Liquid crystal x-ray detector comprising heterogeneous photoconductive unit, and x-ray detection method using same

Abstract

The present invention relates to a liquid crystal X-ray detector comprising a heterogeneous photoconductive unit, and an X-ray detection method using same. Disclosed is an X-ray sensing liquid crystal coupling unit comprising: a heterogeneous photoconductive unit including a heterogeneous photoconductive layer having a first electrode layer formed on one surface thereof; and a guest-host liquid crystal unit including a first substrate, a second substrate and a liquid crystal layer injected between both substrates, wherein the first substrate is coupled to be in contact with the other surface of the heterogeneous photoconductive layer. The liquid crystal X-ray detector comprising a heterogeneous photoconductive unit, and the X-ray detection method using same, according to the present invention, can reduce noise caused by a change in response characteristics of liquid crystal according to the charge density induced in the heterogeneous photoconductive layer.

Description

Liquid crystal X-ray detector including heterogeneous photoconductive element and X-ray detection method using the same

[0001] The present invention relates to a liquid crystal X-ray detector including a heterogeneous photoconductive part and an X-ray detection method using the same, and more specifically, to a liquid crystal X-ray detector including a heterogeneous photoconductive part that recognizes a charge density induced by a heterogeneous photoconductive part using a liquid crystal having a guest-host effect and an X-ray detection method using the same.

[0002] X-rays are highly penetrative, allowing them to image the interior of objects. Therefore, they are widely used in medical and non-destructive testing. The amount of X-ray penetration varies depending on the density of the object's interior, and by measuring this difference in penetration, the interior of the object can be imaged.

[0003] There are two methods for obtaining X-ray images: conventional film and DR (Digital Radiography). DR is currently the most widely adopted method.

[0004] DR methods include the direct type, which places a photoconductive layer on a TFT (Thin Film Transistor) substrate, and the indirect type, which places a sinterator. The direct type determines an image by determining the charge density generated when X-rays are incident on the photoconductive layer, while the indirect type determines an image by determining the photon density generated when X-rays are incident on the sinterator.

[0005] [Prior Art Literature]

[0006] [Patent Document]

[0007] 1. International Patent Publication No. W2012034229A1 (2012-03-22)

[0008] 2. Korean Patent Publication No. 2020-0099879 (August 25, 2020)

[0009]

[0010] The purpose of the present invention is to propose a liquid crystal X-ray detector including a heterogeneous photoconductor that recognizes a charge density induced in a heterogeneous photoconductor by X-ray irradiation using a liquid crystal layer having a guest-host effect, and an X-ray detection method using the same.

[0011]

[0012] The above object of the present invention can be achieved by an X-ray detection liquid crystal combination comprising a heterogeneous photoconductive part including a heterogeneous photoconductive layer having a first electrode layer formed on one surface, and a guest host liquid crystal part including a first substrate, a second substrate, and a guest host liquid crystal layer injected between the two substrates, wherein the first substrate is joined so as to be in contact with the other surface of the heterogeneous photoconductive layer.

[0013] It is preferable that the guest host liquid crystal display further include a transparent electrode layer on the second substrate.

[0014] Another object of the present invention is to provide a method for detecting X-rays by irradiating X-rays to a subject using the X-ray detection liquid crystal coupling unit described above, the method comprising: a first step of obtaining a liquid crystal image of all pixels using light incident on a lead beam irradiated on the guest host liquid crystal layer while applying a separation voltage (Vs) for separating electrons and holes formed in a heterogeneous photoconductive layer between the first electrode layer and the transparent electrode layer without positioning the subject and without irradiating X-rays, and a first step of obtaining a reference light intensity graph indicating the light intensity of the liquid crystal according to the bias voltage by performing a first step of repeatedly obtaining liquid crystal images of all pixels in the same manner as the first step while gradually increasing the bias voltage until the bias voltage (Vb) reaches 80% of the separation voltage (Vs), thereby performing the first step.

[0015]

[0016] Since the heterogeneous photoconductive layer scatters light, the conventionally known liquid crystal X-ray detector using a photoconductive layer formed of selenium cannot be applied. In contrast, the liquid crystal X-ray detector including the heterogeneous photoconductive part according to the present invention and the X-ray detection method using the same enable determination of an X-ray image even if the lead beam is scattered by the heterogeneous photoconductor and the light passing through the liquid crystal layer becomes unpolarized (in other words, it can be described as 'even if it is not polarized').

[0017] The liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention and the X-ray detection method using the same can reduce noise caused by changes in the response characteristics of the liquid crystal depending on the charge density induced in the heterogeneous photoconductive layer. That is, the liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention has a high SNR (Signal to Noise Ratio), and thus can reduce the X-ray irradiation dose.

[0018] A photoconductive layer composed of heterogeneous materials traps defect-state charges between the band gaps, which causes noise. The X-ray measurement value varies depending on the trapped charges (also called 'trapped charges'). However, the X-ray detection method using a liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention can eliminate the trapped charges, thereby enabling more accurate X-ray measurements.

