Identification of contrast media in PET/CT using dual energy CT

Full Text: For accurate quantization of radioactivity distribution, PET images require correction for tissue attenuation. In PET/CT, in addition to yielding structural images for comparison with the functional PET image and thus aiding location of PET dings, the CT images are converted to 511keV attenuation maps to provide the necessary attenuation correction. Current conversion methods based on single-energy CT are accurate for biological tissue, but do not account for the presence of metals, and may therefore generate artifacts in the PET images. Both iodine-containing contrast media, used to facilitate interpretation of CT images, and metallic implants (e.g. prostheses, cardiac pacemakers, central venous lines etc) may cause such artifacts. A method is presented in which fractional differences of CT images at two energies (DECT) are interpreted, using well-known simple properties of dual-energy x-ray imaging, to identify regions of contrast media and thus provide reliable separation of contrast from soft tissue and bone on CT. This identification of contrast could be used to avoid contrast errors in PET/CT attenuation correction by preventing erroneous automatic conversion of contrast-containing regions to inaccurate 511keV attenuation coefficients