Influence of pulse pile-up effects on material decomposition with photon-counting CT

The aim of this study is to reveal an influence of pulse pile-up effects on material decomposition with a photon-counting CT system. The photon-counting CT has great advantages compared with a conventional system. Among them we focused on the ability of a material decomposition. However, a photon-counting CT system also has many issues to be solved. The most serious problem is a pulse pile-up effect. When multiple X-ray photons are simultaneously incident on a detector, the recorded spectrum is distorted. It should significantly degrade the material decomposition accuracy. Hence, we investigated influence of the pile-up effect on material decomposition, and feasibility of a spectral distortion-correction method. Using an analytical pile-up model, we performed simulations and found that accuracy of material-density measurements decreased with increasing X-ray intensity. We also found that spectral distortion could not be negligible even in case of impractically low x-ray intensity for an accurate density measurement of low concentration solution, suggesting a requirement of spectral distortion correction. Hence, we provided a correction method based on a least square method. In a simulation, our method successfully corrected the spectral distortion even in case of wide energy windows. The remained uncertainty was less than a few percent for a moderate X-ray intensity.