Helpfulness of effective atomic number image in forensic dental identification: Photon-counting computed tomography is suitable.

The identities of unidentified persons are often confirmed by matching dental treatment information. Although treatment restorations consisting of artificial materials can be confirmed visually and/or by X-ray photography, they should be quantitatively analyzed. This study demonstrates that effective atomic number (Z(eff)) images can be created using photon-counting computed tomography (PC-CT) and used to identify artificial materials employed in dentistry. We examined a multi-energy phantom with known atomic number materials, artificial dental materials, and a head phantom in which various actual dental inlay-materials can be embedded in the tooth. To analyze Z(eff) images, we used (ⅰ) a photon-counting CT (PC-CT), (ⅱ) a dual-energy CT (DE-CT), and (ⅲ) a photon-counting-type scanogram imaging system (PC-scanogram). An algorithm for Z(eff) analysis using PC-CT was newly proposed in this study, in which two virtual monochromatic X-ray images of 70 keV and 100 keV were utilized. The PC-CT results were compared to those of DE-CT and PC-scanogram. The Z(eff) images using PC-CT, DE-CT, and PC-scanogram were created properly with errors of +/-0.40, +/-0.21, and +/-0.24, respectively. We indicated that the Z(eff) value of artificial dental materials can be uniquely determined irrespective of the imaging system. Moreover, the same result could be obtained even when the artificial dental materials were embedded in a head phantom. In conclusion, the Z(eff) values provide an important quantitative indicator for identifying and/or discriminating artificial dental materials. This paper also proposed a new procedure for forensic dentistry by demonstrating the possibility of diagnosis based on the quantitative analysis of artificial dental materials.