Image resolution verification method and inspection apparatus

Abstract

To provide an image resolution confirming method which can easily confirm a resolution of an image by an edge method.SOLUTION: An image resolution confirming method includes: an X-ray irradiation step S1 for uniformly irradiating an X-ray XR on an imaging plate IP; an edge formation step S2 for performing an exposure process in a range of one predefined width or more in a predefined direction while conveying the imaging plate IP to emit the energy accumulated by the X-ray XR on the imaging plate IP from the imaging plate IP, to form an edge E on the imaging plate IP; an edge image acquiring step S3 for performing an optical scan process on an entire image formation surface of the imaging plate IP to acquire an edge image in the X-ray image; a line spread function calculation step S4 for calculating the line spread function LSF from the edge image; a modulation transfer function calculation step S5 for calculating a modulation transfer function MTF; and a resolution calculation step S6 for calculating a resolution of an imaging plate scanner.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an image resolution confirmation method and an inspection apparatus.

Background Art

[0002] Conventionally, in order to confirm the resolution of an X-ray image recorded using X-rays, a line spread function (LSF: Line Spread Function, hereinafter appropriately referred to as "LSF") obtained by photographing a slit formed on a metal plate is Fourier-transformed to measure a modulation transfer function (MTF: Modulation Transfer Function, hereinafter appropriately referred to as "MTF"), or an edge method in which an edge image obtained by photographing the edge of a metal plate is differentiated to obtain an LSF and then the MTF is measured has been used. In the slit method, generally, a slit-shaped X-ray image is formed on an imaging plate using a metal slit (fixture) such as tungsten or aluminum with a slit width of about 10 μm, and it is determined how sharp the X-ray image is from the slit image. The slit-shaped X-ray image is formed by arranging a slit formed on a metal plate in the X-ray irradiation range and irradiating the X-rays. In the edge method, generally, an X-ray image is formed on an imaging plate using a metal plate (fixture) such as tungsten or aluminum, and the resolution of an edge (an image corresponding to the outer shape of the metal plate) included in the X-ray image is confirmed to determine how sharp the X-ray image is (see, for example, Patent Document 1). The X-ray image including the edge is formed by arranging a metal plate in a part of the X-ray irradiation range and irradiating the X-rays.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Thus, determining the resolution of X-ray images required the use of metal plates, which presented a time-consuming problem.

[0005] In view of the above-mentioned problems, the present invention aims to provide a resolution confirmation method and inspection apparatus that can easily confirm the resolution of an X-ray image using the edge method. [Means for solving the problem]

[0006] To solve the aforementioned problems, the image resolution confirmation method according to the present invention includes: an X-ray irradiation step of uniformly irradiating the entire image-forming surface of an imaging plate with X-rays; an edge formation step of releasing energy accumulated on the imaging plate by X-rays from the imaging plate by performing an exposure process on a range of a certain width or more in a predetermined direction while transporting the imaging plate, thereby forming edges which are different parts of the imaging plate where energy has accumulated; an edge image acquisition step of performing an optical scan process on the entire image-forming surface of the imaging plate to obtain an edge image including the edges in the X-ray image; a modulation transfer function calculation step of calculating a modulation transfer function based on the edge image; and a resolution calculation step of calculating the resolution of the imaging plate scanner based on the modulation transfer function.

[0007] Furthermore, the inspection apparatus according to the present invention is an inspection apparatus that self-diagnoses image resolution capability by reading an X-ray image recorded on an imaging plate, calculating a modulation transfer function, and calculating the resolution from the modulation transfer function, and comprises an optical scanning system that irradiates the image forming surface of the imaging plate, which is uniformly irradiated with X-rays, with laser light to form an X-ray image, and irradiates the X-ray image formed on the imaging plate with laser light to read the X-ray image formed on the imaging plate, a transport system that transports the imaging plate in a predetermined direction, an image processing system that optically reads the X-ray image formed on the imaging plate and detects the X-ray image, and a control device that controls the optical scanning system, the transport system and the image processing system, wherein the control device controls the transport system so that the X-rays are uniform While transporting the imaging plate irradiated with X-rays, the optical scanning system performs exposure processing on a range of a certain width or more in a predetermined direction, thereby releasing the energy accumulated on the imaging plate by the X-rays and forming edges, which are areas with different energies, on the imaging plate. While transporting the imaging plate again by the transport system, the optical scanning system and the image processing system perform optical scanning processing on the entire image-forming surface of the imaging plate to obtain an edge image including the edges in the X-ray image. The image processing system calculates the modulation transfer function based on the edge image and calculates the resolution of the imaging plate scanner based on the modulation transfer function. [Effects of the Invention]

