Radiographic apparatus and radiographic method

Abstract

A control section of a radiation imaging apparatus has: an exposure time control section that controls subframe exposure times of an image sensor so that in-focus fluorescent light at a depth of field of radiation that reaches a scintillator and out-of-focus fluorescent light other than the depth of field are discretely captured at a light-receiving surface of the image sensor per particle of the radiation; an in-focus signal discrimination section that discriminates sensor signals of light-receiving pixel groups discretely included in each subframe, which correspond to spots of the in-focus fluorescent light and sensor signals of light-receiving pixel groups corresponding to spots of the out-of-focus fluorescent light; and an image signal processing section that generates an image by superimposing subframe data based on the sensor signals of the light-receiving pixel groups corresponding to the spots of the in-focus fluorescent light.

Description

TECHNICAL FIELD

[0001] The present application relates to a radiation imaging apparatus, and particularly to a new radiation imaging apparatus and a radiation imaging method that achieve an improvement in spatial resolution through super-resolution. BACKGROUND

[0002] Radiation imaging apparatuses, particularly imaging apparatuses that utilize X-rays, are used as non-destructive inspection tools for microfabricated products such as semiconductor devices, or as excellent observation and analysis tools in a wide range of fields from material science and life science to fundamental physics. An X-ray imaging apparatus of an indirect photography type used in such uses is generally configured to have a camera optical system that converts an X-ray image into a visible light image through a scintillator and exposes the visible light image through an image sensor, and a signal processing system that performs image processing based on a camera signal from the image sensor to obtain a resolved image. On the other hand, in the field of semiconductor integrated circuit devices, in recent years, the progress in the miniaturization of line width is fast, and a high-resolution X-ray imaging apparatus corresponding thereto is required. In response to the requirement, various improvements in high resolution have been made in the camera optical system and the signal processing system respectively so far. One of the improvement measures for the spatial resolution of the camera optical system including the scintillator is shown in Patent Literature 1.

[0003] PRIOR ART DOCUMENT

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2019-20336 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Patent Literature 1 proposes the following: in an X-ray imaging apparatus of a so-called indirect photography system, by employing a lens-integrated scintillator obtained by forming a scintillator that converts incident X-rays into visible light, a so-called solid immersion lens (SIL) in a manner that maintains uniformity of refractive index on one face of a lens-shaped substrate composed of a solid optical material having a refractive index close to that of the scintillator, the spatial resolution is increased to approximately 100 nm close to a theoretical limit value. However, such a solid immersion lens has a high technical difficulty in fabrication, and thus there are problems in practical use. That is, in reality, due to reasons such as the fact that practical use of such a SIL requires an extremely thin scintillator film of submicron or less, the optical quality in the scintillator is easily deteriorated at the time of thin film processing and thus high-precision optical design cannot be performed, and the like, it is difficult to obtain a product of stable quality. In addition, even if an X-ray imaging apparatus using a SIL as in Patent Literature 1 is realized, it is a theoretical limit value in terms of an optical system, and thus it is not expected that the spatial resolution greatly exceeds the theoretical limit value, and there is a problem in that it is not possible to meet the observation requirements of a subject of photography that is increasingly miniaturized on a nanometer scale.

[0008] General Disclosure

[0009] Here, the basic idea of the present application is to photograph the radiation that has reached the scintillator a plurality of times with an extremely short exposure time at a level at which the visible point images that have been discretized in units of photons or particles can be observed, to discriminate the visible point images as in-focus signals and out-of-focus signals, and to generate a radiation observation image using only the in-focus signals. By controlling the exposure time of the image sensor to be short, it is possible to obtain the X-ray image that has reached the scintillator as a group of visible point image subframes that are discretized in space in units of one photon of X-rays. Furthermore, it is possible to discriminate the in-focus signals and the out-of-focus signals by comparing the light-receiving pattern of the visible point images on the image sensor with the light-receiving pattern (Airy disk) of the theoretically in-focus visible point images corresponding to the numerical aperture of the optical system and the fluorescent wavelength of the scintillator.

[0010] In this way, even if the penetration distance of the X-ray photons that have reached the fluorescent film as the scintillator is not fixed and thus the visible light conversion is performed at a position outside the depth of field of the objective lens, it is possible to constitute an observation image by superimposing only the group of subframes of the in-focus signals that have excluded the out-of-focus signals, and thus to obtain a clear image while relaxing the requirements for the thickness of the fluorescent film.

[0011] From another aspect of the present application, it is characterized in that, in the focus signal identified and extracted as described above, a photon localization method for determining the center position of the point image of the focus signal with higher accuracy than the pixel size of the image sensor is further applied, thereby achieving super high refinement of the X-ray image. The photon localization method itself is a method of super resolution processing of the image signal which, when used together with the image signal processing of the above-mentioned focus signal sub-frame group, can obtain a clearer refined image.

[0012] Further, from another aspect of the present application, it is characterized in that, in the focus signal identified and extracted as described above, the energy of the X-ray transmitted through the imaging target sample is identified based on the number of visible light photons corresponding to one photon of the X-ray. Thereby, specific information of the constituent material of the observation target sample can be obtained with high accuracy.

[0013] In summary, the present application is a kind of radiation imaging device, with: radiation camera, it has scintillator, imaging optical system and image sensor, from the radiation source transmitted through the imaging object of radiation incident to the scintillator, and the scintillator emits the fluorescence with longer wavelength than the wavelength of the radiation, the imaging optical system is imaged on the imaging surface by matching the object lens with the depth of field set in the sample surface of the scintillator, the image sensor is configured on the imaging surface, with light receiving surface composed of a plurality of pixels;And control unit, based on the sensor signal of each pixel output from the image sensor of the radiation camera to generate an image,

[0014] The control unit has: exposure time control unit, which controls the exposure time of the image sensor, so that the focus fluorescence at the depth of field of the radiation reaching the scintillator and the out-of-focus fluorescence outside the depth of field are dispersedly photographed at the light receiving surface of the image sensor for each particle of the radiation;Focus signal identification unit, for identifying the sensor signals of the light receiving pixel group corresponding to the focus fluorescence spot and the sensor signals of the light receiving pixel group corresponding to the out-of-focus fluorescence spot dispersedly contained in each sub-frame with the width of each fluorescence spot;And image signal processing unit, which generates the image based on the sensor signals from the light receiving pixel group corresponding to the focus fluorescence spot.

[0015] In addition, the radiation referred to in the present application herein can be understood as X-ray, ultraviolet, or particle line such as electron, and in the following description, X-ray is taken as the representative of the most preferred application example of the present application.

[0016] In one embodiment of the present application, a radiation imaging apparatus is provided. The radiation imaging apparatus can include a radiation camera including a scintillator that emits fluorescent light having a longer wavelength than a wavelength of radiation transmitted through a subject from a radiation source, an imaging optical system that images an image surface by matching a depth of field to an objective lens set in a sample surface of the scintillator, and an image sensor disposed at the image surface and having a light receiving surface composed of a plurality of pixels. The radiation imaging apparatus can include a control unit that generates an image based on a sensor signal of each of the plurality of pixels output from the image sensor of the radiation camera. The control unit can include an exposure time control unit that controls a sub-frame exposure time of the image sensor such that in-focus fluorescent light at a depth of field and out-of-focus fluorescent light other than the depth of field generated by the radiation reaching the scintillator are discretely captured at the light receiving surface of the image sensor per particle of the radiation. The control unit can include a focus signal discrimination unit that discriminates a point image sensor signal of a light receiving pixel group corresponding to a spot of the in-focus fluorescent light and a point image sensor signal of a light receiving pixel group corresponding to a spot of the out-of-focus fluorescent light discretely included in each sub-frame. The control unit can include an image signal processing unit that generates an image by accumulating sub-frame data based on the point image sensor signal of the light receiving pixel group corresponding to the spot of the in-focus fluorescent light.

[0017] The image signal processing unit can include a point image signal detection unit that processes the point image sensor signal of the light receiving pixel group corresponding to the spot of the in-focus fluorescent light to calculate a center position of a point image in the light receiving pixel group, and generates an image based on the center position.

[0018] The image signal processing unit can include a radiation energy resolution image generation unit that divides a light receiving sensor signal level of each spot of the in-focus fluorescent light corresponding to radiation having different energies and discretely incident to the scintillator in a plurality of sub-frames into a plurality of level ranges, and generates an image corresponding to an energy distribution of the radiation based on the sensor signals of the spots of the in-focus fluorescent light included in the same level range.

[0019] The exposure time control unit can control the exposure time according to an intensity of the radiation such that a frequency of radiation detection in the image sensor is 0.02 photons / pixel / sub-frame or less, and generate an image by obtaining at least 6.4 x 105 continuous captured signals composed of a plurality of sub-frames.

[0020] The objective lens can include a frontmost lens of a solid immersion lens structure integrally formed with a fluorescent film as the scintillator on a radiation incident surface side.

[0021] The objective lens can include a frontmost lens composed of a fluorescent film as a scintillator and a lens-shaped base having the fluorescent film integrally formed on the side of an incident surface of a radiation, and the fluorescent film can be composed of a solid optical material obtained by using a solid optical material constituting the lens-shaped base as a master batch and adding a predetermined activator.

[0022] The objective lens can have a frontmost lens composed of a fluorescent film as a scintillator and a lens-shaped base having the fluorescent film integrally formed on the side of an incident surface, and a difference in refractive index between the fluorescent film and the lens-shaped base can be less than 0.1%.

[0023] The objective lens can include a frontmost lens of a solid immersion lens structure formed of a material having a scintillator function.

[0024] The lens-shaped base can be formed of an un-doped garnet crystal, and the fluorescent film can be formed of a garnet crystal obtained by adding an activator to the un-doped garnet crystal.

[0025] The lens-shaped base can be formed of an un-doped gadolinium aluminum gallium garnet (GAGG), and the fluorescent film can be formed of a gadolinium aluminum gallium garnet (Ce:GAGG) to which cerium as an activator is added.

[0026] The radiation imaging apparatus can have a radiation-signal comprehensive conversion efficiency in which one photon or one particle of a radiation generates a fluorescent light in a fluorescent film, and the fluorescent light is detected as a point image signal of 50 or more electrons by a pixel on a light-receiving surface of an image sensor.

[0027] The radiation can be X-rays, and an X-ray-signal comprehensive conversion efficiency ηTOTAL representing a conversion efficiency of a sensor signal detected by the image sensor satisfies a conditional expression using a luminous efficiency ηLY(E) of the optical system, a light collection efficiency ηCE(NA) of the optical system depending on a numerical aperture NA, a transmittance ηTO of the optical system, and a quantum efficiency ηVQE of the image sensor with respect to the fluorescent light, the conditional expression being ηTOTAL = ηLY(E) × ηCE(NA) × ηTO × ηVQE > 50.

