The present invention relates to a CT imaging system comprising a second ray tube / detector and a method thereof. The CT imaging system (10) includes a rotatable gantry (12) having an opening (48) to receive an object (22) to be scanned, a first x-ray emission source (90, 190) attached to the rotatable gantry (12) and configured to emit x-rays toward the object (22), and a second x-ray emission source (92, 192) attached to the rotatable gantry (12) and configured to emit x-rays toward the object (22). A first detector (100, 200) is configured to receive x-rays that emit from the first x-ray emission source (90, 190), and a second detector (106, 206) configured to receive x-rays that emit from the second x-ray emission source (92, 192). A first portion of the first detector (100, 200) is configured to operate in an integration mode and a first portion of the second detector (106, 220) is configured to operate in at least a photon-counting mode.