[0008] According to the present invention, the resolution of the X-ray image can be easily confirmed using the edge method. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram (partially a block diagram) of an inspection apparatus according to an embodiment of the present invention. [Figure 2] This is a flowchart showing a method for verifying image resolution according to an embodiment of the present invention. [Figure 3]This is an explanatory diagram showing the state when X-rays are irradiated over the entire image-forming surface of an imaging plate. [Figure 4] This is an explanatory diagram showing the state when an imaging plate is transported while being irradiated with laser light to form a band-shaped laser light image. [Figure 5] This is an explanatory diagram showing an image resolution confirmation method according to an embodiment of the present invention, where (a) is an explanatory diagram of an imaging plate on which a laser beam image is formed, and (b) is an explanatory diagram of a waveform showing the energy level when an ideal image is formed on the image forming surface in accordance with the laser beam image of the imaging plate. [Figure 6] This is an explanatory diagram illustrating an image resolution verification method according to an embodiment of the present invention, where (a) is a graph showing the Gaussian distribution of laser light intensity, (b) is a graph showing the laser light image formed by the laser light, and (c) is a graph showing the waveform of an ideal edge image. [Figure 7] This figure shows an image resolution verification method according to an embodiment of the present invention, where (a) is an explanatory diagram of an imaging plate on which a band-shaped laser beam image is formed, (b) is a graph showing the Gaussian distribution of the laser beam intensity for image scanning, (c) is a graph showing the edge image formed by the laser beam, (d) is a graph showing the edge detection position of the edge image formed by the laser beam, (e) is a graph showing the edge detection position of an ideal edge image when a metal plate is used, and (f) is the equation of the function representing the edge. [Figure 8] This is a comparison diagram of an image resolution confirmation method according to an embodiment of the present invention and a conventional method, where (a)-1 is an explanatory diagram of an X-ray edge image projected onto a metal plate using a conventional method, and (a)-2 is a graph showing the pixel values ​​(gray levels) near the edge when using a metal plate in units of 10 pixels on the horizontal axis, and (b)-1 is an explanatory diagram of an edge image formed by scanning with laser light according to an embodiment of the present invention, and (b)-2 is a graph showing the pixel values ​​(gray levels) near the edge of the edge image formed by scanning with laser light in units of 20 pixels on the horizontal axis. [Figure 9]This graph compares the image resolution verification method according to an embodiment of the present invention with a conventional method, showing the MTF obtained based on the edge image when using a conventional metal plate and the MTF obtained based on the edge image formed by scanning with laser light according to an embodiment of the present invention. [Figure 10] This is a schematic diagram (partially a block diagram) of a modified example of an inspection apparatus according to an embodiment of the present invention. [Figure 11] This is a schematic diagram showing multiple strip-shaped laser light images formed on an imaging plate. [Modes for carrying out the invention]

[0010] First, an image resolution verification method and inspection apparatus 1 according to an embodiment of the present invention will be described with reference to Figures 1 to 9. In this embodiment, in the inspection apparatus 1 shown in Figure 1, the direction in which the imaging plate IP and the line sensor 31 face each other is defined as the vertical direction, with the imaging plate IP side being the downward direction and the line sensor 31 side being the upward direction. Before describing the inspection apparatus 1, we will explain the imaging plate IP, the necessity of measuring the resolution of the X-ray image, the method for understanding the degree of the resolution of the X-ray image, and the operating principle of the phototactic light emitter.

[0011] ≪Imaging Plate≫ The imaging plate IP shown in Figure 1 is a recording medium on which image data obtained by X-ray imaging equipment, etc., is recorded. The imaging plate IP is formed, for example, by coating a base material with a photostimulable phosphor (storable phosphor) that can store light according to the dose of X-rays (XR), and consists of a roughly rectangular film when viewed in the thickness direction (vertical direction). When the stimulable phosphor is irradiated with X-rays XR in the ground state, it absorbs the X-rays XR and enters the primary excited state. Then, when it is irradiated with visible light having a wavelength longer than that of the X-rays XR (for example, laser light LB. Hereinafter, the explanation will be given taking the laser light LB as an example), it enters the secondary excited state and emits light (emits light in response to the primary excitation), and has the property of returning to the ground state. Therefore, the imaging plate IP can be used repeatedly.

[0012] Such an imaging plate IP is used in a computed radiography (CR) system. In the computed radiography system, two-dimensional information in the primary excited state is read as a digital image, accumulated, and output.

[0013] <Necessity for measuring the resolution of X-ray images> Generally, in a medical institution, medical equipment is obliged to perform maintenance inspections (daily inspections, regular inspections) in order to maintain the functions, quality, effectiveness, and safety of the equipment and prevent failures, accidents, etc. In the computed radiography system as well, in order to ensure that the inspection is performed normally, it is necessary to measure the resolution of the X-ray image as one item of the regular inspection to confirm whether the equipment is operating as expected.

[0014] <Method for grasping the condition of the resolution of X-ray images> As a method for grasping the condition of the resolution of the X-ray image, as described above, there is a method called the edge method. In the edge method, both an exposed part (formed area) and an unexposed part (non-formed area) are formed in the image formation surface of the imaging plate IP that has been uniformly irradiated with X-rays XR in advance. That is, in the edge method, an X-ray image including both the formed area and the non-formed area is formed.

[0015] Then, the resolution is calculated based on the MTF obtained from the edge image, which is the boundary part between the formed area and the non-formed area, of the scan image obtained by scanning the image formation surface of the imaging plate IP on which such an X-ray image is formed.

[0016] By thus grasping the resolution near the boundary between the formation region and the non-formation region, the resolution of the X-ray image (the entire X-ray image) can be grasped.

[0017] <Operating Principle of Photostimulable Phosphor> The photostimulable phosphor once accumulates the energy of the X-ray XR irradiated thereon and emits light according to the amount of absorption of the X-ray XR. When the irradiation of the X-ray XR is stopped, the emission of the photostimulable phosphor also stops, but even after the passage of time, when irradiated with laser light LB of a specific wavelength, it is excited and emits light according to the irradiation amount of the X-ray XR. X-ray imaging is performed using a resin thin plate (imaging plate IP) coated with a photostimulable phosphor. By irradiating the imaging plate IP with laser light LB and detecting the light emitted from the imaging plate IP with a photomultiplier tube or a line sensor 18, an X-ray image is obtained. When the information of the obtained X-ray image is converted from an analog signal to a digital signal and output to a personal computer or the like, the X-ray image can be viewed on the monitor 34. Thus, the X-ray image, which is a stored image on the photostimulable phosphor plate, can be taken out by scanning with the laser light LB, subjected to computer processing, and output as digital information.

[0018] ≪Inspection Device≫ The inspection device 1 shown in FIG. 1 is a device that reads the X-ray image recorded on the imaging plate IP and calculates the modulation transfer function (MTF). The inspection device 1 has both a function of forming an edge image on the imaging plate IP and a function of an imaging plate scanner that reads the formed image from the imaging plate IP. Here, the edge image refers to an image representing the object including the boundary line (outline) between the object and the outside of the object (background).