[0028] In one embodiment of the present application, a radiation imaging method is provided. The radiation imaging method can use a radiation imaging apparatus mainly including a camera unit that observes a visible light image from a solid-immersion front lens by an image sensor having a light-receiving surface composed of a plurality of pixels, the camera unit can include a scintillator that converts incident radiation into visible light on the incident surface side, and the camera unit can include a solid-immersion front lens that has a lens shape on the exit surface side. The exposure time of each subframe of the image sensor can be controlled to extract radiation incident to the scintillator as a point image signal of a visible light spot dispersed by each particle. The point image signals in each subframe can be discriminated as a point image signal of an in-focus light spot obtained by emitting light at a depth of field of the solid-immersion front lens and a point image signal of an out-of-focus light spot obtained by emitting light outside the depth of field. Subframe data based on the point image signal of the in-focus light spot can be superimposed to generate a radiation observation image.

[0029] In one embodiment of the present application, a radiation imaging method is provided. The radiation imaging method can include a control stage in which an image is generated in a radiation imaging apparatus based on a sensor signal of each of a plurality of pixels output from an image sensor, the radiation imaging apparatus having: a scintillator to which a radiation transmitted through an object of photography from a radiation source is incident, the scintillator emitting fluorescent light having a longer wavelength than the wavelength of the radiation; an imaging optical system that images an imaging surface by an objective lens having a depth of field matched to a sample surface of the scintillator; and the image sensor disposed on the imaging surface, having a light-receiving surface composed of a plurality of pixels. The control stage can include an exposure time control stage in which a subframe exposure time of the image sensor is controlled so that in-focus fluorescent light at a depth of field and out-of-focus fluorescent light other than the depth of field generated by the radiation reaching the scintillator are captured at the light-receiving surface of the image sensor dispersed by each particle of the radiation. The control stage can include a focus signal discrimination stage in which a sensor signal of a light-receiving pixel group corresponding to a spot of the in-focus fluorescent light and a sensor signal of a light-receiving pixel group corresponding to a spot of the out-of-focus fluorescent light, which are dispersed in each subframe, are discriminated. The control stage can include an image signal processing stage in which subframe data based on the sensor signal from the light-receiving pixel group corresponding to the spot of the in-focus fluorescent light is superimposed to generate an image.

[0030] The radiation can be X-rays, and the radiation camera can be an X-ray camera including a scintillator and an objective lens that are optically designed so that the conversion efficiency of each photon of X-rays that is converted into a sensor signal detected by an image sensor becomes 50 or more in terms of electrons, and the control stage can further include a stage of performing signal processing of detecting the point image center position of the focus fluorescent spot. The control stage can further include a stage of generating a super-resolution X-ray image by superimposing sub-frame data constituted by the detected point image center position.

[0031] According to the present application, only the in-focus signal on the scintillator is extracted to constitute an image, and thus a high-quality X-ray image with high contrast can be obtained, and the scintillator can be thinned. Thus, a solid immersion lens with high optical quality in which strain is suppressed during scintillator processing can be provided at low cost. In addition, by applying signal processing using the photon localization method, nanoscale super-resolution X-ray imaging beyond the theoretical spatial resolution limit of the solid immersion lens can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 (a) to (d) of FIG. 1 show the outline structure of the SIL 11 in the present embodiment.

[0033] Figure 2 (a) to (d) of FIG. 1 show the outline structure of the SIL 11 in the present embodiment.

[0034] Figure 3 (a) and (b) of FIG. 1 are diagrams for explaining the in-focus fluorescent light F1 and the out-of-focus fluorescent light F2 in the present embodiment.

[0035] Figure 4 (a) to (d) of FIG. 1 are diagrams for explaining imaging using the photon localization method.

[0036] Figure 5 (a) to (c) of FIG. 1 are diagrams for explaining the density of the signal of the fluorescent spot.

[0037] Figure 6 is a diagram showing the flow of processing of the image signal in the present embodiment.

[0038] Figure 7 is a flowchart showing the imaging operation of the radiation imaging apparatus 100 in the present embodiment.

[0039] Figure 8 (a) to (c) of FIG. 1 are diagrams for explaining the image processing in the other embodiment. DETAILED DESCRIPTION

[0040] Hereinafter, the present application will be described by way of embodiments of the application, but the following embodiments are not intended to limit the application claimed in the claims. In addition, the combination of features described in the embodiments is not necessarily all essential to the solution of the application.

[0041] [Outline structure of imaging device]

[0042] Figure 1 An outline structure of a radiation imaging device 100 in the present embodiment is shown. The radiation imaging device 100 has a radiation camera 10 and a control section 20. The radiation imaging device 100 is a device that acquires an image of a sample 900 at a prescribed spatial resolution using radiation from a radiation source 200. The radiation camera 10 has a solid immersion lens (hereinafter also referred to as SIL) 11, a post-objective lens group 12, a band-pass filter 13, an imaging lens 14, and an image sensor 15. The solid immersion lens (SIL) 11 and the post-objective lens group 12 form an objective lens 16. The objective lens 16, the band-pass filter 13, and the imaging lens 14 form an imaging optical system 17.

[0043] The control section 20 has a camera control section 21 and an image signal processing section 22. The camera control section 21 includes an exposure time control section 21a and an image data read control section 21b. The exposure time control section 21a has a so-called shutter function of a camera, and controls a sub-frame exposure time of the image sensor 15 so that the radiation that has been converted into visible fluorescent light upon reaching the SIL 11 is discretely captured at the light-receiving surface of the image sensor 15 per fluorescent light spot corresponding to one particle of the radiation. The image data read control section 21b sends a group of sub-frame data obtained by reading a sensor signal from a pixel array constituting the light-receiving surface of the image sensor 15 for each sub-frame to an image data storage section 22b.

[0044] The image signal processing section 22 has a focus signal discrimination section 22a, the image data storage section 22b, a point image signal detection section 22c, and an X-ray energy resolution image generation section 22d. The focus signal discrimination section 22a discriminates a sensor signal of a group of light-receiving pixels corresponding to an in-focus fluorescent light spot and a sensor signal of a group of light-receiving pixels corresponding to an out-of-focus fluorescent light spot discretely contained in each sub-frame, in comparison with a theoretical in-focus spot pattern (Airy disk). The image data storage section 22b stores image data output from the image sensor 15.

[0045] The image signal detection unit 22c and the X-ray energy decomposition image generation unit 22d perform additional functions for photon localization processing, which will be described later. The image signal detection unit 22c processes the image sensor signal from the group of light-receiving pixels corresponding to the spot of the focused fluorescence to calculate the center position of the image in the group of light-receiving pixels and generates a subframe group based on the center position. The X-ray energy decomposition image generation unit 22d divides the light-receiving sensor signal level of each spot of focused fluorescence generated corresponding to radiation with different energies and discretely incident on SIL 11 in a series of subframes into multiple level ranges, and generates an image corresponding to the energy distribution of the radiation based on the sensor signals of the focused fluorescence spots within the same level range. The image signal processing unit 22 is connected to a display 41 and a storage unit 42, and the image generated by the image signal processing unit 22 is displayed on the display 41.

[0046] The radiation can be gamma rays, X-rays, electron beams, or ultraviolet light (especially, for example, extreme ultraviolet light). When the radiation is X-ray, the radiation imaging device 100 can be used for X-ray photography, X-ray CT, X-ray computed tomography, X-ray morphology, and X-ray imaging microscopy, etc. In this embodiment, X-rays are used as the radiation source. Figure 1 The symbol is represented as X-ray R.

[0047] like Figure 1 As shown, X-rays R from radiation source 200 are irradiated onto sample 900 after their intensity is controlled by radiation attenuation plate 400. The X-rays R, either passing through sample 900 or scattered by sample 900, are incident on a fluorescent film 11a, which serves as a scintillator, integrally disposed on the front surface of the lens-shaped substrate 11b constituting the foremost lens of objective lens 16. The lens-integrated SIL 11, consisting of fluorescent film 11a and lens-shaped substrate 11b with a convex lens-shaped exit surface, constitutes an optical element known as a solid immersion lens. Fluorescent film 11a converts the incident X-rays R into fluorescence F, which can be received (sensed) as visible light by image sensor 15. The image formed by the fluorescence F from SIL 11 is magnified by imaging optical system 17 (and sometimes reduced) and projected onto image sensor 15, thereby enabling the acquisition of structural information of sample 900 at a predetermined spatial resolution.

[0048] The theoretical limit value of the spatial resolution in such a radiation imaging apparatus 100 is expressed by the Rayleigh resolution of the camera optical system, as with an optical microscope. In the radiation imaging apparatus 100 in which the scintillator-integrated solid immersion lens is placed at the foremost portion, the spatial resolution δ is expressed by "δ = 0.61 x λ / NA". Here, λ represents the wavelength of the fluorescence F that is the visible light converted by the fluorescent film 11a. NA represents the numerical aperture of the camera optical system, defined by "NA = n x sin θ". n represents the refractive index of the lens-shaped base 11b itself as the medium between the fluorescent film 11a that becomes the imaging target surface and the lens-shaped base 11b. θ is the aperture angle, representing the maximum angle of the visible light ray incident from the fluorescent film 11a to the convex surface of the lens-shaped base 11b with respect to the optical axis.

[0049] For a concrete description, a three-dimensional orthogonal coordinate system composed of mutually orthogonal X, Y, and Z axes is assumed. The traveling direction of the X-ray R irradiated to the sample 900 is parallel to the Z axis, and thus the traveling direction of the X-ray R transmitted through the sample 900 is also parallel to the Z axis.

[0050] A fluorescent film 11a is provided on the surface of the incident side of the incident X-ray R of the SIL 11. The portion of the SIL 11 in which the fluorescent film 11a is not formed is referred to as a lens-shaped base 11b. Thus, there is no gap between the lens-shaped base 11b and the fluorescent film 11a, which is filled with the material of the lens-shaped base 11b as the medium. The fluorescent film 11a is composed of a fluorescent material as a scintillator that emits fluorescence F as visible light upon receiving the X-ray R transmitted through the imaging target sample 900.

[0051] The fluorescence F emitted from the fluorescent film 11a is typically set to a wavelength range in which the image sensor 15 has sensitivity. It can also be light in the visible light, ultraviolet region. For example, it has a wavelength in the range of 200 nm to 700 nm.

[0052] The fluorescence F generated at the fluorescent film 11a by exciting the incident X-ray photon becomes parallel light from the lens-shaped base 11b after the objective lens rear-stage lens group 12, with the generation position corresponding to the depth of incidence of the X-ray R as a starting point, and is imaged on the image sensor 15 by the imaging lens 14 disposed at the rear stage.

