This work has been dedicated to the search for a new possibility to use multi-energy digital radiography (MER) for medical applications. Our work has included both theoretical and experimental investigations of 2-energy (2E) and 3- energy (3Е) radiography for imaging the structure of biological objects. Using special simulation methods and digital analysis based on the X-ray interaction energy dependence for each element of importance to medical applications in the X-ray range of energy up to 150 keV, we have implemented a quasi-linear approximation for the energy dependence of the X-ray linear mass absorption coefficient μm (E) that permits us to determine the intrinsic structure of the biological objects. Our measurements utilize multiple X-ray tube voltages (50, 100, and 150 kV) with Al and Cu filters of different thicknesses to achieve 3-energy X-ray examination of objects. By doing so, we are able to achieve significantly improved imaging quality of the structure of the subject biological objects. To reconstruct and visualize the final images, we use both two-dimensional (2D) and three-dimensional (3D) palettes of identification. The result is a 2E and/or 3E representation of the object with color coding of each pixel according to the data outputs. Following the experimental measurements and post-processing, we produce a 3Е image of the biological object – in the case of our trials, fragments or parts of chicken and turkey.
An original dual-energy detector and medical instrument have been developed to measure the output voltages and dose rates of X-ray sources. Theoretical and experimental studies were carried out to characterize the parameters of a new scintillator-photodiode sandwich-detector based on specially-prepared zinc selenide crystals in which the low-energy detector (LED) works both as the detector of the low-energy radiation and as an absorption filter allowing the highenergy fraction of the radiation to pass through to the high-energy detector (HED). The use of the LED as a low-energy filter in combination with a separate HED opens broad possibilities for such sandwich structures. In particular, it becomes possible to analyze and process the sum, difference and ratio of signals coming from these detectors, ensuring a broad (up to 106) measurement range of X-ray intensity from the source and a leveling of the energy dependence. We have chosen an optimum design of the detector and the geometry of the component LED and HED parts that allow energy-dependence leveling to within specified limits. The deviation in energy dependence of the detector does not exceed about 5% in the energy range from 30 to 120 keV. The developed detector and instrument allow contactless measurement of the anode voltage of an X-ray emitter from 40 to 140 kV with an error no greater than 3%. The dose rate measurement range is from 1 to 200 R/min. An original medical instrument has passed clinical testing and was recommended for use in medical institutions for X-ray diagnostics.
A large-area X-ray CMOS image sensor (LXCIS) is widely used in mammography, non-destructive inspection, and animal CT. For LXCIS, in spite of weakness such as low spatial and energy resolution, a Indirect method using scintillator like CsI(Tl) or Gd2O2S is still well-used because of low cost and easy manufacture. A photo-diode for X-ray imaging has large area about 50 ~ 200 um as compared with vision image sensors. That is because X-ray has feature of straight and very small light emission of a scintillator. Moreover, notwithstanding several structure like columnar, the scintillator still emit a diffusible light. This diffusible light from scintillator can make spatial crosstalk in X-ray photodiode array because of a large incidence angle. Moreover, comparing with vision image sensors, X-ray sensor doesn’t have micro lens for gathering the photons to photo-diode. In this study, we simulated the affection of spatial crosstalk in X-ray sensor by comparing optical sensor. Additionally, the chip, which was fabricated in 0.18 um 1P5M process by Hynix in Korea, was tested to know the effect of spatial crosstalk by changing design parameters. From these works, we found out that spatial crosstalk is affected by pixel pitch, incident angle of photons, and micro lens on each pixels.
Presently, most X-ray security systems for luggage inspection use dual-energy detector. A drawback of this approach is
that overlap in energy sensitivity of the low- and high-energy detectors creates the potential for ambiguity and
inaccuracy. We have made an attempt to improve the identification quality of organic materials using a three-energy
receiving–detecting circuit. New model calculations and several new algorithms for the detection of organic and nonorganic
materials under multi-energy radiography were proposed, developed and experimentally verified. The purpose of
the present work is study of the possibility of separation between substances with small effective atomic numbers for
increasing the detection probability of explosives. Using a spectrum of the X-ray tube with a tungsten anode, evaluation
has been carried out of the signal ratio from high-energy detector, medium-energy detector and low-energy detectors.
Using differential energy sensitivity of detectors of different thickness, varying X-ray source anode voltages and filter
for each array, special software it is possible to reconstruct images of the inspected object at the different energy scales.
It was shown that using standard X-ray beams and specially-chosen scintillator types with different thicknesses, we can
achieve accuracy in determination of Zeff up to 95%, that significantly better as compared with systems based on
conventional X-ray inspection. Using two-coordinate identification palette, one can discern between imitators of
explosives even when the difference in their Zeff values is small (from 7.08 to 8.07).
