Development of a spectral micro-CT system using a photon counting detector with anti-coincidence corrections

There is potential to improve CT imaging by adding spectral capabilities as given by photon counting detectors (PCD). Here we describe and assess performance of a new spectral micro-CT prototype system using a CdTe-based PCD with 100-μm pixel size (model XC-Thor, made by Direct Conversion) benefitting from anti-coincidence corrections. To assess the PCD in terms of spectral response, a Ba-133 nuclear source was scanned using full spectrum scanning by sweeping thresholds with 2 keV increments. In a different experiment, we used small vials containing water, iodine (I), gadolinium (Gd), and gold (Au) placed on the surface of the detector and acquired X-ray data in full spectrum mode to verify that the PCD threshold positions yielded the expected changes in contrast around the K edges of these elements. Detector performance was assessed using micro-CT phantoms and during cancer experiments in mice injected with nanoparticle (NP)-based contrast agents. Both phantom and mouse micro-CT data were reconstructed using our iterative, multi-channel algorithm based on the split Bregman method and regularization with rank-sparse kernel regression. A post-reconstruction decomposition method was used. The system is capable of high resolution (11.9 lp/mm, 10% MTF) tomographic imaging. Despite the anti-coincidence corrections, the spectral performance of the PCD is, however, not perfect, and it seems to be affected mostly at lower keVs, making accurate iodine decomposition challenging. Our cancer imaging results illustrate that our spectral micro-CT can benefit both nanotechnology and cancer research by providing an imaging method that can help test/optimize various nanoparticle for theranostics.