EA010121B1 - Method of x-ray identification of matter type of the objects placed on human body - Google Patents

Abstract

The invention belongs to the field of X-ray inspection. In particular the X-ray is used to identify unauthorized objects placed on human body, object thickness and materials from which they are made. The invention can be used in X-ray control at checkpoints by air, sea ports and other buildings with enhanced security measures.The technical purpose of invention is to create a method of materials identification, which would perform quantitatively and independently of the inspector. An additional condition is the low dose of surveyed human.The method includes a scanning of human body by means of the X-ray pencil beam, detection of the signals from reflected and transmitted X-ray radiation, data archiving and following analysis which side by side with the visual images from reflected and transmitted X-Ray radiation are used for the quantitative estimation of the matter type and thickness of objects which placed on human body. For identification of matter type and estimation of object thickness the signal change of reflected and transmitted X-ray radiation is calculated relative to the following beam positions: first – pencil beam intersects both the object and human body, second – pencil beam intersects only human body near the object. After that the calculated relative signal changes are compared with tabulated values of relative signal changes for different matter types and object thicknesses. This comparison gives the quantitative estimation of object matter type and thickness.

Description

The invention relates to x-ray technology, in particular to x-ray identification of foreign objects and materials from which they are made, and can be used to identify explosives, drugs, metal products and other materials located on the human body, with x-ray control at air points , seaports and enterprises with enhanced security measures.

Modern methods of x-ray identification of objects and materials from which they are made, and x-ray installations that implement these methods are divided into three groups.

Group 1. Methods and installations operating on radiation transmitted through a controlled person.

Examples: US patent No. 7016473, installation - X-ray scanner KONTUR CJSC SPC NELK Company (human radiation dose ~ 1.5 μSv / inspection), installation - X-ray control system (SCS) CJSC Nauchpribor (human radiation dose ~ 1 μSv / inspection), installation - X-ray control system SibScan (human radiation dose ~ 3 μSv / inspection).

A person is scanned by a narrow fan-shaped bundle. The radiation transmitted through a person is detected by a ruler in one column of detecting cells (pixels). The resolution is determined by the transverse size of the detecting cell ~ 0.2-1.0 mm

In the image of a computer monitor, foreign objects are visible located both on the surface of the human body and inside the person. The identification of the materials from which the objects are made is difficult, since the amplitude of the signal from the transmitted radiation is mainly determined by the thickness and density of the radiation transmission medium and to a much lesser extent by the chemical composition of the medium. The operator can only make a qualitative conclusion about the density of the material from which the object is made by the degree of obscurity of the image of the object in relation to the image of the human body.

Group 2. Methods and installations operating on reflected (scattered back from a controlled person) radiation.

Examples: US Patent No. 5181234, KarBSai Zesige 1000 (human exposure dose ~ 0.1 μSv / inspection), AZ&E ZshaySjesk Reg8opie1 1i8res1yu ZuChesh installation (human radiation dose ~ 0.1 μSv / inspection).

A person is scanned with a thin (pencil) beam. Reflected radiation is detected by either a scintillation detector or an ionization chamber. The resolution is determined by the cross section of the scanning pencil beam at the surface of the human body ~ 3-10 mm.

The image of a computer monitor shows objects that are located on the human body from the side of the radiation or are embedded in the surface layer of human soft tissue to a depth of about 3 cm. The operator can make the following conclusions regarding the brightness of the image of the object relative to the brightness of the image of the human body: if the brightness of the image an object is higher than the brightness of the image of the human body, this object can be made of organic material, if the brightness of the image of the object is lower than the brightness of the image of the human body, this The item can be made from inorganic material.

Group 3. Methods and installations operating simultaneously on the radiation reflected from the object and on the radiation transmitted through the object.

Examples: US Patent No. 4,799,247 (for baggage control), US Patent No. 5,260,982 (for baggage control), US Patent No. 6,665,373 (for human control), baggage control unit AZ & E аск Waskxayeg tey Tgapkschshyop. Models 101Ζ and 101ΖΖ (baggage dose not specified). No settings for human control were found.

The object is scanned with a thin (pencil) beam. The reflected and transmitted radiation is detected either by a scintillation detector or by an ionization chamber. The resolution of images from reflected and transmitted radiation is determined by the cross section of the scanning pencil beam in the area of the scanned object.

