Pixelated Scintillator Research Articles

High-Speed Real-Time X-Ray Image Recognition Based on a Pixelated SiPM-Coupled Scintillator Detector With Radiation Photoelectric Neural Network Structure

In monitoring scenarios for material processing and accident status evaluation, high-speed X-ray imaging at the microsecond or even nanosecond level is utilized. Real-time, long-term high speed x-ray image processing is difficult to realize with existing technology; main limitations are detector system structure and the need for high-speed transfer and storage of a large number of digital signals. Therefore, this paper proposes an irradiated photoelectric neural network for high-speed real-time X-ray image recognition based on a pixelated radiation detector. We use a SiPM coupled scintillator to realize this pixelated radiation detector. The weights of a neural network are mapped to the bias voltage of SiPM pixels, so that the SiPM array itself constitutes a neural network. By analyzing the output signals of an array of SiPMs, X-ray image can be recognized in real-time. The whole process does not involve complicated digital circuits and digital signal processing. The feasibility of the method was verified by experiments. As the initial stage of the study, we achieved an X-ray image recognition speed of 500,000 frames per second. The simplicity and innovation of this detector fully demonstrate its future application prospects. It is especially suitable for applications that require long-term continuous monitoring of radiographic images and immediate feedback of results, such as online monitoring of high-speed material processing, observation of the cosmic environment and other continuously changing scenes of X-ray images.

Development of Tracer Particles for Positron Emission Particle Tracking

Positron Emission Particle Tracking (PEPT) is a radioactive tracer-based approach to studying dynamic physical processes and multiphase flows. Short-lived positron-emitting isotopes are loaded onto suitable substrates used as tracer particle flow followers in physical and engineering-relevant systems. Coincident photons from electron-positron annihilation are detected using large arrays of pixelated scintillators, with the reconstructed photon trajectories collectively used to determine tracer particle dynamics. We have developed indirect radiochemical, and direct physical activation, techniques for producing tracer particles for such studies, and we report on the current state of the art with focus on the direct approach with high-energy alpha-particle beams. The 16O(α,x)18F reactions have been explored as viable candidates in producing the pure positron emitter 18F from natural 16O-bearing targets. Silicon dioxide (SiO2) glass spheres of diameters of 5 to 10 mm were irradiated in a 100-MeV alpha-particle beam of around 800-nA current for approximately 2 h. Radioisotope activation yields were characterized by half-life measurements and gamma-ray spectroscopy, with the highest yield being 18F (<2.5 mCi). Contaminants from other reaction channels were observed and characterized, including the positron emitter 43Sc and negative beta emitter 24Na, produced from alpha and neutron activation of contaminant species in the target material, respectively. The activation technique is shown to be a reasonable candidate to complement and enhance existing tracer particle production techniques for PEPT and other radiotracer-based studies.

Copper Organometallic Iodide Arrays for Efficient X-ray Imaging Scintillators.

Lead-free organic metal halide scintillators with low-dimensional electronic structures have demonstrated great potential in X-ray detection and imaging due to their excellent optoelectronic properties. Herein, the zero-dimensional organic copper halide (18-crown-6)2Na2(H2O)3Cu4I6 (CNCI) which exhibits negligible self-absorption and near-unity green-light emission was successfully deployed into X-ray imaging scintillators with outstanding X-ray sensitivity and imaging resolution. In particular, we fabricated a CNCI/polymer composite scintillator with an ultrahigh light yield of ∼109,000 photons/MeV, representing one of the highest values reported so far for scintillation materials. In addition, an ultralow detection limit of 59.4 nGy/s was achieved, which is approximately 92 times lower than the dosage for a standard medical examination. Moreover, the spatial imaging resolution of the CNCI scintillator was further improved by using a silicon template due to the wave-guiding of light through CNCI-filled pores. The pixelated CNCI-silicon array scintillation screen displays an impressive spatial resolution of 24.8 line pairs per millimeter (lp/mm) compared to the resolution of 16.3 lp/mm for CNCI-polymer film screens, representing the highest resolutions reported so far for organometallic-based X-ray imaging screens. This design represents a new approach to fabricating high-performance X-ray imaging scintillators based on organic metal halides for applications in medical radiography and security screening.

