WO2019202841A1

WO2019202841A1 - Radiographic image processing device, radiographic image processing method, and program

Info

Publication number: WO2019202841A1
Application number: PCT/JP2019/006465
Authority: WO
Inventors: 高澤　徹
Original assignee: キヤノン株式会社
Priority date: 2018-04-16
Filing date: 2019-02-21
Publication date: 2019-10-24
Also published as: JP2019181039A

Abstract

A radiographic image processing device according to the present invention acquires images having a plurality of radiation distributions due to different radiation energies from a radiographic imaging device, generates a processed image in which a specific substance is emphasized on the basis of the images having a plurality of radiation distributions, and determines a region to be set in a radiographic image on the basis of info of the specific substance in the processed image.

Description

Radiation image processing apparatus, radiation image processing method and program

The present invention relates to a radiation image processing apparatus, a radiation image processing method, and a program.

Generally, various operations are performed when displaying an X-ray image in order to facilitate interpretation of the X-ray image by a radiology doctor. For example, a region unnecessary for interpretation outside the irradiation field is masked and displayed, a small target region (region of interest) is enlarged and displayed, or the target region is moved to the center by panning and displayed. In addition, when X-ray image data is sent to an external interpretation system server, image data trimmed based on an irradiation field in the X-ray image is sent in order to prevent transmission of extra data. Yes.

If the radiologist performs the above-mentioned operations every time X-rays are taken, the imaging efficiency is poor and the burden on the radiologist is great. In Patent Document 1, an area of an irradiation field is recognized from a captured X-ray image and the outside of the area is masked, the area is enlarged to an appropriate magnification, the area is shifted to the center, and the area is based on the area. It has been proposed to perform processing such as trimming.

Japanese Patent Publication No. 05-049143

When automatically recognizing the irradiation field from the X-ray image, the irradiation field is extracted by finding the shading edge of the diaphragm from the shading information corresponding to the X-ray transmitted through the subject. However, depending on the posture, physique, and imaging method of the subject, an image similar to the edge of the aperture may appear in the X-ray image, and there is a problem that an erroneous irradiation field is recognized. For example, when photographing using a metal auxiliary tool is performed to fix the subject, the image of the auxiliary tool is recognized as an edge of the diaphragm, which may affect the recognized irradiation field.

Also, when obtaining a radiological moving image (radioscopy image), a virtual collimator may be set to limit the display area. In this case, if the region of interest deviates from the center in the virtual collimator, the position of the virtual collimator must be manually moved, and there is a problem that the operation becomes complicated. Or, in the case of fluoroscopic imaging of the stomach, the imaging posture of the subject is changed from the standing position to the prone position in order to fill the contrast medium, but the position of the virtual collimator needs to be moved because the position of the stomach moves due to gravity. Arise.

The present invention provides a technique that makes it possible to appropriately set a region in a radiographic image.

A radiographic image processing apparatus according to an aspect of the present invention has the following configuration. That is,
Acquisition means for acquiring images of a plurality of radiation distributions with different radiation energies from the radiation imaging apparatus;
Generating means for generating a processed image in which a specific substance is emphasized based on the plurality of radiation distribution images;
Determining means for determining a region to be set in the radiation image based on the information on the specific substance in the processed image.

According to the present invention, it is possible to appropriately set a region in a radiographic image.

Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are denoted by the same reference numerals.