In the image from the reflected radiation visible objects located on the surface of the body (patent 6665373), or items of luggage located in the area of direct exposure with a pencil beam (patents 4799247, 5260982). In the image from the transmitted radiation, items of luggage that are in the shadow of objects directly irradiated with a pencil beam (patents 4799247, 5260982), or the shadow outline of a person and objects placed on the side surface of the body (patent 6665373) are visible. In patent 6665373, transmitted radiation is registered only in the counting mode (there is a signal, there is no signal), therefore, the image from the transmitted radiation looks like a shadow outline of a person and objects on the side surface of the body.

When inspecting baggage, the operator can use the images from reflected and transmitted radiation to make a conclusion about the objects and materials from which they are made, within the scope of the capabilities of the methods and settings of groups 1 and 2. When controlling a person using the method of patent 6665373, the operator can make a conclusion about objects and the materials from which they are made are limited by the capabilities of the methods and apparatuses of group 2 with the addition of the ability to see the contour of objects placed on the sides in the shadow image from the transmitted radiation th surface of the human body.

- 1 010121

From an analysis of patented methods for x-ray identification of materials and installations that implement these methods, it was found that the closest analogues to the proposed invention are the method of identification of materials implemented by the X-ray imaging system, specially adapted for identification of materials with a low charge Ζ according to US patent No. 4799247 from 17.01. 1989, the method of identification of materials implemented by the Installation for the formation of images of scattered radiation according to US patent No. 5260982 from 11/09/1993, and The method of identification according to US patent No. 6665373 dated December 16, 2003 for human control.

Technical solutions for US Patent Nos. 4,799,247 and 5,260,982 are for baggage control. Both of them are related. The only difference is in the direction of irradiation with a pencil bundle of luggage on the conveyor. In the first patent, the luggage transported via the conveyor is shown on the side, in the second patent, the luggage is shown on the bottom. In the image from the transmitted radiation, the inspector sees the inside of the luggage. In the image from the reflected radiation, the inspector sees only objects on which a pencil beam directly falls. In this case, the inspector can only make a visual assessment (by the degree of brightness of the object in the image from the reflected radiation) that this object is from organic or inorganic. The inspector does not have any other information from the computer.

The closest analogue (prototype) is the method of X-ray identification of materials from which the objects placed on the human body are made, implemented by the X-ray image forming system by means of an active detector according to US patent No. 6665373, including scanning the human body with a pencil X-ray beam, registration of reflected and transmitted x-ray signals radiation, archiving the received data in a personal computer for comparative analysis and identification with subsequent visa noy assessment results.

A pencil beam scans the human body. From the reflected radiation, the signal amplitude is recorded. Not the signal amplitude, but the conditional code is written from the transmitted radiation: there is a signal, there is no signal. In the image from the transmitted radiation, the inspector sees only the monophonic contour of the human body and does not see his internal structure. The inspector needs a profile contour of the human body only in order to see the silhouettes of objects located on the side surface of the body. According to the image from the reflected radiation, the inspector only visually evaluates the material from which the object is made: inorganic (the image of the object is darker than the image of the human body) or organic (the image of the object is lighter than the image of the human body). The inspector does not have any other information from the computer.

Thus, in the known technical solutions, the identification of materials is based on a visual (subjective) assessment of the operator of the values of the amplitudes of the signals from the transmitted and reflected radiation, allows only two types of materials to be identified from which the objects are made (inorganic, organic), and there is absolutely no estimate of the thickness of the controlled object .

In addition, well-known Russian installations for human control allow a dose of human exposure for 1 inspection at the level of 1-5 microsievert (μSv). Foreign installations have a lower exposure standard of 0.1 μSv (this dose is equivalent to 10 micro-roentgen).

An object of the invention is the implementation of such a method for the identification of materials, which at a low dose to a person, not exceeding 0.1 μSv / inspection, allows you to:

1) have independent of the inspector, calculated by software, assessment of the type of material from which a foreign object on the human body is made;

2) significantly increase in comparison with known methods the number of groups of identifiable materials;

3) have an assessment not only of the type of material of the foreign object, but also an estimate of the thickness of this object.