Effect of different scintillator choices on the X-ray imaging performance of CMOS sensors

The ability of wafer scale Complementary Metal Oxide Semiconductor (CMOS) imagers to integrate sensing with analogue to digital conversion at the pixel level has led to their widespread appeal in a variety of imaging applications. This has led to significant improvement in speed and reduction in read-out noise in these imagers when compared to charge-coupled devices (CCDs) and amorphous silicon/selenium based flat panel imagers (FPIs). This paper compares the performance characteristics of CMOS X-ray detectors in various configurations by varying certain parameters of a typical X-ray detector such as fibre optic face plate (FOP), scintillator substrate coating, sensor pixel pitch and scintillator thickness. The evaluations were carried out using RQA5 (70 kV) radiation beam quality aimed at general radiography applications. At comparable Air Kerma values, detectors with a fibre optic plate showed an overall better DQE performance at most spatial frequencies, starting slightly lower at low frequencies then overtaking the “no-FOP” case at mid and high frequencies. The analysis of detectors with different substrate coatings for the scintillators showed comparatively higher DQE for the white-coated aluminium substrate scintillator compared to the black-coated one. The DQE comparison of detectors with 50μm and 100μm pixel pitch resulted in a higher DQE for the 100μm pixel pitch one, with the caveat that the scintillator was thick enough as to render differences in pMTF negligible. Finally, the comparison of scintillators with varying thicknesses showed that the thickest scintillator yielded the highest DQE. These characterisation studies helped in understanding the suitability of these different configurations in various general radiography application scenarios and could be of help to prospective users to determine the overall configuration that best fits their specific imaging needs.

Design of a Depth-Encoding Detector for PET Through Insertion of Light Guide Between Crystal Arrays

To improve the spatial resolution of preclinical positron emission tomography (PET), a detector consisting of a two-layer scintillator pixel array was designed. A light guide was inserted between the arrays of scintillators to change the distribution of light generated in each layer. By analyzing the different light distributions, it is possible to track where the gamma rays interacted. To this end, a gamma ray event was generated at the center of the flashing pixel and a lookup table was created based on the signal obtained from the light sensor. The optimal position of the scintillation pixel was tracked through comparison and analysis of the newly detected signal with the look-up table through maximum likelihood position estimation. As a result, excellent accuracy was shown. If this detector is used in a preclinical PET system, it is expected to show excellent spatial resolution, and since an optical sensor that is not affected by magnetic fields is used, it is considered that it can be applied to PET/MRI in the future.

A detector block-pairwise dead time correction method for improved quantitation with a dedicated BrainPET scanner

‘Objective. Dead time correction (DTC) is an important factor in ensuring accurate quantification in PET measurements. This is currently often achieved using a global DTC method, i.e., an average DTC factor is computed. For PET scanners designed to image dedicated organs, e.g., those used in brain imaging or positron emission mammography (PEM), a substantial amount of the administered radioactivity is located outside of the PET field-of-view (FOV). This activity contributes to the dead time (DT) of the scintillation detectors. Moreover, the count rates of the individual scintillation detectors are potentially very inhomogeneous due to the specific irradiation of each detector, especially for combined MR/PET systems, where radiation shields cannot be applied. Approach: We have developed a block-pairwise DTC method for our Siemens 3T MR BrainPET insert by extending a previously published method that uses the delayed random coincidence count rate to estimate the DT in the individual scans and planes (i.e., scintillation pixel rings). The method was validated in decay experiments using phantoms with a homogenous activity concentration and with and without out-of-FOV activity. Based on a three-compartment phantom, we compared the accuracy and noise properties of the block-pairwise DTC and the global DTC method. Main results. The currently used global DTC led to a substantial positive bias in regions with high activity; the block-pairwise DTC resulted in substantially less bias. The noise level for the block-pairwise DTC was comparable to the global DTC and image reconstructions without any DTC. Finally, we tested the block-pairwise DTC with a data set obtained from volunteer measurements using the mGluR5 (metabotropic glutamate receptor subtype 5) antagonist [11C]ABP688. When the relative differences in activity concentrations obtained with global DTC and block-pairwise DTC for the ACC and the cerebellum GM were compared, the ratios differed by a factor of up to 1.4 at the beginning—when the first injection is administered as a bolus with high radioactivity. Significance. In this work, global DTC was shown to have the potential to introduce quantification bias, while better quantitation accuracy was achieved with the presented block-pairwise DTC method. The method can be implemented in all systems that use the delayed window technique and is particulary expected to improve the quantiation accuracy of dedicated brain PET scanners due to their geometry.’