FIG. 1 is a block diagram illustrating a configuration example of a radiation imaging system according to an embodiment. FIG. 2 is a timing chart illustrating an imaging operation of the radiation imaging apparatus according to the embodiment. FIG. 3A is a diagram illustrating energy subtraction. FIG. 3B is a diagram showing the correspondence between substances and effective atomic numbers. FIG. 4 is a block diagram illustrating a functional configuration example of the imaging control apparatus according to the first embodiment. FIG. 5 is a flowchart illustrating an example of processing performed by the imaging control apparatus of the first embodiment. FIG. 6A is a diagram illustrating an example of the relative positional relationship between the diaphragm and the radiation imaging apparatus and an irradiation field. FIG. 6B is a diagram illustrating an example of an irradiation field and a relative positional relationship between the diaphragm and the radiation imaging apparatus. FIG. 6C is a diagram illustrating an example of the relative positional relationship between the diaphragm and the radiation imaging apparatus and an irradiation field. FIG. 7 is a diagram illustrating an example of a surface density image and a mask image. FIG. 8A is a flowchart illustrating another example of processing performed by the imaging control apparatus according to the first embodiment. FIG. 8B is a flowchart illustrating another example of processing performed by the imaging control apparatus according to the first embodiment. FIG. 9 is a block diagram illustrating a functional configuration example of the imaging control apparatus according to the second embodiment. FIG. 10 is a diagram for explaining extraction of an irradiation field according to the second embodiment. FIG. 11 is a flowchart illustrating an exemplary process performed by the imaging control apparatus according to the second embodiment. FIG. 12 is a block diagram illustrating a functional configuration example of the imaging control apparatus according to the third embodiment. FIG. 13 is a diagram illustrating the determination of the visual field area according to the third embodiment. FIG. 14 is a flowchart illustrating an exemplary process performed by the imaging control apparatus according to the third embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the term “radiation” may include, for example, α rays, β rays, γ ray particle beams, cosmic rays, and the like in addition to X rays. In the following embodiments, a radiation imaging system including a radiation generator, a radiation imaging apparatus (a flat panel detector (FPD), and an imaging control apparatus (radiation image processing apparatus)) that generates an energy subtraction image will be described. According to the embodiment, in the processed image obtained by energy subtraction in which the specific substance is emphasized, the irradiation field, the region, the subject, and the missing region are recognized, and the recognition result is used for radiation. By improving the recognition accuracy of the irradiation field in the image, the part of the subject, and the element missing recognition, it is possible to appropriately cut out the region in the radiographic image.

In addition, the radiation imaging systems of the following embodiments can be applied to both still image shooting and movie shooting. However, since one shot in a movie can be considered as a still image, an example is given in the movie system. Indicates. Further, when the energy subtraction image and the diagnostic radioscopic image are acquired at the same timing, the irradiation field can be more accurately recognized as much as possible. Therefore, the radiation imaging system of the embodiment acquires a high-energy image and a low-energy image for energy subtraction and a diagnostic radioscopic image with a single irradiation of radiation. Hereinafter, each embodiment will be described in detail. Hereinafter, the radiographic image is referred to as a fluoroscopic image.

<First Embodiment>
FIG. 1 is a block diagram illustrating a configuration example of a radiation imaging system according to the first embodiment. The radiation generator 101 generates radiation and irradiates the radiation in a desired direction. The radiation control device 102 controls the dose / ray quality and irradiation timing of the radiation generated by the radiation generation device 101. The imaging control device 103 is connected to the radiation control device 102 to control the irradiation timing of the radiation by the radiation generation device 101 and is connected to the radiation imaging device 104 to capture the radiation image, thereby controlling the operation of radiation imaging. To do. In addition, the imaging control device 103 performs radiographic image processing including energy subtraction on the radiographic image captured from the radiographic imaging device 104. The radiation imaging apparatus 104 includes an FPD, receives radiation irradiated from the radiation generation apparatus 101, generates an image as radiation intensity distribution information, and transmits the image to the imaging control apparatus 103. The display device 105 is connected to the imaging control device 103 and displays a radiation image that has been subjected to radiation image processing (hereinafter, image processing) by the imaging control device 103.

The photographing control apparatus 103 includes a CPU 131 as a processor and a memory 132, and the CPU 131 executes various programs described below by executing predetermined programs stored in the memory 132. The imaging control apparatus 103 uses an energy subtraction method that obtains new images (for example, bone images and soft tissue images) by processing a plurality of radiographic images with different radiation energies applied to the subject. When imaging by the energy subtraction method is performed, at least two radiographic images captured with different radiation energies are required to generate one subtraction image. The radiation imaging apparatus 104 performs sampling a plurality of times during an imaging period of one frame (between adjacent reset signals). Thereby, the radiation imaging apparatus 104 can acquire an image (low energy image) with low energy radiation and an image (high energy image) with high energy radiation in one frame period. Hereinafter, the operation of the radiation imaging apparatus 104 will be described with reference to FIG.