The technical problem is achieved by the fact that in the method of x-ray identification of materials from which the objects placed on the human body are made, including scanning the human body with a pencil x-ray beam, recording the amplitudes of the signals from the reflected and transmitted x-rays, archiving scan data, comparative analysis and identification with visual assessment of the material of the object by x-ray image, in the identification of materials along with a visual assessment of the material of the object by x-ray The image is quantified using the material of the object and its thickness using the archived scanning database, for which at the suspicious points on the human body the value of the relative change in the signal amplitude from the reflected x-ray radiation and the value of the relative change in the signal amplitude from the person passing through the suspicious object and at the same time are calculated x-ray radiation, a comparison of these values with pre-tabulated values relative x changes in the amplitudes of the signals for different materials, identify the materials and evaluate the thickness of the object.

The calculation of the values of the relative changes in the amplitudes of the signals from the reflected and transmitted x-rays, the comparison of these values with the tabulated values of the relative changes in the amplitudes of the signals for different materials, the identification of the material and the assessment of the thickness of the object placed on the human body, is carried out according to a given program using a computer.

The essence of the invention lies in the fact that the simultaneous use of numerical values of the relative change in the amplitudes of the signals from the transmitted and reflected radiation allows

- 2010121 to identify seven types of materials (existing methods allow the identification of two types of materials) and make an assessment of the thickness of objects on the human body.

When identifying, two quantitative characteristics of the change in the amplitudes of the signals are simultaneously used when the X-ray pencil beam is displaced from the human body to an object located on the surface of the human body:

the value of the relative change in the amplitude of the signal from the reflected (scattered back) x-ray radiation is a characteristic of the change in the chemical composition of the material from which the radiation is reflected;

the value of the relative change in the amplitude of the signal from the x-ray radiation transmitted through the object and the person is a characteristic of the change in the thickness of the media and the density of the material of the media through which the radiation passes.

The proposed method is illustrated by drawings, in FIG. 1 is a diagram of scanning a human body with a pencil x-ray beam and detecting reflected and transmitted radiation through a human, FIG. 2 - population zones of relative changes in the amplitudes of signals from transmitted and reflected radiation, depending on the type of irradiated materials and their thickness.

In FIG. 1 shows an x-ray source 1, a pencil x-ray beam 2, a reflected radiation detector 3, a detector of radiation transmitted through a person 4, a stylized image of the human body 5.

The proposed method is implemented as follows.

The human body 5 (Fig. 1), on which objects from different materials are placed, is scanned with a thin (pencil) X-ray beam 2. Two types of radiation are detected:

reflected - scattered back from the person;

the past is the direct, passing through a person without scattering, and the secondary, passing through a person with scattering.

To verify the feasibility of the proposed method for identifying materials, the calculations were performed for one of the possible detector options, the components of which are a scintillator and a photomultiplier (PMT) - are produced by domestic industry. An organic polystyrene scintillator was taken as a radiation detector. The light collection from each scintillator is carried out on the photocathode of a photoelectronic multiplier that generates an electrical signal proportional to the number of light photons formed in the scintillator under the action of x-ray radiation.

The transmitted radiation detector 4 is located behind the scanned person. The reflected radiation detector 3 is located in front of the scanned person from the side of the radiation source 1. Both detectors 3 and 4 can be either stationary or move in the vertical direction, following the vertical movement of the scanning beam.

In FIG. 1 shows a variant with a fixed radiation source 1, a mobile reflected radiation detector 3 and a stationary transmitted radiation detector 4. The reflected radiation detector 3 has a horizontal slit that allows the scanning beam to pass when it is horizontally moved. The vertical movement of the reflected radiation detector 3 is synchronized with the vertical movement of the scanning beam 2. The stationary reflected radiation detector 3 can be made of two vertical detecting strips separated by a gap sufficient for the free movement of the pencil beam 2 when scanning a person in the vertical and horizontal directions.

The passage of x-ray radiation through a substance was calculated using the Monte Carlo program ΟΕΆΝΤ. This program is used in all physical laboratories in the world to describe the passage of charged particles and gamma radiation through a substance.

The calculations were performed with the following initial parameters:

the cross section of the pencil beam at the surface of the human body is 1 cm ² , the scanning speed of the surface of the human body is 1 cm ² / ms, the distance from the person to the focus of the radiation source is 120 cm, the voltage on the x-ray tube is 30, 60, 100, 140 kV, current on an X-ray tube — 1 mA, the time of collecting the signal from the PMT — 1 ms, the scintillator thickness — 1 cm, the average energy loss of radiation due to the formation of one light photon in the scintillator — 100 eV, the light collection efficiency from the scintillator — 0.01, the quantum yield of the photomultiplier photomultiplier - 0.1, the gain of the PMT - 10 ⁶ , The global aperture of the collection of signals from transmitted and reflected radiation is 60 °.

