A Framework for Iterative Reconstruction in Phase-Contrast Computed Tomography Dedicated to the Breast

We present the implementation of a computed tomography (CT) iterative reconstruction strategy developed within the SYRMA-CT project for in vivo phase-contrast CT of uncompressed breast, ongoing at the ELETTRA synchrotron radiation facility (Trieste, Italy). Propagation-based phase-contrast imaging exploits the high spatial coherence of the monoenergetic laminar X-ray beam, as well as the large object-to-detector distance and the use of a Pixirad-8 high-resolution photon-counting CdTe detector. The signal in projection views depends on the X-ray absorption as well as on the phase shift introduced by the breast tissue in the beam path. A phase retrieval algorithm allowed recovering the projected 2-D phase information of the irradiated tissue layer, which was input to the CT reconstruction; then, the breast slices were reconstructed via a simultaneous algebraic reconstruction technique algorithm. Our iterative reconstruction - coupled with a filtering process for reducing the noise level and ring artifacts while preserving edges sharpness - showed better image quality than conventional filtered back projection (FBP) reconstruction. This phantom study showed that our iterative reconstruction produced images with higher contrast-to-noise ratio and spatial resolution than those obtained with FBP. Finally, the developed algorithm removed ring-like artifacts, without worsening the image quality.