[0053] Further, the rear group 12 of the objective lens is composed of one or more lenses. The rear group 12 of the objective lens cooperates with the lens-like base 11b of the SIL 11 to make the fluorescence F from the fluorescent film 11a into parallel light. Only the wavelengths of a specific band of the fluorescence F made into parallel light are passed through by the band-pass filter 13 and then incident on the imaging lens 14. The imaging lens 14 images the fluorescence F made into parallel light on the imaging surface of the image sensor 15. By performing optical design including the SIL 11 including the fluorescent film 11a, the rear group 12 of the objective lens, and the imaging lens 14, various aberrations can be reduced, and the spatial resolution and the image quality can be improved. In addition, it can also be configured to not include the band-pass filter 13. In addition, in the description of the above Figure 1 In the description of the above, an example in which the lens system is composed of an infinite distance correction optical system is shown, but it can also be composed of a finite distance correction optical system obtained by performing optical design including the SIL 11, the rear group 12 of the objective lens, and the imaging lens 14 as one objective lens 16. At this time, the light emitted from the rear group 12 of the objective lens can also not be parallel, and in addition, it can also not include the band-pass filter 13.

[0054] Any of the SIL 11, the rear group 12 of the objective lens, the imaging lens 14, and the image sensor 15 is configured in a manner capable of position adjustment, and the image formed by the fluorescence F is imaged on the image sensor 15 by the position adjustment, whereby the focus of the imaging optical system 17 is performed.

[0055] Further, it can also have a lens support body for supporting each lens constituting the imaging optical system 17 including the objective lens 16 and the imaging lens 14 at a prescribed position. It can be that all the lenses constituting the imaging optical system 17 are supported by a single lens support body, or it can be that the lens support body is composed of a plurality of lens support bodies.

[0056] The image sensor 15 is, for example, a so-called two-dimensional image sensor having a light-receiving surface on which a plurality of photoelectric conversion pixels are arranged in the vertical and horizontal directions, such as a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like. An image signal is generated as an electric signal by photoelectric conversion. The image imaged on the image sensor 15 is an image corresponding to the emission position and emission intensity of the fluorescence F at the fluorescent film 11a, and the emission position and emission intensity of the fluorescence F at the fluorescent film 11a depend on the incident position and incident intensity of the X-rays R on the fluorescent film 11a.

[0057] As for the imaging signal representing the image (optical image) imaged on the light receiving surface, the exposure time (sensing time) of one sub-frame is controlled to be extremely short according to a control signal from an exposure time control section 21a in the camera control section 21 as described later, and an image data signal of a visible light spot corresponding to one photon of X-rays can be output in response to a signal from an image data read control section 21b. The image signal processing section 22 performs processing for discriminating in-focus signals and out-of-focus signals on the image data signal of the visible light spot within the sub-frame output from the image sensor 15 in an in-focus signal discriminating section 22a, obtains a plurality of sub-frames of only in-focus signals to constitute an observation image, and thereby a very clear high-resolution image can be obtained.

[0058] The control section 20 is connected to a stage control section 300 outside the radiographic imaging apparatus 100, and can issue an instruction to the stage control section 300. The stage control section 300 can move the SIL stage 11f on which the SIL 11 is placed and the sample stage 910 on which the sample 900 is placed to appropriate positions based on the instruction received from the control section 20. In addition, the stage control section 300 can insert and remove the radiological attenuating plate 400 based on the instruction received from the control section 20. In addition, the control section 20 is connected to a radiation source control section 500, and can control the intensity and timing of X-rays R emitted from the radiation source 200, and the irradiation time. Furthermore, any one of the SIL 11, the lens group 12, the imaging lens 14, and the image sensor 15 can be placed on a stage to perform focusing, or any combination of them can be placed on a plurality of stages to perform focusing.

[0059] The size ε of blur formed due to diffraction of X-rays R generated in the sample 900 is represented by The blur formed due to X-ray diffraction becomes larger when the distance d between the sample 900 and the fluorescent film 11a is large. Therefore, in order to minimize the blur formed due to diffraction of X-rays R, the sample 900 is moved and disposed so as to approach the fluorescent film 11a or be in close contact with the fluorescent film 11a by the sample stage 910. Also, by making the radiation source center of the radiation source 200 approach the sample 900, the intensity per unit area of X-rays R on the fluorescent film 11a can be increased.

[0060] In Figure 1Although not shown in the diagram, the structure can also be configured as follows: an imaging optical system for X-rays that diffracts, refracts, or reflects X-rays R is positioned between the sample 900 and the fluorescent film 11a, so that the X-ray image of the sample 900 is magnified, reduced, or imaged on the fluorescent film 11a at the same magnification, thereby preventing blurring caused by X-ray diffraction. Simultaneously, an illumination optical system for X-rays can also be positioned between the radiation source 200 and the sample 900.

[0061] [Lens-integrated scintillator, solid-state immersion lens]

[0062] Next, we will again describe the lens-integrated scintillator used in this embodiment, the so-called solid immersion lens (SIL) 11. Figure 2 Images (a) to (c) show the outline structure of SIL 11 in this embodiment. The SIL 11 of this embodiment is based on the structure disclosed in the aforementioned Patent Document 1, and can be as follows: Figure 2 As shown in (a), it is hemispherical, or it can be like... Figure 2 As shown in (b), it is a super-hemispherical shape. Figure 2 (a) and (b) show the type of SIL 11 having a fluorescent film 11a as a scintillator and a lens-shaped substrate 11b as separate components. Figure 2 (c) shows a type where the SIL 11 is integrally formed from a lens-shaped fluorescent substrate 11e, which is a solid optical material having the same scintillator function. That is, Figure 2 In (c), SIL 11 is formed from a lens-shaped fluorescent substrate 11e that emits fluorescence throughout. In this embodiment, SIL 11 is as follows: Figure 2 The description focuses on a convex lens-shaped component, as shown in (a), in which a fluorescent film 11a is formed on the incident surface side of the lens-shaped substrate 11b, and the exit surface side is machined into the foremost lens of the objective lens 16. Alternatively, it can be described as follows... Figure 2 As shown in (d), SIL 11 is a flat plate shape.

[0063] The SIL 11 including the fluorescent film 11a and the lens-shaped base 11b is formed of a substance that is transparent to the fluorescence F, the fluorescent film 11a emits fluorescence F by absorbing the energy of the radiation, the lens-shaped base 11b does not emit fluorescence even if it absorbs the energy of the radiation, or does not emit fluorescence having the same wavelength as that of the fluorescence F, or the lens-shaped base 11b is less intense than the fluorescent film 11a. As long as it has this characteristic, the kind of the constituent substance of the SIL 11 can be arbitrary. In the present embodiment, in the SIL 11, the fluorescent film 11a is formed of cerium-added gadolinium aluminum gallium garnet (Ce:GAGG), and the lens-shaped base 11b is formed of gadolinium aluminum gallium garnet (GAGG) without addition.

[0064] The fluorescent film 11a is made of the same substance as that of the lens-shaped base 11b (i.e., the material of the lens-shaped base 11b) to which a prescribed proportion of Ce as an activator is added. Thus, the difference in refractive index between the fluorescent film 11a and the lens-shaped base 11b is suppressed to 0.1% or less. The fluorescent film 11a having a function as a scintillator receives the X-rays R and emits fluorescence F in the visible light region, for example, of 520 nm.

[0065] One objective lens 16 is optically designed so as to have a sample surface on the surface layer of the fluorescent film 11a of the SIL 11 including the SIL 11 and the objective lens rear-stage lens group 12, thereby becoming a solid immersion objective lens having a high spatial resolution in which various aberrations are suppressed. For example, in the case where the fluorescent film 11a is composed of Ce:GAGG and the mouth angle of the objective lens 16 is set to 72 degrees, the numerical aperture becomes NA = n • sin θ = 1.85 x 0.95 = 1.76. Thus, the spatial resolution reaches δ = 0.61 x λ / NA = 0.61 x 520 nm / 1.76 = 180 nm.

[0066] Moreover, the material of the SIL 11 composed of the fluorescent film 11a and the lens-shaped base 11b is not limited to this, and various solid optical materials can be employed. As the material of the SIL 11 (solid optical material), a transparent solid having no birefringence to the wavelength of the fluorescence F is a condition. For example, a single crystal and a polycrystal having an amorphous or cubic crystal structure of glass or the like as an optically homogeneous body. In the case of a polycrystal, by removing the voids within the crystal to make the size of the grain boundary sufficiently smaller than the wavelength of the fluorescence F, thereby maintaining the continuity of the refractive index to the wavelength of the fluorescence F becomes a condition to have transparency. In addition, a crystal having a crystal structure with optical anisotropy can also be employed, but is not limited to a polycrystal. In this case, by removing the voids within the crystal, not only the size of the grain boundary is made sufficiently smaller than the wavelength of the fluorescence F, but also the size of the crystal grain is made sufficiently smaller than the wavelength of the fluorescence F, thereby preventing the occurrence of birefringence, and maintaining the continuity of the refractive index to the wavelength of the fluorescence F becomes a condition to have transparency.

[0067] As long as the above conditions are satisfied, in the present embodiment, the material can be either inorganic or organic, and can also be a material obtained by mixing two or more kinds of inorganic and organic materials.

[0068] That is, in the case where the SIL 11 is composed of an inorganic material, as a specific scintillator material having a crystal structure of cubic system as optically isotropic body, there are Lu3Al5O 12 (LuAG), Y3Al5O 12 (YAG), Gd3Ga5O 12 (GGG), Lu2O3, Y2O3, Gd2O3, Sc2O3 as a sesquioxide type crystal, CaF2, BaF2 as a fluorite type crystal, CsI, Nal as an iodide crystal. In addition, Cs2HfC l6 , Cs2HfI6, and the like are also cubic system scintillator materials. In addition, as perovskite type crystals having a crystal structure with optical anisotropy, LuAlO3(LuAP), YAlO3(YAP), GdAlO3(GAP), Lu2SiO5(LSO), Y2SiO5(YSO), LuYSiO5(LYSO), Gd2SiO5(GSO) as silicate type crystals, Lu2Si2O7(LPS), Y2Si2O7(YPS), Gd2Si2O7(GPS), (Gd, La)2Si2O7(La-GPS), PbWO4 as tungstate crystals, LiCaAlF6 as cordierite type crystals, Lu2O2S, Y2O2S, Gd2O2S as oxysulfide type crystals, and other inorganic crystals Bi4Ge3O 12 , Yb2SiO5, LaBr3, CeBr3, SrI2 can also be used. In addition, crystals having a composition in which two or more kinds of elements are composed in an arbitrary ratio at each site within the crystal, such as (Gd, Lu, Y)3(Al, Ga)5O 12 , (Lu, Y)2SiO5 can also be used.

[0069] The fluorescent film 11a is made by adding a prescribed proportion of an additive as an activator to a base material having the same composition as the constituent material of the lens-shaped base 11b (i.e., the material of the lens-shaped base 11b). As for the activator, an element suitable for the base material is selected in a manner that emits fluorescent light F having a wavelength that can be sensed by the image sensor 15, and that makes the light emission amount and light emission decay time desired values, and is adjusted to a concentration and oxidation value suitable for the base material. In the present embodiment, the fluorescent film 11a is configured of Ce:GAGG obtained by adding Ce to GAGG. The fluorescent film 11a receives the X-rays R and, for example, emits fluorescent light F of 520 nm.

