Image artifacts in digital breast tomosynthesis: Investigation of the effects of system geometry and reconstruction parameters using a linear system approach

Abstract

Digital breast tomosynthesis ͑DBT͒ is a three-dimensional ͑3D͒ x-ray imaging modality that reconstructs image slices parallel to the detector plane. Image acquisition is performed using a limited angular range ͑less than 50 degrees͒ and a limited number of projection views ͑less than 50 views͒. Due to incomplete data sampling, image artifacts are unavoidable in DBT. In this preliminary study, the image artifacts in DBT were investigated systematically using a linear system approximation. A cascaded linear system model of DBT was developed to calculate the 3D presampling modulation transfer function ͑MTF͒ with different image acquisition geometries and reconstruction filters using a filtered backprojection ͑FBP͒ algorithm. A thin, slanted tungsten ͑W͒ wire was used to measure the presampling MTF of the DBT system in the cross-sectional plane defined by the thickness ͑z-͒ and tube travel ͑x-͒ directions. The measurement was in excellent agreement with the calculation using the model. A small steel bead was used to calculate the artifact spread function ͑ASF͒ of the DBT system. The ASF was correlated with the convolution of the two-dimensional ͑2D͒ point spread function ͑PSF͒ of the system and the object function of the bead. The results showed that the cascaded linear system model can be used to predict the magnitude of image artifacts of small, high-contrast objects with different image acquisition geometry and reconstruction filters.

Design and development of a phantom for tomosynthesis with potential for automated analysis via the cloud

“…Additionally, when one encounters iterative reconstructions in both Computed Tomography (CT), and DBT, the questions of linearity is even further strained and should probably be avoided. This being noted, the term has already been used in several studies 2, 10 and will be used in this paper, duly noting these caveats. The “MTF” data shown in this paper is obtained from the Fourier Transform of the PSF 5…”

“…The same beads as used in the section Beads for z Axis Geometry can be used for what has been identified as the Artifact Spread Function (ASF)2, 4 is closely related to the SSP in the z axis direction. The ASF has been determined by calculating the z axis response of a small steel bead.…”

“…The same bead ramps provide a series of point sources (beads)5, 9, 10 These beads with their small diameter (18 mm) can be considered small enough to constitute “points” sources to determine the point spread function (PSF) and resulting MTF2, 5 for current levels of DBT resolution (typically 100 microns or better in DBT mode), particularly when one deconvolves the effective size of the small bead 11. It can be noted, that strictly speaking, the term MTF should be approached with caution for DBT, because the formal conditions for MTF are not met in systems that may be nonlinear and non‐Isoplanatic 5.…”

“…The resulting MTF plots show the known anisotropy between the MTF (x) and MTF (y) results due to the influence of the tube travel direction lowering the MTF in that direction 12. Anisotropic distributions can often lead to an MTF rising above the MTF (0) value2 Additional aspects of reconstruction filters and differences between In‐Plane MTF and other regions should be kept in mind http://www.aapm.org/meetings/amos2/pdf/42-11930-81688-724.pdf.…”

“…The recent development of Tomosynthesis,1, 2 and in particular the commercialization of Digital Breast Tomography (DBT) has led to interest in developing Phantoms for assessment of image quality as well as Quality Assurance (QA). Several studies are underway to investigate the effectiveness of Tomosynthesis Mammographic Image Screening, including the large TMIST project as funded by the National Cancer Institute https://www.cancer.gov/about-cancer/treatment/clinical-trials/nci-supported/tmist.…”