Purpose: To study the bias-voltage dependent operational characteristics of an energy-resolving pixelated cadmium telluride (CdTe) detector system coupled with a parallel-hole collimator within an experimental benchtop x-ray fluorescence (XRF) imaging system.
Methods: An experimental XRF CT (XFCT) system was revamped with a commercially available energy-resolving x-ray detector system, known as High-Energy X-ray Imaging Technology (HEXITEC), consisting of 1-mm-thick CdTe sensor with 80 × 80 pixels on a 250-μm pitch. HEXITEC was coupled with a 2mm-diameter aperture parallel-hole collimator. A cone-beam was produced from an x-ray tube operated at 125kVp and 24mA. This cone-beam beam was filtered with 1.8mm Tin and used to irradiate a phantom containing 200-μL of 0.1wt.% gold nanoparticle (GNP) solution placed at 15-cm from the x-ray source. The detector-collimator system was placed at 10cm from the phantom, orthogonal to the excitation beam direction. The Compton/XRF photon spectra from the GNP solution were measured for 60s at different bias-voltages ranging from -100 to -600V. The x-ray spectra from all the detector pixels corresponding to the 2-mm collimator aperture were added to obtain the final spectra. The net XRF signal was extracted using the deconvolution method developed in-house. The gold Kα1 XRF peak at 68.8keV was fitted with Gaussian distribution to obtain the energy resolution (FWHM). The net XRF signals and energy resolution at 68.8keV were used to determine the optimal bias-voltage setting for the benchtop XFCT system.
Results: As the bias-voltage increased from -100 to -500V, the net gold XRF signal, mean per-pixel energy resolution, and the homogeneity of energy resolution across the collimated 7 x 7 detector pixel area were improved by ~44, ~41, and ~66%, respectively.
Conclusion: This work investigated the bias-voltage dependent operational characteristics of HEXITEC consisting of 1-mm-thick CdTe sensor, and determined the optimal bias-voltage under typical operating conditions of benchtop XRF imaging/XFCT systems.
Funding Support, Disclosures, and Conflict of Interest: Supported by NIH/NIBIB R01EB020658