Coincidence Counters for Charge Sharing Compensation in Spectroscopic Photon Counting Detectors

Hsieh, Scott S.

doi:10.1109/tmi.2019.2933986

Cited by 21 publications

(32 citation statements)

References 29 publications

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“…Further, it has also been suggested that, instead of correcting the charge-sharing events, the coincidences can be registered in so-called coincidence counters, read out from the ASIC and handled in post-processing (Hsieh 2020).…”

Section: Charge Summing and Anti-coincidence Logicmentioning

confidence: 99%

Photon-counting x-ray detectors for CT

2021

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The introduction of photon-counting detectors is expected to be the next major breakthrough in clinical x-ray computed tomography (CT). During the last decade, there has been considerable research activity in the field of photon-counting CT, in terms of both hardware development and theoretical understanding of the factors affecting image quality. In this article, we review the recent progress in this field with the intent of highlighting the relationship between detector design considerations and the resulting image quality. We discuss detector design choices such as converter material, pixel size, and readout electronics design, and then elucidate their impact on detector performance in terms of dose efficiency, spatial resolution, and energy resolution. Furthermore, we give an overview of data processing, reconstruction methods and metrics of imaging performance; outline clinical applications; and discuss potential future developments.

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Section: Charge Summing and Anti-coincidence Logicmentioning

confidence: 99%

Photon-counting x-ray detectors for CT

2021

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“…Hsieh [32], [33] proposed a reading-based post-acquisition scheme with a use of one coincidence counter (which we call "1CC" in this article) to record the number of doublecounting events with neighboring pixels with no energy information. Being inspired by Hsieh's 1CC, we recently proposed another scheme for reading-based post-acquisition correction/compensation called MEICC for multienergy interpixel coincidence counter [34].…”

Section: Introductionmentioning

confidence: 99%

Assessment of Multienergy Interpixel Coincidence Counters (MEICC) for Charge Sharing Correction or Compensation for Photon Counting Detectors With Boxcar Signals

Taguchi

2021

IEEE Trans. Radiat. Plasma Med. Sci.

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Recently, multienergy interpixel coincidence counter (MEICC) has been proposed for charge sharing (CS) correction and compensation for photon counting detectors (PCDs), which uses energy-dependent coincidence counters to record coincident events between multiple energy windows of a pixel-of-interest and those of neighboring pixels. A Monte Carlo (MC) simulation study was performed to assess the performance of MEICC; however, the performance might have been overestimated in a previous study. The CS increases the number of photons recorded at a PCD pixel at the expense of the spatial resolution, and therefore, when spatially uniform flat-field X-ray signals are used, it gives PCDs with CS more signals than a PCD without CS. In this article, we propose to use spatially contained boxcar signals for evaluating the performances for high spatial frequency tasks because they provide consistent signals regardless of the presence or absence of CS. The flat-field signals must be used for low spatial frequency tasks. We assessed the performances of MEICC and other PCDs with both flat-field signals and boxcar signals, with optimal threshold energies, and with two different pixel sizes. As it is expected, normalized Cramér-Rao lower bounds (nCRLBs) measured with the boxcar signals were worse than those with flat-field signals in general. The nCRLBs of MEICC with 225-µm pixel were close to the current 450-µm PCD. We studied a combination of flat-field signals and N × N super-pixels, where the output of N × N pixels were added, using an MC simulation and a simple CS counting model. The study showed that CS had two opposing impacts on the conventional computed tomography imaging-a negative impact with double-counting among N × N pixels and a positive impact with single-counting spill-in and spill-out across the super-pixel boundary-and the positive impact diminished with increasing N. A use of large N × N super-pixels such as N ≥ 25 was suggested to approximate the zero-frequency detection quantum efficiency of PCD with CS. Index Terms-Charge sharing (CS), computed tomography (CT), photon counting detectors (PCDs).

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“…One coincidence counter: Recently, Hsieh proposed to add one coincidence counter per pixel to the standard PCD in order to count the number of double-counting events with four neighboring pixels. 34,35 The idea is intriguing and in fact, has led to this study. With no energy resolution in the coincidence counter, however, it cannot tell how many events were spill-in and how many were spill-out, nor can it tell how many counts went into each energy window.…”

Section: B3 Pcds With Reading-based Post-acquisition Charge Sharimentioning

confidence: 94%

“…Recently, Hsieh proposed to add one coincidence counter per pixel to the standard PCD in order to count the number of double‐counting events with four neighboring pixels . The idea is intriguing and in fact, has led to this study.…”

Section: Introductionmentioning

confidence: 99%

Multi‐energy inter‐pixel coincidence counters for charge sharing correction and compensation in photon counting detectors

Taguchi

2020

Medical Physics

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Purpose: Smaller pixel sizes of x-ray photon counting detectors (PCDs) are advantageous for count rate capabilities but disadvantageous for charge sharing. With charge sharing, the energy of an x-ray photon may be split and one photon may produce two or more counts at adjacent pixels, both at lower energies than the incident energy. This "double-counting" increases noise variance and degrades the spectral response. Overall, it has a significantly negative impact on the performance of PCD-based computed tomography (CT). Charge sharing is induced by the detection physics and occurs regardless of count rates; thus, it is impossible to avoid. We propose in this paper a method that has a potential to address both noise and bias added by charge sharing. Methods: We propose applying a multi-energy inter-pixel coincidence counter (MEICC) technique, which uses energy-dependent coincidence counters, keeps the book of charge sharing events during data acquisition, and provides the exact number of charge sharing occurrences, which can be used to either correct or compensate for them after the acquisition is completed. MEICC does not interfere with the primary counting process; therefore, PCDs with MEICC will remain as fast as those without MEICC. MEICC can be implemented using current electronics technology because its inter-pixel coincidence counters used to handle digital data are rather simple. We evaluated Cram er-Rao lower bound (CRLB) of PCDs with and without MEICC using a Monte Carlo simulation. Results: When the number of energy windows was four or larger and eight neighboring pixels were used, the CRLBs of 225-µm PCD with MEICC normalized by those of the current PCD with the same number of windows were 0.361-0.383 for water density images of two basis functions, which was only 5.7-16.4% worse than those of a PCD without charge sharing (which were at 0.329-0.358). In contrast, the normalized CRLBs of the PCD with one coincidence counter were 0.466-0.499, which were 37.3-45.6% worse than the PCD without charge sharing. The use of eight neighboring pixels provided~10% better CRLB values than four neighboring pixels for MEICC. With four energy windows, decreasing the number of coincidence counters from 16 to 9 only slightly increased the CRLB from 0.255 to 0.269 (which corresponded to as little as a 5.5% change). The normalized CRLBs of MEICC for K-edge imaging (gold) were 0.295-0.426, while those of the one coincidence counter were 0.926-0.959 and the ideal PCDs were 0.126-0.146. Conclusions:The proposed MEICC provides spectral information that can be used to address charge sharing problems in PCDs and is expected to satisfy the requirements for clinical x-ray CT. MEICC is very effective, especially for K-edge imaging, which requires accurate spectral information.

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Coincidence Counters for Charge Sharing Compensation in Spectroscopic Photon Counting Detectors

Cited by 21 publications

References 29 publications

Photon-counting x-ray detectors for CT

Photon-counting x-ray detectors for CT

Assessment of Multienergy Interpixel Coincidence Counters (MEICC) for Charge Sharing Correction or Compensation for Photon Counting Detectors With Boxcar Signals

Multi‐energy inter‐pixel coincidence counters for charge sharing correction and compensation in photon counting detectors

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