[0019] The liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention and the X-ray detection method using the same provide a measurement method that minimizes the response characteristics of the liquid crystal and the change in charge density in the photoconductive layer.

[0020] In addition, by specifying the FWC (Full Well Capacity) of a camera constituting a liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention, the amount of light of the lead beam can be increased, thereby minimizing lead beam noise.

[0021]

[0022] Figure 1 is an optical system of a liquid crystal X-ray detector including a heterogeneous photoconductive part according to the present invention.

[0023] Figure 2 is a configuration diagram of an X-ray detection liquid crystal coupling unit constituting a liquid crystal X-ray detector according to the present invention.

[0024] Figure 3 is a configuration diagram of a heterogeneous photoconductive section.

[0025] Figure 4 is a diagram explaining the operation of the guest host liquid crystal display unit.

[0026] Figure 5 shows a voltage waveform and a camera synchronization signal applied to measure a reference light intensity graph of an X-ray detection liquid crystal combination according to the present invention.

[0027] Figure 6 is an example of a reference light quantity graph.

[0028] Figure 7 shows a voltage waveform and a camera synchronization signal for measuring a liquid crystal image of an X-ray detection liquid crystal combination according to the present invention.

[0029] Figure 8 is an explanatory diagram for explaining the process of finding a voltage value from the light quantity of a liquid crystal image using a reference light quantity graph.

[0030] Figure 9 is a flow chart for measuring an X-ray image in a liquid crystal X-ray measuring device according to the present invention.

[0031] Figure 10 is a transmission spectrum of PIB HgI2.

[0032] Fig. 11 is a palm liquid crystal image measured using a liquid crystal X-ray detector manufactured as an embodiment of the present invention.

[0033] Figure 12 is an image of the liquid crystal image of Figure 11 converted into a voltage image.

[0034] Figure 13 is a gain-calibrated image of the image of Figure 12.

[0035]

[0036] The terminology used in the present invention is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0037] Additionally, in this specification, "on or above" means located above or below the target portion, and does not necessarily mean located on the upper side with respect to the direction of gravity. Furthermore, when a portion such as an area, plate, etc. is said to be "on or above" another portion, this includes not only cases where it is in contact with or spaced apart from the other portion "directly on or above" the other portion, but also cases where there is another portion in between.

[0038] Additionally, in this specification, when a component is referred to as being “connected” or “connected” to another component, it should be understood that the component may be directly connected or connected to the other component, but may also be connected or connected via another component in between, unless there is a specific description to the contrary.

[0039] Additionally, in this specification, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

[0040] Hereinafter, in order to enable those skilled in the art to easily practice the present invention, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0041]

[0042] Figure 1 is an optical system of a liquid crystal X-ray detector including a heterogeneous photoconductive portion according to the present invention. The liquid crystal X-ray detector according to the present invention is a device for obtaining an X-ray image of a subject (100), and is composed of an X-ray output portion (10), an X-ray detection liquid crystal coupling portion (50), a lead beam output portion (15a, 15b), a detector (61), an imaging portion (60), a control portion (70), and an operation portion (80). The detector (61) is installed so as to have a polarization axis that matches the rubbing direction of an alignment film formed on the liquid crystal portion.

[0043] The X-ray output unit (50) is a device that generates X-rays and emits them to the outside. The X-rays output from this unit pass through the subject (100) and are then input to the imaging unit (60) through the inspection plate (61) by utilizing the phenomenon that the absorption rate of the lead beam changes depending on the position in the X-ray detection liquid crystal coupling unit (100).

[0044] The X-ray detection liquid crystal combination (100) is composed of a combination of a heterogeneous photoconductive portion (20) and a liquid crystal portion (30).

[0045] The lead beam output unit (15a, 15b) is a device that irradiates a lead beam to the guest host liquid crystal display unit (30), and can be configured with, for example, an LED element that outputs light in the visible light wavelength range.

[0046] The imaging unit (60) is a device that captures an image of a subject by detecting a lead beam reflected by the liquid crystal unit (30) and analyzing its characteristics. The imaging unit (85) may be configured as, for example, a CCD camera or a CMOS camera.

[0047] The control unit (70) is a logic unit that generates an operation timing signal for controlling the X-ray output unit (10), the lead beam output unit (15a, 15b), and the imaging unit (60), and controls the application timing of the separation voltage, bias voltage, and measurement voltage for measuring the liquid crystal image.

[0048] The operation unit (80) is a logic unit that has a memory inside and stores a separation voltage, a bias voltage, and a measurement voltage, and calculates a systemless zero-ray voltage image, an inorganic X-ray voltage image, an object zero-ray voltage image, and an object X-ray voltage image from the measured reference light quantity graph, the inorganic zero-ray liquid crystal image, the inorganic X-ray liquid crystal image, the object zero-ray liquid crystal image, and the object X-ray liquid crystal image described later, and calculates an X-ray operation of the subject using the four voltage images. It goes without saying that the control unit (70) and the operation unit (80) can be implemented as a single integrated semiconductor chip without being configured separately.

