Energy calibration of a photon-counting CT with K-edge absorption features

The aim of this study is to develop an energy calibration method of a photon counting CT, which provides spectral information of incident X-rays. The spectral information enables us to perform material decomposition. To estimate the density of each composed material, an accurate energy calibration should be performed. However, it is difficult to perform an accurate calibration with conventional methods with radioisotopes or the maximum energy of an X-ray spectrum. In this study, we propose a new method with K-edge absorption features. It can provide an accurate calibration because the K-edge energy is determined by an atomic number, and intense X-rays lead to a clear absorption peak with enough statistics. The feasibility of our method was experimentally confirmed. We used X-rays generated with a tube voltage of 100 kV and a vial filled with gadolinium, platinum or gold solution. We measured the absorption spectra and detected the K-edge features. We also measured the tungsten characteristic X-rays in the spectrum. Using these features, we performed an energy calibration. Our calibration was consistent with a conventional radioisotope method, showing a reliability of our method. We also found that our method is consistent with a maximum X-ray energy method at E <; 60 keV but not at higher energy. We attributed this to an uncertainty in the measurement of the maximum X-ray energy.