1. CT imaging system comprising a X-ray source; a first detection and collection unit which is disposed to be opposite to the X-ray source and configured to perform a first CT scanning on an object to be detected to obtain scanning data; a reconstruction unit configured to reconstruct an image of a first resolution based on the scanning data; a second detection and collection unit which includes at least a photon counter detector and is configured to perform a second CT scanning on an area of interest in the image of the first resolution, the second CT scanning including scanning on the area of interest under a plurality of energy windows by the photon counter detector to obtain truncated energy spectrum data; wherein the reconstruction unit is further configured to supplement the truncated energy spectrum data by using the image of the first resolution as a priori image, and to reconstruct an image of a second resolution from the supplemented energy spectrum data, the second resolution being higher than the first resolution.