Abstract
The effect of acquisition geometry in digital breast tomosynthesis was evaluated with studies of contrast-to-noise ratios (CNRs) and observer preference. Contrast-detail (CD) test objects in 5 cm thick phantoms with breast-like backgrounds were imaged. Twelve different angular acquisitions (average glandular dose for each ~1.1 mGy) were performed ranging from narrow angle 16° with 17 projection views (16d17p) to wide angle 64d17p. Focal slices of SART-reconstructed images of the CD arrays were selected for CNR computations and the reader preference study. For the latter, pairs of images obtained with different acquisition geometries were randomized and scored by 7 trained readers. The total scores for all images and readings for each acquisition geometry were compared as were the CNRs. In general, readers preferred images acquired with wide angle as opposed to narrow angle geometries. The mean percent preferred was highly correlated with tomosynthesis angle (R = 0.91). The highest scoring geometries were 60d21p (95%), 64d17p (80%), and 48d17p (72%); the lowest scoring were 16d17p (4%), 24d9p (17%) and 24d13p (33%). The measured CNRs for the various acquisitions showed much overlap but were overall highest for wide-angle acquisitions. Finally, the mean reader scores were well correlated with the mean CNRs (R = 0.83).
Highlights
Digital breast tomosynthesis (DBT) is a quasi-3D x-ray breast imaging method that reduces the tissue superposition problems associated with 2D mammography
We describe studies that were performed to evaluate the effects of acquisition geometry on observer preference of DBT images of contrast-detail (CD) test objects within phantoms with breast-like backgrounds and on the measured contrast-to-noise ratios (CNRs) of those test objects
Notice that the background varies in these images because the slabs above and below the CD insert are different in each case, which results in the interplane blurring of different patterns from above and below the CD insert extending into the focal plane
Summary
Digital breast tomosynthesis (DBT) is a quasi-3D x-ray breast imaging method that reduces the tissue superposition problems associated with 2D mammography. Many researchers have performed studies to determine the optimum geometry (angular range and number of projection views) for DBT. We have a unique prototype General Electric tomosynthesis system at our institution that was recently modified to include an “advanced research mode” for phantom imaging that allows us to vary the acquisition angular range and angular increment. We describe studies that were performed to evaluate the effects of acquisition geometry on observer preference of DBT images of contrast-detail (CD) test objects within phantoms with breast-like backgrounds and on the measured contrast-to-noise ratios (CNRs) of those test objects. The preference study allowed us to subjectively evaluate the overall impressions of the observers of their perception of CD test objects in DBT images including factors such as contrast, sharpness, noise, artifacts, background smoothness, etc. Preference studies have been used by investigators to determine the optimal kVps for dual energy digital radiography of the chest (Shkumat et al, 2008; Williams et al, 2007), to evaluate radiologists’ visual judgments of the similarity of masses and/or microcalcifications in mammograms (Muramatsu et al, 2007; Tourassi et al, 2013), and to compare digital with screen-film radiography. (Hamers et al, 2001)
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