A proposal for a quality control protocol in breast CT with synchrotron radiation

The SYRMA-3D collaboration is setting up the first clinical trial of phase-contrast breast CT with synchrotron radiation at the Elettra synchrotron facility in Trieste, Italy. In this communication, a quality control protocol for breast CT is proposed, and a first test of image quality measurements is performed by means of a custom-made radiographic phantom. A set of projections is acquired and used to perform a CT reconstruction of two selected portions of the phantom. Such portions contain a uniform layer of water and a set of radiographic inserts, respectively. Together, they allow to perform several image quality measurements, namely CT number linearity, reconstruction accuracy, uniformity, noise, and low contrast resolution. All measurements are repeated at different beam energies in the range of interest, and at two different dose values. Measurements show a good linearity in the soft tissue range, paired to a high accuracy of the CT number reconstruction. Uniformity and noise measurements show that reconstruction inhomogeneities are bound to a few percent of the average pixel values. However, low contrast detectability is limited to the higher portion of the explored energy range. The results of the measurements are satisfactory in terms of their quality, feasibility and reproducibility. With minimal modifications, the phantom is promising to allow a set of image quality measurements to be used in the upcoming clinical trial.