Low intensity gamma-ray monitor for in-situ solids fraction measurements in liquids

A novel detection system has been designed to measure the settling of solids in tailing ponds in order to facilitate the reuse of water in oil sands extraction processing, tailings excavation, transportation and management. The system is based on a weak gamma ray source and an inexpensive scintillator-based detector. The system measures gamma ray photons which are transmitted through the material of interest which are detected by a combined scintillator and Multi Pixel Photon Counter (MPPC) detector. This non-destructive measurement allows the determination of the solids contents profile versus depth in a tailing pond. The attenuation of gamma radiation depends on the density of the solids within the fluid tailings and thus varies with the weight fraction of solids content of the tailings. Modelling of the system was carried out by Geant4 simulations. The system was deployed using a weak 133Ba gamma-ray source together with a simple microprocessor controller readout circuit to analyze the pulse height response of a Cerium doped Lutetium Yttrium Orthosilicate (LYSO (Ce)) scintillator crystal. The detection system is calibrated with the known samples and can measure solids content with a relative precision of within ∼2%.

Pulse shape discrimination using a stilbene scintillator array coupled to a large-area SiPM array for hand-held dual particle imager applications

A dual-particle imager (DPI) is configured in a hand-held form factor, then one can efficiently and conveniently deploy the DPI to detect the presence of special nuclear materials (SNM) and identify any isotopic variations that differ from their natural abundances. Here we show that by maximizing the areal coupling between a pixelated scintillator array and the partitioned photosensor readout such as a silicon photomultiplier (SiPM), the information utilization of the gamma-ray and neutron information in the radiation field can be enhanced, thus enabling one to rapidly acquire spatial maps of the distributions on gamma-ray and neutron emitters.

The performance study of developed cost-effective Compton Camera based on Ce:GAGG scintillator using experimental measurements and CCMod of GATE simulation module

In our previous work, a cost-effective Compton camera (CC) using Ce doped Gd3(Al,Ga)5O12(Ce:GAGG) scintillator consisting of two detectors, scatterer (20.8 × 20.8 × 5 mm3) and absorber (41.7 × 41.7 × 10 mm3), was developed to image gamma rays having energy more than 511 keV. This study fabricated a newly developed CC with a larger scatterer and thinner absorber. The system consists of two detectors: a scatterer and an absorber of Ce:GAGG scintillator. The size of the scatterer and absorber is the same; a 40-mm × 40-mm × 5-mm array block consists of 40 × 40 pixels. The size of each scintillator pixel is 0.85 mm × 0.85 mm for both systems. Imaging experiments of Na-22 and Cs-137 point sources were performed to investigate the imaging capability of the new camera, and then the obtained data were compared to the previous CC. The current CC's absolute detection efficiency (DE a ) and photopeak detection efficiency (DE p ) are improved by 1.6 and 2 times greater than the previous one. At the same time, both systems' spatial and angular resolutions are almost the same value at 511 keV. The Compton camera module (CCMod) in GATE v9.0 was employed for Monte Carlo simulations to reproduce the experimental data showing a good agreement.