[0049]

[0050] Hereinafter, the operating principle of the liquid crystal X-ray detector according to the present invention will be briefly described. X-rays irradiated from the X-ray output unit (50) pass through the subject (100) and then are irradiated to the heterogeneous photoconductive unit (20). As they pass through the subject (100), the amount of X-ray light penetrating therethrough varies depending on the density of the material constituting the subject (100). The transmitted X-rays reach the heterogeneous photoconductive unit (20) and generate electrons and holes, and the voltage applied to the guest host liquid crystal layer is formed differently for each cell by the generated electrons and holes. The lead beam incident on the liquid crystal unit (30) is reflected at the boundary with the heterogeneous photoconductive unit (20), passes through the liquid crystal unit (30) again, and is then input to the imaging unit (61) to acquire an image. The lead beam is reflected at the boundary with the heterogeneous photoconductive portion (20) and then passes through the guest host liquid crystal portion (30) again, and the absorption rate changes according to the potential difference formed differently for each cell by the subject (100), so that an image of the subject (100) can be obtained.

[0051]

[0052] FIG. 2 is a configuration diagram of an X-ray detection liquid crystal coupling unit constituting a liquid crystal X-ray detector according to the present invention, and FIG. 3 is a configuration diagram of a heterogeneous photoconductive unit. The X-ray detection liquid crystal coupling unit (50) is composed of a heterogeneous photoconductive unit (17) composed of a first electrode layer (21) and a heterogeneous photoconductive layer (23), and a liquid crystal unit (30) composed of a UTG (31, an ultra-thin glass substrate, also referred to as a 'first substrate'), a liquid crystal layer (35), a transparent electrode layer (37), and a second substrate (33). On the opposing surfaces of the ultra-thin glass substrate (31) and the transparent electrode layer (37), alignment films (32, 34) processed in opposite directions are formed, and a liquid crystal driving voltage is applied between the first electrode layer (21) and the transparent electrode layer (37).

[0053] Generally, UTG (Ultra Thin Glass) refers to ultra-thin tempered glass, and refers to glass that is very thin, with a thickness of approximately 30 to 100 μm (micrometers), so that it can be flexibly folded and has the characteristics of glass material that is resistant to scratches. In the present invention, if it refers to glass with a thickness of 100 μm or less, it does not need to be tempered. Generally, UTG is called ultra-thin tempered glass, but in the present invention, since it does not need to be tempered, it will be called an ultra-thin glass substrate.

[0054] The second substrate (33) can be used regardless of the transparent material. For example, it can be used as a synthetic resin film such as PI film or PET film, and of course, an organic substrate can be used.

[0055] As illustrated in FIGS. 2 and 3, the heterogeneous photoconductive portion (20) is composed of a first electrode layer (21) and a heterogeneous photoconductive layer (23). The photoconductive layer (23) may have a structure in which photoconductive particles (23a) and a binder (23b) are mixed, i.e., a PIB (Particle-In-Binder) structure. The photoconductive particles (23a) serve to impart photoconductive properties, i.e., photoelectric conversion properties, to the photoconductive layer (PL1), and the binder (23b) may serve to impart adhesive strength by being mixed with the photoconductive particles (23a). The binder (23b) may facilitate the formation process of the photoconductive layer (23a). A photoconductive layer (23) can be formed by applying a paste containing photoconductive powder, a binder material, a solvent, etc. and heat-treating (drying). The thickness of the photoconductive layer (23) can be about 100 to 250 ㎛, for example, about 120 to 180 ㎛.

[0056] The photoconductive particle (23a) may include, for example, at least one of HgI2, PbI2, PbO, TlBr, CdTe, CdZnTe, CdS, BiI3, and mixtures thereof. These materials have large atomic weights and densities, so they can absorb radiation (X-rays, gamma rays, etc.) well even with a thin thickness, and since the ionization energy by the radiation is small, they can exhibit excellent photoconductive characteristics. In particular, HgI2 may have excellent photoconductive characteristics. However, the specific material of the photoconductive particle (23a) disclosed herein is exemplary, and other photoconductive materials may be used. The photoconductive particle (23a) may have a spherical or nearly spherical shape. The shape of the photoconductive particle (23a) may affect the characteristics (sensitivity, etc.) of the heterogeneous photoconductive layer (23). When the photoconductive particles (23a) have a spherical or nearly spherical shape, the characteristics (sensitivity, etc.) of the heterogeneous photoconductive layer (23) can be improved. The size of the photoconductive particles (23a) is also distributed in a variety of particle sizes, ranging from several microns to tens of microns.