[0019] More specifically, the inspection device 1 transports an imaging plate IP irradiated with X-rays XR in a predetermined direction (the sub-scanning direction, which is the transport direction perpendicular to the vertical direction: the direction of arrow b) and irradiates (exposes) its image-forming surface with laser light LB for image scanning to form an edge image (laser light image LBI described later). Furthermore, the device returns the imaging plate IP to its initial position and transports it again while scanning the edge image with laser light LB, and calculates the MTF from the edge image near the boundary between the formed region where the edge image is formed and the non-formed region where the edge image is not formed. The inspection device 1 mainly comprises an optical scanning system 10, a transport system 20, an image processing system 30, and a control device 40.

[0020] <<Optical scanning system>> As shown in Figure 1, the optical scanning system 10 is a device that has the function of irradiating laser light LB to form an image (edge ​​image) on the imaging plate IP, and the function of irradiating laser light LB to read the formed image (edge ​​image) from the imaging plate IP. The optical scanning system 10 is composed of a semiconductor laser 11, a polygon mirror 12, a motor 12A, a scanning lens 13, and a mirror 14.

[0021] The semiconductor laser 11 is a laser light source that emits laser light LB. The polygon mirror 12 is a rotating polyhedron mirror used to scan the laser beam LB emitted from the semiconductor laser 11 with respect to the imaging plate IP in the main scanning direction (direction of arrow a) which is orthogonal to both the vertical direction and the sub-scanning direction (main scanning). Motor 12A is a rotational drive source that rotates the polygon mirror 12. The scanning lens 13 is a lens used to focus the laser beam LB reflected by the polygon mirror 12 to a predetermined position. Mirror 14 is a reflecting mirror for reflecting the laser beam LB that has passed through the scanning lens 13 onto the imaging plate IP. This mirror 14 is formed in the shape of a long plate, and is installed so that its longitudinal direction is aligned with the main scanning direction (direction of arrow a).

[0022] <<Conveyor System>> The transport system 20 is a transport device that transports the imaging plate IP in a predetermined direction. The transport system 20 is configured to have a plurality of transport rollers 21 for transporting the imaging plate IP in the transport direction (sub-scanning direction: direction of arrow b), and a motor 22 as a rotational drive force source for rotating these plurality of transport rollers 21.

[0023] Image Processing Systems The image processing system 30 is a device for optically reading an X-ray image (an X-ray image including edge images) formed on an imaging plate IP, that is, for detecting an X-ray image formed on an imaging plate IP. The image processing system 30 is composed of a line sensor 31, an A / D converter 32, an image processing device 33, and a monitor 34.

[0024] The line sensor 31 is formed in a long, roughly rectangular parallelepiped shape, and its longitudinal direction is arranged parallel to the main scanning direction. The line sensor 31 is an image sensor in which the light-receiving surface faces downward, and multiple photodetectors that convert light incident on the light-receiving surface into electrical signals are arranged along the main scanning direction. The line sensor 31 can obtain a two-dimensional image (X-ray image on the imaging plate IP) by detecting light from the image-forming surface of the imaging plate IP when the laser beam LB is scanned in the main scanning direction by the optical scanning system 10 and the imaging plate IP is moved in the sub-scanning direction by the transport system 20. The A / D converter 32 is a device that converts the image signal (analog signal) it receives into a digital signal and outputs it.

[0025] As shown in Figure 1, the image processing device 33 is a device equipped with, for example, image processing software and calculation software for calculating MTF. The image processing device 33 performs not only image processing on X-ray images but also MTF acquisition (calculation). After acquiring (calculating) the MTF, the image processing device 33 further determines its spatial frequency [cycles / mm] value and outputs and displays it on the monitor 34.

[0026] The monitor 34 displays images corresponding to the image data output from the image processing device 33, the spatial frequency values, and other information related to the image on a display unit (for example, the display area of ​​a liquid crystal screen). The user judges the degree of blurring (resolution) of the X-ray image from these displayed values. In this embodiment, the A / D converter 32, image processing device 33, and monitor 34 are located within the inspection device 1. However, the system is not limited to this configuration, and at least one of the A / D converter 32, image processing device 33, and monitor 34 may be located on an external device, such as a personal computer.

[0027] ≪Control device≫ As shown in Figure 1, the control device 40 is a device for performing various controls on the optical scanning system 10, the transport system 20, and the image processing system 30 that constitute the inspection apparatus 1. For example, the control device 40 controls the operation of the semiconductor laser 11 and motor 12A of the optical scanning system 10, the motor 22 of the transport system 20, the line sensor 31 and the image processing device 33 of the image processing system 30, etc.

[0028] In this embodiment, the control device 40 transports the imaging plate IP, which has been uniformly irradiated with X-rays XR by the transport system 20, and performs exposure processing on a range of a certain width (width in the sub-scanning direction) or more by the optical scanning system 10. This causes the energy accumulated on the imaging plate IP by the X-rays XR (energy at the location irradiated with laser light LB) to be released from the imaging plate IP, thereby forming edges E on the imaging plate IP, which are regions with different energies (boundary portions between regions with different energies). Furthermore, while the imaging plate IP is transported again by the transport system 20, the control device 40 performs an optical scan (laser scan) on the entire image-forming surface of the imaging plate IP using the optical scanning system 10 and the image processing system 30 to acquire an edge image including the edge E in the X-ray image. The image processing system 30 calculates a modulation transfer function MTF based on the edge image, and calculates the resolution of the imaging plate scanner (inspection device 1) based on the modulation transfer function MTF.

[0029] ≪Procedure for forming an edge image using laser beam LB and displaying the spatial frequency of the MTF≫ Next, referring mainly to Figures 1 to 5, we will explain the procedure from irradiating the imaging plate IP with X-ray XR, forming an edge image with laser beam LB, and displaying the spatial frequency of the MTF on the monitor 34. Figure 3 is an explanatory diagram showing the state when the entire image-forming surface of the imaging plate IP is irradiated with X-ray XR. Figure 4 is an explanatory diagram showing the state when the imaging plate IP is transported while irradiating with laser beam LB to form a band-shaped laser beam image LBI. Figure 5 is an explanatory diagram showing an image resolution confirmation method according to an embodiment of the present invention, where (a) is an explanatory diagram of the imaging plate IP on which the laser beam image LBI has been formed, and (b) is an explanatory diagram of the waveform d showing the energy level when an ideal image is formed on the image-forming surface in accordance with the laser beam image LBI of the imaging plate IP.