[0070] The thickness of the fluorescent film 11a is thinner than the thickness of the lens-shaped base 11b, and is, for example, in the range of 50 nm to 2 mm. By making the thickness of the fluorescent film 11a smaller than the depth of field of the imaging optical system 17, it is possible to prevent the generation of fluorescent light F that is not focused on the image sensor 15 as an imaging surface, and to suppress a decrease in the spatial resolution of the radiation imaging apparatus 100. From the viewpoint of achieving such a high spatial resolution, it is preferable to make the fluorescent film 11a of the solid immersion lens thin, but according to the idea of the present embodiment that the X-ray image is configured only of signals of focused fluorescent light spots generated at the fluorescent film 11a, it is possible to alleviate the difficulty of producing a high-quality thin fluorescent film.

[0071] The fluorescent film 11a is formed on the lens-shaped base 11b in a manner that maintains continuity of the refractive index. Here, the formation in a manner that maintains continuity of the refractive index means that the fluorescent film 11a and the lens-shaped base 11b have a small difference in refractive index, are directly joined without a foreign object therebetween, and the refractive index is substantially uniform. For example, the difference between the refractive index of the lens-shaped base 11b and the refractive index of the fluorescent film 11a is less than 0.1% from the viewpoint of the refractive index of the lens-shaped base 11b. Thereby, it is possible to suppress scattering, refraction, and reflection of the fluorescent light at the interface of the joining. As for the joining method, it is desirable to directly join the fluorescent film 11a and the lens-shaped base 11b, such as solid-phase diffusion joining, surface activation joining, and the like, and to have no gap at the interface of the joining, on the basis of satisfying the continuity of the refractive index described above. Furthermore, as long as the refractive index is substantially uniform, the fluorescent film 11a can be directly formed on the lens-shaped base 11b by a vapor phase method such as a physical vapor deposition method (PVD), a chemical vapor deposition method (CVD), or the like. For example, the PVD has a thermal evaporation method, an ion beam evaporation method, a molecular line epitaxial method, an ion plating method, a sputtering method, a pulsed laser deposition method, and the like. The CVD has a thermal CVD, a plasma CVD, a light CVD, a spray CVD method, and the like. In particular, if it is a method of epitaxial growth, it is possible to form a high-quality single-crystal film. In addition thereto, a liquid phase epitaxial growth method, a solid phase epitaxial growth method, a sol-gel method can also be used. In addition, an adhesive having a small difference in refractive index between the fluorescent film 11a and the lens-shaped base 11b can also be used.

[0072] From the viewpoint of reducing the refractive index difference, it is most desirable that the fluorescent film 11a is made of a base material having the same composition as the constituent material of the lens-shaped base 11b to which a prescribed proportion of an additive as an activator is added, and secondly desirable that it has a crystal structure homologous to that of the lens-shaped base 11b. For example, the former can also be that the lens-shaped base 11b is formed of an additive-free lutetium aluminum garnet (LuAG), and the fluorescent film 11a is formed of a praseodymium-added lutetium aluminum garnet (Pr: LuAG) or a cerium-added lutetium aluminum garnet (Ce: LuAG). The latter can also be that the fluorescent film 11a is made of Ce: GAGG having a garnet crystal structure, and the lens-shaped base 11b is made of an additive-free lutetium aluminum garnet (LuAG) having a garnet crystal structure. In addition, a single crystal can be used in the material of the fluorescent film 11a, and a polycrystal can be used in the material of the lens-shaped base 11b, or vice versa.

[0073] Although not shown in Figure 1 , as shown in Figure 2 , in the SIL 11, an antireflection film 11c is arranged on the lens-shaped convex surface portion on the fluorescent exit surface side, and a reflection film 11d is arranged on the flat surface portion on the incident surface side.

[0074] The antireflection film 11c can also be, for example, a multilayer film formed of two or more dielectric films.

[0075] Like the antireflection film 11c, the reflection film 11d is configured of a dielectric multilayer film or a metal reflection film. A chromium coating layer or the like can also be arranged on the dielectric multilayer film to improve the light shielding property. The reflection film 11d has the effect of causing the fluorescent light F emitted in the direction opposite to the image sensor 15 to be reflected toward the image sensor 15 side, thereby effectively increasing the transmission efficiency of the fluorescent light F by nearly two times.

[0076] As described above, by using the SIL 11 in which the fluorescent film 11a as a scintillator and the lens-shaped base 11b as the foremost lens of the objective lens rear-stage lens group 12 are integrally formed so as to have a substantially uniform refractive index, it is possible to obtain an imaging optical system 17 having a high numerical aperture exceeding NA = 1.0 with the fluorescent film 11a having a sample surface, and it is possible to improve the spatial resolution of the radiographic camera 10. On the other hand, if the numerical aperture is set to be high, the depth of field becomes small, and thus a thinner fluorescent film 11a is required.

[0077] The depth of field d includes the front and back, and by d tot = λ · n / NA 2Let λ be the wavelength of the fluorescence F, n be the refractive index of the fluorescent film 11a relative to wavelength λ, and NA be the numerical aperture of the objective lens 16. For example, in a structure where the refractive index of Ce:GAGG relative to the fluorescence wavelength of 520 nm is set to 1.85 and the numerical aperture of the objective lens 16 is set to 1.76, the depth of field is 311 nm. Technically, it is difficult to fabricate the fluorescent film 11a to be thinner than 1 micrometer while suppressing optical degradation such as distortion.

[0078] [Focused fluorescence and off-focus fluorescence]

[0079] That is, when it is impossible to form a fluorescent film 11a with a depth of field when using an imaging optical system 17 with a large numerical aperture NA to improve spatial resolution, the fluorescent film 11a must be made deeper than the depth of field of the imaging optical system 17. In this case, some X-rays R are absorbed within the depth of field, and some X-rays R penetrate beyond the depth of field and are absorbed, generating fluorescence F from the locations where X-rays R are absorbed. In other words, the fluorescence F imaged on the image sensor 15 is a mixture of fluorescence F generated at locations within the depth of field that are the focusing positions (hereinafter also referred to as focusing fluorescence F1) and fluorescence F generated at locations outside the depth of field that are the off-focus positions (hereinafter also referred to as off-focus fluorescence F2).

[0080] Figure 3 Figures (a) and (b) are used to illustrate the focused fluorescence F1 and the off-focus fluorescence F2 in this embodiment. Figure 3 (a) shows the focusing fluorescence F1, emitted near the left side of the fluorescent film 11a, which determines the focal position of the rear lens group 12 of the objective lens, focusing on the image sensor 15. Figure 3 (b) shows a blurred, out-of-focus fluorescence F2 emitted near the right side of the fluorescent film 11a, outside the focal depth of the objective lens 16, which is out of focus on the image sensor 15.

[0081] like Figure 3 As shown in the right figure of (a), when the fluorescence F is imaged on the image sensor 15 as a focusing spot, the fluorescence F becomes a focusing fluorescence F1 with an illumination distribution having an Airy spot or a spot shape close to an Airy spot. Its diameter D is obtained by multiplying twice the Rayleigh spatial resolution δ by the optical magnification M of the imaging optical system 17, resulting in "D = 1.22 × λM / NA". On the other hand, as Figure 3 As shown in the right figure of (b), when the fluorescence F is not imaged as a focused spot on the image sensor 15, the fluorescence F becomes an off-focus fluorescence F2 with an illumination distribution having a spot shape larger than the Ally spot shown by the dashed circle f. The contrast quality and spatial resolution of the image containing the electrical signal obtained by photoelectric conversion of this off-focus fluorescence F2 are reduced.

[0082] That is, even if an optical system is constructed that maximizes the numerical aperture (NA) using a solid immersion lens (SIL), the off-focus fluorescence (F2) will still be mixed in as a component of the image, reducing spatial resolution, even if the thickness of the fluorescent film 11a cannot be reduced to the depth of field. As a result, even with an optical system that maximizes the numerical aperture (NA) to the limit of manufacturing precision, it is extremely difficult to achieve diffraction-limited spatial resolution. To address this problem, in this embodiment, a method is provided where, in a structure where the fluorescent film 11a has a greater depth of field than the imaging optical system 17, and the fluorescence F imaged on the image sensor 15 includes both focused fluorescence (F1) and off-focus fluorescence (F2), the signal of the off-focus fluorescence (F2) is removed, and only the signal of the focused fluorescence (F1) is extracted. This method can avoid reducing spatial resolution.

[0083] [X-ray signal conversion efficiency, a prerequisite for focusing fluorescence discrimination]

[0084] This method utilizes the following detection process: In a radiation camera 10 using a scintillator, after X-ray photons are absorbed by the scintillator and converted into visible light, diffraction phenomena generated during transmission through the lens system form a visible light image. Figure 3 (a) and Figure 3 The image is a dot image of a specified size, as shown in the right image of (b). The dot image is observed in units of X-ray photons, and only the signal corresponding to the focusing fluorescence F1 is extracted to reconstruct the image.

[0085] In order to accurately observe a point image in units of X-ray photons, a highly sensitive radiation camera 10 capable of detecting a single X-ray photon (X-ray photon counting) and a control unit 20 that divides the signal of the X-ray photon group that constitutes the sample image into units of X-ray photons are required.

[0086] The sensitivity of the measurement system used as a camera is determined by the inherent conversion efficiency η of the scintillator material. SE The luminous efficiency η is determined by the photon energy E of the X-rays from the light source. LY (E)=η SE ×E, Light recovery efficiency η of an optical system dependent on numerical aperture NA CE (NA), transmittance η of the optical system TO The quantum efficiency η of the image sensor 15 for fluorescence F VQE The product of X-ray and signal conversion efficiency is expressed through η. TOTAL (E, NA) = η LY (E)×η CE (NA)×η TO ×η VQEis emitted toward a random direction. That is, when one photon of the X-rays of the photon energy E is absorbed by the scintillator, η LY (E) of the visible light region is emitted toward the imaging optical system 17 at the ratio of the quantum efficiency η CE (NA) of the fluorescent light F, and is transmitted through the dry objective lens having the transmittance η TO , the quantum efficiency η VQE , and is detected on the image sensor 15 as an average of η TOTAL (E, NA) of the electrons.

[0087] The light recovery efficiency of the optical system depending on the numerical aperture NA is expressed by η . r is the reflectance of the reflective film 11d of the X-ray incident surface of the scintillator, NA is the numerical aperture of the objective lens 16, and n s is the refractive index of the scintillator.

