Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

Purpose: Within the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility (Trieste, Italy) the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis. Methods: Test objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and Noise Power Spectrum (NPS). Phase-contrast CT images as well as images obtained after the application of a phase-retrieval algorithm were evaluated. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were explored. Results: For a voxel size of (60 μm)3, phase-contrast images showed higher spatial resolution (6.7 mm-1 at 10% MTF) than corresponding phase retrieval images (2.5 mm-1). Phase retrieval produced a reduction of the noise level as well as an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. CaCO3 microcalcifications with a diameter down to 130 μm were detected both in phase-contrast and in phase retrieval images of the test object. Conclusions: The investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Phase-retrieved images showed the best performance in the trade-off between spatial resolution and image noise.