Counting response and beam hardening calibration method for a full size photon-counting CT system

A method processing projection image data acquired by a photon counting computed tomography (CT) system, the method comprising:

• performing a plurality of calibration scans comprising an air scan and scans using a plurality of slabs of different materials, at an initial current intensity and at plural tube voltage settings of an X-ray tube, for each scan, to obtain counts for each energy bin;
• estimating calibration parameters based on the counts;
• obtaining a group of projection image data for each of a plurality of energy bands;
• generating, based on the group of projection image data, a first group of projection data corresponding to a first basis material and a second group of projection data corresponding to a second basis material;
• calculating a first beam hardening correction term relating to the first basis material based on the first group of projection data;
• calculating a second beam hardening correction term relating to the second basis material based on the second group of projection data;
• and
• generating an energy bin image corresponding to one energy band by using the first beam hardening correction term, the second beam hardening correction term and the one energy band among the plurality of energy bands, wherein
• estimating the calibration parameters comprises
• estimating first parameters, which are dependent on energy, based on counts;
• estimating second parameters which are dependent on total counts of all energy bins, based on the first parameters;
• and
• repeating, using each of a plurality of slabs, the steps of estimating first and second parameters for different current intensities other than an initial current intensity and at a same tube voltage to obtain the second parameters, respectively, for different current intensities, to generate tables of the estimated first parameters and second parameters.