FIG. 2 shows an example of a timing chart for X-ray irradiation and image acquisition. The radiation imaging apparatus 104 of the present embodiment can acquire images of a plurality of radiation distributions by performing sampling a plurality of times during a single irradiation of radiation. As shown in FIG. 2, radiation (radiation (X _L ) and radiation (X _H )) of two different energies (X _L , X _H ) is irradiated by one irradiation. Radiation (X _L ) is a lower energy radiation than radiation (X _H ) and is used to generate a low energy image (X _L ), and radiation (X _H ) generates a high energy image (X _H ). Used to do. In addition, imaging conditions are set so that an image (X _L + X _H ) obtained by irradiation with radiation (X _L ) and radiation (X _H ) becomes a diagnostic fluoroscopic image suitable for interpretation of the target site. ing. Note that Tcyc indicates one cycle. Since the radiographic imaging system 100 of the present embodiment performs video imaging (perspective imaging), irradiation and readout are repeated with Tcyc1, Tcyc2, and Tcyc3.

First, radiation distribution information that has already been accumulated in the radiation imaging apparatus 104 is initialized with a Reset signal. Using the sampling hold signal (SHold), the radiation distribution information (X _L ) accumulated during the period from the start of irradiation of radiation (X _L ) to the completion of irradiation (immediately before the start of irradiation of radiation (X _H )) is sampled and held. , Temporarily stored in the radiation imaging apparatus 104. Further, by using the SHold signal, radiation (X _L) radiation distribution information _(X L ₊ X _H) accumulated during the period of irradiation to completion of the radiation from the irradiation start (X _H) of the sampling hold radiographic apparatus 104 Temporarily save in. The radiation imaging apparatus 104 can accumulate a plurality of pieces of radiation distribution information.

Since the radiation distribution information temporarily stored in the radiation imaging apparatus 104 can be read out after sampling and holding, the imaging control apparatus 103 receives radiation distribution information (X _L ) and radiation distribution information ( (X _L + X _H ) is read out. When the reading of the radiation distribution information is completed, the imaging control unit 103, by subtracting the radiation distribution information _{(X L)} from the radiation distribution information _{_(X} L + X _H), obtain radiation distribution information _{(X H).} Here, the radiation distribution information (X _L ) is the base image of the low energy image, the radiation distribution information (X _H ) is the base image of the high energy image, and the radiation distribution information (X _L + X _H ) is read by the doctor. This is the base image of the diagnostic fluoroscopic image.

It is known that by performing the energy subtraction method, it is possible to identify a substance from a difference image obtained from a high energy image and a low energy image. For example, it is possible to detect a lumbar vertebra, a lateral projection region, and a soft tissue from such a difference image, and use the pixel values of the soft tissue to correct the lumbar region of the difference image to calculate the bone density. In addition, there is a method of using a concept called effective atomic number for substance identification. Effective atomic number is an atomic number that corresponds to the average of the constituent elements of an element, compound, or mixture, and is a quantitative index that indicates the atomic number of a hypothetical element that attenuates photons at the same rate as the substance. It is.

As shown in FIG. 3A, by setting two equations from a high energy image (X _H ) and a low energy image (X _L ) and obtaining a solution, an image of effective atomic number (Z) and an area density (D) You can ask for an image. In order to solve the equation, Newton-Raphson method, bisection method or the like can be used. FIG. 3B shows the effective atomic number of the material. For example, since the material of the radiation movable aperture stop (hereinafter abbreviated as the aperture stop) is lead (Pb), the effective atomic number is 82. From the effective atomic number (Z) image and the surface density (D) image, the surface density image of the effective atomic number of the specific substance can be generated, and the generated image is an image in which the specific material is emphasized. Therefore, if a surface density image having an effective atomic number of 82 is generated, an image in which the lead, that is, the image of the aperture region is enhanced can be obtained.

The imaging control device 103 calculates the relationship between the effective atomic number and the surface density from the low energy image and the high energy image, generates a surface density image of lead (Pb: effective atomic number 82), which is the material of the diaphragm, Extract the aperture area from the image. The lead surface density image is an image in which the lead image is enhanced, and the aperture region can be easily extracted. By using the extracted aperture region, the imaging control device 103 can perform generation of a mask, calculation of a cutout region, and calculation of a display region in a diagnostic fluoroscopic image with high accuracy. The final interpretation image (diagnosis radiation image) is displayed on the display device 105.

FIG. 4 is a block diagram illustrating a functional configuration example related to image processing of the imaging control apparatus 103 according to the first embodiment. Each functional block may be realized by the CPU 131 executing a program stored in the memory 132 or the like, or may be realized by dedicated hardware, or by the cooperation of the CPU 131 and dedicated hardware. It may be realized. As described above, the image acquisition unit 201 acquires images of a plurality of radiation distributions with different radiation energies from the radiation imaging apparatus 104. The image separation unit 202 generates a processed image in which a specific substance is emphasized based on the result of performing energy subtraction on a plurality of radiation distribution images. In the present embodiment, the specific substance is an aperture 107 (lead). The substance extraction unit 203 and the irradiation field determination unit 204 determine an area (an irradiation field in a fluoroscopic image in the present embodiment) to be set in the radiation image based on information on a specific substance in the processed image. Hereinafter, each functional unit will be described in more detail.

