Contrast and depth resolution of breast lessions in a digital breast tomosynthesis system

Abstract

Introduction Digital breast tomosynthesis (DBT) provides a quasi-three-dimensional structural information of the breast, solving the issue of overlapping mammographic parenchyma in breast lesion visualization. Purpose This study investigates the effect of lesion position along the z-axis and breast thickness on image quality of DBT reconstructed images. Materials and methods Mass objects (size: 3 mm) of varying nominal contrast values (1.5%, 2%, 3% and 4%) and microcalcification objects (size ∼300 μm) at two different nominal contrast values, of a mammographic phantom (Leeds, TORMAM), were imaged with a DBT system (Hologic, Selenia Dimensions) at clinical settings. Four object positions along the z-axis were investigated by increasing test object distance from the detector, considering a breast thickness of 45 mm. In addition, for a specific phantom position along the z-axis, four breast thickness values (17, 30, 45, 65 mm) were investigated. Image quality metrics considered are CNR at focal plane and depth resolution, estimated using the full-width-at-half maximum (FWHM) of the artifact spread function (ASF) of lesion objects. Results Lesion CNR at focal plane remained constant for increasing object-detector distance, while increasing with objects’ nominal contrast, as expected. CNR decreased for increasing phantom thickness, for both lesion types. Depth Z-resolution differed with respect to lesion size at detector plane, as estimated by ASF, yielding 30.5 ± 4.3 mm for masses and 3.3 ± 0.4 mm for microcalcifications. Finally, lesion depth resolution was not affected by position along z-axis or phantom thickness. Conclusion Breast thickness and lesion size should be considered when assessing DBT image quality.