Assessment of multi‐energy inter‐pixel coincidence counters for photon‐counting detectors at the presence of charge sharing and pulse pileup: A simulation study

Taguchi, Katsuyuki; Iwanczyk, Jan S.

doi:10.1002/mp.15112

Cited by 4 publications

(7 citation statements)

References 38 publications

(93 reference statements)

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“…Similarly, Taguchi et al. evaluated five different PCDs to find that counting efficiency dropped and linearity between count rate and tube current distorted as tube current increased 3 . In another similar study, Yu et al.…”

Section: Discussionmentioning

confidence: 95%

“…8 Similarly, Taguchi et al evaluated five different PCDs to find that counting efficiency dropped and linearity between count rate and tube current distorted as tube current increased. 3 In another similar study, Yu et al found that the performance of whole-body CdTe-based photon-counting CT degraded slightly when the tube current exceeded 300 mA at 140 kV with 77 mm water filtration. 11 These studies did not use clinical photoncounting CT, and had different detector configurations and acquisition settings.…”

Section: Discussionmentioning

confidence: 96%

“…Pulse pileup, on the other hand, happens at high flux situations when the pulses from photons arriving simultaneously to the detector pile into one another due to the limited readout speed of the electronics in PCDs. 3 Crosstalk affects the detective quantum efficiency, distorts the energy response, increases the image noise, and deteriorates the spatial resolution. 1,4 Pulse pileup causes detector saturation resulting in count loss, Poisson statistics distortion, and energy resolution degradation which deteriorates the image quality.…”

Section: Introductionmentioning

confidence: 99%

“…Charge sharing is another form of crosstalk that happens due to the spread of a charge cloud to multiple neighboring detector elements. Pulse pileup, on the other hand, happens at high flux situations when the pulses from photons arriving simultaneously to the detector pile into one another due to the limited readout speed of the electronics in PCDs 3 . Crosstalk affects the detective quantum efficiency, distorts the energy response, increases the image noise, and deteriorates the spatial resolution 1,4 .…”

Section: Introductionmentioning

confidence: 99%

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Exploration of the pulse pileup effects in a clinical CdTe‐based photon‐counting computed tomography

Bhattarai,

Bache,

Abadi

et al. 2023

Medical Physics

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BackgroundHigh tube current generates a high flux of x‐rays to photon counting detectors (PCDs) that can potentially result in the piling up of pulses formed by concurrent photons, which can cause count loss and energy resolution degradation.PurposeTo evaluate the performance of clinical photon‐counting CT (PCCT) systems in high flux, potentially influenced by pulse pileup effects, in terms of task‐generic image quality metrics.MethodsA clinical phantom was scanned on a commercial PCCT scanner (NAEOTOM Alpha, Siemens) at 120 kV under fourteen different tube current levels (40–1000 mA) with a rotation time of 0.25 s and a pitch of 1. The dose levels corresponded to CTDIvol (32 cm phantom) of 0.79–19.8 mGy. CT sinograms were reconstructed using QIR‐off mode (noniterative reconstruction algorithm), Br44 kernel, and a voxel size of . imQuest, an open‐source MATLAB‐based software package was used to calculate noise power spectrum (NPS), task transfer function (TTF), contrast‐to‐noise ratio (CNR), and CT number according to AAPM Task Group 233 metrology.ResultsThe 50% cut‐off frequency of TTF (f50) remained mostly constant across all higher tube currents for all inserts, namely polyethylene, bone, air, and acrylic. Using the lowest two data points (40 and 80 mA), the expected relationship between noise magnitude and tube current was determined to be noise mA−0.47. The measured noise magnitude were up to 11.1% higher than the expected value at the highest tube current. The average frequency of NPS (fav) decreased from 0.32 to 0.29 mm−1 as tube current increased from 40 to 1000 mA. No considerable effects were observed in CT number measurement of any insert; however, CT numbers for air and bone changed almost monotonically as tube current increased. Absolute CNR increased monotonically for all inserts; however, the difference between measured and expected CNRs were approximately −6% to 12% across all tube currents.ConclusionsIncreasing tube currents did not affect the spatial resolution, but slightly affected the CT number and noise measurements of the clinical PCCT system. However, the effects were only considerable at clinically irrelevant tube currents used on a small 20‐cm phantom. In general clinical practices, automatic exposure control techniques are used to decrease the variation of flux on the detector, which alleviates the chances of detector saturation due to high count rates. The observed effects could be due to pulse pileup, signal‐dependent filtration of the system, or nonlinearities in the reconstruction algorithm. In conclusion, either the deadtime of the detector used in the photon‐counting CT system is shorter such that count losses due to pulse pileup are negligible, or pulse pileup has inconsiderable effects on the image quality of clinical photon‐counting CT systems in routine clinical practice due to possible corrections applied on the system.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Exploration of the pulse pileup effects in a clinical CdTe‐based photon‐counting computed tomography