In the imaging control apparatus 103, the image acquisition unit 201 acquires radiation distribution information (a high energy image and a low energy image) from the radiation imaging apparatus 104. The image acquisition unit 201 of the present embodiment acquires a plurality of radiation distribution images including an image that is a source of a fluoroscopic image for each single irradiation of radiation from the radiation imaging apparatus 104 described above. The image separation unit 202 performs energy subtraction shown in FIG. 3A using the high energy image and the low energy image acquired by the image acquisition unit 201, and generates an image of effective atomic number and surface density. Furthermore, the image separation unit 202 generates a surface density image of the specific substance (the aperture 107 in the present embodiment) as a processed image from the generated effective atomic number and surface density image. The substance extraction unit 203 extracts a specific substance region from the processed image generated by the image separation unit 202. The irradiation field determination unit 204 determines the irradiation field on the X-ray fluoroscopic image based on the extraction result by the substance extraction unit 203. The image display unit 205 corrects the mask of the irradiation field area of the diagnostic fluoroscopic image and displays it on the display device 105. The image output unit 206 outputs an image cut out based on the irradiation field to a desired image server 108 via the in-hospital network 106.

Also, the low energy image holding unit 207 holds the low energy image acquired by the image acquisition unit 201. The high energy image holding unit 208 holds the high energy image acquired by the image acquisition unit 201. The fluoroscopic image holding unit 209 holds the diagnostic fluoroscopic image acquired by the image acquisition unit 201. The processed image holding unit 210 holds a processed image such as an effective atomic number and surface density image generated by the image separating unit 202 and a surface density image of a specific substance. The extraction data holding unit 211 holds the substance extraction data generated by the image separation unit 202. The correction data holding unit 212 holds data for correcting the measurement error of the calculated effective atomic number and data for correcting the measurement error of the surface density.

FIG. 5 is a flowchart showing processing by the imaging control apparatus 103 (mainly, the image separation unit 202, the substance extraction unit 203, the irradiation field determination unit 204, and the image display unit 205) of the present embodiment.

Before describing the flowchart of FIG. 5, the irradiation field according to the present embodiment will be described. The radiation emitted from the radiation generation apparatus 101 passes through the subject and is acquired as a radiation transmission image by the radiation imaging apparatus 104. At this time, the irradiation area of the radiation from the radiation generation apparatus 101 is limited by the aperture 107 so that the radiation is not irradiated to an area other than the area where the subject needs to be imaged. The area narrowed by the diaphragm 107 is called an irradiation field on the photographed image. 6A to 6C show the relative positional relationship between the diaphragm 107 and the radiation imaging apparatus 104 and the relationship between the irradiation fields. As the shape of the diaphragm 107, a rectangle and a circle are generally used as shown in FIGS. 6A to 6C. FIG. 6A shows a state where the center of the diaphragm 107 is aligned with the center 601 of the radiation imaging apparatus 104. FIG. 6B shows a state where the diaphragm 107 is rotated and / or translated. Due to the parallel movement, the center 602 of the diaphragm is displaced from the center 601 of the radiation imaging apparatus 104. FIG. 6C shows a state in which radiation is irradiated obliquely rather than perpendicularly to the radiation imaging apparatus 104. Although not shown, a diaphragm having a shape other than a rectangle or a circle is also used.

In step S500, the image acquisition unit 201 acquires the radiation distribution information (X _L ) and the radiation distribution information (X _L + X _H ) from the radiation imaging apparatus 104 that operates at the timing described with reference to FIG. Acquire low-energy images and diagnostic fluoroscopic images. The image acquisition unit 201 holds the acquired low energy image and fluoroscopic image in the low energy image holding unit 207 and the fluoroscopic image holding unit 209, respectively. Further, the image acquisition unit 201 calculates the radiation distribution information (X _H ) by obtaining the difference between the radiation distribution information (X _L + X _H ) and the radiation distribution information (X _L ), and based on this, the high energy image Is stored in the high energy image holding unit 208. Further, in step S500, the image separation unit 202 performs an energy subtraction process using the high energy image and the low energy image, and calculates an effective atomic number and an areal density. The obtained effective atomic number image and surface density image are held in the processed image holding unit 210.

