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 $\mathrm{\mu }$m and two different thicknesses — 300 and 500 $\mathrm{\mu }$m. 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/$\mathrm{\mu }$CT (50 kVp) and extremities/$\mathrm{\mu }$CT (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.

具有高Z传感器材料（例如CdTe，CdZnTe和GaAs）的X射线光子计数检测器有可能极大地改善医学成像领域。在这项工作中，我们研究了两种新颖的概念验证混合光子计数探测器的能量分辨能力和成像性能，这些探测器基于IBEX ASIC和铬补偿的GaAs作为X射线成像应用的直接检测传感器材料。两个传感器的像素大小为75 $\mathrm{\mu }$m和两种不同的厚度-300和500 $\mathrm{\mu }$米 通过分析来自荧光靶标（Ge，Mo，Ba）的能谱和与乳腺摄影相关的直接X射线管束质量（28 kVp，35 kVp），儿科/动物/$\mathrm{\mu }$CT（50 kVp）和四肢/$\mathrm{\mu }$CT（70 kVp）成像应用。在上述直接X射线束条件下并根据阈值能量评估了MTF和DQE方面的成像性能。能量分辨率在1.6-2.2 keV FWHM范围内，随着传感器厚度和目标荧光能量的增加而增加。对于较薄的传感器，电荷共享效果不如预期的那样突出。MTF和DQE的行为与阈值能量不是单调的，因此我们提取了它们的最佳值。在这种条件下，对于所有研究的厚度和光束质量，MTF等于理想像素之一，而在乳腺摄影条件下，DQE相同。在较高的光束能量下，由于较低的X射线吸收效率，对于较薄的传感器，DQE降低的幅度更大。