[0030] <Step S1> First, as shown in Figure 3, an external X-ray irradiation device (not shown) uniformly irradiates the entire surface of the imaging plate IP (the entire image-forming surface) with X-rays (X-ray irradiation step; hereinafter referred to as "step S1").

[0031] In this embodiment, as shown in Figure 1, the X-ray irradiation device (not shown) is separate from the inspection device 1, but it is not limited to this and may be incorporated into the inspection device 1. In other words, the inspection device 1 may be a single device that integrates an X-ray image forming device and an X-ray image reading device.

[0032] <Step S2> Next, as shown in Figure 4, the imaging plate IP is transported (first transport) while the imaging plate IP is irradiated with laser light LB to form a band-shaped laser light image LBI (edge ​​formation step; hereinafter referred to as "step S2").

[0033] In step S2, the imaging plate IP is removed from the X-ray irradiation device (not shown) used in step S1 and set in the inspection device 1 shown in Figure 1. Inside the inspection device 1, the imaging plate IP, which has been irradiated with X-rays XR, is transported in a predetermined direction (sub-scanning direction: direction of arrow b) by the transport system 20, while the optical scanning system 10 (laser beam LB for image scanning to read the image) performs a laser scan (more precisely, the formation of an edge image by the laser beam LB) over the entire range (entire width) in the main scanning direction (direction of arrow a) and over a certain width or more in the sub-scanning direction (direction of arrow b).

[0034] As shown in Figure 4, in the area of ​​the imaging surface of the imaging plate IP irradiated with laser light LB, the energy (excitation energy) of the X-rays XR accumulated by the irradiated X-rays XR is released and lost. As a result, a band-shaped laser beam image LBI is formed on the imaging plate IP, extending along the main scanning direction (arrow a direction) and having a predetermined width in the sub-scanning direction (arrow b direction).

[0035] <Step S3> Next, the imaging plate IP is transported again (second transport) while the imaging plate IP is irradiated with laser light LB, and the entire image-forming surface of the imaging plate IP is scanned and imaged (edge ​​image acquisition step; hereinafter referred to as "step S3"). In step S3, the imaging plate IP on which the laser beam image LBI has been formed is returned to the transport start position in step S2, and transported again in a predetermined direction (sub-scanning direction: direction of arrow b). Then, the entire image-forming surface of the imaging plate IP is scanned and imaged.

[0036] At this time, in the band-shaped laser beam image (LBI) formed on the imaging plate IP, the energy (excitation energy) accumulated by the X-ray irradiation is lost, as mentioned above. Therefore, the X-ray image will include an edge E. In the scanned image (X-ray image including the edge image), it is possible to distinguish between the formation region where the band-shaped laser beam image (LBI) is formed and the non-formation region where the laser beam image (LBI) is not formed. In other words, on the scanned image, it is possible to detect the edge E of the band-shaped laser beam image (LBI) at the boundary between the formation region and the non-formation region.

[0037] <Step S4> Next, on the scan image acquired in step S3, a graph of pixel values ​​(gray levels) near edge E of the band-shaped laser beam image LBI (including the area before and after edge E in the sub-scanning direction (arrow b direction)) is created, and the horizontal axis of the graph (distance in the sub-scanning direction) is corrected to 1 / 2 to calculate the LSF (Line Spread Function) (Line Spread Function Calculation Step; hereinafter referred to as "Step S4"). By correcting the horizontal axis of the graph to 1 / 2 and calculating the LSF, it is possible to obtain an LSF equivalent to that obtained when calculated from edge images formed using the conventional method (method using a metal plate).

[0038] <Step S5> Next, the LSF is Fourier transformed to calculate the MTF (Modulation Transfer Function) (Modulation Transfer Function Calculation Step; hereinafter referred to as "Step S5").

[0039] <Step S6> Next, the spatial frequency of the MTF (resolution of the imaging plate scanner (inspection device 1)) is determined and the spatial frequency is displayed on the monitor 34 (see Figure 1) (resolution calculation step; hereinafter referred to as "step S6"). In step S6, the spatial frequency value of the MTF calculated in step S5 is calculated and output to monitor 34. As a result, the spatial frequency value is displayed on the display unit of monitor 34. From the spatial frequency value displayed on monitor 34, the user can determine whether the resolution of inspection device 1 is low or high, that is, what the resolution of inspection device 1 is.

[0040] ≪Explanation of how to calculate MTF≫ Next, with reference to Figures 6 to 9, the method for determining the MTF using the image resolution confirmation method according to an embodiment of the present invention will be explained.

[0041] Figure 6 is an explanatory diagram showing an image resolution confirmation method according to an embodiment of the present invention, where (a) is a graph showing the Gaussian distribution of the laser light LB intensity, (b) is a graph showing the edge image (laser light image LBI) formed by the laser light LB, and (c) is a graph showing the waveform e of an ideal edge image.

[0042] In conventional edge image formation methods, X-ray XR is irradiated onto an imaging plate IP, which is an imaging plate IP with a metal plate placed on the image formation surface. As shown in Figure 6(c), the shape of the X-ray image (the shape of the energy level graph) near the edge E of the edge image is a shape that rises at a 90-degree angle. When the laser beam LB shown in Figure 6(a) is scanned in the main scanning direction against the imaging plate IP and gradually shifted in the sub-scanning direction, an edge image like the one shown in Figure 6(b) is formed by the laser beam LB near edge E. If the edge image formed on the imaging plate IP is ideal, the energy distribution will have a shape that rises by 90 degrees at the formation position of edge E, as shown in Figure 6(c). The width of the peak portion of the energy distribution shape caused by the laser beam LB for the edge image in Figure 6(b) (width in the sub-scanning direction) matches the width of the energy distribution shape in Figure 6(c) (width in the sub-scanning direction).

