Monte Carlo simulation of primary electron production inside an a-selenium detector for x-ray mammography: physics

Sakellaris, T; Spyrou, George M.; Tzanakos, G.; Panayiotakis, George

doi:10.1088/0031-9155/53/19/c02

Cited by 3 publications

(4 citation statements)

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“…The primary electron generation model simulates the primary electron production from x-raymatter interactions (incoherent scattering, photoelectric absorption) as well as due to atomic deexcitation (fluorescent photon production, Auger and Coster-Kronig (CK) electron emission) inside the photoconducting materials mentioned above [1,2]. It is based on a validated model developed by Spyrou et al [3] that simulates the x-ray energy spectrum sampling as well as the x-ray photon interactions.…”

Section: Methodsmentioning

confidence: 99%

“…Consequently, the characteristics of the mammographic image strongly depend on the characteristics of the primary electrons. Distributions of primary electrons such as energy, angular and spatial distributions have been studied with the development of a Monte Carlo model that simulates the primary electron production inside suitable photoconducting materials such as a-Se, a-As 2 Se 3 , GaSe, GaAs, Ge, CdTe, CdZnTe, Cd 0.8 Zn 0.2 Te, ZnTe, PbO, TlBr, PbI 2 and HgI 2 [1,2]. Using this model, in this paper the arithmetics of: (i) fluorescent photons, (ii) forwards and backwards escaping primary and fluorescent photons and (iii) primary electrons are being investigated for the case of CdTe, CdZnTe, Cd 0.8 Zn 0.2 Te and ZnTe, for monoenergetic x-ray spectra in the mammographic energy range.…”

Section: Introductionmentioning

confidence: 99%

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Photon and primary electron arithmetics in photoconductors for digital mammography: Monte Carlo simulation studies

Sakellaris¹,

Spyrou²,

Tzanakos³

et al. 2009

J. Inst.

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Materials like CdTe, CdZnTe, Cd 0.8 Zn 0.2 Te and ZnTe are suitable photoconductors for direct conversion digital flat panel x-ray image detectors. The x-ray induced primary electrons inside photoconductor's bulk comprise the initial signal that propagates and forms the final signal (image) on detector's electrodes. An already developed Monte Carlo model that simulates the primary electron generation in photoconducting materials, such as those mentioned above, has been used to study the arithmetics of fluorescent photons, escaping photons and primary electrons in these materials in the mammographic energy range. In this way insights are gained concerning the primitive stage of signal formation that lead to the investigation of the factors that affect the primary electron generation. It was found that for the typical photoconductor thicknesses (300-1000 µm): (i) in all materials and incident energies the escaping of primary photons is negligible and does not influence the number of primary electrons, (ii) the overwhelming majority of escaping photons is backwards escaping fluorescent photons, (iii) the number of primary electrons increases at energies higher than Cd and Te K-edges where the fluorescent photon escaping decreases and their absorption is followed by long atomic deexcitation cascades and (iv) ZnTe has the maximum number of primary electrons produced for energies between 16 and 26 keV while CdTe for higher energies. KEYWORDS: Materials for solid-state detectors; Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); X-ray radiography and digital radiography (DR)

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photon and primary electron arithmetics in photoconductors for digital mammography: Monte Carlo simulation studies

Sakellaris¹,

Spyrou²,

Tzanakos³

et al. 2009

J. Inst.

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“…In order to illustrate the results in a pictorial form, the exposure map under the phantom ͑which is provided with a spatial resolution of 50 m͒ was converted to an eight-bit gray scale representation, with the exposure of 2 mR corresponding to the gray level value of 125. This output signal can be utilized in the form of subject contrast ͑if the characteristic curve is considered͒ or exit spectrum per detector pixel ͑for complete detector studies͒, as the input to a conventional screen film 29 or a digital detector, 30,31 and the image can be generated, taking into account the effect of the actual response curve of the detector.…”

Section: Simulation Of the Mammographic Processmentioning

confidence: 99%

“…Although this approximation can be considered simplified, since it is based on analytical calculations, and not on Monte Carlo, and it does not take into account the angle of the exiting photon, it was considered adequate for the purpose of this study. A more sophisticated approach must include the simulation of the physical properties of the detector and the extraction, though Monte Carlo techniques, of the deposited dose, or the generated optical photons, 35 generated electrons, 31 given as input the spectrum of the photons exiting the mathematical phantom per detector pixel. number of about 5 ϫ 10 9 initial x-ray photons, and a mean computational time of 28 h, on a 3.2 GHz, P-IV computer.…”

