Purpose: To analyze the effects of projection-view (PV) distribution on the contrast and spatial blurring of microcalcifications on the tomosynthesized slices (X-Y plane) and along the depth (Z) direction for the same radiation dose in digital breast tomosynthesis (DBT).Methods: A GE GEN2 prototype DBT system was used for acquisition of DBT scans. The system acquires PV images from 21 angles in 3° increments over a ±30° range. From these acquired PV images, the authors selected six subsets of PV images to simulate DBT of different angular ranges and angular increments. The number of PV images in each subset was fixed at 11 to simulate a constant total dose. These different PV distributions were subjectively divided into three categories: uniform group, nonuniform central group, and nonuniform extreme group with different angular ranges and angular increments. The simultaneous algebraic reconstruction technique (SART) was applied to each subset to reconstruct the DBT slices. A selective diffusion regularization method was employed to suppress noise. The image quality of microcalcifications in the reconstructed DBTs with different PV distributions was compared using the DBT scans of an American College of Radiology phantom and three human subjects. The contrast-to-noise ratio (CNR) and the full width at half maximum (FWHM) of the line profiles of microcalcifications within their in-focus DBT slices (parallel to detector plane) and the FWHMs of the interplane artifact spread function (ASF) in the Z-direction (perpendicular to detector plane) were used as image quality measures.Results: The results indicate that DBT acquired with a large angular range or, for an equal angular range,with a large fraction of PVs at large angles yielded superior ASF with smaller FWHM in the Z-direction. PV distributions with a narrow angular range or a large fraction of PVs at small angles had stronger interplane artifacts. In the X-Y focal planes, the effect of PV distributions on spatial blurring depended on the directions. In the X-direction (perpendicular to the chestwall), the normalized line profiles of the calcifications reconstructed with the different PV distributions were similar in terms of FWHM; the differences in the FWHMs between the different PV distributions were less than half a pixel. In the Y-direction (x-ray source motion), the normalized line profiles of the calcifications reconstructed with PVs acquired with a narrow angular range or a large fraction of PVs at small angles had smaller FWHMs and thus less blurring of the line profiles. In addition, PV distributions with a narrow angular range or a large fraction of PVs at small angles yielded slightly higher CNR than those with a wide angular range for small, subtle microcalcifications; however, PV distributions had no obvious effect on CNR for relatively large microcalcifications.Conclusions: PV distributions affect the image quality of DBT. The relative importance of the impact depends on the characteristics of the signal and the direction (perpendicular or parallel) relative to the direction of x-ray source motion. For a given number of PVs, the angular range and the distribution of the PVs affect the degree of in-plane and interplane blurring in opposite ways. The design of the scan parameters of tomosynthesis systems would require proper consideration of the characteristics of the signals of interest and the potential trade-off of the image quality of different types of signals.

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.

Purpose: To develop a processing method to reduce the effects of x‐ray scatter in images acquired with portable x‐ray systems without an anti‐scatter grid. Method and Materials: Due to the varying geometry inherent in portable x‐ray systems, the use of anti‐scatter grids with a high ratio is challenging. For clinical applicability, the algorithm must be fast and preserve the image texture. First an adequate understanding of the x‐ray scatter signal present in different radiography applications was obtained using Monte Carlo (MC) simulations of several clinical applications. From the simulations it was confirmed that the x‐ray scatter fields consisted of a low‐frequency offset, with very different shapes and magnitudes depending on the image being acquired. The developed algorithm, a modified version of unsharp masking, involves masking the open field area and the thin sections of the body, replacing these areas with the mean signal from the edges of the body, applying a low pass filter, and then subtracting a weighted version of the latter from the original image. The masking is performed to avoid the inclusion of the very high signal areas from the low pass image, which would result in an overestimation of the signal to be removed. Results: The algorithm reduced the x‐ray scatter signal in simulated MC images by 50&–80%, depending on the image and the location analyzed. When applied to images of a thorax phantom obtained with a portable x‐ray system without a grid, the quality of the images were improved enough to be comparable to those obtained with a clinical fixed system with a grid. Conclusion: The use of the developed scatter reduction algorithm seems to compensate for the inability to use a high ratio grid in portable systems. Further testing will be performed. Conflict of Interest: Research sponsored by GE Global Research.

Digital Breast Tomosynthesis (DBT) Mammography is an emerging technique that has the potential to improve breast cancer detection. In DBT, low-dose mammograms are acquired at a number of projection angles over a limited range and the 3D breast volume is reconstructed. In this study, we investigated the effect of different distributions of projection-view (PV) images that included different angular range and angular spacing on the reconstruction image quality. A GE prototype DBT system was used to acquire a total of 21 PVs in 3º increments over a ±30º range, from which multiple subsets containing the same number of 11 PV images were selected. A custom-built breast phantom and a selected patient case were used to evaluate the image quality. For breast phantom study, the contrast-to-noise ratio (CNR), the normalized line profiles of test objects, and an artifact spread function (ASF) were used as performance measures to compare the results for the different subsets and for the full set. The simultaneous algebraic reconstruction technique (SART) was used to reconstruct the DBT under all conditions. Our results demonstrated that large DBT angular range gave superior CNR and ASF for masses and less interplane blurring for high-density objects. Narrow angular range favors in-plane edge sharpness for high-density objects.