The effects of spectral distortion on multi-energy X-ray imaging based on photon counting detector

We studied the effect of spectral distortions on X-ray imaging observed by photon-counting detectors. The photon counting-based imaging system used in this study consisted of a micro focus X-ray source and cadmium telluride (CdTe) detector. The energy spectra and phantom images were obtained at 70 kVp with aluminum filters of various thicknesses (1, 5, and 10 mm), which acted as a photon rejecter to reduce the pulse pile-up effect by decreasing incident number of photons. The phantom included high atomic number materials that were imaged to evaluate the effect of spectrum distortions on X-ray imaging. The spectral distortion was degraded image quality by increasing low energy photons including electronic noise but image quality can be increased with optimal thickness of photon rejecter. In the experiment, 10 mm photon rejecter minimized pulse pile-up effects and increase contrast noise ratio (CNR) of materials by selectively removed electrical noise. The quantum noise according to the thickness of photon rejecter was a negligible quantity in experiment because photon counting detector already limited acceptable number of photons by detector electronics. The results indicate that the optimized photon rejecter has the potential to reduce the degradation of image by spectral distortion. If we optimize photon rejecter for various exposure conditions, we should be able to achieve even better image quality without complex spectral distortion modeling.