Design of DOI Detector Through Analysis of Light Distribution Change According to the Depth Direction of the Scintillation Pixel

Design of DOI Detector Through Analysis of Light Distribution Change According to the Depth Direction of the Scintillation Pixel

Coded aperture and Compton imaging capability of spherical detector system design based on GAGG scintillators: A Monte Carlo study

In the study of this paper, based on the symmetry of regular icosahedron, a spherical detector system for 4π field-of-view (FOV) gamma imaging was proposed based on 80 GAGG (Ce:GAGG, Gd3Al2Ga3O12) scintillator pixels. The spherical detector system combines both coded aperture (CA) and Compton imaging (CI) modalities. The detector system was simulated precisely with an experimental test of one representative GAGG pixel. Several radionuclides with characteristic energy ranging from 59.5 keV to 1.33 MeV were imaged under the far-field situation. Both imaging modes realize the 4π view while the coded aperture method achieves a higher image quality for radioactive sources with lower energy and the Compton method performs conversely. The imaging system can localize a 10 mCi 137Cs point source at 10 m within 1 s in the two modes and the Compton imaging mode reaches a high detection efficiency of up to 200 cps/μSv/h for 137Cs. And the angular estimation full-width-at-half-maximum (FWHM) was approximately 5.2°for coded aperture mode and 14°for Compton mode. The angular resolution was evaluated to be better than 30°. The high intrinsic imaging sensitivity and reasonable imaging quality make this detector system design attractive for far-field radiation imaging.

Far-Field 3-D Localization of Radioactive Hotspots via Four-Eyes Stereo Gamma Camera

In the fields of radiation environment monitoring and unknown radioactive materials search, locating the far-field gamma-ray sources with high accurate coordinates is an important and necessary capability for a gamma imager. However, traditional coded gamma-ray imaging systems only provide 2-D radiation images without distance information. In this work, a four-eyes stereo gamma camera is proposed, which consists of four independent coded aperture detectors with an adjacent spacing of 286 mm. Each detector is comprised of pixelated scintillators with a pixel array of 44 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times44$ </tex-math></inline-formula> , forming a global detection area of 140 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times140$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The ranging capability is related to the resolution and the adjacent spacing of the detectors. With the setup of the above device, the traditional binocular-based ranging method has a short measurement range and a large measurement deviation. Here, a min-area distance measurement algorithm based on a four-eyes stereo gamma camera is proposed, combined with “manual” fine sampling and Gaussian fitting method to successfully achieve the high-precision localization of the far-field source. The simulation results show that compared with the traditional binocular-based ranging method, the min-area method based on a four-eyes stereo camera lengthens the range from 20 m to more than 50 m and improves the ranging accuracy within 20 m by more than six times. The accuracy of 20 and 50 m is less than 1.4 m (7.13%) and 10.5 m (21%), respectively. The reliability of the simulation results has been verified by experiments. Furthermore, the ranging capability of this algorithm for multipoint sources in the far field has been verified.

Studies on fast neutron imaging with a pixelated stilbene scintillator detector

For simultaneous imaging with fast neutrons and gammas we have developed a 16-pixel detector that uses the organic scintillator stilbene as active material. Sixteen stilbene cuboids of size 5×5×25mm3 are arranged in a 4 × 4 grid and read out by silicon photomultipliers. The usage of stilbene allows to distinguish neutron and gamma signals via pulse shape discrimination techniques. In this paper, attenuation measurements and first tomographies of objects containing aluminum and PMMA are presented. Fast neutrons and gammas are delivered by an Americium–Beryllium source. The performance of the tomographic reconstructions with neutrons and gammas is evaluated. It is shown that the combination of the two images can improve the material distinction in the reconstructed object.

Technical note: Comparison of arithmetic mean and energy-weighted mean flood histogram generation methods for dual-ended readout positron emission tomography detectors.

