Technical note: Realization and uncertainty analysis for an adjustable 3D structured breast phantom in digital breast tomosynthesis

Background: Projection imaging phantoms are often optimized for 2-dimensional image characteristics in homogeneous backgrounds. Therefore, evaluation of image quality in tomosynthesis (DBT) lacks accepted and established phantoms.

Purpose: We describe a 3D breast phantom with a structured, variable background. The phantom is an adaptable and advanced version of the L1 phantom by Cockmartin et al. Phantom design and its use for quality assurance measurements for DBT devices are described. Four phantoms were compared to assess the objectivity.

Methods: The container size was increased to a diameter of 24 cm and a total height of 53.5 mm. Spiculated masses were replaced by five additional non-spiculated masses for higher granularity in threshold diameter resolution. These patterns are adjustable to the imaging device. The masses were printed in one session with a base layer using two-component 3D printing. New materials compared to the L1 phantom improved the attenuation difference between the lesion models and the background. Four phantoms were built and intra-human observer, inter-human observer and inter-phantom variations were determined. The latter assess the reproducibility of the phantom production. Coefficients of variance (V) were calculated for all three variations.

Results: The difference of the attenuation coefficients between the lesion models and the background was 0.20 cm^-1 (with W/Al at 32 kV, equivalent to 19-20 keV effective energy) compared to 0.21 cm^-1 for 50/50 glandular/adipose breast tissue and cancerous lesions. PMMA equivalent thickness of the phantom was 47.0 mm for the Siemens Mammomat Revelation. For the masses, the $V_{intra}$ for the intra-observer variation was 0.248, the averaged inter-observer variation, ${\overline{V}}_{inter}$ was 0.383. $V_{phantom}$ for phantom variance was 0.321. For the micro-calcifications, $V_{intra}$ was 0.0429, ${\overline{V}}_{inter}=$ 0.0731 and $V_{phantom}=$ 0.0759.

Conclusions: Position, orientation and shape of the masses are reproducible and attenuation differences appropriate. The phantom presented proved to be a candidate test object for quality control.