Characterisation of a breast tomosynthesis unit to simulate images

The aim of this work is to characterise the image quality of a mammography system in both planar and tomosynthesis imaging modes for the purpose of realistic image simulation. The simulation technique will be applied to projected images from voxelised breast phantoms to investigate the imaging properties of different configurations of tomosynthesis systems. Methods: A Hologic Dimensions mammography system was characterised in terms of noise, sharpness, and lag in both planar and tomosythesis modes. The noise power spectra (NPS) were measured for both imaging modes. The contributions (noise coefficients) to the NPS from electronic, quantum and structure noise were calculated. Results: The MTF was shown to be affected by the focal spot size and the movement of the X-ray tube. These effects can be modelled in the tomosynthesis projection images using an extended source. The quantum noise coefficients for the two imaging modes showed a close match up to the Nyquist frequency of the tomosynthesis mode, while the electronic and structure noise showed differences. The effect of lag and ghosting caused the signal in the last projection of a tomosynthesis run to be between 2 and 4% higher than the first. Conclusions: We have characterised the noise and resolution properties of images from a Hologic Dimensions tomosynthesis system. This forms the basis of further work required to create a model for applying imaging characteristics to mathematically produced images. More work is required on detector lag and ghosting and the influence of oblique X-ray incidence.