[0043] Figure 7 shows an image resolution verification method according to an embodiment of the present invention, where (a) is an explanatory diagram of an imaging plate IP on which a band-shaped laser beam image LBI is formed, (b) is a graph showing the Gaussian distribution of the laser beam LB intensity for image scanning, (c) is a graph showing the edge image (laser beam image LBI) formed by the laser beam LB, (d) is a graph showing the edge detection position in the edge image formed by the laser beam LB, (e) is a graph showing the edge detection position in an ideal edge image when a metal plate is used, and (f) is the equation of the function f(x) that represents edge E. Note that the rectangular waveform e (thick line portion) shown in Figure 7(c) shows the waveform (graph shape of the energy level) of an ideal edge image when a metal plate is used.

[0044] In this embodiment, in a method of forming an edge image (a band-shaped laser beam image LBI) using a laser beam LB for image scanning, the shape of the laser beam LB (beam intensity distribution) follows a Gaussian distribution. Therefore, the shape of the X-ray image near the edge E of the laser beam image LBI (the graph shape of the energy level; more specifically, the graph shape of the energy level at edge E of the laser beam image LBI in the transport direction (sub-scanning direction)) is the right half or left half of the Gaussian distribution shape of the laser beam LB, as shown in Figure 7(c).

[0045] As shown in Figures 7(b) to 7(d), when the laser beam LB (center of distribution function f: x=-a) for image scanning is brought closer to the left edge E (center of distribution function f: x=0) of the laser beam LBI (LBI) from the left side of edge E, the laser beam LB detects the left edge E of the band-shaped laser beam LBI for the first time when the center position of its distribution function f(x+a) becomes x=-t (when the distance from the left edge E of the laser beam LBI becomes t).

[0046] Since the shape of the distribution function f(x) and the shape of the distribution function f(x+a) are originally the same for the laser beam LB and the left edge E of the laser beam image LBI (because the laser beam image LBI is also formed by the same laser beam LB), the laser beam LB will detect the left edge E at their central position x = -t / 2 (a position shifted by t / 2 towards the left edge E from the position (central position) x = -t of the laser beam LB used for image scanning at this time).

[0047] Incidentally, in conventional edge image formation methods, an edge image was formed by irradiating the image-forming surface of an imaging plate IP with X-ray XR. Therefore, when the edge image formed by this method (where the energy level graph shape rises 90 degrees like a step function at x=0) is scanned with a laser beam LB, the left edge E (x=0) is detected at a position t / 2 on the edge image side from the center position of the laser beam LB. In other words, the laser beam LB only detects the left edge E when its center position is x=-t / 2 (see Figure 7(e)). The center position of the laser beam LB that detects the left edge E is t / 2 closer to the left edge E than the edge of the edge image formed by the laser beam LB. In other words, since the edges of the edge image formed by the laser beam LB have a Gaussian distribution shape, it can be considered that the distance to the edge detection position is twice as long as that of the edge image formed using a metal plate.

[0048] Therefore, in this embodiment, the following processing was performed. First, a graph of pixel values ​​(gray level) near the left edge E of the laser beam LBI (including the area before and after edge E in the sub-scanning direction) was created, and the horizontal axis of the graph (distance in the sub-scanning direction) was corrected to 1 / 2 to calculate the LSF. Next, the LSF was Fourier transformed to calculate the MTF. By processing in this way, it is possible to obtain an MTF equivalent to that obtained when detecting an edge E created by the conventional method (edge ​​E created using a metal plate) with laser beam LB, in a simple and highly accurate manner.

[0049] Figure 8 is a comparison diagram of an image resolution confirmation method according to an embodiment of the present invention and a conventional method, where (a)-1 is a scanned image obtained by scanning the image forming surface of an imaging plate IP onto which a metal plate has been projected using a conventional method, and (a)-2 is a pixel value (gray level) graph showing the pixel values ​​(gray levels) near edge E (front-back direction) of scanned image (a)-1 in units of 10 pixels on the horizontal axis, and (b)-1 is a scanned image obtained by scanning the image forming surface of an imaging plate IP according to an embodiment of the present invention, and (b)-2 is a pixel value (gray level) graph showing the pixel values ​​(gray levels) near edge E (front-back direction) of scanned image (b)-1 in units of 20 pixels on the horizontal axis.

[0050] Here, when scanning an X-ray image formed on an imaging plate IP, the intensity of the laser beam LB exhibits a Gaussian distribution. Therefore, in the conventional method using a metal plate (see Figure 8(a)-1), there is a distance (hereinafter referred to as the "detection reference interval") between the actual edge position and the laser detection position (the center position of the Gaussian distribution of the laser beam LB when edge E is detected by the laser beam LB). This distance is "half of the full width at half maximum (FWHM) of the intensity distribution of the laser beam LB (FWHM is just an example. Here, we will explain using the example where the sensitivity is set to detect edge E at the x value that takes FWHM (the rightmost of the two x-directions). The same applies hereinafter.)." However, in the method of this embodiment (see Figure 8(b)-1), since edge E of the edge image formed by the laser beam LB also has a Gaussian distribution shape similar to the intensity distribution of the laser beam LB, there is a distance of "twice the detection reference interval" between the actual edge position and the laser detection position. It can be seen that the shape of the graph showing edge E shown in Figure 8(a)-2 and the shape of the graph showing edge E shown in Figure 8(b)-2 become approximately the same shape if the horizontal axis is corrected to the same unit (horizontal axis correction).

[0051] Figure 9 is a comparison graph of an image resolution verification method according to an embodiment of the present invention and a conventional method, showing the MTF obtained based on edge E when using a conventional metal plate and the MTF obtained based on edge E when using an edge image formed by scanning with laser light LB according to an embodiment of the present invention.