Section: E Detector Characteristics-image Formationmentioning

confidence: 99%

Suitability of new anode materials in mammography: Dose and subject contrast considerations using Monte Carlo simulation

et al. 2006

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Mammography is the technique with the highest sensitivity and specificity, for the early detection of nonpalpable lesions associated with breast cancer. As screening mammography refers to asymptomatic women, the task of optimization between the image quality and the radiation dose is critical. A way toward optimization could be the introduction of new anode materials. A method for producing the x-ray spectra of different anode/filter combinations is proposed. The performance of several mammographic spectra, produced by both existing and theoretical anode materials, is evaluated, with respect to their dose and subject contrast characteristics, using a Monte Carlo simulation. The mammographic performance is evaluated utilizing a properly designed mathematical phantom with embedded inhomogeneities, irradiated with different spectra, based on combinations of conventional and new (Ru, Ag) anode materials, with several filters (Mo, Rh, Ru, Ag, Nb, Al). An earlier developed and validated Monte Carlo model, for deriving both image and dose characteristics in mammography, was utilized and overall performance results were derived in terms of subject contrast to dose ratio and squared subject contrast to dose ratio. Results demonstrate that soft spectra, mainly produced from Mo, Rh, and Ru anodes and filtered with k-edge filters, provide increased subject contrast for inhomogeneities of both small size, simulating microcalcifications and low density, simulating masses. The harder spectra (W and Ag anode) come short in the discrimination task but demonstrate improved performance when considering the dose delivered to the breast tissue. As far as the overall performance is concerned, new theoretical spectra demonstrate a noticeable good performance that is similar, and in some cases better compared to commonly used systems, stressing the possibility of introducing new materials in mammographic practice as a possible contribution to its optimization task. In the overall optimization task in terms of subject contrast to dose ratio, tube voltage was found to have a minor effect, while with respect to the filter material, a lesion specific performance was noticed, with Al filtered spectra showing improved characteristics in case of the inhomogeneities simulating microcalcifications, while softer k-edge filtered spectra are more suitable for the discrimination of inhomogeneities simulating masses.

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A Monte Carlo study of primary electron production inside photoconductors for digital mammography and indications of material suitability

et al. 2010

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Materials like a-Se, a-As2Se3, GaSe, GaAs, Ge, CdTe, CdZnTe, Cd0.8Zn0.2Te, ZnTe, PbO, TlBr, PbI2 and HgI2 are possible photoconductors for direct conversion digital mammography detectors. The physical characteristics of primary electrons, such as their number, energies, direction angles and spatial distributions, strongly affect the characteristics of the final signal and hence image quality. In previous work, a Monte Carlo model has been developed that simulates the generation of primary electrons inside these materials for x-ray spectra in the mammographic energy range. Using this model the energy, angular and spatial distributions of primary electrons have been studied. For the case of CdTe, CdZnTe, Cd0.8Zn0.2Te and ZnTe, an investigation was also made concerning the dependence of the primary electron production on the incident x-ray energy. In this paper, this investigation has been extended to include the rest of the photoconducting materials. The investigation is realized studying the number of primary electrons produced along with the escaping of photons (both incident and fluorescent) and the number of fluorescent photons emitted for 39 monoenergetic x-ray spectra with energies between 2 and 40 keV. The information obtained from the overall investigation of the primary signal in the various photoconductors gives some good indications of the suitability of PbI2 and HgI2.

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Monte Carlo simulation of primary electron production inside an a-selenium detector for x-ray mammography: physics

Cited by 3 publications

References 0 publications

Photon and primary electron arithmetics in photoconductors for digital mammography: Monte Carlo simulation studies

Photon and primary electron arithmetics in photoconductors for digital mammography: Monte Carlo simulation studies

Suitability of new anode materials in mammography: Dose and subject contrast considerations using Monte Carlo simulation

A Monte Carlo study of primary electron production inside photoconductors for digital mammography and indications of material suitability

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