Characterization of a Pixelated Cadmium Telluride Detector System Using a Polychromatic X-Ray Source and Gold Nanoparticle-Loaded Phantoms for Benchtop X-Ray Fluorescence Imaging.

Pixelated semi-conductor detectors providing high energy resolution enable parallel acquisition of x-ray fluorescence (XRF) signals, potentially leading to performance enhancement of benchtop XRF imaging or computed tomography (XFCT) systems utilizing ordinary polychromatic x-ray sources. However, little is currently known about the characteristics of such detectors under typical operating conditions of benchtop XRF imaging/XFCT. In this work, a commercially available pixelated cadmium telluride (CdTe) detector system, HEXITEC (High Energy X-ray Imaging Technology), was characterized to address this issue. Specifically, HEXITEC was deployed into our benchtop cone-beam XFCT system, and used to detect gold Kα XRF photons from gold nanoparticle (GNP)-loaded phantoms. To facilitate the detection of XRF photons, various parallel-hole stainless steel collimators were fabricated and coupled with HEXITEC. A pixel-by-pixel spectrum merging algorithm was introduced to obtain well-defined XRF + scatter spectra with parallel-hole collimators. The effect of charge sharing addition (CSA) and discrimination (CSD) algorithms was also investigated for pixel-level CS correction. Finally, the detector energy resolution, in terms of the full-width at half-maximum (FWHM) values at two gold Kα XRF peaks (~68 keV), was also determined. Under the current experimental conditions, CSD provided the best energy resolution of HEXITEC (~1.05 keV FWHM), compared with CSA and no CS correction. This FWHM value was larger (by up to ~0.35 keV) than those reported previously for HEXITEC (at ~60 keV Am-241 peak) and single-crystal CdTe detectors (at two gold Kα XRF peaks). This investigation highlighted characteristics of HEXITEC as well as the necessity for application-specific detector characterization.