The dual-energy computer tomography compared with its traditional single-energy variant ensures substantially higher
contrast sensitivity. The evaluation of the signal ratio from high-energy and low-energy detectors has been carried out
using a simplified model of the dual-energy detector array and accounting for the X-ray tube spectrum. We proposed to
use of a dual-energy receiving–detecting circuit with a detector pair ZnSe/CsI or ZnSe/CdWO that allows efficient
distinction between muscular and bone tissues, which supports our earlier theoretical assumptions that this method could
be successfully used for separate detection of materials differing in their effective atomic number Zeff and local density
(e.g., calcium contents in bone densitometry), so as can be turn to account for new generation instruments. A possibility
of dual energy tomography use for osteoporosis diagnostics was considered. Direct image reconstruction of biological
objects has been carried out, demonstrating details of bones with different density. The density of the bone depends on
the calcium content, which is not more than 20 % for the narrow part and about 18,5 % in the broad part. This results
obtained were in good agreement with the results of the independent chemical analysis.
The film radiographic inspection remains among the most reliable methods for inspection of pipelines and metalwares.
The worldwide trend of transition from film radiography to digital radiography requires creation of advanced digital
radiography systems. The main direction of digital radiography systems development is improvement of spatial
resolution. The pixel size of the X-ray film is several microns, while solid-state detector pixels have dimensions of
several hundred or several thousand microns. For the most common detectors of "scintillator-photodiode" type, it is
impossible in principle to obtain the film pixel sizes. However, the detecting ability for substances that differ by their
density and atomic number achieved using "scintillator-photodiode" detectors is by several orders higher. Using a
standard experiment scheme with dual-energy detector arrays, our aim was to show that it could be possible to
substantially increase the accuracy of supervision of the inspected object. For obtaining shadow X-ray images, a
receiving-detecting circuit with a detector array was developed for 200 mm scanning field. Using model digital
radiographic systems and standard testing we have evaluated spatial resolution (not worse than 1.25 line pairs/mm) and
detecting ability (better than 0.2 mm steel wire behind 6 mm steel).
Development and studies of characteristics are reported for X-ray radiation detectors of "scintillator-photodiode" type
showing improved spatial resolution with photosensitive area step of 1.6, 0.8, 0.4 and 0.2 mm and number of channels
16, 32, 128 and 256, respectively. The receiving-detecting channel has been adjusted and tested, appropriate software has
been developed, and shadow X-ray images of tested objects were obtained. Evaluations were made of spatial resolution,
resolution over thickness and detecting ability of the digital radiographic sysyem based on the detector array.
Recommendations are formulated on application of such devices for non-destructive testing and technical diagnostics.
Further studies on obtaining two-energy images show possibilities of substantial broadening of the application fields of
the digital radiographic system, allowing determination of the effective atomic number Zeff for component substances of
the tested objects. A possibility is shown of substance discrimination by their effective atomic number even for "light"
elements with Zeff from 6 to 13. Clear distinction could be observed between such substances as water (H2O) with
Zeff≈7.43 and glycerol (CH2OHCHOHCH2OH) with Zeff≈ 6.87.
Development is reported of a small-sized ultraviolet (UV) radiometer designed for measurements of energy
characteristics of UV radiation - energy illuminance and energy exposure. Main characteristics are considered of
nZnSe(O, Te)/Ni Schottky structures created for the developed UV radiometer and used as UV sensors. Characteristics
are presented of optical glass filters and interference light filters designed for separation of different biologically relevant
UV spectral regions.
Detection of X-ray radiation by digital radiographic systems (DRS) is realized using multi-element detector arrays of
scintillator-photodiode (S-PD) type. Accounting for our experience in development of X-ray introscopy systems,
possibilities can be found for improvement of DRS detection efficiency. Namely, a more efficient use of the dynamic
range of the analog-to-digit converter by means of instrumental compensation of scatter of detector characteristics and
smaller apertures of individual detection channels. However, smaller apertures lead to lower levels of useful signals, and
a problem emerges of signal interference over neighboring channels, which is related to optical separation of the
scintillation elements. Also, more compact arrangement of electronic components of preamplifiers is achieved. The latter
problem is solved by using multi-channel (from 32 to 1024 channels) photoreceiving devices (PRD). PRD has a set of
photosensitive elements formed on one crystal, as well as shift registers ensuring preliminary amplification of signals
and series connection to one outlet.
The work envisages creation of receiving-detecting circuit (RDC) with improved spatial resolution (ISR) with the aim of
producing advanced DRS with improved characteristics: density resolution better than 0.9%, and detecting ability
allowing detection of θ 0.5 mm steel wire behind 6 mm steel.
The work will result in the development of RDC with ISR (800-200 microns). In combination with various ionizing
radiation sources and scanning mechanisms this will allow creation of DRS for many tasks of non-destructive testing
(NDT) and technical diagnostics (TD), in particular, for check-up of pipelines, objects of oil and gas industries, etc.
