Image quality of microcalcifications in digital breast tomosynthesis: Effects of projection-view distributions

Abstract

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 630 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 paral...

Patchwork reconstruction with resolution modeling for digital breast tomosynthesis

“…The right column then shows the relative error in the projection by dividing both projections. The maximum error of the projections without resolution model (1) and with resolution model (9) are shown in figure 4. (1)) and with the approximate model (equation (9)).…”

“…Figure 3 shows the projections of five calcifications with diameters 100, 125, 150, 175 and 200 µm, located at 60 mm above the detector plane. The left column shows the projections created using a simulation according to the accurate description in formula (3) and the middle column is simulated using the approximated description in formula (9). The right column then shows the relative error in the projection by dividing both projections.…”

“…Repeating the previous steps for all other planes results in (8). Reverting back to index i for the projection lines and index j for the reconstruction volume and including scatter term s i gives our final approximation of the acquisition process in equation (9).…”

“…with y i the measured transmission scan, i the index of the projection line andŷ i the mathematical model of the transmission scan, such as for example the models in equations (1) or (9). With the model in equation (1), we can construct the update step of a gradient ascent algorithm [26,27,29] using formula (11), where α j ≥ 0 is a design parameter.…”

“…One path to improve visualization of microcalcifications is to optimize the dose and angular distribution of the limited angle set of projections [7][8][9]. These projections are then usually reconstructed with filtered backprojection (FBP) although this reconstruction by FBP is not always optimal [10,11] because of the limited angular range and low dose acquisitions, * koen.michielsen@uzleuven.be especially for small angular range [12].…”