System design to realize functional and conventional images during single X-ray irradiation using a photon counting detector

Energy-resolving photon-counting detectors (ERPCDs) have the potential to extract functional diagnostic information such as the effective atomic number ($\left.\mathrm{Z}_{\text {eff }}\right)$ from X-ray images. Our study aims to construct an imaging system for obtaining both functional and conventional images during single X-ray irradiation. Taking advantage of the characteristics of EPRCD to analyze multiple energy information, we propose an optimal system that fully guarantees the performance of both $\mathrm{Z}_{\text {eff }}$ image and conventional image. Our previously developed imaging simulator was used, which takes the following into consideration: (a) attenuation for polychromatic X-rays, (b) detector response, and (c) statistical fluctuation. Virtual phantoms with mass thickness ($\rho$ t) values of 0.1-80 $\mathrm{g} / \mathrm{cm}^{2}$ composed of aluminum (bone) and polymethyl methacrylate (soft tissue), and digital phantoms of the hand and pelvic region generated from computed tomography images were analyzed. The accuracy of $\mathrm{Z}_{\text {eff }}$ images and the contrast-to-noise ratio of conventional images were evaluated. As a result, a high tube voltage setting of 120 kV was found to be the optimal condition. The accuracy of $\mathrm{Z}_{\text {eff }}$ images was drastically improved under this condition compared with that under low tube voltage conditions. The contrast of conventional images for certain objects ($\rho$ t $\lt2$ $\mathrm{g} / \mathrm{cm}^{2}$) was slightly worse when using all energy images, but when using low and middle energy images, the contrast of all objects was improved systematically. Furthermore, it was found that high-quality pre-clinical images could be generated even when the optimal condition was determined based on single-element phantoms of bone and soft tissue. In conclusion, we proposed a novel ERPCD system using high tube voltage imaging and verified its clinical applicability through a simulation study.