[0052] When employing the method of the embodiment of the present invention, the MTF can be calculated in the same way as in the conventional method by using a graph in which the horizontal axis (distance in the sub-scanning direction) of the graph of pixel values ​​(gray level) near edge E of the edge image formed by scanning with laser light LB is multiplied by 1 / 2. As a result, even when employing the method of the embodiment of the present invention, the MTF can be obtained simply and with high accuracy, with the same level of accuracy as in the conventional method (see Figure 9).

[0053] As described above, in the image resolution confirmation method according to the embodiment of the present invention, an X-ray image including an edge image can be formed on the imaging plate IP without using a metal plate (jig). In other words, the present invention makes it possible to form an edge image simply by irradiating the image-forming surface of the imaging plate IP with laser light LB for image scanning within a scanner device (inspection device 1) without using a metal plate. Furthermore, the present invention allows for the detection of the edge E of an edge image formed by laser light LB and the determination of the resolution of an X-ray image by the edge method, enabling the simple and highly accurate determination of the MTF with the same level of accuracy as that achieved by conventional edge image formation methods. The processing after obtaining the MTF is the same as with conventional technology, so we will omit the explanation.

[0054] As described above, the image resolution confirmation method according to the embodiment of the present invention includes, as shown in Figure 1 or Figure 2, an X-ray irradiation step S1 in which X-rays XR are uniformly irradiated onto the entire surface of the image forming surface of an imaging plate IP; an edge formation step S2 in which, while transporting the imaging plate IP, exposure processing is performed over a range of a certain width or more in a predetermined direction (sub-scanning direction) to release the energy accumulated on the imaging plate IP by X-rays XR and form an edge E which is a part on the imaging plate IP where the accumulated energy is different (a part where the energy changes); an edge image acquisition step S3 in which an edge image including the edge E in the X-ray image is obtained by performing an optical scan process on the entire surface of the image forming surface of the imaging plate IP; a line spread function calculation step S4 in which a graph of pixel values ​​(gray levels) near the edge E of the edge image is created and a line spread function LSF is calculated; a modulation transfer function calculation step S5 in which a modulation transfer function MTF is calculated based on the line spread function LSF; and a resolution calculation step S6 in which the resolution (spatial frequency) of the imaging plate scanner (inspection device 1) is calculated based on the modulation transfer function MTF.

[0055] Furthermore, the modulation transfer function calculation step S5 includes creating a graph of pixel values ​​of the edge image, calculating the line spread function LSF based on a graph obtained by correcting the horizontal axis of the pixel value graph to 1 / 2, and calculating the modulation transfer function MTF based on the line spread function LSF.

[0056] According to the image resolution verification method of the present invention, the resolution of the inspection device 1 itself can be easily and simply measured and self-diagnosed without the use of special jigs. Furthermore, according to this image resolution verification method, if the degree of blurring of edge E is large, it can be determined that there is an abnormality somewhere in the inspection device 1. In addition, the present invention can calculate a resolution equivalent to that obtained when using a metal plate, even without using a metal plate. As a result, the present invention ensures image quality during adjustments such as shipment, installation, repair, and periodic maintenance of the inspection device 1, as well as during daily inspections. Furthermore, the present invention allows for confirmation during equipment adjustment of the inspection device 1 whether the X-ray images used for daily diagnosis are performing at a sufficient level.

[0057] Furthermore, the resolution calculation step S6 includes the process of displaying the resolution (spatial frequency) of the imaging plate scanner (inspection device 1) on the monitor 34.

[0058] With this configuration, by displaying the resolution of the inspection device 1 on the monitor 34, even users (not just specialists who perform repairs, maintenance, or inspections) can easily check the functional status of the inspection device 1.

[0059] Furthermore, as shown in Figure 1 or Figure 2, the present invention relates to an inspection device 1 that self-diagnoses image resolution capability by reading an X-ray image recorded on an imaging plate IP, calculating a modulation transfer function (MTF), and calculating the resolution from the modulation transfer function (MTF), comprising: an optical scanning system 10 that irradiates the image-forming surface of an imaging plate IP uniformly irradiated with X-rays (XR) with laser light LB to form an X-ray image, and irradiates the X-ray image formed on the imaging plate IP with laser light LB to read the X-ray image formed on the imaging plate IP; a transport system 20 that transports the imaging plate IP in a predetermined direction; an image processing system 30 that optically reads the X-ray image formed on the imaging plate IP and detects the X-ray image; and a control device 40 that controls the optical scanning system 10, the transport system 20, and the image processing system 30, wherein the control device 40 controls the transport system 20 While transporting the imaging plate IP uniformly irradiated with X-rays XR, the optical scanning system 10 performs exposure processing on a range of a certain width or more in the sub-scanning direction, thereby releasing the energy accumulated on the imaging plate IP by the X-rays XR, forming edges E, which are regions with different energies, on the imaging plate IP. Then, while transporting the imaging plate IP again by the transport system 20, the optical scanning system 10 and the image processing system 30 perform optical scanning processing on the entire image-forming surface of the imaging plate IP to acquire an edge image including the edges E in the X-ray image. The image processing system 30 calculates a modulation transfer function MTF based on the edge image, and calculates the resolution of the imaging plate scanner (inspection device 1) based on the modulation transfer function MTF.

[0060] According to the inspection device 1 of the present invention, the control device 40 can easily measure the resolution of the inspection device 1 itself and perform self-diagnosis by calculating the resolution of the imaging plate scanner (inspection device 1) from the modulation transfer function MTF calculated based on the edge image of the imaging plate IP. Furthermore, since the present invention can determine the resolution without using a metal plate, it is easy to confirm whether the X-ray images used for daily diagnosis are performing adequately during adjustments such as shipment, installation, repair, and periodic maintenance of the inspection device 1, as well as during daily inspections. For this reason, users can easily check the functional status of the inspection device 1 themselves without having to request repairs, maintenance, inspections, etc.

