Verification of the accuracy of a partial breast imaging simulation framework for virtual clinical trial applications

Aim: The impact of x-ray system parameters on detectability of specific (clinical) signals can be studied with simulation platforms if these tools are sufficiently accurate and realistic. This work describes the steps taken to verify and confirm the accuracy of a local platform developed for the use in virtual clinical trials of breast tomosynthesis. The (gold standard) reference data will be made available to the community. Materials and methods: Our simulation platform simulates specific targets, including microcalcifications into existing 2D FFDM and DBT background images, a method called partial simulation. There are three steps: (1) creation of a voxel model or 3D analytical object to be inserted into the 'For Processing' projections; (2) generation of a realistic object template for the geometry under study and the relevant resolution, scatter and noise properties; (3) insertion of the target into the projections and DBT reconstruction plus image processing. Three objects were simulated as part of the verification: a small high contrast 0.5 mm aluminum (Al) sphere in a poly(methyl methacrylate) (PMMA) stack, a 0.2 mm thick Al sheet in a PMMA stack and a 0.8 mm steel edge. For the small Al sphere, the peak contrast, the signal difference to noise ratio (SDNR), the profile in the (in plane) xy-direction and the artifact spread function (ASF) were compared to results from real acquisitions. Contrast and SDNR were compared to data from a real 0.2 mm Al sheet. Sharpness modelling was verified by comparing the modulation transfer function (MTF) calculated from real and simulated edges. The study was performed for a Siemens Inspiration DBT system. Results: Comparing peak contrast and SDNR for both sphere and sheet showed good agreement (<5% error) in 2D FFDM and DBT. The similarity of the pixel value profiles through the sphere and the sheet in the xy-direction and the ASF for real and simulated Al spheres confirmed accurate geometric modelling. Absolute and relative average deviation between MTF measured from real and simulated edge in the front-back and left-right directions show a good correlation for frequencies up to the Nyquist frequency for 2D FFDM and DBT mode. Real and simulated objects could not be differentiated visually. Conclusion: The close correspondence between simulated and real objects, both visually and quantitatively, indicates that this simulation framework is a strong candidate for use in virtual clinical studies employing 2D FFDM and DBT.