Image artifacts in digital breast tomosynthesis: Investigation of the effects of system geometry and reconstruction parameters using a linear system approach
The experimental DBT unit operates under partial isocentric motion with a stationary detector. The x-ray tube travels along an arc in the plane with an angular range of .
DBT acquires images over a limited angular range. The sampled region in the frequency domain is in the shape of a double wedge with angle . The effect of the slice-thickness filter is highlighted with gradient shading.
The reconstruction filter functions in their corresponding spatial frequency directions. The RA filter, , is given as a function of and , the SA filter, , is given as a function of , and the slice thickness filter, , is given as a function of . The interpolation filter, , is plotted as a function of however; in two dimensions it is a function of both and .
A tungsten wire phantom is used to image a 2D point spread function (PSF). The wire is tilted at an angle, , with respect to the -axis and oriented orthogonally to the direction of tube motion.
The in-plane image of a tilted W wire phantom reconstructed using simple backprojection (SBP). Both axes are in units of mm. The -dependence of image intensity can be derived from the -dependence using the angle of the wire and Eq. (7).
Flow chart showing the cascaded stages of the linear system model for calculating the 3D MTF of the DBT system. The left column shows the description of each stage, and the graphs on the right show conceptually the change in MTF after each cascaded stage.
Comparison between measured (left) and modeled (right) 2D PSF in the plane. The graphs (a)–(d) correspond to filter schemes 1–4 listed in Table I. The PSF in each graph is plotted from along the -direction, and in the -direction.
The comparison between measured and modeled 1D PSF in -direction (with ). The graphs (a), (b), and (c) correspond to filter schemes 1, 3, and 4, respectively. Plot (d) is a comparison between the modeled 1D PSF in the -direction for each filter scheme.
Comparison between the measured presampling PSF for the angular range of (from left to right): , , , and . The image reconstruction was performed using filter scheme 3.
The comparison between measured and modeled 1D PSF in the -direction with the angular range of (a) ; (b) ; (c) ; and (d) . Filter scheme 3 was used in all cases.
Comparison of modeled 1D PSF in the -direction for the angular ranges of , , and . All results were modeled using filter scheme 3.
Stacked image slices showing the artifact of the steel bead as a function of their distance from the location of the bead. A small ROI with 11 image lines was selected from each slice to include the entire image or artifact of the bead. Images (a)–(d) corresponded to reconstructions using filter schemes 1 to 4.
The stacked images/artifacts of the bead with reconstruction using: (a) a limited angular range of ; and (b) a wider angular separation of with angular range of . Filter scheme 3 was used in all cases.
Comparison between modeled and measured ASF: (a)–(d) correspond to filter schemes 1–4, respectively. The modeled ASF was calculated by multiplying the signal spectrum of a diameter sphere with the presampling MTF of the DBT system, followed by an inverse Fourier transform. The vertical line with was normalized and plotted as the modeled ASF.
Comparison of ASF with different acquisition geometries: 49 views over (solid line); 13 views over (squares); and 13 views over (triangles).
Summary of the reconstruction filter schemes used in our investigation.
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