Dual-ended readout pixelated scintillator array detectors can provide a suitable crystal resolvability and satisfactory depth of interaction (DOI), energy, and timing resolutions. Usually, the flood histogram measured by one-sided readout is depth dependent, and the flood histogram quality degrades as the distance between the interaction site and photodetector increases. Information measured by two photodetectors must be combined to obtain an improved flood histogram yielding a better PET scanner spatial resolution. Two flood histogram generation algorithms for dual-ended readout of pixelated scintillator array detectors were compared by theoretical calculations and experimental measurements. The first algorithm is the arithmetic mean (AM) algorithm, which assigns the same weight to the flood histograms measured by photodetectors 1 and 2. The second algorithm is the energy-weighted mean (EWM) algorithm, which assigns each flood histogram a certain weight proportional to the energy measured by the photodetector. Theoretical equations were derived to determine the quality of the flood histograms obtained with these two algorithms. Experimental measurements were performed with an 18 × 18 lutetium-yttrium oxyorthosilicate (LYSO) array with a crystal size of 0.62 × 0.62 × 20 mm3 read out by two multi-anode photomultiplier tubes at both ends. Flood histograms of the whole array and five specific depths were compared between the above two algorithms. The theoretical results indicated that the flood histograms obtained with the EWM method matched those obtained with the AM method at the middle detector depth and were better at other detector depths when the distance (S) between the locations of the same crystal in the flood histograms measured by photodetectors 1 and 2 reached 0. The advantage of the EWM method decreased with increasing S value since the crystal position in the flood histogram obtained with the EWM method varies with the depth when S does not equal 0. The advantage of the EWM method decreased with increasing S value. The experimental results generally agreed with the theoretical predictions. Compared to the AM method, the EWM method provided a similar flood histogram at a depth of 10 mm but generated a better flood histogram at depths of 2 and 18 mm. Although an inverse correlation between Q (a quality factor representing the advantage of the EWM method) and S was observed, the variation in Q given the same S value was high. The average Q value at the same S still agreed with the theoretical predictions. Theoretical equations were derived, and experimental measurements were performed to compare two flood histogram generation algorithms for dual-ended readout PET detectors. The results indicated that the EWM method based on inverse variance weighting theory could provide better flood histograms than those provided by the AM method.

Organic glass scintillator formulations and mold development towards scalable and cast-in-place pixelated fabrications

Herein we describe the development of organic glass scintillator (OGS) additives to enable the rapid and simple fabrication of form factors necessitated by pixelated neutron detection systems. These systems, developed for national security purposes, utilize arrays of many (O(100–1000))​ bar-shaped scintillators which are optically isolated and coupled to photodetectors. We describe two overall methods to address the construction of pixelated scintillator arrays at scale: individual bars cast directly in single bar molds, reducing the need to cut the bars to size, and casting directly into pixelated molds, eliminating both the need to cut the bars to size and to fabricate the array from individual bars. The mechanical blending of pre-polymerized plastic pellets of polystyrene and polycarbonate in OGS can be formulated up to 5% by weight into OGS to rigidify high aspect-ratio bars capable of withstanding the additional stress of being cast simultaneously side by side in a single pour with a variety of new mold materials. In addition, the inclusion of 15%–20% of “2-(p-tolyl)-1,3,2-dioxaborinane” (TDB) can enable direct, cast-in-place of OGS bars into aluminum or acetal sheet molds of arrays. We also describe the developments into the new mold materials and assembly to support the casting into these form factors. As a proof of concept, we cast a single pixel directly into a mold lined with 3M’s enhanced specular reflector (ESR) and characterize its performance for neutron detection applications.

