Feasibility study of photon counting detector for producing effective atomic number image

Abstract

Currently, energy resolving photon counting detectors (ERPCD) are the focus of attention as a promising technique for material identification based on the analysis of X-ray energies. To accomplish highly accurate material identification, consideration of the response of a multi-pixel-type ERPCD is important. This is because the detector response distorts initial energy information which is strongly related to material information such as effective atomic number (Z eff ). In the analysis using the ERPCD, we should take into consideration the beam hardening effect depending on the Z eff of an object. The aim of our study is to propose a novel material identification method with correction for both detector response and beam hardening effect. In order to derive the Z eff of an object, we used the differences in attenuation factors which are calculated from the analysis of three different energy bins in the detected X-ray spectrum. For the detected X-ray spectrum, correction of detector response and beam hardening effect were applied to attenuation factors. Next, Z eff of the object was derived from a novel procedure in which the theoretical relationship between attenuation factors and Z eff s was parameterized as a reference curve. In order to demonstrate the accuracy of Z eff determination, we evaluated our method by applying it to each pixel of an X-ray image measured with a proto-type imaging detector and the produced Z eff image. In most of the cases, we verified that the Z eff image can be obtained with an accuracy of Z eff +/- 0.5. This study gives us the prospect to establish a novel quantitative diagnosis using an Z eff image determined from plain X-ray diagnosis.