[0057] The binder (23b) is mixed with the photoconductive particles (P10) to provide adhesiveness. The binder (23b) may include an organic polymer material. For example, the binder (23b) may include at least one of a polyvinyl butyral-based material, an acrylic-based material, a polyester-based material, a phenoxy-based material, a polyvinyl formal-based material, a polyamide-based material, a polystyrene-based material, a polycarbonate-based material, a polyvinyl acetate-based material, a polyurethane-based material, an epoxy-based material, and a mixture thereof. The content ratio of the binder (B10) to the mixture of the photoconductive particles (23a) and the binder (23b) may be about 2.5 to 12 wt%. In other words, [{binder / (photoconductive particles + binder)} × 100] may be about 2.5 to 12 wt%. Since the photoconductive layer (23) can be formed through a low-temperature (about 150°C or less) heat treatment (drying) process from the paste, the binder (B10) can be maintained without being removed by the heat treatment. The type and content of the binder (B10) may affect the characteristics (sensitivity, etc.) of the photoconductive layer (PL1).

[0058] The heterogeneous photoconductive layer (23) has a rough surface, so when polarized light is irradiated on the surface, it is scattered and becomes unpolarized. When passing through the inside of the heterogeneous photoconductive layer (23), it is also diffusely reflected by the photoconductive particles and becomes unpolarized. Therefore, a mode that utilizes a change in the polarization state cannot be used in the heterogeneous photoconductive layer. In the case of the PDLC (Polymer Dispersed LC) or PNLC (Polymer Network LC) liquid crystal mode, the proportion of polymer additives that form a network or dopant is high, and the liquid crystal is contaminated during the UV irradiation process, so the voltage holding ratio (VHR) of the liquid crystal is low, and there is a problem that screen information disappears during charge collection and measurement, so it is not suitable for use in combination with the heterogeneous photoconductive layer (23).

[0059] Since the photoconductive particles (23a) have the property of corroding metal, the first electrode layer (21) cannot be formed of metal. In the present invention, the first electrode layer (21) is formed of carbon.

[0060]

[0061] Figure 4 is a diagram illustrating the operation of a guest host liquid crystal unit. The liquid crystal unit applicable to the present invention can utilize a liquid crystal layer that operates in various modes. Preferably, the liquid crystal layer can be implemented as a liquid crystal layer having a gate host effect. Hereinafter, the present invention will be described with reference to a liquid crystal unit having a liquid crystal layer that operates in guest host mode. In addition, in the description of the present invention, the liquid crystal layer that operates in guest host mode is referred to as a "guest host liquid crystal layer," and the liquid crystal unit having the guest host liquid crystal layer is referred to as a "guest host liquid crystal unit."

[0062] As illustrated in Fig. 2, a guest host liquid crystal mixed with a liquid crystal and a dye is injected between a thin glass substrate (31) and a second substrate (33). A transparent electrode layer (37) is applied to the opposite surface of the second substrate (33) facing the thin glass substrate (31), and alignment films (32, 34) are rubbed in parallel but opposite directions on the opposite surfaces of the thin glass substrate (31) and the transparent electrode layer (37) so that the liquid crystals are aligned in parallel.

[0063] Guest-host liquid crystals are liquid crystals with a dye mixed between the liquid crystals, and they exhibit anisotropic light absorption (guest-host effect) in a dichroic liquid crystal layer containing dissolved dye. Guest-host liquid crystals are representative absorptive liquid crystals. The dichroic dye is mixed in an amount of less than 5% (preferably 2-4%) relative to the weight of the liquid crystal, and is a substance whose light absorption rate varies depending on the polarization direction. If the light absorption rate for long-axis polarized light is high, it is called p-type dye, and if the light absorption rate for short-axis polarized light is high, it is called n-type dye. Nematic liquid crystals mixed with p-type dye are injected into a parallel-aligned liquid crystal cell, and the upper and lower plates are rubbed in opposite directions so that the alignment direction is parallel to the transmission direction. When no voltage is applied, the long axis of the dye is the same as the vibration direction of light, so light is absorbed. When a voltage is applied to the liquid crystal layer, the liquid crystal and dye are aligned perpendicularly, and the light vibrates in the short-axis direction of the dye, so absorption is low and transmission occurs.

[0064] When a detector (61) having a polarization axis that matches the rubbing direction of an alignment film formed on a guest host liquid crystal portion is installed, when a voltage lower than the threshold is applied to the guest host liquid crystal layer, light is absorbed by a dichroic dye in the liquid crystal layer, and when a voltage higher than the threshold is applied, light that passes through the detector is formed.

[0065] The transparent electrode layer (37) can be formed of any one selected from among ITO (Indium Tin Oxide), graphene, silver nanowire, carbon nanotube, metal mesh, and zinc oxide (ZnO).

[0066]

[0067] Hereinafter, a process for manufacturing an X-ray detection liquid crystal combination constituting a liquid crystal X-ray detector according to the present invention will be briefly described. An alignment film and a spacer, etc. are formed on a glass substrate (second substrate) having a thickness of about 0.7 mm on which ITO is deposited and an ultra-thin glass substrate (Ultra Thin Glass) having a thickness of 0.05 mm, and a nematic liquid crystal doped with a dichroic dye is injected between the two glass substrates to form a guest host liquid crystal portion. A PVB (Polyvinyl Butyral) binder is mixed with HgI2 or PbI2 and dissolved in a BC (Butyl Cellosolve) solvent to make a paste, which is then coated on an ultra-thin glass substrate using a screen printer or a coating machine to have a thickness of about 0.2 to 0.4 mm to form a heterogeneous photoconductive layer.

