Analogous Lubberts effect in photon counting detectors

Ke Li

doi:10.1117/12.2549785

16 March 2020 Analogous Lubberts effect in photon counting detectors

Ke Li

Proceedings Volume 11312, Medical Imaging 2020: Physics of Medical Imaging; 113120Z (2020) https://doi.org/10.1117/12.2549785
Event: SPIE Medical Imaging, 2020, Houston, Texas, United States

Abstract

For a light burst generated by an x ray-scintillator interaction, the quasi-isotropic spreading of optical quanta determines that both the light collection efficiency and the spread function of the light burst depend on the depth (z) of interaction: the closer the initial position of light burst to the light sensor, the less light loss and spatial resolution degradation a detector system encounters. For scintillator-based indirect-conversion detectors, the variation of the x-ray conversion gain and the MTF along the z direction contributes to a significant fraction of DQE loss and is known as the Lubberts effect. Understanding the physics behinds the effect and developing solutions to reduce the effect have led to tremendous improvements in the performance of indirect-conversion detectors. In contrast, for direct-conversion photon counting detectors (PCDs), since no optical quanta generation or transport is involved, there is no classical Lubberts effect. However, the transport properties of the generated charge carriers in semiconductors do depend on their travel distance. As a result, the performance of direct conversion detectors may depend on z. This dependence can be considered as a counterpart of the classical Lubberts effect. The purpose of this work is to analyze the contributions of a variety of physical mechanisms that may contribute to a Lubberts-like effect in direct-conversion PCDs. The results show that the Lubberts-like effect is primarily caused by the depth-dependent charge trapping and recombination likelihood. Based upon the physics analysis, PCD electrode design can be optimized to minimize the Lubberts-like effect and the associate DQE loss.

Citation Download Citation

Ke Li "Analogous Lubberts effect in photon counting detectors", Proc. SPIE 11312, Medical Imaging 2020: Physics of Medical Imaging, 113120Z (16 March 2020); https://doi.org/10.1117/12.2549785

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KEYWORDS

Sensors

X-rays

Modulation transfer functions

Electrodes

Photon counting

X-ray detectors

Electrons

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