In recent years, novel computed tomography (CT) systems with semiconductor-based photon counting detectors have been actively researched and developed [1], [2], [3]. Photon counting detectors have many advantages over conventional scintillation detectors, and have been reported to significantly improve dose-utilization efficiency, image contrast, and resolution [3], [4], [5], [6]. In addition, image noise reduction or radiation exposure reduction has been achieved [6], [7]. While dual energy CT has been commonly used for spectral analysis, in PCD-CT, it is possible to discriminate the detected photon signal by setting the energy threshold, and spectral analysis can be performed from multiple energy data obtained. Spectral analysis enables material discrimination analysis, iodine-enhanced images, virtual monochromatic X-ray images, effective atomic number analysis and electron density analysis, and is expected to provide new information for radiation diagnosis and radiotherapy.

Although there are various materials for semiconductor detectors, clinical research using CZT-based photon counting detector CT (CZT-based PCD-CT) has been conducted under the collaboration with Canon Medical Systems. In this study, we focused on electron density, which has not yet been reported by CZT-based PCD-CT, and compared electron density value calculated from spectral data obtained by CZT-based PCD-CT with nominal values to verify the accuracy of electron density quantification.