[0088] For example, in a case where the X-rays of 10 keV are detected by the radiation camera composed of the imaging optical system and the image sensor in the conventional manner as disclosed in Japanese Laid-Open Patent Publication No. 2016-45183, it becomes [η LY (10 keV) = 160, η CE (0.95 NA) = 0.14, η TO = 0.9, and η VQE = 0.9], the X-ray-signal comprehensive conversion efficiency of the radiation camera as a whole is [η TOTAL (10 keV, 0.95 NA) = ~ 18 electrons / X-ray photon], the imaging optical system has the flat plate-shaped Ce:LuAG scintillator having the refractive index n s = 1.85 for the wavelength of the fluorescent light and having the light emission efficiency [160 visible photons / X-ray photon] for the X-rays of 10 keV, and the reflective film having the reflectance r = 0.95 is applied to the X-ray incident surface of the scintillator, and the dry objective lens having the numerical aperture NA = 0.95 and the transmittance 0.9 for the wavelength of the fluorescent light F, and the image sensor has the quantum efficiency 0.9 for the wavelength of the fluorescent light F. That is, the fluorescent light F generated when one photon of the X-rays is absorbed by the fluorescent film of the radiation camera in the conventional manner is detected on the image sensor as an average of 18 electrons.

[0089] In order to observe the irradiation distribution of the fluorescent light F, it is necessary to measure the signal by a plurality of pixels much smaller than the irradiation distribution of the fluorescent light F. In the X-ray camera of the dry lens structure described above, for example, in a case where one photon of X-rays incident on the radiation camera is distributed to 9 pixels on the image sensor 15 with a total of 18 electrons, the signal is detected by dividing it into 9 according to its irradiation distribution. That is, since there are many pixels of the image sensor that become a signal equal to or lower than the noise value (1 to 2 electrons) possessed by each pixel, not only is the number of statistics extremely insufficient for observing the irradiation distribution, but it is also difficult to distinguish the signal of one photon of X-rays from the noise signal (X-ray photon counting). That is, it is not possible to classify the fluorescent light F generated by one photon of X-rays into the in-focus fluorescent light Fl and the out-of-focus fluorescent light F2.

[0090] On the other hand, in the Figure 1 embodiment of the present embodiment, by employing a Ce:GAGG structure fluorescent film 11a having a refractive index n s = 1.85 and a light emission efficiency [600 visible photons / X-ray photon] for 10 keV X-rays R as the scintillator, an SIL 11 obtained by integrally forming the lens-shaped base 11b in a convex lens shape with the exit surface side being a hemi-spherical or super-hemispherical shape on the incident surface side, to configure an imaging optical system 17 with a numerical aperture improved to NA = 1.85 x 0.95 = 1.76. At this time, the various parameters are [η LY (10 keV) = 600, η CE (1.76 NA) = 0.69, η TO = 0.9, η VQE = 0.9], and the X-ray-signal comprehensive conversion efficiency of the radiation camera 10 is [η TOTAL (10 keV, 1.76 NA) = 335 electrons / X-ray photon]. That is, the fluorescent light F generated when one photon of X-rays is absorbed by the fluorescent film 11a of the radiation camera 10 is detected as an average of 335 electrons on the image sensor 15.

[0091] [Discrimination of in-focus fluorescent point image and out-of-focus fluorescent point image]

[0092] In the radiation camera 10 of the present embodiment using the scintillator-integrated SIL 11 as described above, the light collection efficiency η CE is about 5 times that of the past, and the light emission efficiency η LY is about 4 times that of the past, and as a result, the X-ray-signal comprehensive conversion efficiency η TOTAL[335 electrons / X-ray photon]. Even if 335 electrons are detected by 9 pixels, the signal value of each pixel is enough to exceed the noise value (1 to 2 electrons) that the image sensor 15 has per pixel, the signal value becomes large, and thus the influence of the light shot noise of the fluorescent light F is greatly improved, and thus it is possible to observe the irradiation distribution of the fluorescent light F with a sufficient statistical amount per X-ray photon. Therefore, if the fluorescent light F generated per X-ray photon is imaged on the image sensor 15 in an irradiation distribution of the spot shape of the Airy disk f or close to the Airy disk f, it is possible to distinguish as the in-focus fluorescent light Fl, and if imaged in an irradiation distribution of the spot shape larger than the Airy disk f, it is possible to distinguish as the out-of-focus fluorescent light F2. Here, the Airy disk f indicates the smallest imaged spot at the in-focus position determined theoretically in the diffraction phenomenon of light, and the irradiation distribution thereof is determined depending on the wavelength λ of the fluorescent light F, the numerical aperture NA of the objective lens 16, and the optical magnification M of the imaging optical system 17. Thus, the Airy disk f is appropriate as a reference for the allowable irradiation distribution for discriminating the in-focus point image. Further, the point image formed is an ideal condition, i.e., a perfect optical system without aberration, and if formed by the fluorescent light generated at a position from the center of the depth of field as a starting point, it becomes the Airy disk f, but actually the optical system has a prescribed aberration, and thus the point image of the in-focus fluorescent light Fl detected within the depth of field also becomes slightly larger than the Airy disk f. Thus, a value obtained by multiplying a reference value by an allowable factor is used to classify into the in-focus fluorescent light Fl and the out-of-focus fluorescent light F2. For example, if the allowable factor is set to 1.5, and the measured point image has a diameter of 1.5 times or less of the Airy disk f, it is classified as the in-focus fluorescent light Fl, and if 1.5 times or more, it is classified as the out-of-focus fluorescent light F2. The allowable factor can be arbitrarily adjusted depending on the spatial resolution as a target, the detection efficiency as a target, and the size of the aberration of the optical system. In addition, here, the discrimination reference is set to the diameter size of the Airy disk f, but it is not limited to the reference object. Other features such as the aspect ratio of the diameter, the approximation to the shape of the Airy disk f, or the like can be adopted, or a plurality of them can be simultaneously set as the reference.

[0093] Further, if only the objective lens 16 of the X-ray camera is set to a solid immersion structure of a scintillator-integrated type, the light recovery efficiency η CE is improved only by -5 times, and thus the X-ray-signal comprehensive conversion efficiency becomes [η TOTAL = 89 electrons / X-ray photon], and in addition, for a dry objective lens structure in which only the material of the fluorescent film 11a as a scintillator is set to a Ce:GAGG crystal, the light emission efficiency η LY is improved only by -4 times, and thus the X-ray-signal comprehensive conversion efficiency becomes [η TOTAL[With 68 electrons / X-ray photons], the discrimination accuracy between focused fluorescence F1 and unfocused fluorescence F2 is reduced. Therefore, in order to implement the idea of ​​distinguishing only the focused image from the unfocused image to form the observed image, it is desirable to include optical materials selected in the foreground optical system of the camera in a way that generates at least 100 electrons per X-ray photon on the image sensor 15. In this regard, as explained below, it is most preferable to arrange a solid immersion objective lens at the foreground of the X-ray camera, which is formed integrally with a Ce-added GAGG fluorescent film 11a and a lens-shaped substrate 11b made of GAGG. However, regarding the method of distinguishing focused fluorescence in this embodiment, if the number of electrons detected by photoelectric conversion of the fluorescence incident on the light-receiving surface of the image sensor 15 per X-ray photon is 50 or more, then the ability to distinguish between focused fluorescence F1 and unfocused fluorescence F2 can be obtained by using a low-noise image sensor 15 with less than one electron, thus achieving an improved resolution effect. The number of electrons obtained through photoelectric conversion corresponds to the level of the electrical signal obtained from each pixel.

[0094] That is, the above is an example of using X-rays with photon energies of 10 keV as a light source, but in the case of using X-rays with higher photon energies E, η LY (E) increases proportionally to the photon energy E, therefore for η CE (NA), η TO η VQE The requirements have been relaxed. That is, if the photon energy is high, a solid-state immersion objective optical system with an integrated scintillator can be omitted, and a system using... Figure 2 The planar substrate and drying objective optical system shown in (d) are used to reduce the structure of the NA. Alternatively, a conversion efficiency η can be used on the fluorescent film 11a. SE Low-energy scintillators. Conversely, if the photon energy E is low, then η... LY (E) decreases, therefore for η CE (NA), η TO η VQE Scintillator conversion efficiency η SE The requirements are becoming more stringent, necessitating imaging optics systems with higher photon energy (NA)17 and scintillators with high conversion efficiency. Regardless of the photon energy E used, the overall X-ray-signal conversion efficiency [η] must be met. TOTAL =η LY (E)×η CE (NA)×η TO ×η VQE>50]becomes an index for efficiently obtaining the effect of the present method. That is, it is important to maintain the total conversion efficiency until the visible fluorescent light generated by one photon of the X-rays reaching the scintillator is received by the image sensor 15 and converted into electrons as 50 or more. In order to perform the classification of the in-focus fluorescent light Fl and the out-of-focus fluorescent light F2 with higher precision, it is desirable to set η TOTAL (E, NA) > 300.

[0095] As described above, by employing the solid immersion objective optical system using the SIL 11, the scintillator having a high conversion efficiency, such as the Ce:GAGG scintillator, the X-ray-signal comprehensive conversion efficiency η TOTAL can be sufficiently improved, it is possible to distinguish the in-focus fluorescent light Fl and the out-of-focus fluorescent light F2 in units of X-ray photons, or to improve the precision thereof. Thereby, by reconstructing the sample image from only the signal of the in-focus fluorescent light Fl, even in the case where the fluorescent film 11a is thicker than the depth of field of the imaging optical system 17, it is possible to avoid the reduction in spatial resolution. In addition, even in the case where the lens-shaped fluorescent base 11e having the scintillator function as a whole is used as in (c) of Figure 2 , it is possible to constitute the image by distinguishing only the in-focus fluorescent light Fl, and thus it is possible to avoid the reduction in spatial resolution.

[0096] By constituting the image from only the signal of the in-focus fluorescent light Fl, it is no longer necessary to strictly control the thickness of the fluorescent film 11a in the case where the fluorescent film 11a is formed as in (a) of Figure 2 , (b) of Figure 2 , and thus it is possible to suppress the reduction in optical quality such as distortion generated at the time of thin film processing. Thereby, it is possible to perform optical design of the imaging optical system 17 including the SIL 11 with high precision, and as a result, it is possible to improve the spatial resolution. In the case where the lens-shaped fluorescent base 11e is used as in (c) of Figure 2 , the optical quality reduction is further suppressed since there is no process of forming a processed thin film. At the same time, since the number of processing steps is reduced, the manufacturing cost is also improved.

[0097] In addition, the present method accumulates the signal of the in-focus fluorescent light Fl in units of X-ray photons, that is, applies the photon counting method, and thus, during the counting, signals other than the signal originating from the X-ray photons, that is, noise of the image sensor 15, stray light generated by the scattering light inside the lens which does not contribute to imaging, ghosting, and the like are eliminated, and it is possible to obtain an image with higher contrast.