[0068] A nanocarbon electrode (first electrode layer) is coated on top of the heterogeneous photoconductive layer. Instead of the nanocarbon electrode, a perylene may be coated on the heterogeneous photoconductive layer and then an electrode layer may be formed with platinum (Au).

[0069]

[0070] In the case of a heterogeneous photoconductor mixed with HgI2 or PbI2 and a binder, the resistivity is 10 11 ∼10 12 Since it is Ωcm, the separated charge from the photoconductor disappears within several hundred milliseconds. The difference in the response time of the liquid crystal is also a problem. The smaller the difference between the initial and final voltage applied to the guest host liquid crystal layer, the longer the response. The time for applying the separation voltage and the time for applying the measurement voltage must be shortened, but in this case, the response characteristic becomes an issue, so the reference light intensity graph must be measured in a form that includes the response characteristic.

[0071]

[0072] FIG. 5 is a voltage waveform and a camera synchronization signal applied to measure a reference light intensity graph of an X-ray detection liquid crystal combination according to the present invention. As shown in FIG. 5(a), a separation voltage (Vs) is constantly applied to the first electrode layer and the transparent electrode layer in a state where X-rays are not irradiated, and then a bias voltage (Vb) is applied, and the light intensity with respect to the bias voltage of all pixels by the lead beam is measured. Thereafter, the same operation is repeated while increasing the bias voltage (Vb) step by step until it reaches n% of the separation voltage (Vs), thereby obtaining a reference light intensity graph. The bias voltage (Vb) may be applied below the separation voltage (Vs), and the inventor of the present invention obtained a reference light intensity graph while increasing the bias voltage (Vb) step by step until it reaches 80% (n=80) of the separation voltage (Vs). The camera is synchronized to the bias voltage (Vb), and the lead beam is synchronized to the camera signal. The brightness of the light source can be controlled by the opening time of the camera shutter.

[0073] Figure 6 is an example of a reference light quantity graph, and it can be seen that the light quantity increases as the bias voltage applied to the guest host liquid crystal layer increases.

[0074]

[0075] Fig. 7 shows a voltage waveform and a camera synchronization signal for measuring a liquid crystal image of an X-ray detection liquid crystal combination according to the present invention. Fig. 7(a) shows a voltage waveform applied to measure a liquid crystal image, and Fig. 7(b) shows a camera synchronization signal.

[0076] After X-rays are irradiated, a separation voltage (Vs) is applied to separate electrons and holes in the first electrode layer and the transparent electrode layer, and when the electrons and holes excited by the X-rays are attracted in opposite directions and the distribution becomes stable, a measurement voltage (Vm) formed as a voltage higher than the threshold is applied to all pixels of the guest host liquid crystal, and then the light quantity of each pixel is measured. Since the separation voltage is applied at approximately 1 V per 1 μm of the thickness of the heterogeneous photoconductor, if the heterogeneous photoconductor is formed to have a thickness of 200 μm, approximately 200 V must be applied to the heterogeneous photoconductor layer and the guest host liquid crystal layer. A DC voltage of approximately 5 V is applied to the guest host liquid crystal layer having a thickness of 5 μm, so that the vertical alignment component of the liquid crystal increases. Then, a measurement voltage (Vm) is applied, and after a certain period of time (200 to 300 ms), the liquid crystal image is measured when the liquid crystal layer is stabilized.

[0077]

[0078] When the bias voltage of the reference light quantity graph having the same light quantity as the light quantity of the measured pixel after applying the measurement voltage (Vm) in the liquid crystal image is V(r), the charge density (ρ) excited by the X-ray has a proportional relationship as in Equation 1.

[0079]

[0080]

[0081] In Equation 1, C(LC) is the capacitance of the guest host liquid crystal layer.

[0082]

[0083] After irradiating the X-ray and applying the measurement voltage, if the light quantity of the measured pixel is determined, the charge quantity due to the X-ray can be determined using Equation 1 from the reference light quantity graph.

[0084] When a separation voltage (Vs) is applied to the guest host liquid crystal layer and X-rays are irradiated, electrons and holes generated in the heterogeneous photoconductive layer move in opposite directions, with holes accumulating on the ultra-thin glass substrate and electrons moving to the carbon electrode (first electrode). The principle of the liquid crystal X-ray detector according to the present invention is that the voltage applied to the liquid crystal layer changes due to the holes, and this is imaged with a camera to measure the amount of charge.

[0085] By controlling the polarity of the separation voltage, holes and electrons can be selected. According to the inventor's experiments, the amount of extracted charge was similar, but the hole trap charge was eliminated faster and the resolution was also better.

[0086] In addition, the measurement voltage (Vm) was applied so that a voltage slightly higher than the threshold of the liquid crystal layer was applied so that the brightness of the reference light quantity graph and the pixel brightness of the liquid crystal image were equivalent to 1:1.

[0087]

[0088] Below, the process of quantifying an image measured by a liquid crystal X-ray detector according to the present invention will be described.

