Purpose: In this work we present equivalent breast thickness and dose sensitivity of a next iteration 3D structured breast phantom with lesion models to demonstrate its potential use for quality assurance measurements in breast imaging. Methods: PMMA equivalent thickness was determined employing the automatic exposure control (AEC) of Siemens Mammomat Inspiration and Siemens Mammomat Revelation. A 2D projection image of the phantom was acquired and the corresponding AEC settings recorded as reference. Equivalent PMMA thickness was found by interpolating between three PMMA thicknesses with mAs values close to the reference settings selected by AEC. Dose sensitivity of the reconstructed digital breast tomosynthesis (DBT) images was assessed by two experienced readers using a four alternative forced choice (4-AFC) study. Three different dose levels for lesion models and microcalcifications were evaluated. Results: PMMA equivalent thickness of the phantom was 46.8 mm and 47.0 mm for measurements on Siemens Mammomat Inspiration and Siemens Mammomat Revelation which equals to a breast equivalent thickness of 55.5 mm and 55.8 mm, respectively, compared to a physical phantom thickness of 53.5 mm. For lesion models dose sensitiviy of the detectability was not obvious. For microcalcification the diameter threshold was found to increase for decreasing dose from high dose to AEC to low dose. Conclusions: We found the measured equivalent breast thickness of our phantom to be close to its physical thickness. It can be concluded that changes in dose can be detected by the presented phantom for the tested dose levels.
In this work we tested different materials for 3D printing of spiculated mass models for their incorporation into an existing 3D structured phantom for performance testing of FFDM and DBT. Counting the number of spicules as a function of dose was then evaluated as a possible extra test feature expressing conspicuity next to detectability. Seven printable materials were exposed together with a PMMA step wedge and material samples with known linear attenuation coefficient to determine PMMA equivalent thickness and linear attenuation coefficient, respectively. Next, two models of spiculated masses were created each with a different complexity in terms of number of spicules. The visibility of the number of spicules of a 3D printed spiculated mass model loosely placed in the phantom or embedded into two different printing materials was assessed for FFDM and DBT. Vero White pure was chosen as the most appropriate material for the printing of masses whereas Vero Clear and Tango+ were chosen as background materials. The visibility of spicules was best in the loose mass models and better in the background material Tango+ compared to Vero Clear. While the discrimination of the different spicules could be assessed in FFDM and DBT, as expected only a limited dose sensitivity was found for the visibility of spicules evaluated for the different background materials and at different beam energies.