Abstract
Most modern energy resolving, photon counting detectors employ small (sub 1 mm) pixels for high spatial resolution and low per pixel count rate requirements. These small pixels can suffer from a range of charge sharing effects (CSEs) that degrade both spectral analysis and imaging metrics. A range of charge sharing correction algorithms (CSCAs) have been proposed and validated by different groups to reduce CSEs, however their performance is often compared solely to the same system when no such corrections are made. In this paper, a combination of Monte Carlo and finite element methods are used to compare six different CSCAs with the case where no CSCA is employed, with respect to four different metrics: absolute detection efficiency, photopeak detection efficiency, relative coincidence counts, and binned spectral efficiency. The performance of the various CSCAs is explored when running on systems with pixel pitches ranging from 100 µm to 600µm, in 50 µm increments, and fluxes from 106 to 108 photons mm−2 s−1 are considered. Novel mechanistic explanations for the difference in performance of the various CSCAs are proposed and supported. This work represents a subset of a larger project in which pixel pitch, thickness, flux, and CSCA are all varied systematically.
Highlights
X-ray photon counting spectral imaging (x-CSI) is currently a hot topic in the medical research field due to the potential of this technique to reduce patient doses in routine procedures [1,2] as well as to provide better material differentiation than dual energy computed tomography (CT) [3]
In order to maximise the energy resolution of an x-CSI detector, semiconductor materials are often proposed as the conversion material over scintillators, due to the lower noise associated with the direct conversion of photons to electrical current as opposed to via an optical intermediary
The discussion of the generated data will focus on a single flux (107 photons mm−2 s−1 ) to make establishing and explaining trends simpler, demonstrating the mechanisms responsible for the observed trends can often be assisted by showing data from a higher or lower fluxes, to emphasise the roles of pulse pileup or charge sharing effects (CSEs), respectively
Summary
X-ray photon counting spectral imaging (x-CSI) is currently a hot topic in the medical research field due to the potential of this technique to reduce patient doses in routine procedures [1,2] as well as to provide better material differentiation than dual energy computed tomography (CT) [3]. Due to its photon counting nature, x-CSI promises to produce images free from electronic noise [4] that can be used to derive quantitative spectral information rather than just qualitative data with a greater accuracy and less noise than dual energy CT [5]. This opens the possibility that X-ray systems will be able to move beyond the largely structural images they currently deliver and enter the field of molecular imaging [6,7]. Of the various materials proposed, CdTe and CdZnTe (CZT) have drawn particular attention, due to their low pair production energy, high charge carrier mobility and high absorption efficiency across the range of energies commonly used for medical X-ray imaging
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