[0089] To quantify the image of the liquid crystal X-ray detector according to the present invention, a reference intensity graph of all pixels and four types of liquid crystal images are required. (1) a bodyless X-ray liquid crystal image obtained by irradiating X-rays without a subject, (2) an object X-ray liquid crystal image obtained by irradiating X-rays after positioning a subject, (3) a bodyless zero-ray liquid crystal image obtained without irradiating X-rays without a subject, and (4) an object zero-ray liquid crystal image taken while positioning a subject and without irradiating X-rays.

[0090]

[0091] Using a reference light intensity graph, the light intensity of four types of liquid crystal images is converted into corresponding voltages using interpolation. Figure 8 is an explanatory diagram illustrating the process of finding voltage values ​​from the light intensity of a liquid crystal image using a reference light intensity graph.

[0092] If the light quantity of a pixel measured by irradiating an X-ray and applying a separation voltage (Vs) and a measurement voltage (Vm) is T, and the light quantity T is between T(n) and T(n+1), which are the light quantities between the bias voltages V(n) and V(n+1) of the reference light quantity graph, the voltage value V(T) corresponding to the light quantity T is as shown in Equation 2.

[0093]

[0094]

[0095] Using Equation 2, four types of liquid crystal images can be converted into corresponding voltage images. For example, 'non-body X-ray liquid crystal image' is converted into 'non-body X-ray liquid crystal voltage ( V (z,x,r) )', 'object X-ray liquid crystal image' is converted into 'object X-ray voltage image ( V (z,x,x) )', 'bodyless zero-line liquid crystal image' is converted into 'bodyless zero-line voltage image ( V (z,r) )', and 'object zero-line liquid crystal image' is converted into 'object zero-line voltage image ( V (z,s) )'.

[0096] Heterogeneous photoconductors used in liquid crystal X-ray detectors must be calibrated to compensate for the signal distortion caused by the trapped charge in empty states between some band gaps. To improve measurement precision, the reference irradiance graph must be determined in a state where no internal charge has accumulated.

[0097] The ratio of voltage values ​​according to X-rays depending on the presence or absence of a subject in a state where trapped charges have been removed can be obtained from Equation 3.

[0098]

[0099]

[0100] Figure 9 is a flow chart of measuring an X-ray image in a liquid crystal X-ray measuring device according to the present invention. When started, a reference light intensity graph is measured (ST910). The light intensity of each pixel for each bias voltage is obtained from the reference light intensity graph. Next, a bodyless liquid crystal image (ST920) measured without applying X-rays and without a subject is acquired, and a bodyless X-ray liquid crystal image (ST930) measured with applying X-rays and without a subject is acquired.

[0101] Next, an object zero-line liquid crystal image (ST940) is acquired by positioning the subject and measuring without applying X-rays, and an object X-ray liquid crystal image (ST950) is acquired by positioning the subject and measuring with X-rays applied. The four acquired liquid crystal images are converted into voltage images according to Equation 2 (ST960). After converting into a voltage image, a voltage ratio according to the presence or absence of X-ray irradiation by the subject in a state where noise is removed by trapped charges is acquired using Equation 3 (ST970).

[0102] If there is a new subject to measure X-rays (ST980), repeat steps ST940 to ST970, and when there are no more subjects to measure, the measurement is completed.

[0103]

[0104] Example

[0105] An alignment film was coated on a 0.7 mm glass substrate coated with ITO and a 50 ㎛ thick UTG (NEG, Japan), and a mixture containing TN-1239 liquid crystal and 3% AC4 (NEMATEL, Germany) anisotropic dye (dichroic dye) relative to the weight of the liquid crystal was injected.

[0106] The liquid crystal cells were oriented in parallel and opposite directions, and the transmission axis of the analyzer was aligned with the rubbing direction. On the opposite side of the UTG where the liquid crystal cells were formed, HgI2, PVB (Polyvinyl Butyral), and BC (Butyl Celesolv) were mixed in a weight ratio of 80:7.5:21.5, respectively, and ground with a 3R-Mill to a particle size of approximately 10㎛. After coating with a coating machine to a thickness of approximately 150㎛ as a HgI2 heterogeneous photoconductive layer, it was dried at 65℃ for 72 hours to volatilize BC.

[0107] A carbon electrode layer was formed by mixing carbon, PVB as a binder, and BC in a weight ratio of 3:1:6 on a heterogeneous photoconductive layer.

[0108]

[0109] Figure 10 is a transmission spectrum of PIB HgI2. The band gap of HgI2 is approximately 2.13 eV, and the corresponding wavelength is approximately 580 nm. Since the read beam must have a wavelength larger than the band gap when absorbed by the photoconductive layer composed of HgI2, which causes trap charges, and the read beam must be well absorbed by the dichroic dye, so an LED with a dominant wavelength of 660 nm was used as the read beam light source. The light from the LED passes through the guest host liquid crystal layer, passes through the ultra-thin glass substrate, is diffusely reflected by the PIB HgI2 film, passes through the guest host liquid crystal layer again, is selectively transmitted by the detector, and is incident on the camera.