[0098] The focus signal discrimination section 22a of the image processing system that divides the signal of the X-ray photons that constitute the sample image by each photon, i.e., the image signal processing section 22, performs the following discrimination process. The generation of the image is performed using only the electric signal (hereinafter also referred to as focus signal) obtained by photoelectrically converting the in-focus fluorescent light Fl, whereas the electric signal (hereinafter also referred to as out-of-focus signal) obtained by photoelectrically converting the out-of-focus fluorescent light F2 is not used in the generation of the image. Details of the process of dividing the signal of the X-ray photon group by X-ray photon as a unit for discriminating the in-focus fluorescent light Fl and the out-of-focus fluorescent light F2, and details of the process of generating the image using only the focus signal will be described in detail in the flowcharts of FIGS. 10 and 11. Figure 7

[0099] As described above, by generating the image using only the focus signal, it is possible to improve the contrast quality of the generated image, and it is possible to achieve the spatial resolution of the diffraction limit even in the case of using the X-ray camera having the scintillator with the fluorescent film 11a thicker than the depth of field. In addition, in the present embodiment, in addition to the generation of the image using only the focus signal, imaging using the photon localization method, which is one of super-resolution techniques, is performed, and thus it is possible to obtain the resolution exceeding the diffraction limit that is the theoretical spatial resolution. Hereinafter, the imaging using the photon localization method will be described.

[0100] [Photon localization method]

[0101] Figure 4 (a) to (d) of FIG. 9 are used to explain the super-high-precision imaging method of the photon localization method using the function of the point image signal detection section 22c in the system configuration of FIG. 8. Figure 1 A diagram of the super-high-precision imaging method of the photon localization method using the function of the point image signal detection section 22c in the system configuration of FIG. 8. In the X-ray camera using the scintillator, when observed in units of X-ray photons, the X-ray photon group constituting the sample image is converted into visible light by the scintillator in the case where the X-ray photon group is absorbed at the in-focus position, and thereafter, becomes a bright spot (point image) blurred in shape of the Airy disk f due to the diffraction phenomenon generated in the transmission process of the lens system, and thus is detected by the image sensor 15. That is, the minimum signal unit in which the point image is generated as one X-ray photon and which is constituted by accumulating the X-ray photons according to the incident position of the X-ray photons and the number of X-ray photons is received by the image sensor 15. The spatial resolution δ is defined by the radius of the point image of the Airy disk f, [δ = 0.61 x λ / NA] as described in paragraph 0017.

[0102] The photon localization method is a method of highly accurately determining the incident position of the X-ray photon by detecting the center position of the detected point image of the X-ray photon, and the accuracy of localization depends on the number N of photons of the fluorescent light F constituting the point image, and is expressed using the radius δ of the point image of the Airy disk f as​ In other words, the more photons N of fluorescence F detected on image sensor 15, the greater the improvement in localization accuracy. This formula is an approximation assuming that the noise value of image sensor 15 is extremely small, thus ignoring the influence of pixel size.

[0103] When localization is applied, the radius of the point image, which is the smallest unit of signal, is effectively reduced from the radius δ of the point image of the Allied disk f to the detection error δ at the center position. SUPER After reducing the size of the point image, when the signals of the detected X-ray photon groups are accumulated again to construct an image, the spatial resolution becomes δ. SUPER Compared to the original image before processing, it has been improved to times.

[0104] To implement this method, it is necessary to measure each X-ray photon independently and apply localization processing. In conventional imaging processes where the signals of a group of transmitted X-ray photons are aggregated and exposed in a single frame, the resulting image is an accumulation of photons, making it impossible to measure and evaluate each individual X-ray photon. Therefore, by dividing the frame into a large number of subframes with short exposure times (frame-by-frame images) and capturing them sequentially, the signal density of the X-ray photon group in each subframe is reduced. If... Figure 4 As shown in (a), the density can be reduced to a level that allows for discrete observation of X-ray photons within a subframe, thus enabling the determination of the fluorescence F irradiation distribution for each point image, and enabling... Figure 4 The localization is applied as shown in (c).

[0105] Even if the exposure time of the image sensor 15 is set to the minimum, it is still not possible to sufficiently discretize the X-ray photon signal within a subframe. In such cases, the X-ray output from the radiation source 200 can be reduced, or the X-ray intensity can be attenuated by inserting a radiation attenuation plate 400 between the radiation source 200 and the sample 900, thereby further reducing the density of the X-ray photon group reaching the sample 900.

[0106] exist Figure 5 Figures (a) to (c) illustrate the signal density of the fluorescence spot corresponding to the X-ray photon group detected within the subframe, which serves as the indicator. In the figures, for simplicity, the focusing fluorescence (focus signal) F1 is arranged at equal intervals, but in reality, it includes the off-focus fluorescence (off-focus signal) F2, which is larger than the focusing fluorescence F1, and the detection positions are random. Furthermore, the effective pixel size A on the detection surface is set to 1 / 2 to 1 / 3 of the radius (Alyfell disk radius) of the focusing fluorescence F1. Figure 5 (a) shows the detection density I, which detects an average of 16 X-ray photons per 400 pixels. DET= 9 photons / 400 pixels = 0.023 photons / pixel), Figure 5 (b) shows a detection density I of 400 pixels detecting an average of 9 X-ray photons DET = 9 photons / 400 pixels = 0.023 photons / pixel), Figure 5 (c) shows a detection density I of 400 pixels detecting an average of 4 X-ray photons DET = 4 photons / 400 pixels = 0.01 photons / pixel).

[0107] In the case of (a) and (b) of Figure 5 In the case of (a) and (b) of Figure 5 In the case of (c) of, the point images are detected separately at a high frequency, and each point image can be evaluated one by one. Thus, the index of the detection density of the X-ray photons can be observed discretely within the subframe as 0.01 photons / pixel, and a value close thereto or a value smaller than that is recommended. However, even around 0.02 photons / pixel, the point image signals that have overlapped can be detected by the enlargement of the light-receiving pixels, and thus can be applied to the localization processing by performing processing such as excluding the point image from the data.

[0108] Regarding the minimum exposure time of the image sensor 15, in addition to being limited by the characteristics of the sensor device itself and the limit value on the signal line, it is also limited by the decay time τ until the fluorescence F of the scintillator emits and extinguishes. For example, in the case where the subframe exposure time is not sufficiently longer than that value, the signal of one photon of the X-ray reaches the image sensor 15 at the boundary time of the subframes, and the frequency of the signal splitting into two continuous subframes becomes high. In order to sufficiently reduce the frequency of the splitting, it is desirable to set the exposure time to around 10 times the decay time τ. Although it is not possible to make the frequency of the signal splitting completely zero, in the case where the size of the number N of the detected photons of the fluorescence F is smaller than a prescribed value and there are point image signals at the same position of the two continuous subframes, the quality of the data can be maintained by performing processing such as removing these signals or aggregating to restore one X-ray photon signal.

[0109] For example, in the case where Ce:GAGG is used for the fluorescence film 11a, the fluorescence afterimage time or the decay time τ of the Ce:GAGG is around 100 ns, and thus it is recommended to set the exposure time of the image sensor 15 to 1000 ns or more, which is 10 times, and the maximum frame rate to 1 MHz or less.

[0110] An example is shown of the application of this embodiment in the applicant's radiation facility known as SPring-8. For example, when a quasi-monochromatic X-ray with a photon energy of 10 keV is set as the radiation source 200, the X-ray R reaches its maximum [I PH =1×10 14 photons / second / mm 2 The intensity of X-rays R is incident on the detection surface (scintillator surface). In a solid-state immersion lens optical system and a solid-state immersion lens material using a GAGG structure, the numerical aperture is set to NA = 1.76, and the spatial resolution is set to δ = 180 nm. The effective pixel size A on the detection surface is set to approximately 1 / 2 to 1 / 3 of the spatial resolution δ, which is set to 60 nm in this case. Furthermore, the Ce:GAGG thickness that yields the focused fluorescence F1 is 311 nm, and the probability (X-ray quantum efficiency) η of X-ray R being absorbed by the scintillator is... XQE η is given by X-ray energy of 10 keV. XQE =3.2%. When the image sensor 15 performs exposure at a frame rate of 1 MHz, the detection density I of X-ray photons in the subframe is... DET Become [I DET =I PH ×η XQE ×T=1×10 14 (photons / second / mm) 2 )×3.2(%)×1000(ns)=3.2×10 6 (Photons / mm 2 ) = 1.15 × 10 -2 [(photons / pixel)]. That is, for 100 pixels, which is an indicator of the discretization of a visible point image, a value close to that of one photon of an X-ray (=0.01 photons / pixel) can be obtained.

[0111] As described above, if the light source intensity is determined, then for 100 pixels, which serves as an index for discretization of the visible point image, it is determined that the intensity satisfies one photon or less of the X-ray (I DET The minimum frame rate under the condition of ≤~0.01 photons / pixel. For example, in the above embodiment, the frame rate is 1×10⁻⁶ when X-ray R is at a minimum. 10 (photons / second / mm) 2 When the intensity of the image sensor 15 incident on the detection surface is ~100Hz or higher, the frame rate of the image sensor 15 is preferably ~100Hz or higher.

[0112] Figure 4 (a) is a group of subframes acquired by irradiating the sample 900 with X-rays R and taking continuous images at specified time intervals. By shortening the exposure time, subframes are formed that are sufficiently fragmented in time, thereby enabling discrete observation of the X-ray signal within the image in units of X-ray photons. Furthermore, inFigure 4 In (a), only the use of Figure 3 The image generated by the focus signal shown in (a). Figure 4 (b) shows that Figure 4 The image data obtained by accumulating the subframe group shown in (a) (in the figure, it is indicated by an unclear "R" as an example).

[0113] like Figure 4 As shown in (a), even when only the focus signal is selected, because the focus signal is Figure 3 The signals within the predefined size range in (a), that is, signals with an Airy disk f or a similar shape to Airy disk f, are therefore slightly blurred. When these signals are accumulated, it is possible to obtain... Figure 4 The image data is slightly blurry, as shown in (b). Furthermore, Figure 4 In (a), a point (circle) within the frame represents the fluorescence F generated corresponding to a photon of an X-ray R emitted from the radiation source 200 and absorbed by the fluorescent film 11a.

[0114] Figure 4 (c) shows the target Figure 4 The subframes shown in (a) are localized. Specifically, the subframes are calculated through image processing. Figure 4 The central location of the fluorescence F generated corresponding to a single photon of the X-ray in (a) is represented by a point at that central location (the center of the dot image). That is, the signal of the focused fluorescence spot detected across multiple pixels shows a distribution close to a Gaussian distribution in the Airy disk f, thus the coordinates (x, y) of the center location of the spot can be determined by comparing the signal levels of each pixel. Figure 4 As shown in (c), the subframe image after localization represents each X-ray photon with a point at the image center, thus providing high-precision data on the X-ray incident position. Therefore, as... Figure 4 As shown in (d), when Figure 4 When the subframe group of (c) is accumulated, a clear image can be obtained (in the figure, it is indicated as a clear "R" as an example).

[0115] As described above, by selecting only the focus signal (refer to...) Figure 3 And perform imaging using photon localization (see...) Figure 4), it is possible to increase the spatial resolution of the radiation imaging apparatus 100 to a value exceeding the diffraction limit. In the present embodiment, the spatial resolution of the radiation camera 10 using Ce:GAGG in the material of the fluorescent film 11a of the SIL 11 is δ = 180 nm, and the average value of the number of photons N of the fluorescent F and the X-ray-signal comprehensive conversion efficiency η TOTAL is uniform and is η TOTAL = 335 electrons / X-ray photon, and thus, when the photon localization method is applied, a super-resolution spatial resolution (= 4.9 nm line & space) is achieved. Thus, compared to 96 nm (48 nm line & space), which is the theoretical limit value as the related art, the spatial resolution can be greatly increased.

