| Abstract [eng] |
Breast cancer is one of the leading causes of death for women worldwide. Early and accurate detection of malignancies is essential for improving the outcome of cancer treatments. Conventional X-ray imaging is based purely on contrasts of attenuation and, since no contrast difference between cancerous and glandular tissues is evident, the diagnosis is mainly based on the morphological characteristics of cancer. On the other hand, advanced imaging techniques allow the extraction of quantitative information. We aim to exploit a technique of spectral decomposition to quantify the difference in chemical composition between healthy and malignant dense tissues. The study was carried out using a custom-made phantom, filled with water and containing inserts of plastic materials (polyethylene, nylon, polymethyl methacrylate, polyoxymethylene, polytetrafluoroethylene) that mimic the attenuation properties of breast tissues. Imaging was performed at Elettra, the Italian synchrotron facility, using monochromatic beams of several energies in the breast CT imaging energy range (25-35 keV). 3D tomographic maps of attenuation coefficients were obtained by acquiring projections in a free space propagation phase-contrast setup and further processing them utilizing a phase retrieval filter, a procedure resulting in a significant noise reduction without loss of spatial resolution. Images were processed by a spectral decomposition algorithm, resulting in composition maps in terms of a selected pair of basis materials. Material choice matched the tissue range of interest inside the breast. Using a dedicated mathematical procedure, we managed to decouple the information about the material density and its chemical composition. Finally, a calibration allowed for the extraction of the effective atomic number associated to each reconstructed voxel. The range of effective atomic numbers among the plastic inserts matched the slight differences among tissues in the breast. Compared to previous studies, the present approach exhibits a much higher sensitivity in material discrimination, which is necessary for the context of breast diagnostic imaging. The decoupling of the information about the chemical composition allows very accurate discrimination of similar tissues composing the breast. The proposed technique of spectral decomposition and decoupling allows a quantitative description of imaged samples composition, opening the possibility of significant contributions to a breast cancer diagnosis. |