[0110]

[0111] Camera Selection

[0112] In the X-ray liquid crystal detector according to the present invention, when the X-ray irradiation amount is low, read (or electron) noise is generated, and when the irradiation amount is high, shot noise and fixed pattern noise are generated. Read noise is noise generated in the process of collecting and moving electrons and converting them into a digital signal voltage in an ADC (Analogy Digital Converter), and is noise generated from interaction with surrounding electrodes and external electromagnetic waves and DC power sources.

[0113] Shot noise is a fundamental noise arising from instability in the photon distribution of an X-ray source. It is proportional to the square root of the X-ray dose and cannot be overcome. Fixed-pattern noise is an example of noise resulting from differences in the characteristics of each ADC block when there are multiple ADC blocks. The absolute amount of noise can be expressed as shown in Equation 4.

[0114]

[0115] Liquid crystal X-ray detectors can dramatically reduce read noise by increasing the intensity of light passing through the liquid crystal layer. The brightness of the light source is determined by the camera's Full Well Capacity (FWC).

[0116] Table 1 shows the camera's key specifications. Assuming the LCD image's dynamic range is FWC 20ke to 60ke, camera read noise, including dark noise of 22.9e, can be calculated using Equation 5.

[0117] Item SpecificationManufacture(Model)FLIR(BFS-U3-17S7M-C)Resolution1,600x1,100Sensor(CMOS)Sony IMX425Pixel Size9㎛Full Well Capacity(Saturation)98,654e-Dark Noise22.99e-

[0118]

[0119]

[0120] In this optical system, the read noise of the liquid crystal is 0.41 to 0.71% of the signal. The image noise corresponding to FWC is the shot noise (20,000) from Equations 4 and 5. 0.5 )e If the dark noise is 23, the total lead noise is 141.5 according to formula 1, and since the signal is 20,000e, the lead noise compared to the signal is 0.7%.

[0121] With the same image sensor specifications, if the FWC is 500ke and the dynamic range of the liquid crystal image is set to 100ke~400ke, the read noise can be limited to 0.32% of the signal.

[0122] Since the SNR of medical X-ray detectors is usually over 100, the camera used in the liquid crystal X-ray detector must have a FWC of at least 100 Ke.

[0123]

[0124] Fig. 11 is a palm liquid crystal image measured using a liquid crystal X-ray detector manufactured as an embodiment of the present invention. Fig. 11(a) is a zero-line liquid crystal image of an object, Fig. 11(b) is a zero-line liquid crystal image of an object, Fig. 11(c) is a zero-line liquid crystal image of an object, and Fig. 11(d) is a X-ray liquid crystal image of an object.

[0125] Fig. 12 is an image converted from the liquid crystal image of Fig. 11 into a voltage image. Fig. 12(a) is an inorganic zero-line voltage image, Fig. 12(b) is an inorganic X-ray voltage image, Fig. 12(c) is an object zero-line voltage image, and Fig. 12(d) is an object X-ray voltage image.

[0126] Figure 13 is an image with gain calibration performed and contrast inverted. Compared to the voltage image, Figure 13 shows that much of the noise has been reduced.

[0127]

[0128] The size of the liquid crystal X-ray detector according to the present invention is determined according to the size of the liquid crystal panel, and since liquid crystal panels are commercialized up to large screens, a large screen liquid crystal X-ray detector can be easily commercialized.

[0129]

[0130] Although the present invention has been described with reference to the drawings exemplified above, it is to be understood that the present invention is not limited to the embodiments and drawings disclosed in this specification, and that various modifications may be made by those skilled in the art within the scope of the technical idea of ​​the present invention. Furthermore, even if the operational effects according to the configuration of the present invention have not been explicitly described while describing the embodiments of the present invention, it is natural that the effects predictable by the corresponding configuration should also be acknowledged.

[0131] [Explanation of symbols]

[0132] 10: X-ray output section

[0133] 20: Heterogeneous photoconductor

[0134] 21: First electrode layer

[0135] 23: Heterogeneous photoconductive layer

[0136] 23a: Photoconductive particles

[0137] 23b: Binder

[0138] 30: Guest Host LCD

[0139] 31: UTG (Ultra Thin Glass), ultra-thin glass substrate, first substrate

[0140] 32: First alignment film

[0141] 33: Second substrate

[0142] 34: Second alignment film

[0143] 35: Guest host liquid crystal layer

[0144] 37: Transparent conductive layer

[0145] 50: X-ray detection liquid crystal joint

[0146] 15a, 15b: Lead beam output section

[0147] 60: Camera unit

[0148] 61: The sword board

[0149] 70: Control unit

[0150] 80: Operation section

[0151] 100: Subject

Claims

1. A heterogeneous photoconductive part including a heterogeneous photoconductive layer having a first electrode layer formed on one side thereof, and A liquid crystal part including a first substrate, a second substrate, and a liquid crystal layer injected between the two substrates - The first substrate is bonded so as to be in contact with the other surface of the heterogeneous photoconductive layer - An X-ray detection liquid crystal combination comprising:

2. In paragraph 1, An X-ray detection liquid crystal bonding unit characterized in that the first substrate is made of glass having a thickness of 100 μm or less.

