may enable 3D quantitative applications in X-ray tomosynthesis.