This work was supported by the Ministry of Education and Science of Ukraine, the U.S. Civilian Research and
Development Foundation (CRDF), and by the NATO Science for Peace and Security Program (Project SfP-982823).
Scintillators on the basis of AIIBVI compounds, such as ZnSe(Te), can be used for detection of secondary charged particles coming from nuclear reactions in which neutrons interact with target nuclei of atoms present in transparent materials of dispersion scintillation detectors matrices.
Using unique properties of scintillator ZnSe(Te) we show possibility of increase detection efficiency for soft x-ray radiation (20 - 90 keV).
The amorphous silicon flat panels and the photodiode arrays wide used for non-destructive testing and medical imaging (spatial resolution 20 - 400 mkm). By our estimations, using of such detectors in combination with thin film of ZnSe(Te) can increase efficiency of registration of x-ray radiation (for the source of 60-140kV) in 1,2 - 2 times.
We obtained thin films (10-450mkm) of scintillator ZnSe(Te) on the different substrate materials and estimated the relative light yield of the layers deposited on the graphite and Al2O3 ceramic substrates and the bulk ZnSe(Te) crystal.
Use of ZnSe(Te) in the low-energy "scintillator - photodiode" type detector allowed to increase accuracy of authentication of explosives (HEIMANN X-RAY INSPECTION SYSTEM EDtS10080).
Using the dual energy digital radiography system prototype we obtained the x-ray images (60 projections of each object). These images are basic data for computer tomography and three-dimensional reconstruction of density and effective atomic number. The color identification palette provides clearly show variations of effective atomic number in biological and inorganic objects. So, for example, changes of calcium concentration in a bone.
The research described in this publication was supported by STCU #4115 and NATO SfP-982823.
Due to disadvantages of scintillator ZnSe(Te) - poor transparence to own emission (10-1 cm-1), long decay time, low density and Zeff-this material had no practical applications in the ranges of X-ray energies about 120-140 keV. After the development of dual energy X-ray inspection scanners, CT and digital radiography situation changed on the contrary at whole. Both theory and experiments show that now it is the best material for low energy array detectors. The pilot-industrial production of ZnSe(Te) crystals is organized, their usage in CT and inspection X-rays scanners being already started.
It has become possible to get tomography imaging simultaneously with automatic recognition of dangerous objects and substances, which is due to the unique parameters of ZnSe(Te). Presently several leading western companies look for possibilities to use ZnSe(Te) for medical X-ray CT.
Our aim was to unveil the nature of luminescence centers and the emission mechanism in crystals of ZnSe(Te) compounds with isovalent dopants from the results of our studies of optical, spectroscopic and kinetic characteriestics of these crystals. Basing on the obtained understanding of the emission centers, we aimed at creation of a reproducible production technology of scintillators for application in inspection and medical equipment.
The research described in this publication was made possible in part by INTAS Project Ref. Nr. 05-104-7519.
We used detector arrays of types "scintillator-photodiode" (S-PD) and scintillator-photoreceiving device (PRD). In non-destructive testing systems using S-PD arrays it is possible to use scintillators of different atomic number and density, which allows functioning in the energy range from 20 keV to 10 MeV, i.e., steel equivalent thickness I from 100μm to 300mm. For different objects and different purposes, different types of detector arrays and methods of control can be recommended. Results of experimental studies of detector arrays S-PD and S-PRD used for X-ray digital radiography have shown that there exist further possibilities to increase spatial resolution of this system for up to 2-3 line pairs per mm. It was investigated experimental results with used two array detectors for low-energy and high - energy detections (HED and LED). It is show in principle to distinguish not only organic from inorganic materials, but so as safety organic from explosive. Our aim was to show (theoretically and experimentally) that is could be possible to substantially increase the accuracy of separation of substances in the inspected object by their atomic number, as well as to increase the sensitivity of the method as a whole by using a multi-energy approach and detectors that have substantially different sensibility in the low-and high-energy range of the X-ray emitter spectrum. It was show the possibility to distinct materials with effective atomic number difference about 10-15%. It can be used in inspection systems, including anti-terrorist activities, in technical diagnostics, medicine.
Properties are reported of new types of active module 32- channel scintielectronic detectors of 'scintillator- photodiode' type with step h equals 0,8 mm for low-energy x-ray introscopic systems. As scintillator, 'fast' modification of crystal ZnSe(Te) was used in three variants: individual single crystal elements for each channel, a single crystal plate common for all channels, and a small crystalline composite plate with grain size d equals 0,25 divided by 0,5 h. Active detectors based on ZnSe(Te) scintillators and active 32-channel photoarrays with combined pattern of preliminary transformation and sequential sampling ensures x-ray sensitivity of 0,8 divided by 2.
The receiving-detecting unit using scintillator-photodiode type detectors can be a basis for introscopic systems, industrial non-destructive testing instruments, devices for medical and technical tomography, fluorography, etc., have been developed.
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