Comparison of the X-ray tube spectrum measurement using BGO, NaI, LYSO, and HPGe detectors in a preclinical mini-CT scanner: Monte Carlo simulation and practical experiment

Background: In diagnostic X-ray computed tomography (CT) imaging, some applications, such as dose measurement using the Monte Carlo method and material decomposition using dual/multi-energy approaches, rely on accurate knowledge of the energy spectrum of the X-ray beam. In this regard, X-ray detectors providing an accurate estimation of the X-ray spectrum could greatly impact the quality of dual/multi-energy CT imaging and patient-specific dosimetry. Purpose: The aim of this study is to estimate the intrinsic efficiency and energy resolution of different types of solid-state gamma-ray detectors in order to generate a precise dual-energy X-ray beam from the conventional x-ray tube using external X-ray filters. Materials and methods: The X-ray spectrum of a clinical X-ray tube was experimentally measured using a high purity Germanium detector (HPGe) and the obtained spectrum validated by Monte Carlo (MC) simulations. The obtained X-ray spectrum from the experiment was employed to assess the energy resolution and detection efficiency of different inorganic scintillators and semiconductor-based solid-state detectors, namely HPGe, BGO, NaI, and LYSO, using MC simulations. The best performing detector was employed to experimentally create and measure a dual-energy X-ray spectrum through applying attenuating filters to the original X-ray beam. Results: The simulation results indicated 9.16% energy resolution for the HPGe detector wherein the full width-at-half-maximum (FWHM) of the energy resolution for the HPGe detector was about 1/3rd of the other inorganic detectors. The X-ray spectra estimated from the various source energies exhibited a good agreement between experimental and simulation results with a maximum difference of 6%. Owing to the high-energy discrimination power of the HPGe detector, a dual-energy X-ray spectrum was created and measured from the original X-ray spectrum using 0.5 and 4.5 mm Aluminum external filters, which involves 70 and 140 keV energy peaks with 8% overlap. Conclusion: The experimental measurements and MC simulations of the HPGe detector exhibited close agreement in high-energy resolution estimation of the X-ray spectrum. Given the accurate measurement of the X-ray spectrum with the HPGe detector, a dual-energy X-ray spectrum was generated with minimal energy overlap using external X-ray filters.