Signal-to-Noise Ratio and Contrast-to-Noise Ratio Measurements for Next Generation Tomosynthesis.

It is standard for the x-ray source in conventional digital breast tomosynthesis (DBT) acquisitions to move strictly along the chest wall of the patient. A prototype, next-generation tomosynthesis (NGT) system has been developed that is capable of acquiring customized geometries with source motion parallel and perpendicular to the chest wall. One well-known consequence of acquiring projections with the x-ray source anterior to the chest wall is that a small volume of tissue adjacent to the chest wall is missed. Here we evaluate strategies in DBT to avoid missing tissue while improving overall image quality. Acquisition geometries tested in this study include the conventional (control), "T-shape," and "bowtie" geometries. To evaluate the impact of moving the x-ray source away from the chest wall, the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured as a function of location within the reconstructed volume. Using simulations and physical experiments, the SNR and CNR were compared with conventional DBT. Simulations of two different phantoms were performed: a "tube" phantom and a "lattice" phantom. Experiments with uniform and textured phantoms were also conducted. While the image quality was slightly reduced immediately adjacent to the chest wall, there was no missed tissue and both the T-shape and Bowtie geometries exhibited SNR and CNR improvement over the vast majority of the reconstruction volume; the overall result being an improvement in image quality with both the T-shape and bowtie geometries.