[0061] [Differentiation] It should be noted that the present invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of its technical concept, and the present invention naturally extends to such modified and altered inventions. Furthermore, components already described are denoted by the same reference numerals, and their descriptions are omitted.

[0062] Figure 10 is a schematic diagram (partially a block diagram) of inspection apparatus 1A, which is a modified example of inspection apparatus 1 according to an embodiment of the present invention. Figure 11 is a schematic diagram when multiple strip-shaped laser beam images (LBIs) are formed on an imaging plate IP.

[0063] As shown in Figures 10 and 11, the modified inspection device 1A of the present invention is an inspection device 1 described in the embodiment (see Figure 1) with the added function of being able to detect any malfunction in the optical scanning system 10 and the transport system 20. Compared to the aforementioned inspection device 1, the inspection device 1A further includes a scanning start detection sensor 15 for detecting the start of scanning of the optical scanning system 10 and a scanning end detection sensor 16 for detecting the end of scanning of the optical scanning system 10. The control device 40 transports the imaging plate IP in a predetermined direction at a constant speed and forms multiple laser light images LBI at predetermined distances apart. The control device 40 detects the detection interval of the laser light LB between the scanning start detection sensor 15 and the scanning end detection sensor 16. If there is a deviation in the detection interval of the laser light LB, the control device 40 determines that there is an abnormality in the optical scanning system 10 and detects the distance L between the laser light images LBI. If there is an unevenness in the distance L, the control device 40 determines that there is an abnormality in the transport system 20.

[0064] The scanning start detection sensor 15 and the scanning end detection sensor 16 are, for example, located next to one end of the mirror 14 in the longitudinal direction (main scanning direction) and next to the other end. In this way, the inspection device 1A can reliably detect the start and end of scanning of the laser beam LB, so it can determine the timing for reading the laser beam image LBI.

[0065] In this modified example, as shown in Figure 11, if a configuration is used in which multiple strip-shaped laser beam images LBI are formed on the imaging plate IP in a predetermined direction (sub-scanning direction: direction of arrow b) at intervals of L (a configuration in which adjacent strip-shaped laser beam images LBI are formed at a distance L apart), then if there is a deviation in the distance L between the laser beam images LBI when reading the X-ray image (for example, if the distance L at the time of edge image reading does not match the distance L set when forming the edge image, or if there is variation in the multiple distances L read at the time of edge image reading), the control device 40 can determine that there is an abnormality somewhere in the transport system 20, provided that the optical scanning system 10 is operating normally (if the detection interval (time interval) of the laser beam LB between the scanning start detection sensor 15 and the scanning end detection sensor 16 is constant). Furthermore, if there is a discrepancy in the detection interval of the laser beam LB between the scanning start detection sensor 15 and the scanning end detection sensor 16, the control device 40 can determine that there is an abnormality in the optical scanning system 10.

[0066] To elaborate further, as shown in Figure 11, the inspection device 1A forms multiple strip-shaped laser light images LBI by placing a certain distance L between laser light images LBI in a predetermined direction (sub-scanning direction: direction of arrow b). In inspection device 1A, the imaging plate IP is transported at a constant speed in a predetermined direction (sub-scanning direction: direction of arrow b), and the first laser image LBI scanned is used to allow the user to understand the resolution of inspection device 1A. Therefore, similar to inspection device 1 described above, the spatial frequency of MTF can be determined and displayed on monitor 34. Furthermore, the inspection device 1A monitors the time required for scanning the laser beam LB (total width in the main scanning direction: direction of arrow a) and detects the edges E of adjacent laser beam images LBI (the right edge E and the left edge E for each laser beam image LBI) in the sub-scanning direction. Based on the detection time (or the difference in detection timing) of the multiple detected edges E and the amount of the imaging plate IP fed by the transport roller 21 per unit time, the distance L between adjacent laser beam images LBI (the amount the imaging plate IP is fed by the transport roller 21 in the sub-scanning direction) is measured. Alternatively, instead of measuring the physical distance L between adjacent laser beam images LBI, the time interval between the detection of two opposing edges E between adjacent laser beam images LBI by the line sensor 31 may be measured.

[0067] Here, if there is unevenness in the distance L between the laser beam images LBI in the sub-scanning direction, it indicates that there is unevenness (transport unevenness) in the feed rate of the imaging plate IP (feed rate in the sub-scanning direction).

[0068] In other words, in the case of inspection device 1A, instead of a vague statement like "there is something wrong with the inspection device 1A itself," it is possible to more specifically identify the faulty part of the inspection device 1A (narrow down the faulty part), such as "there is some kind of problem with the transport system 20," compared to the aforementioned inspection device 1.

[0069] As explained above, the inspection device 1A forms a strip-shaped laser beam image LBI extending along the main scanning direction and forms laser beam images LBI at regular intervals (distance L between adjacent laser beam images LBI) in the sub-scanning direction. Therefore, during the scanning process of each laser beam image LBI, in addition to checking the degree of blurring of the edges E of the laser beam image LBI, if the detection interval of the laser beam LB between the scanning start detection sensor 15 and the scanning end detection sensor 16 is constant, it is possible to check for things like uneven transport in the transport system 20.

[0070] In other words, since the inspection device 1A includes the configuration of the inspection device 1 described above (the main components are the same as those of the inspection device 1), it also has the same functions and effects as the embodiment described above. Furthermore, when the inspection device 1A reads multiple formed laser beam images LBI, if there is unevenness (variation) in the reading interval (time) between the laser beam images LBI, it can more specifically identify the problem (the problem area within the inspection device 1), indicating that there is some kind of problem with the transport system 20. As a result, the inspection device 1 can detect malfunctions in the transport system 20 as described above, and when a malfunction occurs in the transport system 20, it can repair or adjust the transport system 20 in a timely manner to restore it to a normal state and maintain that normal state.