Next, in step S501, the image separation unit 202 extracts the pixel of the effective atomic number of the diaphragm from the image of the effective atomic number and surface density calculated in step S500, and generates a surface density image of the diaphragm. Stored in the processed image holding unit 210. At this time, the image separation unit 202 corrects the surface density image using the correction data obtained from the correction data holding unit 212. As described with reference to FIGS. 6A to 6C, the irradiation field is an area limited by the diaphragm, and conversely, the area outside the irradiation field is the area of the diaphragm itself. Although the diaphragm is made of lead, it is difficult for X-rays to pass therethrough, but there is also energy that is detected by the radiation imaging apparatus 104 without being completely blocked. As shown in FIG. 3B, the effective atomic number of lead is 82, and there is almost no substance having an effective atomic number higher than this in the radiographic image. Therefore, by creating a surface density image for effective atomic numbers within a predetermined value range, for example, a processed image in which the aperture (lead) is emphasized can be obtained. For example, if a surface density image for an effective atomic number of 70 or more is created, an image in which lead, which is a substance having an effective atomic number of 70 or more, is emphasized, that is, an aperture surface density image is obtained. Further, if an areal density image for an effective atomic number of 13 or more is created, an image in which aluminum, enamel, iron, and lead, which are substances having an effective atomic number of 13 or more, are emphasized, that is, an areal density image of a metal is obtained. . The user can arbitrarily select a predetermined value range by the imaging control apparatus 103. An example of the surface density image of the aperture generated as described above is shown in an image 700 in FIG. In addition, although the effective atomic number of the substance to extract was set to 70 or more, it is not restricted to this. What is necessary is just to set the effective atomic number of the substance extracted including the effective atomic number 82 of lead and not including a human body or air.

Next, in step S502, the substance extraction unit 203 extracts a diaphragm region based on the surface density image of the diaphragm held in the processed image holding unit 210, and shapes of the boundary (irradiation field) of the diaphragm region Whether or not can be represented by a rectangle or a circle. For example, in the case of a rectangle as shown in the upper part of FIGS. 6A to 6C and a circle as shown in the lower part of FIGS. 6A to 6B, it is determined that the shape of the diaphragm is determined by the rectangle or the circle, and the process Advances to step S503. On the other hand, when it is irradiated obliquely using a circular diaphragm as shown in FIG. 6C (elliptical irradiation field), when the shape of the side forming the irradiation field is uneven, etc., a simple rectangle, It is determined that the irradiation field cannot be defined as a circle. In this case, the process proceeds from step S502 to step S506. Alternatively, even in the case of a rectangular diaphragm, when the center of the diaphragm 107 is significantly deviated from the center of the radiation imaging apparatus 104 and the shape of the irradiation field cannot be determined, the process proceeds from step S502 to step S506.

In steps S503 to S505, the irradiation field determination unit 204 determines a geometric shape applicable to the shape defined by the specific substance from the processed image, and detects the irradiation field from the fluoroscopic image using the determined geometric shape. By doing so, the area of the irradiation field is determined. The geometric shape used in this example is a rectangle or a circle as described above. In step S503, the substance extraction unit 203 performs image processing such as edge enhancement on the surface density image of the diaphragm, extracts a straight line or a circle edge that is a boundary between the irradiation field and the diaphragm, and geometrics of the irradiation field. Determine the shape. The geometric shape of the field can be defined by coordinates, for example. For example, if the irradiation field is rectangular, the irradiation field can be determined by the positions of the four vertices, and if it is circular, the irradiation field can be determined by the center coordinates and the radius. The substance extraction unit 203 holds the determined coordinates in the extraction data holding unit 211.

Subsequently, in steps S504 to S505, the irradiation field determination unit 204 determines the irradiation field on the diagnostic fluoroscopic image. First, in step S504, the irradiation field determination unit 204 sets an irradiation field candidate (initial value) based on the coordinates of the irradiation field held in the extraction data holding unit 211 on the fluoroscopic image, and sets the irradiation field from the fluoroscopic image. Recognize and confirm. In step S505, the irradiation field determination unit 204 generates a mask image from the coordinates of the irradiation field determined in step S504 (four vertices if rectangular, center coordinates and radius if circular).

