The influence of position within the breast on microcalcification detectability in continuous tube motion digital breast tomosynthesis

In digital breast tomosynthesis (DBT), the detectability and characterization of all lesions, especially microcalcifications, is still an issue under investigation. For DBT systems equipped with an x-ray tube that moves continuously during exposure, theory predicts some influence of the focal spot motion blur on detectability and diagnosis of small lesions, such as microcalcifications. Motion blur experienced by a lesion at some position in the breast is known to depend on the height of the lesion above the table within the breast. In this study, we investigated the influence of position above the table on microcalcification contrast and signal difference to noise ratio (SdNR) (as a surrogate for detectability) in tomosynthesis images, by means of a hybrid simulation method. Microcalcifications, represented by spheres of calcium with 400 μm diameter, were simulated into projection images of homogeneous objects and into anatomical backgrounds. The influence of system sharpness was included via the modulation transfer function (MTF) model that included detector, focus size, tube motion and x-ray oblique entry components. Results show contrast reductions for spheres at increasing heights above the detector in all datasets. For example, contrast drops of 31.5% and 43.1% for a sphere inserted at 1 mm height compared to insertions at 40 mm and 69 mm above the table, respectively, were found for spheres simulated near the chest wall for homogeneous background. For the same cases, the corresponding drops in SdNR were 30.6% and 40.3%, respectively. Similar trends were also seen for sphere contrasts measured in anatomical backgrounds.

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