Dose reduction in medical X-ray imaging using noise free photon counting

Francke, T.; Eklund, Mathias; Ericsson, Leif; Kristoffersson, Tomas; Peskov, V.; Rantanen, Juha; Sokolov, S.N.; Soderman, Jan E.; Ullberg, Christer

doi:10.1016/s0168-9002(01)00920-2

Cited by 25 publications

(7 citation statements)

References 3 publications

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“…Model parameter Description 35 kVp 70 kVp q 0 /X Incident fluence per exposure (X) 2.88 × 10 5 x-rays/mm 2 /mR 6.64 × 10 5 x-rays/mm 2 /mR g 1 Photon interaction probability 0.68 0.26 g 2 Gain in secondary quanta 8000 electrons 11 500 electrons T 3 Charge cloud diffusion σ 3 = 0.015 mm g 4 Charge collection efficiency 0.99 T 5 Aperture a x = 0.05 mm, a y = 0.55 mm σ 6 Additive noise σ add 6 = 200 electrons t 7 Threshold 1500 electrons III 8 Sampling function b x = 0.05 or 0.1 mm While the underlying physics of PCD systems has been studied extensively over the last decade, with investigation of spectral models, 22 detector scatter models, 23 and computer simulation, 24 there has been less work on the fundamental image quality characteristics, modeling, and analysis of Fourier metrics of modulation transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). 25,26 A cascaded systems model of signal and noise transfer characteristics, as previously developed for flat panel detectors (FPDs) [27][28][29] and other types of energy-integrating detectors (EIDs) [30][31][32] would provide a powerful tool for system development and understanding the factors that govern imaging performance, especially in the early stages of system design, development, and optimization.…”

Section: -2mentioning

confidence: 99%

Cascaded systems analysis of photon counting detectors

Zbijewski

Gang

et al. 2014

Medical Physics

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Purpose: Photon counting detectors (PCDs) are an emerging technology with applications in spectral and low-dose radiographic and tomographic imaging. This paper develops an analytical model of PCD imaging performance, including the system gain, modulation transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). Methods: A cascaded systems analysis model describing the propagation of quanta through the imaging chain was developed. The model was validated in comparison to the physical performance of a silicon-strip PCD implemented on an experimental imaging bench. The signal response, MTF, and NPS were measured and compared to theory as a function of exposure conditions (70 kVp, 1-7 mA), detector threshold, and readout mode (i.e., the option for coincidence detection). The model sheds new light on the dependence of spatial resolution, charge sharing, and additive noise effects on threshold selection and was used to investigate the factors governing PCD performance, including the fundamental advantages and limitations of PCDs in comparison to energy-integrating detectors (EIDs) in the linear regime for which pulse pileup can be ignored. Results: The detector exhibited highly linear mean signal response across the system operating range and agreed well with theoretical prediction, as did the system MTF and NPS. The DQE analyzed as a function of kilovolt (peak), exposure, detector threshold, and readout mode revealed important considerations for system optimization. The model also demonstrated the important implications of false counts from both additive electronic noise and charge sharing and highlighted the system design and operational parameters that most affect detector performance in the presence of such factors: for example, increasing the detector threshold from 0 to 100 (arbitrary units of pulse height threshold roughly equivalent to 0.5 and 6 keV energy threshold, respectively), increased the f 50 (spatial-frequency at which the MTF falls to a value of 0.50) by ∼30% with corresponding improvement in DQE. The range in exposure and additive noise for which PCDs yield intrinsically higher DQE was quantified, showing performance advantages under conditions of very low-dose, high additive noise, and high fidelity rejection of coincident photons. Conclusions: The model for PCD signal and noise performance agreed with measurements of detector signal, MTF, and NPS and provided a useful basis for understanding complex dependencies in PCD imaging performance and the potential advantages (and disadvantages) in comparison to EIDs as well as an important guide to task-based optimization in developing new PCD imaging systems. C

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Section: -2mentioning

confidence: 99%

Cascaded systems analysis of photon counting detectors

Zbijewski

Gang

et al. 2014

Medical Physics

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“…This improvement was not only due to the more narrow induced charge profile, but also due to the fact that at high gains the detector operated in a noise free mode, when electronic noise pulses were fully discriminated. As was mentioned in the introduction, this is an important feature of the avalanche gaseous detectors operating in the photon counting mode [7]. Note also that result of these measurements were practically independent of X-ray energy.…”

Section: Resultsmentioning

confidence: 64%

“…This allows one to reduce the dose delivered to the patient during the examination [7]. However, the stopping power of gases is very low and this restricts the application of the gaseous detectors.…”

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confidence: 99%

A high position resolution X-ray detector: an "Edge on" illuminated capillary plate combined with a gas amplification structure

Iacobaeus

Francke

Lund‐Jensen

et al. 2006

IEEE Trans. Nucl. Sci.