On the other hand, when the process proceeds from step S502 to step S506, the irradiation field determination unit 204 generates a mask image using the surface density image of the diaphragm. In the present embodiment, the irradiation field is determined based on the binarized image obtained by binarizing the processed image. That is, in step S506, the irradiation field determination unit 204 generates a mask image using pixels corresponding to the diaphragm in the surface density image of the diaphragm held in the extraction data holding unit 211 as pixels of the mask image, and extracts the extracted image data. Hold in the holding unit 211. For example, the irradiation field determination unit 204 can generate a binary mask image (701 in FIG. 7) by performing binarization processing by setting an appropriate threshold value in the surface density image of the stop. Therefore, a mask image can be easily generated even with a simple rectangular or circular aperture. The irradiation field determination unit 204 provides the generated mask image to the image display unit 205 and the image output unit 206.

When the mask image is generated in step S505 or S506, the process proceeds to processing step S507. In step S507, the irradiation field determination unit 204 calculates the coordinates of each vertex of the circumscribed rectangle with respect to the irradiation field of the mask image for trimming the image area, and provides the calculated coordinates to the image output unit 206. In step S508, the image display unit 205 generates an image (703 in FIG. 7) in which the mask image (701 in FIG. 7) generated in step S505 or S506 and the fluoroscopic image (702 in FIG. 7) are superimposed, and the display device To 105. In step S509, the image output unit 206 trims (cuts out) the superimposed image (703 in FIG. 7) with respect to each vertex coordinate of the circumscribed rectangle calculated in step S507 (output image 704 in FIG. 7). Output to the image server 108.

In the above embodiment, the area of the aperture is extracted by generating an area density image of a substance having an effective atomic number of 70 or more, and a mask image is generated based on this, but the present invention is not limited to this. An area other than the stop in the radiographic image may be extracted to detect the irradiation field. For example, a surface density image may be generated by selecting an effective atomic number so as to include a substance constituting the human body and air but not a substance constituting a diaphragm, and an irradiation field may be determined based on the generated surface density image. . More specifically, by generating a surface density image of a material having an effective atomic number of 70 or less, an image of a material other than lead, that is, a surface density image of an irradiation field that is an area not blocked by the diaphragm is generated. Based on this, the irradiation field may be determined.

As described above, according to the first embodiment, the mask image corresponding to the stop is generated based on the surface density image of the stop or the surface density image of the irradiation field obtained by the energy subtraction process. As a result, erroneous recognition of the irradiation field is reduced.

<Modification>
In the first embodiment, a surface density image of the stop or a surface density image of a region (irradiation field) other than the stop is generated from the effective atomic number of the stop, and a mask image is generated using the result. In the modified example, a configuration in which a mask image is generated based on the surface density image of the background missing area will be described. The surface density image of the unexposed region is an image obtained by detecting the radiation energy transmitted through the air. Therefore, by creating a surface density image of 7.76 (FIG. 3B), which is the effective atomic number of air, a surface density image without blanks can be obtained.

7 is a diagram illustrating an example of a surface density image of the blank region 712. The irradiation field determination unit 204 generates a mask image by extracting the irradiation field from the outer side of the background region 712. The generation method of the display image 703 and the output image 704 using the generated mask image is the same as that in the first embodiment described above. Hereinafter, a processing procedure according to this modification will be described with reference to the flowcharts of FIGS. 8A and 8B. 8A and 8B, the same step numbers are assigned to the same processes as those in the first embodiment (FIG. 5) described above.

In step S500, the image acquisition unit 201 calculates a low energy image, a high energy image, and a fluoroscopic image, and stores them in the low energy image holding unit 207 and the fluoroscopic image holding unit 209, respectively. In step S <b> 500, the image separation unit 202 generates an effective atomic number image and an area density image from the high energy image and the low energy image, and holds them in the processed image holding unit 210.

