Methodology for undertaking quality control testing of ghosting in digital breast tomosynthesis systems

Abstract

Purpose: Low levels of ghosting are found during quality control of digital mammography (DM). In digital breast tomosynthesis (DBT) mode, the x-ray detector is not cleared during the series of exposures potentially leading to ghosting issues. Methods: The ghosting image factor (GIF) was calculated for systems from three manufacturers as follows. A 45 mm thick polymethyl methacrylate (PMMA) block covering half the detector was imaged, followed by the PMMA block plus 0.1 mm thick aluminium sheet centred on the block, this time positioned to fully cover the detector. This was undertaken for (1) DM and (2) between separate DBT scans. Inter-projection ghosting (3) was measured by moving the PMMA block from covering half the detector to covering the whole detector after the first projection. In method (4), a 3 mm thick aluminium plate with a 0.1 mm thick aluminium sheet on top was placed on the compression paddle at 100 mm above the breast covering half of the detector. Results: The GIF measured via test (1) and (2) was lower than the 0.3 tolerance set in the European guidelines for DM, however higher values were found for one system in DBT mode. Test 3, inter-projection GIF values were between 0.08 and 0.89, mostly above 0.3. Test 4 was a practical method and gave larger GIF values of between 1.07 and 8.01. Conclusions Ghosting factors measured between projections are considerably higher than the GIF measured between separate DBT scans. We propose a simple method using an aluminium plate to estimate the GIF.