Phase-contrast breast-CT: Optimization of experimental parameters and reconstruction algorithms

Abstract

X-ray breast computed tomography (breast-CT) is a new emerging technique for breast imaging however its application is still limited because of low spatial resolution and high delivered dose. In this framework, synchrotron radiation provides ideal X-ray imaging conditions. Tunable and monochromatic laminar X-ray beam, along with large propagation distance, allows acquiring images with high quality, low scatter and dose reduction, due to the selection of the most suitable energy for the given thickness and breast composition. Moreover, the high spatial coherence permits to exploit the phase-contrast effects enabling a better image quality and soft tissue contrast. At the Elettra synchrotron facility, in Italy, a project for in vivo low-dose, high-contrast and high-resolution breast-CT is under development using a high-efficiency photon-counting detector. Due to the vertical size of the beam (~3.5 mm) the scan requires a sequence of vertical steps. Thus reducing the number of projections is essential to shorten the total acquisition time. Optimized preprocessing algorithms (phase-retrieval) and the state of the art of tomographic reconstruction methods are crucial to improve image quality. In this work, performances of standard and iterative reconstruction algorithms at different experimental conditions are compared, evaluating quantitatively the image quality in terms of Contrast-to-Noise ratio and edge sharpness. Preliminary results suggest that, in the light of a clinical exam where a short scan time is desirable, the projection number can be reduced without a major loss in image quality by applying FBP based reconstruction algorithms and phase-retrieval pre-processing.