Effective atomic number estimation based on linear attenuation coefficient obtained by current mode energy resolved computed tomography

In X-ray computed tomography (CT), the information of X-ray energy spectrum will bring advantages such as the enhancement of contrast agent signal. For the energy-resolved CT, a 'transXend' detector has been developed in our laboratory. In our previous study, a CT measurement for a cylindrical polymethyl methacrylate phantom (3 cm dia.) with four kinds of resin rods (5 mm dia.) was performed. The obtained linear attenuation coefficients of each material showed excellent agreement with the theoretical values. In this study, effective atomic numbers (Z_eff) are estimated for five kinds of resins with the linear attenuation coefficients and the possibility of material identification using the energy-resolved CT is discussed. For the estimation of Z_eff, we applied a new method using a lookup table (LUT). By comparing the obtained linear attenuation coefficients to the LUT using a least square method, Z_eff of materials were estimated. The estimated Z_eff were compared with their theoretical values. The standard deviation for the pixel values of 5 x 5 pixels in the respective region of the CT image was ± 0.2 at the largest. The estimated Z_eff are smaller than the theoretical ones. With a calibration line, Z_eff estimation method is useful for identifying materials. (author)