[0116] Further, the position of the fluorescent F imaged by the image sensor 15 sometimes fluctuates in association with the sample 900 moving due to the intensity of the X-rays R being too strong, the device for fixing and position adjusting of the sample 900 shaking, and the like. In the present embodiment, drift correction that corrects the fluctuation of the position of the fluorescent F is performed. In the present embodiment, in the drift correction, the spot center x coordinate and the spot center y coordinate of each fluorescent F at time t are found to correct the prescribed values Δx and Δy. Further, whether or not to perform the drift correction can be arbitrary, and the drift correction can not be performed.

[0117] Figure 6 is a diagram showing the processing flow of the image signal in the present embodiment together with the system structure. When the data of the subframe group read from the image sensor 15 of the radiation camera 10 is input to the image signal processing section 22, it is temporarily saved to the frame memory corresponding to the image data storage section 22b (S11). Next, it is discriminated whether each of the spot signals present within the subframe group is an in-focus signal or an out-of-focus signal (S12). Next, the center position of the spot considered to be the in-focus signal present within the subframe group is detected (S13), and the detection data is generated for each spot to obtain a detection data group (S14). The detection data is composed of the spot center position (x, y), the number of photons N (E) of the fluorescent F forming the spot, the standard deviation (σ) of the spot signal distribution, and the time (t) when the spot is detected. Further, in the case where the entire pixel signals of the image sensor 15 are measured at the same time, the time t can be set to the number of the subframe.

[0118] The amount of drift in the space of the detected point image at each point in time t is detected (S15), drift correction of the point image center position is performed based on the detected amount of drift (S16), and a corrected detection data group shown in S17 is obtained. The corrected detection data group obtained in S17 is stored in the storage section 42 (S20). On the other hand, an output frame for reconstructing an image is generated (S18), and by plotting the detection data group obtained in S17 on the output frame, a high resolution frame obtained by accumulating the sub-frame group in which the photon localization processing is substantially performed is obtained (S19). The high resolution frame is stored in the storage section 42 (S21).

[0119] Further, Figure 6 x in the x coordinate of the point image center position of the X-ray photon i i y in the y coordinate of the point image center position of the X-ray photon i i Δx in the x direction of the X-ray photon i i Δy in the y direction of the X-ray photon i i X in the x direction of the X-ray photon i i Y in the x coordinate of the point image center position of the X-ray photon i after drift correction i Y in the y coordinate of the point image center position of the X-ray photon i after drift correction i E in the signal value of the X-ray photon i (a value corresponding to the number N of photons of the fluorescent light F detected by the image sensor 15) i σ in the standard deviation of the point image signal distribution of the X-ray photon i (the standard deviation of the irradiation distribution of the fluorescent light F detected by the image sensor 15) i t in the detected time (or the number for determining the sub-frame)

[0120] It is also possible to exclude low quality detection data when plotting the detection data obtained in S17 in the step of S19. Low quality data is, for example, a case where the value of the standard deviation σ is large, or a case where the value of the signal value is small. As for the threshold value, the numerical aperture, the magnification of the optical system, the spatial resolution targeted, the theoretical Airy disk f shape corresponding to the wavelength of the fluorescent light F of the scintillator, the X-ray-signal comprehensive conversion efficiency η TOTAL is set to a predetermined value.

[0121] Figure 7This is a flowchart illustrating the imaging operation of the radiation imaging apparatus 100 in this embodiment. When the imaging operation of the radiation imaging apparatus 100 begins, in step S01, the control unit 20 sets the photon energy, output value, energy spectrum, etc. of the X-rays R from the radiation source 200 used in the measurement. Next, the imaging optical system 17 is focused so that the area near the incident surface of the X-rays R on the fluorescent film 11a is imaged on the image sensor 15. Furthermore, imaging conditions such as the exposure time and intensity of the X-rays R are set to spatially separate the X-rays by each photon. Specifically, the exposure time control unit 21a shortens the exposure time of the image sensor 15, or reduces the intensity of the X-rays R, thereby reducing the signal density of the X-rays R in each subframe. Figure 5 As shown in (c), the imaging conditions are set up to allow X-rays R to be spatially separated into individual photons.

[0122] Here, in the case of using high-energy X-rays with strong penetrating power, or using... Figure 2 In cases where the foreground optical system, such as in (c), is entirely composed of a SIL 11 made of phosphor material, or where two components constitute the radiation camera 10, the proportion of detected out-of-focus signals can sometimes become extremely high. In such cases, even if the signal density of X-ray R per frame is reduced, if the diameter of the blurred spot generated by the out-of-focus signal is large, the background noise increases due to the overlap of multiple out-of-focus signals, and the point image of the focused signal is sometimes buried by noise and cannot be distinguished. In such situations, further shortening the exposure time or reducing the intensity of X-ray R, setting each subframe to detect only one photon of X-ray, can separate the focused and out-of-focus signals into different subframes, thereby addressing the problem.

[0123] Next, the camera conditions constructed in step S01 are used to generate the expected spatial resolution δ. SUPER The output of the reconstructed image corresponding to the field of view is in frames.

[0124] Next, in step S02, the camera control unit 21 continuously captures images of the sample 900 according to the set imaging conditions to obtain a group of subframes of the sample 900.

[0125] Next, in step S03, the image signal processing unit 22 processes all the bright spots within the subframe group obtained in step S02 to acquire the outline of each bright spot. Next, in step S04, the outline of each bright spot is evaluated to determine whether the signal is a focus signal or an out-of-focus signal. Here, a focus signal is as follows: Figure 3 As shown in (a), the signal detected is converged within a predetermined range on the image sensor 15, that is, the shape of the light spot, either the Ally spot f or close to the Ally spot f. On the other hand, the off-focus signal, such as Figure 3signal, that is, a light spot shape larger than the Airy disk f, is detected as shown in (b) of FIG. 9, and thus by detecting and evaluating the distribution of the signal, it is possible to discriminate whether the signal is an in-focus signal or an out-of-focus signal.

[0126] Next, in step S05, the image signal processing section 22 detects the point image center of the bright spot classified as an in-focus signal in step S04 by image processing. In step S06, the image signal processing section 22 corrects the drift of the point image center position based on the detected drift amount. In step S07, the image signal processing section 22 constructs a high-resolution frame in which the entire image is reconstructed by plotting the detected respective point image centers on the output frame.

[0127] As described above, according to the radiation imaging apparatus 100 of the present embodiment, an image is constituted using only in-focus signals, and data processing using the photon localization method is performed, whereby it is possible to improve the contrast quality of the image, and it is possible to increase the spatial resolution of the radiation imaging apparatus 100 to δ SUPER = 9.8 nm (= 4.9 nm for line and space).

[0128] The number of subframe groups required is determined by the detection density I DET , the ratio of the effective pixel size A on the detection surface to the pixel size A SUPER of the high-resolution frame finally output, and the dynamic range D (the maximum value of the number of X-ray photons within one pixel) of the high-resolution frame finally output, and is expressed by N FRAME = D / (I DET × (A SUPER / A) 2 ).

[0129] In the case where super-resolution processing such as photon localization is performed, the detection density value that becomes the index is I DET = 0.01 photons / pixel, the spatial resolution is increased to about 10 times the original image, and the maximum tone that the human eye can confirm is about 8 bits (= 256), and thus N FRAME = 256 / (0.01 x (1 / 10) 2 ) = 2.56 x 10 6 subframe groups become the index. In fact, even if a value less than this value, for example, D = 6 bits and N FRAME = 6.4 x 10 5 or so, the photon localization processing described above can be applied, and a high-resolution image in which the spatial resolution is increased is obtained.

[0130] Using the parameters of the present embodiment, in the case where I DET= 0.01 photons / pixel, A = 60nm, pixel size A SUPER For spatial resolution δ SUPER Approximately 1 / 3, and set as A SUPER =δ SUPER / 3 = 9.8nm / 3 = 3.3nm, Dynamic Range D = 8bit = 2 8 With 256 photons, the required number of subframes can be estimated as N. FRAME =256 / (0.01×(3.3 / 60)) 2 ) = 8.5 × 10 6 Zhang. Given a structure capable of acquiring subframes at 1MHz, the total camera time becomes T. TOTAL =8.5×10 6 / 1MHz = 8.5 seconds.

[0131] [Generation of energy decomposition image]

[0132] The above are examples where all X-ray photons, such as in a radiation facility, have monochromatic or quasi-monochromatic energy. On the other hand, Figure 8 (a) to (c) are for illustrating the X-ray energy decomposition image generation unit 22d when using an X-ray source with mixed energy. Figure 1 The image processing performed using the above embodiments. Figure 7 The focused fluorescence F1, which is acquired by continuous shooting in step S02 and identified and extracted in step S04, is detected on the image sensor 15 as a point image composed of different photon numbers N because the energy of the incident X-ray photons is different. Figure 8 (a)). The total number of pixels constituting the dot image (detection data E) is proportional to the photon energy, thus allowing the determination of the X-ray energy for each focused fluorescence F1. Its detection error is a Poisson error dependent on the number of photons N of the fluorescence F forming the dot image, obtained through… express.

[0133] For example, in the case where fluorescence F is detected on image sensor 15 with a photon number N = 335, it has The detection error. If the X-ray is 10 keV, it means that it can be measured with an energy resolution of 0.54 keV. Thus, the larger the number N of photons of the detected fluorescence F, the smaller the detection error, and therefore the greater the improvement in energy resolution. That is, when using a solid-state immersion lens optical system, a scintillator with high conversion efficiency such as Ce:GAGG, etc., the X-ray-signal integrated conversion efficiency η of the radiation camera 10 is improved. TOTAL At that time, the energy resolution is improved.

[0134] Next, a plurality of ranges of X-ray energy is set, and the focused fluorescent light F1 is classified into each range. Figure 8 (b) of FIG. 6 shows a case where three ranges of X-ray energy are set and each sub-frame is divided by energy range to perform accumulation. In actual data processing, for each point image of detected data, an output frame is selected and plotted according to the size of the number of photons N of the fluorescent light F forming the point image. Thereby, an image (c) of FIG. 6 can be generated for each energy range. Further, in (b) and (c) of FIG. 6, a deep shade (left drawing) indicates fluorescent light F having a large number of photons N, a medium shade (center drawing) indicates fluorescent light F having an intermediate number of photons N, and a light shade (right drawing) indicates fluorescent light F having a small number of photons N. Figure 8 Figure 8 (b) and (c) of FIG. 6, a deep shade (left drawing) indicates fluorescent light F having a large number of photons N, a medium shade (center drawing) indicates fluorescent light F having an intermediate number of photons N, and a light shade (right drawing) indicates fluorescent light F having a small number of photons N.

