Abstract
X-ray photon counting detectors featuring high-Z sensor materials such as CdTe, CdZnTe and GaAs have the possibility to greatly improve the field of medical imaging. In this work, we investigated the energy resolving capabilities and imaging performance of two novel proof-of-concept hybrid photon counting detectors based on the IBEX ASIC and on Chromium-compensated GaAs as direct-detection sensor material targeted for X-ray imaging applications. The two sensors feature a pixel size of 75 μm and two different thicknesses — 300 and 500 μm. Spectral properties were assessed by analyzing energy spectra from fluorescence targets (Ge, Mo, Ba) and direct X-ray tube beam qualities relevant for mammographic (28 kVp, 35 kVp), pediatric/animals/μCT (50 kVp) and extremities/μCT (70 kVp) imaging applications. Imaging properties in terms of MTF and DQE were assessed at the aforementioned direct X-ray beam conditions and as a function of the threshold energy. The energy resolution lies in the range 1.6-2.2 keV FWHM, increasing with the sensor thickness and fluorescence energy of the target. Charge sharing effects are as expected less prominent for thinner sensors. The behavior of the MTF and DQE is not monotonic with the threshold energy and we extracted their optimal values. In this conditions, the MTF equals the one of an ideal pixel for all studied thicknesses and beam quality and the same does the DQE at mammographic conditions. At higher beam energies the DQE decreases the more for thinner sensors due to lower X-ray absorption efficiency.
Published Version
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