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Abstract-We have developed and successfully tested a prototype of a new high position resolution hybrid X-ray detector. It contains a thin-wall lead glass capillary plate converter of X-rays combined with a microgap parallel-plate avalanche chamber operating in various gas mixtures at 1 atm.The operation of these converters was studied in a wide range of X-ray energies (from 6 to 60 keV) at incident angles varying from 0-90 . The detection efficiency, depending on the geometry, photon's energy, incident angle and the mode of operation was between 5-30% in single step mode and up to 50% in a multi-layered combination. Depending on the capillary's geometry, the position resolution achieved was between 50-250 m in digital form and was practically independent of the photon's energy or gas mixture. The usual lead glass capillary plates operated without noticeable charging up effects at counting rates of 50 Hz/mm 2 and hydrogen treated capillaries-up to 10 5 Hz/mm 2 . The developed detector has several important potential advantages over the exciting X-ray detectors and may open new possibilities for medical imaging, for example in mammography, portal imaging, radiography (including security devices), as well as many other applications.

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“…They offer potential benefits in image quality and dose, arising from reduced electronics noise, capability for energy discrimination, and better use of low-energy photons (optimal energy weighting) compared to energy-integrating detectors (Tapiovaara and Wagner 1985, Tanguay et al 2013, Xu et al 2014). A variety of PCD-based x-ray systems have been proposed for applications such as mammography (Thunberg et al 2004, Fredenberg et al 2010a, Cole et al 2012), radiography (Francke et al 2001, Weigel et al 2014), tomography (Maidment et al 2005, Schmitzberger et al 2011, Alivov et al 2014), and energy-resolved imaging (Wang et al 2011, Alessio and MacDonald 2013, Silkwood et al 2013). A comprehensive review of current implementations, potential benefits, and clinical and preclinical applications of PCDs can be found in (Taguchi and Iwanczyk 2013).…”

Section: Introductionmentioning

confidence: 99%

Volumetric CT with sparse detector arrays (and application to Si-strip photon counters)

et al. 2015

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Novel x-ray medical imaging sensors, such as photon counting detectors (PCDs) and large area CCD and CMOS cameras can involve irregular and/or sparse sampling of the detector plane. Application of such detectors to CT involves undersampling that is markedly different from the commonly considered case of sparse angular sampling. This work investigates volumetric sampling in CT systems incorporating sparsely sampled detectors with axial and helical scan orbits and evaluates performance of model-based image reconstruction (MBIR) with spatially varying regularization in mitigating artifacts due to sparse detector sampling. Volumetric metrics of sampling density and uniformity were introduced. Penalized-likelihood MBIR with a spatially varying penalty that homogenized resolution by accounting for variations in local sampling density (i.e. detector gaps) was evaluated. The proposed methodology was tested in simulations and on an imaging bench based on a Si-strip PCD (total area 5 cm × 25 cm) consisting of an arrangement of line sensors separated by gaps of up to 2.5 mm. The bench was equipped with translation/rotation stages allowing a variety of scanning trajectories, ranging from a simple axial acquisition to helical scans with variable pitch. Statistical (spherical clutter) and anthropomorphic (hand) phantoms were considered. Image quality was compared to that obtained with a conventional uniform penalty in terms of structural similarity index (SSIM), image uniformity, spatial resolution, contrast, and noise. Scan trajectories with intermediate helical width (~10 mm longitudinal distance per 360° rotation) demonstrated optimal tradeoff between the average sampling density and the homogeneity of sampling throughout the volume. For a scan trajectory with 10.8 mm helical width, the spatially varying penalty resulted in significant visual reduction of sampling artifacts, confirmed by a 10% reduction in minimum SSIM (from 0.88 to 0.8) and a 40% reduction in the dispersion of SSIM in the volume compared to the constant penalty (both penalties applied at optimal regularization strength). Images of the spherical clutter and wrist phantoms confirmed the advantages of the spatially varying penalty, showing a 25% improvement in image uniformity and 1.8 × higher CNR (at matched spatial resolution) compared to the constant penalty. The studies elucidate the relationship between sampling in the detector plane, acquisition orbit, sampling of the reconstructed volume, and the resulting image quality. They also demonstrate the benefit of spatially varying regularization in MBIR for scenarios with irregular sampling patterns. Such findings are important and integral to the incorporation of a sparsely sampled Si-strip PCD in CT imaging.

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Dose reduction in medical X-ray imaging using noise free photon counting

Cited by 25 publications

References 3 publications

Cascaded systems analysis of photon counting detectors

Cascaded systems analysis of photon counting detectors

A high position resolution X-ray detector: an "Edge on" illuminated capillary plate combined with a gas amplification structure

Volumetric CT with sparse detector arrays (and application to Si-strip photon counters)

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