Preliminary results of a single photon emission computed tomography (SPECT) detector for inspection of spent fuel assembly

SPECT systems are being used by international safeguards organizations for the measurement for structural evaluation of spent fuel assemblies. However, the low sensitivity still limits the verification of spent fuel assemblies within a short measurement time (1–2 h per assembly). In this study, the SPECT detector was optimized and evaluated to identify the structure of spent fuel. The detector module consists of 64 one-dimensional (1-D) multi-slit collimators and 1-D pixelated scintillators coupled to SiPMs. We evaluated and optimized the light collection efficiency and energy resolution according to the shape of scintillator (Trapezoid, Rectangular), and reflector materials (Paint, Teflon tape, BaSO4) by Geant4 Application for Tomographic Emission (GATE) simulation and experiment. As a result, the trapezoidal scintillator coated with BaSO4 showed the highest light collection efficiency among the six models in GATE simulation and in experiments. The spent fuel rods were imaged using trapezoidal scintillator coated with BaSO4, and 1-D projections and line profiles were obtained in order to distinguish the source location. In this study, the scintillator structure and reflector material variables were optimized using Monte Carlo simulation to measure 662 keV gamma-ray of 137Cs for inspection of spent fuel assembly using the SPECT system. In order to confirm the imaging potential of the spent fuel assembly, the detector performance was evaluated using unused fuel rods for testing. The performance of the detector for fuel rod identification has been proven, and we expect that the optimized detector module will contribute to the rapid verification of the spent fuel assembly compared to conventional systems.

On the Use of Pixelated Plastic Scintillator and Silicon Photomultipliers Array for Coded Aperture Gamma-Neutron Imaging

We report the investigations made on the use of pixelated plastic scintillator (PS) and silicon photomultipliers (SiPMs) array applied to coded aperture gamma-neutron imaging. Specifically, verification of the ability of a multiplexing readout to discriminate and localize neutron interactions was studied. In its intended configuration, the gamma-neutron imager design consists of a coded aperture aligned with a matrix of <inline-formula> <tex-math notation="LaTeX">$12\times12$ </tex-math></inline-formula> PS each coupled to a SiPM. The coded aperture is a rank 7 modified uniformly redundant array (MURA), composed of 1.2 cm of tungsten, with a surface area of 100.4 mm <inline-formula> <tex-math notation="LaTeX">$\times100.4$ </tex-math></inline-formula> mm and placed at 5 cm from the detector. The pixelated PS is composed of polystyrene and standard fluorophores (20 wt&#x0025; PPO, 0.03 wt&#x0025; POPOP) loaded with a lithium carboxylate (Li <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-valerate), which allows the triple discrimination between thermal neutrons, fast neutrons, and photons. Each pixel of PS has a dimension of 3.6 mm <inline-formula> <tex-math notation="LaTeX">$\times3.6$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times3.6$ </tex-math></inline-formula> mm and they are separated from each other by 0.6 mm of polytetrafluoroethylene (PTFE). The photonic and electronic readout consists of the ArrayC-30035-144P SiPM from SensL, Cork, Ireland, connected to the diode coupled charge division readout from AiT. First, this neutron imager design was modeled and simulated using the MCNP6 Monte Carlo code. The encoding capability, field of view, and spatial resolution of the neutron imager were therefore evaluated by simulation. Then, we detailed the experimental setups implemented to demonstrate the feasibility of coupling pixelated PS to SiPM to localize radioactive sources and showed the results obtained. Finally, based on this position-sensitive gamma-neutron detector, a gamma-neutron imager was prototyped and tested.

Optimized TOF-PET detector using scintillation crystal array for brain imaging

Research groups in the field of PET instrumentation are studying time-of-flight(TOF) technology to improve the signal-to-noise ratio of PET images. Scintillation light transport and collection plays an important role in improving the coincidence resolving time(CRT) of PET detector based on a pixelated crystal array.Four crystal arrays were designed by the different optical reflection configuration such as external reflectors and surface treatment on the CRT and compared with the light output, energy resolution and CRT. The design proposed in the study was composed of 8 × 8 LYSO crystal array consisted of 3 × 3 × 15 mm3 pixels. The entrance side was roughened while the other five surfaces were polished. Four sides of all crystal pixels were wrapped with ESR-film, and the entrance surface was covered by Teflon-tape. The design provided an excellent timing resolution of 210 ps and improved the CRT by 16% compared to the conventional method using a polishing treatment and ESR-film.This study provided a method for improving the light output and CRT of a pixelated scintillation crystal-based brain TOF PET detector. The proposed configuration might be an attractive detector design for TOF brain PET requiring fast timing performance with high cost-effectiveness.

