Photon counting can discriminate different energy levels in the incoming X-ray beam. Therefore, it enables enhanced tissue differentiation, density measurement and K-edge imaging with reduced contrast media. Multi-energy discrimination allows the detector to image several contrast agents at the same time.
Spectral CT image of various iodine concentrations. Iodine image is computed from spectral information below and above the iodine absorption edge (33.2 keV) (courtesy F.M. Epple, Technical University of Munich, Germany)
Spectral CT image of a mouse in iodine. On the left side is a conventional CT image, on the right side the K-edge image (33.2 keV). Iodine depleted zones are clearly visible on the K-edge image (courtesy F. Pfeiffer, Technical University of Munich, Germany).