The values of the effective radiation doses received by a person for 1 inspection, and the magnitude of the current signals taken from the PMT from transmitted and reflected radiation, are given in table. one.

- 3 010121

Considering that the dark (intrinsic background) current of modern PMTs is of the order of 1 nA, that at 140 kV the error of the current signal is minimal, and the radiation dose for 1 inspection of 0.1 μSv is comparable with the radiation doses in the best modern low-dose inspection installations, we can conclude that the voltage of 140 kV is most acceptable for human control by signals from transmitted and reflected radiation.

Table 1 Effective dose of human exposure for 1 inspection, current signals from transmitted (11) and reflected (12) radiation and their relative errors depending on the voltage on the x-ray tube

and (q) Dose (μSv) 77 (nA) σ (Ι1) / (Ι1) 72 (nA) a (12)! (12) thirty 0.01 0.02 > 100% 2.7 24% 60 0.03 3.1 23% 8.3 nine% one hundred 0.06 eighteen nine% nineteen nine% 140 0.10 42 6% 32 7%

Materials placed on the surface of the human body, according to the fraction of radiation reflected from them, decreasing with increasing effective charge of the material Ζ, are divided into two groups. In brackets for each group, the interval of variation of the effective charge of the materials of the group is indicated. Within each group, the materials are listed in increasing order of their effective charge. Drugs and explosives are in bold.

Organic materials (5.2 <Ζ <7.4): polyethylene, polystyrene, hash, cocaine, heroin, plexiglass, Mylar, TNT, tetryl, wood, melinite, hexogen, paper, TEN, ammonium nitrate, nitroglycerin.

Inorganic materials (Ζ> 10): glass, ceramics, aluminum, steel, gold, lead.

The effective charge of human soft tissue Ζ = 7.7 occupies an intermediate position between the effective charge of organic and inorganic materials.

The calculations were performed both for improvised explosives with a density of about 1 g / cm ³ and for industrial explosives with a density of 1.6-1.8 g / cm ³ .

Objects from different materials were placed on the surface of the human body from the side of radiation. The thickness of the objects in the calculations was: drugs, explosives, wood, paper, plastics - 1, 3, 5 cm, metals - 0.1, 0.3, 0.5 mm, glass, ceramics - 1, 3, 5 mm.

Intervals of variation of current signals from transmitted and reflected radiation when a pencil beam hits objects placed on the human body are given in table. 2 (signals from transmitted radiation) and tab. 3 (signals from reflected radiation).

table 2

Intervals of variation of current signals (11) from transmitted radiation when a pencil beam hits objects of different materials and different thicknesses kV 60 kV 100 kV 140 kV

Materials 77 (nA) 77 (nA) 77 (nA) 77 (nA)

Organic 0.001-0.019 0.75-2.78 6.0-17.1 15.4-39.6

Inorganic 0.000-0.017 0.01-3.00 1.0-17.8 2.3-41.4

Table 3

Intervals of variation of current signals (12) from reflected radiation when a pencil beam hits objects from different materials and different thicknesses

30 kV 60 kV 100 kV 140 kV Materials 72 (nA) 72 (nA) 72 (nA) 72 (nA) Organic 3.1-6.6 8.6-13.7 19.2-26.2 30.3-39.6 Inorganic 0.3-2.5 1.0-8.0 3.0-19.2 6.8-31.5

Of the presented in table. 2 and 3 of the data, two conclusions can be drawn:

by the magnitude of the signal from the transmitted radiation it is not possible to identify the type of material from which the object is placed on the human body;

by the magnitude of the signal from the reflected radiation, two types of materials can be identified: organic and inorganic.

- 4 010121

The use of the values of the relative change in the amplitudes of signals from transmitted and reflected radiation turned out to be more effective for identifying types of materials

ΔΙ / Ι0 = (Ι-Ι0) / Ι0,

Ι0 is the signal amplitude taken during scanning with a pencil beam of the human body;

Ι - the amplitude of the signal, taken when a pencil beam hits an object located on the human body.

In the two-dimensional graphs of FIG. 2, for voltages of 30, 60, 100, 140 kV, zones of population of relative changes in the amplitudes of signals from transmitted and reflected radiation are shown depending on the type and thickness of the material placed on the surface of the human body. The marks in FIG. 2 indicate: triangles - metals, glass, ceramics; small black dots - improvised explosives; black circles - industrial explosives; asterisks - drugs; white circles - plastics; white squares - wood, paper.