Next, in step S801, the image separation unit 202 extracts pixels of the effective atomic number of air from the image of the effective atomic number and surface density calculated in step S500, and obtains the surface density image 711 of the blank region. Generated and stored in the processed image holding unit 210. As shown in FIG. 3B, the effective atomic number of air is 7.76. In step S802, the substance extraction unit 203 determines whether the shape of the irradiation field determined from the surface density image of the blank region generated in step S801 is a simple rectangle or circle. If the shape of the irradiation field is a simple rectangle or circle, the process proceeds to step S803. In step S <b> 803, the irradiation field determination unit 204 extracts the straight line of the diaphragm or the edge of the circle from the surface density image of the unexposed region, and defines the coordinates of the irradiation field geometric shape (in the case of a rectangle, the four vertexes). Coordinates, and in the case of a circle, the center coordinates and radius) are calculated. The substance extraction unit 203 stores the calculated coordinates in the extraction data holding unit 211. Thereafter, the irradiation field determination unit 204 generates a mask image by the same processing as in the first embodiment (steps S504 to S505 in FIG. 5). As described above, in the modified example, an image in which the blank area is emphasized by using the specific substance as air is generated from the image of the effective atomic number and the surface density, and the geometric shape corresponding to the shape defined by the blank area is applied. On the other hand, if the shape of the irradiation field determined from the surface density image of the blank area is neither a simple rectangle nor a circle, the process proceeds from step S802 to step S804. Alternatively, the process proceeds from step S802 to step S804 even if the surface density image of the missing region is generated but the subject is located at the corner of the irradiation field and the outer periphery of the missing region cannot be determined. In steps S804 to S808, the irradiation field in the fluoroscopic image is determined so as to include the extracted background missing region at a predetermined ratio or more. More specifically, the irradiation field determination unit 204 creates an image of the background region obtained by binarizing the surface density image of the background region with a threshold value, and uses this to correct the irradiation field extracted from the fluoroscopic image. A mask image is generated. Hereinafter, the operation in each step will be described.

In step S804, the irradiation field determination unit 204 binarizes the surface density image 711 of the background missing area with a predetermined threshold, and generates a background missing image in which the pixel value of the background missing area is 1. In step S805, the irradiation field determination unit 204 performs image processing that makes the irradiation field easy to understand, such as edge enhancement processing, on the fluoroscopic image held in the fluoroscopic image holding unit 209, and then performs irradiation field candidates. Perform extraction. In step S806, the irradiation field determination unit 204 determines whether or not the irradiation field candidate is appropriate by comparing the irradiation field candidate extracted in step S805 with the blank image generated in step S804. If it is determined that the irradiation field candidate is appropriate, the irradiation field candidate is determined as the irradiation field, and the process proceeds from step S806 to step S807. In step S807, the irradiation field determination unit 204 generates a mask image that masks the area outside the irradiation field extracted in step S805.

On the other hand, if it is determined in step S806 that the irradiation field candidate is not appropriate, the process proceeds to step S808. In step S808, the irradiation field determination unit 204 sets irradiation candidate areas in a direction in which the irradiation field is expanded, and performs extraction of irradiation field candidates again in step S805. In step S806, the irradiation field determination unit 204 determines again whether the irradiation field candidates are appropriate. Although there are various criteria for determination in step S806, for example, when an irradiation field and a missing image are compared, and a predetermined ratio (for example, 80%) or more of the missing images is included in the irradiation field candidates. It is determined that the irradiation field candidate is appropriate. Here, the user may specify the ratio at which the blank field images are included in the irradiation field candidates.

The subsequent generation of the display image and output image using the mask image in steps S507 to S509 is the same as in the first embodiment (FIG. 5). In addition, the irradiation field of the X-ray fluoroscopic image may be determined using the extraction results of both the aperture and the blank region described above.

Further, in the above embodiment, by generating a surface density image of the specific substance (aperture) from the image of the effective atomic number and the surface density, an image in which the specific substance is emphasized is acquired, and the irradiation field is determined using this. However, it is not limited to this. From the effective atomic number (Z) and the surface density (D), an image can be generated when X-rays having an arbitrary energy are irradiated. That is, a monochromatic X-ray image when irradiated with virtual monochromatic X-rays is obtained. Since the X-ray wavelength at which the X-ray absorption rate exhibits a peak varies from material to material, an image in which the specific material is emphasized is generated by creating a monochromatic X-ray image having a wavelength that maximizes the X-ray absorption rate of the specific material. be able to. Therefore, the image separation unit 202 generates a monochromatic radiation image when a monochromatic radiation having a wavelength at which the radiation absorption rate of the specific substance shows a peak is generated from the image of the effective atomic number and the surface density, and this is generated as the specific substance. It may be used as an image in which is emphasized. The same applies to the second and third embodiments described below.