[0135] As described above, the present embodiment can classify each X-ray photon into a plurality of ranges of X-ray energy, and generate an image for each range of X-ray energy. That is, the present image processing functions as an energy filter. Thereby, the energy dependence of the X-ray image can be observed by one-time imaging, and thus the constituent material can be determined in addition to the internal structure of the sample 900. According to the present method, the energy that can be processed as data by the detector can be selected, and thus X-ray imaging using quasi-monochromatic energy can be performed even in an industrial X-ray generating apparatus where energy is mixed in a wide range.

[0136] In addition, the photon localization processing can be applied to the point image in each sub-frame of each energy range shown in (b) of FIG. 6, and a radiation imaging apparatus 100 having both energy resolution and high spatial resolution can be realized. Figure 8

[0137] [Other modifications]

[0138] Figure 6 , Figure 7 Each data processing shown in FIG. 6 can be realized by high-speed processing and real-time data processing using not only the CPU in the computer but also the hardware operation of the integrated circuit such as FPGA, ASIC, GPU, and the like in the electronic circuit of the driving / data reading section of the image sensor 15, that is, the image data reading control section 21b. Alternatively, the circuit equivalent to these functions can be mounted on the image sensor 15.

[0139] The present embodiment can be applied not only to the refractive objective lens but also to the reflective objective lens (Schwarzschild type). In this case, the objective lens design having a high numerical aperture in the short wavelength region UV can be performed, and the spatial resolution is further improved. For example, Pr:LuAG that generates ultraviolet light having a wavelength of 305 nm, that is, fluorescent light F can be used for the fluorescent film 11a.​​

[0140] The imaging optical system 17 can also have a cylindrical lens. By using a cylindrical lens of an appropriate focal length in cooperation with the depth of focus of the rear lens group 12 of the objective lens, as shown in (a) and (b) of FIG. 9, not only the size of the point image profile but also the aspect ratio and the like of the profile are evaluated, whereby the precision of discrimination of the in-focus signal and the out-of-focus signal can be improved, and observation of the sample 900 with high precision can be performed. Figure 3

[0141] The present application has been described above using embodiments, but the scope of the present application is not limited to the range described in the above embodiments. Various changes or modifications can be made to the above embodiments, as will be apparent to those skilled in the art. It is clear from the recitations of the claims that modes obtained by making such changes or modifications are also included in the scope of the present application.

[0142] As for the order of execution of each process such as actions, processes, steps, and stages and the like in the apparatuses, systems, programs, and methods shown in the claims, the specification, and the drawings, it should be noted that, as long as there is no particular indication of "before," "prior to," and the like, and the output of the preceding process is not used in the subsequent process, it can be implemented in any order. As for the action flow in the claims, the specification, and the drawings, even if it is described using "first," "next," and the like for convenience, it does not mean that it must be implemented in that order.

[0143] Explanation of Reference Signs

[0144] 10: radiographic camera; 11: SIL; 11a: fluorescent film; 11b: lens-shaped base; 11e: lens-shaped fluorescent base; 11f: SIL placement stage; 12: rear lens group of objective lens; 13: band-pass filter; 14: imaging lens; 15: image sensor; 16: objective lens; 17: imaging optical system; 20: control section; 21: camera control section; 21a: exposure time control section; 21b: image data read control section; 22: image signal processing section; 22a: in-focus signal discrimination section; 22b: image data storage section; 22c: point image signal detection section; 22d: X-ray energy resolution image generation section; 100: radiographic imaging apparatus; 200: radiographic source; 300: placement stage control section; 400: radiographic attenuation plate; 500: radiographic source control section; 900: sample; 910: sample placement stage; R: X-ray; F: fluorescent light; F1: in-focus fluorescent light; F2: out-of-focus fluorescent light; f: Fleck.​

Claims

1. A radiation imaging apparatus comprising: a radiation camera having a scintillator, an imaging optical system, and an image sensor, radiation transmitted through an object of imaging from a radiation source is incident to the scintillator, and the scintillator emits fluorescent light having a longer wavelength than that of the radiation, the imaging optical system images an imaging surface by an objective lens having a depth of field matched to a sample surface of the scintillator, and the image sensor is disposed on the imaging surface and has a light receiving surface composed of a plurality of pixels; and a control section that generates an image based on a sensor signal of each of the plurality of pixels output from the image sensor of the radiation camera, the control section has an exposure time control section that controls a subframe exposure time of the image sensor so that focused fluorescent light at a depth of field where the radiation reaching the scintillator is focused and unfocused fluorescent light other than the depth of field are separately captured at the light receiving surface of the image sensor for each particle of the radiation, a focus signal discrimination section that discriminates a point image sensor signal of a light receiving pixel group corresponding to a spot of the focused fluorescent light and a point image sensor signal of a light receiving pixel group corresponding to a spot of the unfocused fluorescent light separately included in each subframe, and an image signal processing section that generates the image by accumulating subframe data based on the point image sensor signal from the light receiving pixel group corresponding to the spot of the focused fluorescent light.

2. The radiation imaging apparatus according to claim 1, wherein wherein the image signal processing section includes a point image signal detection section that processes the point image sensor signal from the light receiving pixel group corresponding to the spot of the focused fluorescent light to calculate a center position of a point image in the light receiving pixel group, and generates the image based on the center position.

3. The radiation imaging apparatus according to claim 1 or 2, wherein the image signal processing section includes a radiation energy distribution image generation section that divides a light receiving sensor signal level of each of the spots of the focused fluorescent light corresponding to radiation having different energies and separately incident to the scintillator in units of particles into a plurality of level ranges in a plurality of continuous subframes, and generates the image corresponding to an energy distribution of radiation based on the sensor signals of the spots of the focused fluorescent light included in the same level range.

4. The radiation imaging apparatus according to any one of claims 1 to 3, wherein 5. The radiation imaging apparatus according to any one of claims 1 to 4, wherein the objective lens includes a frontmost lens of a solid immersion lens structure integrally formed with a fluorescent film as a scintillator on an incident surface side of the radiation. The exposure time control section controls the exposure time in accordance with the intensity of the radiation so that the frequency of detection of radiation in the image sensor is 0.02 photons / pixel / subframe or less, and at least 6.4 x 10 5 The image is generated from a continuous video signal.

6. The radiation imaging apparatus according to any one of claims 1 to 4, wherein ​ ​ The objective lens includes a frontmost lens composed of a fluorescent film as the scintillator and a lens-shaped base body in which the fluorescent film is integrally formed on the incident surface side of the radiation, and the fluorescent film is composed of a solid optical material obtained by adding a predetermined activator to a solid optical material constituting the lens-shaped base body as a master batch.

7. The radiation imaging apparatus according to any one of claims 1 to 4, wherein The objective lens has a frontmost lens composed of a fluorescent film as the scintillator and a lens-shaped base body in which the fluorescent film is integrally formed on the incident surface side, and a difference in refractive index between the fluorescent film and the lens-shaped base body is less than 0.1%.

8. The radiation imaging apparatus according to any one of claims 1 to 4, wherein The objective lens includes a frontmost lens of a solid immersion lens structure formed of a material having a scintillator function.

9. The radiation imaging apparatus according to claim 6 or 7, wherein The lens-shaped base body is formed of an un-doped garnet crystal, and the fluorescent film is formed of a garnet crystal obtained by adding an activator to the un-doped garnet crystal.

10. The radiation imaging apparatus according to claim 6 or 7, wherein The lens-shaped base body is formed of an un-doped gadolinium aluminum gallium garnet (GAGG), and the fluorescent film is formed of a gadolinium aluminum gallium garnet (Ce:GAGG) to which cerium as an activator is added.

11. The radiation imaging apparatus according to any one of claims 1 to 10, wherein The radiation imaging apparatus has a radiation-signal comprehensive conversion efficiency that makes one photon or one particle of radiation generate a fluorescent light in a fluorescent film, which is detected as a point image signal of 50 or more electrons by a pixel on a light-receiving surface of an image sensor.

12. The radiation imaging apparatus according to any one of claims 1 to 10, wherein The radiation is X-rays, and indicates an X-ray-signal comprehensive conversion efficiency η of conversion efficiency to a sensor signal detected by the image sensor TOTAL satisfies a conditional expression using a luminous efficiency η of the optical system LY (E), a light recovery efficiency η of the optical system depending on a numerical aperture NA CE (NA), a transmittance η of the optical system TO and a quantum efficiency η of the image sensor for fluorescence VQE The conditional expression is η TOTAL = η LY (E) x η CE (NA) x η TO x η VQE > 50.

13. A radiation imaging method using a radiation imaging apparatus having a camera section as a main body, controlling an exposure time of each subframe of an image sensor having a light-receiving surface composed of a plurality of pixels, to extract radiation incident to a scintillator as a point image signal of a visible light spot dispersed per particle, and thereafter discriminating the point image signal in each subframe as a point image signal of an in-focus light spot obtained by emitting light at a depth of field of a solid-immersion front lens and a point image signal of an out-of-focus light spot obtained by emitting light outside the depth of field, generating a radiation observation image by superimposing subframe data based on the point image signal of the in-focus light spot, wherein, The camera section includes the solid immersion type frontmost lens provided with the scintillator that converts incident radiation into visible light on the incident surface side of the radiation, and the lens shape on the exit surface side, and the camera section observes a visible light image from the solid immersion type frontmost lens by the image sensor.

14. A radiation imaging method including a control stage in which, in a radiation imaging apparatus provided with a radiation camera having: a scintillator through which radiation transmitted through a subject of imaging from a radiation source is incident, and which emits fluorescent light having a longer wavelength than the radiation; an imaging optical system that images an imaging surface by an objective lens having a depth of field matched to a sample surface of the scintillator; and an image sensor disposed on the imaging surface, having a light-receiving surface composed of a plurality of pixels, the control stage includes the following stages: an exposure time control stage of controlling a subframe exposure time of an image sensor so that in-focus fluorescent light at a depth of field generated by radiation reaching a scintillator and out-of-focus fluorescent light other than the in-focus fluorescent light are separately captured on a light-receiving surface of the image sensor for each particle of the radiation; a focus signal discrimination stage of discriminating a sensor signal of a light-receiving pixel group corresponding to a spot of the in-focus fluorescent light and a sensor signal of a light-receiving pixel group corresponding to a spot of the out-of-focus fluorescent light separately contained in each subframe; and an image signal processing stage of generating the image by superimposing subframe data based on the sensor signal of the light-receiving pixel group corresponding to the spot of the in-focus fluorescent light.

15. The radiation imaging method according to claim 14, wherein the radiation is X-rays, and the radiation camera is an X-ray camera including a scintillator and an objective lens optically designed so that a conversion efficiency of each photon of the X-rays converted into a sensor signal detected by the image sensor becomes 50 or more in terms of the number of electrons, the radiation imaging method further includes a stage of performing signal processing of detecting a spot center position of the spot of the in-focus fluorescent light; and superimposing subframe data constituted by the detected spot center data of the spot center position to generate a super-resolution X-ray image.

Images