Simulated sensor characterization for virtual clinical trials in mammography and digital breast tomosynthesis

Virtual clinical trials in X-ray breast imaging permit to compare different technical solutions and imaging modalities at reduced costs, involved personnel, reduced times and reduced radiation risks to patients. In this context, the detector characteristics (spatial resolution, noise level and efficiency) play a key role for an appropriate generation of simulated images. The project AGATA proposes to compute images as dose deposit maps in a detector layer of defined materials. Simulated images are then post-processed on the basis of suitable comparison between intrinsic characteristics of real and simulated detectors. With this scope, as first step for the post-processing manipulations, we evaluated the presampled modulation transfer function (MTF), the detector-response function and the noise power spectrum (NPS) of the simulated detectors. Two detectors were simulated: (1) 0.20 mm-thick a-Se direct flat panel with 70 µm pixel pitch and (2) CsI(Tl) indirect flat panel with 100 µm pixel pitch and scintillator layer 0.25 mm thick. In addition, the impact of simulating the de-excitation processes (Auger emission and fluorescence) was explored. Simulated detector characteristics were evaluated for W/Rh spectra between 25 kV and 31 kV. The in-silico platform used a Monte Carlo software based on Geant4 toolkit (vers. 6). First, the simulation and tracking of electrons generated from photoelectric or Compton interactions was shown to have neglectable influence on the pixel values for the explored spectra, with the produced electrons presenting short ranges with respect to the pixel dimension. In the case of the CsI detector, which has fluorescence energies higher than those of the simulated X-ray photons, the deexcitation processes have not noticeable influence on the calculated pixel values. On the other hand, the MTF of the a-Se detector resulted slightly lower when the fluorescence is simulated in the detector materials, due to the dose spread derived from the fluorescence photons, which can travel far from the initial ionization interaction. Regarding the a-Se detector, the noise power spectrum resulted lower with simulated deexcitation.

Digital Position and Depth of Interaction Measurement of the PET Detector Through the Signal Ratio

A new detector was designed to improve the spatial resolution of positron emission tomography (PET) and acquire digital coordinates of the detector"s scintillation pixels. In order to solve the spatial resolution deterioration phenomenon due to parallax error occurring outside the field of view (FOV), a method of measuring the depth of interaction was developed, and this was accomplished with the acquisition of digital coordinates. A detector using a 4 × 4 × 2 GAGG scintillator was designed using the DETECT2000 simulation tool to acquire digital coordinates of the scintillation pixels and measure the depth of interaction of the two layers. A gamma-ray reaction was generated in all the scintillation pixels, and the signals were obtained from SiPM pixels in a 4 × 4 array. The 16-channels of optical sensor signals were reduced to signals of 4 channels, and these were calculated as a ratio of each signal. The ratio of the signal was obtained from all the flash pixels, and the position was obtained as digital coordinates by comparing it with the ratio of the signal by the gamma ray response generated at the new position. In order to evaluate the accuracy of acquiring the digital coordinates and the accuracy of the layer where the scintillation pixel in which the scintillator and the gamma ray reacted, a signal was obtained by generating a gamma ray response for the entire length of each scintillation pixel. Gamma-ray reactions were generated at intervals of 0.2 mm from 0.1 mm to 19.9 mm. The obtained signals through these reactions were compared with the signals of each scintillation pixel obtained in advance. Then, the accuracy of measured positions on the X, Y, and Z axes were evaluated. The accuracy of both the X and Y axis showed perfect results, and the accuracy of the Z axis was 91.46 %.