Bhattarai,

Bache,

Abadi

et al. 2023

Medical Physics

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“…The inter‐threshold communication is minimal, and each threshold makes the decision (of a count) locally. In our previous simulation study, we had used DB as a necessary component of a new detection circuitry, without realizing its advantages over the conventional TS scheme 19–21 . The contribution of this work is the systematic comparison between DB and TS and the comparison with statistical models.…”

Section: Methodsmentioning

confidence: 99%

Direct energy binning for photon counting detectors: Simulation study

Taguchi,

Hsieh

2023

Medical Physics

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BackgroundPhoton counting detectors (PCDs) for x‐ray computed tomography (CT) face spectral distortion from pulse pileup and charge sharing. The photon counting scheme used by many PCDs is threshold–subtract (TS) with pulse height analysis (PHA), where each counter counts up‐crossing events when pulses exceed an energy threshold. PCD data are not Poisson‐distributed due to charge sharing and pulse pileup, but the counting statistics have never been studied yet.PurposeThe objectives of this study were (1) to propose a modified photon counting scheme, direct energy binning (DB), that is expected to be robust against pulse pileup; (2) to assess the performance of DB compared to TS; and (3) to evaluate its counting statistics.MethodsWith DB scheme, counter k starts a timer upon an up‐crossing event of energy threshold k, and adds a count only if the next higher energy threshold (k+1) was not crossed within a short time window (hence, the pulse peak belongs to the energy bin k). We used Monte Carlo (MC) simulation and assessed count‐rate curves and count‐rate‐dependent spectral imaging task performance for conventional CT imaging as well as water thickness estimation, water–bone material decomposition, and K‐edge imaging with tungsten as the K‐edge material. We also assessed count‐rate‐dependent measurement statistics such as expectation, variance, and covariance of total counts as well as energy bin outputs. The agreement with counting statistics models was also evaluated.ResultsThe DB scheme improved the count‐rate curve, that is, mean measured counts as a function of input count‐rate, and peaked with 59% higher count‐rate capability than the TS scheme (3.5 × 108 counts per second (cps)/mm2 versus 2.3 × 108 cps/mm2). The Cramér–Rao lower bounds (CRLB) of the variance of basis line integrals estimation for DB was better than those for TS by 2% for the conventional CT imaging, 30% for water–bone material decomposition, and 32% for K‐edge imaging at 1000 mA (at 7.3 × 107 cps/sub‐pixel after charge sharing). When count‐rates were lower, PCD data statistics were dominated by charge sharing: the variance of total counts and lower energy bins was larger than the mean counts; the covariance of bin data was positive and non‐zero. When count‐rates were higher, PCD data statistics were dominated by pulse pileup: the variance of data was lower than the mean; the covariance of bin data was negative. The transition between the two regimes occurred smoothly, and pulse pileup dominated the statistics ≥400 mA (when the count‐rate after charge sharing was 2.9 × 107 cps/sub‐pixel and the probability of count‐loss for DB was 37%). Both DB and TS had good agreement with Yu–Fessler's models of total counts; however, DB had a better agreement with Wang's variance and covariance models for energy bin data than TS did.ConclusionsThe proposed DB scheme had several advantages over TS. At low to moderate flux, DB could improve the resilience of PCDs to pulse pileup. Counting statistics deviated from the Poisson distribution due to charge sharing for lower count‐rate conditions and pulse pileup for higher count‐rate conditions.

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Chances and challenges of photon-counting CT in musculoskeletal imaging

Mourad,

Gallego Manzano,

Viry

et al. 2024

Skeletal Radiol

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In musculoskeletal imaging, CT is used in a wide range of indications, either alone or in a synergistic approach with MRI. While MRI is the preferred modality for the assessment of soft tissues and bone marrow, CT excels in the imaging of high-contrast structures, such as mineralized tissue. Additionally, the introduction of dual-energy CT in clinical practice two decades ago opened the door for spectral imaging applications. Recently, the advent of photon-counting detectors (PCDs) has further advanced the potential of CT, at least in theory. Compared to conventional energy-integrating detectors (EIDs), PCDs provide superior spatial resolution, reduced noise, and intrinsic spectral imaging capabilities. This review briefly describes the technical advantages of PCDs. For each technical feature, the corresponding applications in musculoskeletal imaging will be discussed, including high-spatial resolution imaging for the assessment of bone and crystal deposits, low-dose applications such as whole-body CT, as well as spectral imaging applications including the characterization of crystal deposits and imaging of metal hardware. Finally, we will highlight the potential of PCD-CT in emerging applications, underscoring the need for further preclinical and clinical validation to unleash its full clinical potential.

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Assessment of multi‐energy inter‐pixel coincidence counters for photon‐counting detectors at the presence of charge sharing and pulse pileup: A simulation study

Cited by 4 publications

References 38 publications

Exploration of the pulse pileup effects in a clinical CdTe‐based photon‐counting computed tomography

Exploration of the pulse pileup effects in a clinical CdTe‐based photon‐counting computed tomography

Direct energy binning for photon counting detectors: Simulation study

Chances and challenges of photon-counting CT in musculoskeletal imaging

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