Distributions have a radial-angular orientation. Clockwise rotation effectively corresponds to an increase in the charge of the nuclei of the atoms that make up the material. The increase in radius at a given material density corresponds to an increase in the thickness of an object placed on a human body.

A solid line separates inorganic materials (to the left of the line) from organic (to the right of the line). Dotted lines highlight areas in which organic materials of a particular type are concentrated. At 30 and 60 kV, organic materials are grouped into two segments: in the central segment - explosives, wood, paper, in the right segment - drugs and plastics. At 100 and 140 kV, organic materials are grouped into three segments: the left segment is wood and paper, the central segment is homemade explosives, and the right segment is industrial explosives, drugs, and plastics.

At 100 and 140 kV, the population zones of relative changes in the signal amplitudes for inorganic materials reliably distinguish four types of materials: 1) glass, ceramics, 2) steel, 3) gold, 4) lead.

Thus, after scanning a person at a voltage of 140 kV, the operator can identify seven types of materials from which objects located on the human body are made from software values of relative changes in the amplitudes of signals from transmitted and reflected radiation: 1) glass, ceramics, 2) steel, 3) gold, 4) lead, 5) wood, paper, 6) improvised explosives, 7) industrial explosives, drugs, plastics. In addition to this, the operator has the opportunity to evaluate the thickness of these objects.

In the proposed method, as in the known one, the inspector on the computer monitor has two images: one from the past, the other from the reflected radiation. As in the known method, the eye inspector can make a conclusion about a suspicious object on the human body: the type of material of the object is organic, inorganic; the density of the material of the object is dense, loose; the thickness of the object (very approximately) is a thin layer or deep.

The main difference of the proposed method starts from the moment when the inspector, having visually noticed a suspicious object on the human body, marks a point on the image of the human body next to the suspicious object and on the suspicious object using the computer cursor.

Having received the inspector’s instructions, the computer (independent expert), using the software, calculates the relative changes in the amplitudes of the signals from the transmitted and reflected radiation at these points, identifies the material of this object and assigns it to one of the possible seven types, estimates the thickness of the object and all this information , both digitally and in the form of a flickering point on a two-dimensional graph - a stencil of relative changes in signal amplitudes, and displays the inspector information on the monitor, according to which torus already makes the final decision.

The identification of materials based on the methods that have been patented so far is of a qualitative nature - the operator uses a visual (subjective) assessment of the degree of brightness of images from reflected radiation and the degree of darkening of images from transmitted radiation that makes a conclusion about the material from which the object is made: organic or inorganic material.

The identification of materials by this method is quantitative, since the identification of materials and estimation of the thickness of objects placed on the human body are based on quantitative (objective) values of changes in the amplitudes of signals from transmitted and reflected radiations calculated by software.

The main advantages of this method of identification of materials in comparison with existing methods still include:

1) independent of the operator, calculated by software, estimates of the type of material and the thickness of the object placed on the human body;

2) the ability to identify seven types of materials from which objects are placed on the human body;

3) the ability to assess the thickness of an object placed on the human body;

4) a relatively low dose burden per person undergoing screening.

Claims (2)

CLAIM 1. Method of X-ray identification of materials from which objects placed on the human body are made, including scanning the human body with an X-ray pencil, recording amplitudes of signals from reflected and transmitted x-rays, archiving scan data, comparative analysis and identification with a visual assessment of the material of an object using X-ray image, characterized in that in the identification of materials, along with a visual assessment of the material of the object from the x-ray image Use a quantitative assessment of the material of the object and its thickness using an archived scan database, for which the relative changes in the amplitude of the signal from the reflected X-rays and the relative changes in the amplitudes of the signals from the X-rays passed through the suspicious object and the human body are calculated simultaneously , carry out a comparison of these values with pre-tabulated values of the relative changes of the amplitude q signals for different materials, identify the materials and evaluate the thickness of the item. 2. The method according to claim 1, characterized in that the calculation of the values of the relative changes in the amplitudes of the signals from the reflected and transmitted x-rays, comparing these values with the tabulated values of the relative changes in the amplitudes of the signals for different materials, identifying the material and estimating the thickness of the object placed on the human body , carried out on a given program using a computer.