[0071] Furthermore, in inspection device 1A, when scanning in the main scanning direction (arrow a direction) using the laser beam LB is repeated, if there is inconsistency (variation) in the time interval between the detection of the laser beam LB by the "scanning start detection sensor 15" and the detection of the laser beam LB by the "scanning end detection sensor 16", it can be determined that there is some kind of problem with the "optical scanning system 10". However, this can be detected independently of the laser beam image LBI.

[0072] [Other variations] Furthermore, the monitor 34 shown in Figures 1 and 10 may be equipped with a notification means to notify the user of a malfunction in the inspection devices 1 and 1A. The notification means could be, for example, a device that notifies the user of a malfunction through the speaker of the monitor 34, such as by voice or buzzer sound. Alternatively, the notification means could visually indicate to the user that a malfunction has occurred in the inspection device 1. With this configuration, the inspection devices 1 and 1A are equipped with notification means, so that if a malfunction (including failure) occurs in the inspection devices 1 and 1A, the user can be notified in a timely manner.

[0073] Furthermore, the transport system 20 can be any device capable of transporting the imaging plate IP in the sub-scanning direction (direction of arrow b), and is not limited to the configurations shown in Figures 1 and 10. For example, it could be a belt conveyor device that transports the imaging plate IP.

[0074] Furthermore, in inspection devices 1 and 1A, the transport path for the imaging plate IP may also be a circulation path. Here, the imaging plate IP may be fixedly positioned on an endless belt that circulates along a transport path, or fixedly positioned on a disc that rotates around its own center, and may be transported in a circulating manner in such a configuration. As described above, the imaging plate IP can repeatedly pass through the same position by being transported along the same transport path during image formation and image reading. Therefore, there is no need to perform a transport process that moves the imaging plate IP back and forth, and by transporting the imaging plate IP in one direction (for example, 1.5 times, or a maximum of 2 times), both the transport during edge image formation and the transport during edge image reading of the imaging plate IP can be achieved. In addition, the control of the operation of the transport system 20 can be made simpler as a result.

[0075] Furthermore, the MTF can be calculated using the slit method. In step S2, a laser scan is performed in the sub-scanning direction with a width of approximately 10 μm to form a slit-shaped image. In step S3, the slit image is acquired, and the LSF (line spread function) obtained from the slit image is Fourier transformed to calculate the MTF. [Explanation of symbols]

[0076] 1.1A Inspection device (imaging plate scanner) 10 Optical scanning system 15 Scanning start detection sensor 16 Scanning end detection sensor 20 Conveyor Systems 30 Image Processing Systems 40 Control device E-edge IP Imaging Plate L is the distance between laser beam images. LB laser light LBI laser imaging MTF Modulation Transfer Function S1 X-ray irradiation step S2 Edge forming step S3 Edge image acquisition step S4 Line Spread Function Calculation Step S5 Modulation Transfer Function Calculation Step S6 Resolution Calculation Step XR (X-ray)

Claims

1. An X-ray irradiation step in which X-rays are uniformly irradiated onto the entire image-forming surface of the imaging plate, An edge forming step in which, while transporting the imaging plate, exposure processing is performed over a range of a certain width or more in a predetermined direction, thereby releasing the energy accumulated on the imaging plate by X-rays and forming an edge which is a different part of the energy accumulated on the imaging plate, An edge image acquisition step involves performing an optical scan on the entire image-forming surface of the imaging plate to obtain an edge image including the edge in the X-ray image, A modulation transfer function calculation step, which calculates the modulation transfer function based on the edge image, A resolution calculation step in which the resolution of the imaging plate scanner is calculated based on the modulation transfer function, including, How to check image resolution.

2. The above step of calculating the modulation transfer function is: A graph of the pixel values ​​of the aforementioned edge image is created, and the line spread function is calculated based on a graph obtained by correcting the horizontal axis of the said pixel value graph to 1 / 2. And, Calculate the modulation transfer function based on the line spread function. including, The method for confirming image resolution according to claim 1.

3. The resolution calculation step includes the process of displaying the resolution of the imaging plate scanner on a monitor. The method for confirming image resolution according to claim 1 or claim 2.

4. An inspection device that reads an X-ray image recorded on an imaging plate, calculates a modulation transfer function, and calculates the resolution from the modulation transfer function, thereby self-diagnosing image resolution capability, An optical scanning system that irradiates the image-forming surface of an imaging plate, which is uniformly irradiated with X-rays, with laser light to form an X-ray image, and irradiates the image-forming surface of the imaging plate with laser light to read the X-ray image formed on the imaging plate. A transport system for transporting the imaging plate in a predetermined direction, An image processing system for optically reading the X-ray image formed on the imaging plate and detecting the X-ray image, The system comprises a control device for controlling the optical scanning system, the transport system, and the image processing system, The control device is While the imaging plate, which has been uniformly irradiated with X-rays, is being transported by the transport system, By performing exposure processing over a certain width or more in a predetermined direction using the optical scanning system, the energy accumulated on the imaging plate by the X-rays is released from the imaging plate, forming edges on the imaging plate that are regions with different energies. While the imaging plate is transported again by the transport system, the optical scanning system and the image processing system perform an optical scan on the entire image forming surface of the imaging plate to obtain an edge image including the edge in the X-ray image. The image processing system calculates the modulation transfer function based on the edge image, The resolution of the imaging plate scanner is calculated based on the modulation transfer function. Inspection device.

5. A scanning start detection sensor for detecting the start of scanning in the optical scanning system, The system includes a scanning completion detection sensor for detecting the end of scanning in the optical scanning system, The control device, while transporting the imaging plate in a predetermined direction at a constant speed, when multiple laser beam images are formed at predetermined distances apart, The detection interval of the laser beam between the scan start detection sensor and the scan end detection sensor is detected. If a discrepancy occurs in the detection interval of the laser beam, it is determined that there is an abnormality in the optical scanning system. The distance between the laser beam images is detected, and if there is an unevenness in the distance, it is determined that there is an abnormality in the transport system. The inspection apparatus according to claim 4.

Images