3. In paragraph 1, An X-ray sensing liquid crystal combination, characterized in that the above heterogeneous photoconductive layer is formed by combining a photoconductive particle composed of at least one of HgI2, PbI2, PbO, TlBr, CdTe, CdZnTe, CdS, BiI3 and a mixture thereof with a binder.

4. In paragraph 1, The above first electrode layer is an electrode layer formed of carbon, An X-ray detection liquid crystal combination unit characterized in that a transparent electrode layer is provided on a surface of the second plate facing the first substrate.

5. In paragraph 1, The above liquid crystal layer is composed of a guest host liquid crystal layer in which liquid crystal and dye are mixed, An X-ray detection liquid crystal combination unit characterized in that the first substrate and the second substrate are provided with alignment films that are rubbed with opposite orientation directions.

6. An X-ray detection liquid crystal coupling unit selected from any one of the first to fifth clauses, and An X-ray output unit arranged in front of the above-mentioned heterogeneous photoconductor and irradiating X-rays to the above-mentioned heterogeneous photoconductor, A lead beam positioned at the rear end of the liquid crystal section and irradiating visible light wavelengths to the liquid crystal section; and An imaging unit positioned at the rear end of the liquid crystal unit to capture light scattered from the heterogeneous photoconductive layer. A liquid crystal X-ray detector characterized by including a .

7. In paragraph 6, The detector plate placed in front of the above-mentioned imaging unit - The above-mentioned optical plate is arranged so that the polarization axis is parallel to the light transmitted by the alignment direction of the liquid crystal. A liquid crystal X-ray detector characterized by further comprising:

8. In paragraph 6, A liquid crystal X-ray detector characterized in that the full well capacity (FWC) of the above imaging unit is 10ke or more.

9. A method of detecting X-rays by irradiating an X-ray to a subject using the X-ray detection liquid crystal coupling unit of Article 4, Step 1-1 of obtaining a liquid crystal image of all pixels by using light incident by a lead beam irradiated on the liquid crystal layer while applying a separation voltage (Vs) for separating electrons and holes formed in a heterogeneous photoconductive layer between the first electrode layer and the transparent electrode layer and a bias voltage (Vb) applied sequentially to the separation voltage (Vs) without positioning the subject and without irradiating the X-rays; and An X-ray detection method characterized by comprising a first step of obtaining a reference light quantity graph indicating the light quantity of the liquid crystal according to the bias voltage by performing steps 1 and 2 of repeatedly obtaining liquid crystal images of all pixels in the same manner as the first step while increasing the bias voltage (Vb) step by step.

10. In paragraph 9, A second step of obtaining a liquid crystal image in a systemless manner, which is a liquid crystal image of all pixels, by using light incident by a lead beam irradiated on the liquid crystal layer while applying the separation voltage (Vs) and the measurement voltage (Vm) applied sequentially with the separation voltage (Vs) between the first electrode layer and the transparent electrode layer without positioning the subject and without irradiating the X-rays; - The above measurement voltage (Vm) is A third step of obtaining an inorganic X-ray liquid crystal image, which is a liquid crystal image of all pixels, by using light incident by a lead beam irradiated on the liquid crystal layer while applying the separation voltage (Vs) and the measurement voltage (Vm) that is applied sequentially with the separation voltage (Vs) between the first electrode layer and the transparent electrode layer while positioning the subject and irradiating the X-ray, A fourth step of obtaining an object zero line liquid crystal image, which is a liquid crystal image of all pixels, by using light incident by a lead beam irradiated on the liquid crystal layer while applying the separation voltage (Vs) and the measurement voltage (Vm) applied sequentially with the separation voltage (Vs) between the first electrode layer and the transparent electrode layer while positioning the subject and not irradiating it with X-rays. A fifth step of obtaining an object X-ray liquid crystal image, which is a liquid crystal image of all pixels, by using light incident by a lead beam irradiated on the liquid crystal layer while applying the separation voltage (Vs) and the measurement voltage (Vm) that is applied sequentially with the separation voltage (Vs) between the first electrode layer and the transparent electrode layer while positioning the subject and irradiating it with X-rays. An X-ray detection method, characterized in that the second and third steps can be performed regardless of the mutual order, and the fourth and fifth steps can also be performed regardless of the mutual order.

11. In paragraph 10, A sixth step of converting the liquid crystal image of the non-body zero line into a voltage image of the body zero line, the liquid crystal image of the non-body X-ray into a voltage image of the body X-ray, the liquid crystal image of the object zero line into a voltage image of the body zero line, and the liquid crystal image of the object X-ray into a voltage image of the body X-ray, using the reference light quantity graph. An X-ray detection method characterized in that it further includes a seventh step of obtaining an X-ray image of the subject from the above-mentioned zero-line voltage image, the inorganic X-ray voltage image, the object zero-line voltage image, and the object X-ray voltage image.

Images