Photon counting CT apparatus and method of correcting material decomposition map

A photon counting computed tomography (CT) apparatus comprising:

• an X-ray tube that radiates X-rays to an imaging range;
• an X-ray detector that counts a plurality of X-ray photons passing through the imaging range in each of a plurality of energy bands according to energy levels of the respective X-ray photons;
• a map storage unit that stores a material decomposition map indicating measurement values in a plurality of energy bands previously obtained about combinations of two or more types of materials made to have a plurality of respective different thicknesses;
• a material decomposition unit that obtains, by referring to the material decomposition map, a combination of thicknesses of two or more types of materials corresponding to measurement values obtained by the X-ray detector performing counting about a plurality of energy bands in a state in which a subject is arranged in the imaging range;
• and
• a map correction unit that corrects the material decomposition map,
• wherein the map correction unit actually measures corrective measurement values by radiating X-rays from the X-ray tube and counting X-ray photons in each of a plurality of energy bands in a state in which no subject is arranged in the imaging range and/or in a state in which one or more types of corrective materials are arranged at a position through which X-rays radiated from the X-ray tube pass, and corrects the measurement values in the material decomposition map based on the corrective measurement values.