Second Embodiment
In the first embodiment, an image in which the determined irradiation field is masked is generated as a display image, and an image cut out by a rectangle circumscribing the mask is generated as an output image. In the second embodiment, an imaging control apparatus 103 capable of automatically adjusting the display position and size of the determined irradiation area will be described. The system configuration of the second embodiment is the same as that of the first embodiment (FIG. 1). In the following, differences from the first embodiment will be mainly described.

FIG. 9 is a block diagram illustrating a functional configuration example related to image processing of the imaging control apparatus 103 according to the second embodiment. In FIG. 9, the same reference numerals are assigned to functional blocks similar to those in the first embodiment (FIG. 4). The display adjustment unit 220 adjusts the position and display magnification of the irradiation field based on the position and size of the irradiation field determined by the irradiation field determination unit 204. The image display unit 205 displays the adjusted image in which the position of the irradiation field is adjusted and the display magnification is adjusted on the display device 105, and the image output unit 206 extracts a necessary region (irradiation field region) from the fluoroscopic image. The processed image is output to the image server 108 as an output image.

FIG. 10 is a diagram showing an example of an image in the case where the imaging target region is small like a finger joint, and a procedure for performing imaging with the aperture 107 restricting most of the irradiation area is performed. As shown in the perspective image 1002, the target area is located toward the end of the imaging area of the radiation imaging apparatus 104. FIG. 11 is a flowchart showing the operation of the imaging control apparatus 103 according to the second embodiment. The display adjustment unit 220 performs the processing of steps S1101 to S1104 between steps S507 and S509 in the flowchart shown in FIG. 5 or FIGS. 8A to 8B.

As described in the first embodiment, the image acquisition unit 201, the image separation unit 202, the substance extraction unit 203, and the irradiation field determination unit 204 determine the irradiation field and generate a mask image outside the irradiation field. The display adjustment unit 220 determines the amount of movement of the irradiation field image so that the image of the irradiation field is displayed at the center of the display area for displaying the fluoroscopic image on the display device 105 (step S1101). Thereby, the position is adjusted so that the center of the irradiation field coincides with the center of the display area of the fluoroscopic image. Further, when the determined irradiation field size is equal to or smaller than the predetermined value (YES in step S1102), the display adjustment unit 220 determines an enlargement ratio for enlarging the irradiation field display size (step S1103). More specifically, the display adjustment unit 220 has a magnification within a range not subjected to digital zooming determined from the relationship between the resolution of the detector of the radiation imaging apparatus 104 and the resolution of the display apparatus 105, and the image of the irradiation field is a display area. Determine the enlargement ratio so that it does not protrude. In step S1104, the image display unit 205 superimposes the fluoroscopic image 1002 and the mask image 1001 as shown in FIG. 10, for example, and applies the movement amount and the enlargement ratio determined by the display adjustment unit 220 to display the display image 1003. It is displayed on the display device 105. Further, the image output unit 206 cuts out an output image based on the circumscribed rectangle calculated in step S507 and transmits the output image to the image server 108.

When the diaphragm 107 is rotated with respect to the radiation imaging apparatus 104, the display adjustment unit 220 calculates the rotation angle of the irradiation field, and the image display unit 205 returns and displays the rotation based on the rotation angle. It may be. In the above description, the size of the irradiation field is enlarged when the size of the irradiation field is equal to or smaller than a predetermined value. However, the present invention is not limited to this. Irrespective of whether or not the size of the irradiation field is equal to or smaller than a predetermined value, the irradiation field may be enlarged and displayed in a range that is not digitally zoomed and that does not exceed the radiation image display area.

<Third Embodiment>
In the first embodiment and the second embodiment, an image in which a specific substance (aperture) is emphasized is generated from an image of effective atomic number and surface density obtained by energy subtraction, and an irradiation field is determined based on the generated image. In the third embodiment, an image in which a specific tissue (for example, a bone) of a subject is emphasized as a specific material is generated from an image of effective atomic number and areal density, and an appropriate visual field region based on a specific position of the specific material To decide. The specific substance targeted by the first and second embodiments is immobile during imaging, but the specific substance targeted by the third embodiment moves during imaging. Accordingly, the visual field area moves during moving image shooting.

The configuration of the radiation imaging system in the third embodiment is the same as that in the first embodiment (FIG. 1). FIG. 12 is a block diagram illustrating a functional configuration example related to image processing of the imaging control apparatus 103 according to the third embodiment. Functional blocks similar to those in the first embodiment (FIG. 4) are denoted by the same reference numerals. In the third embodiment, as illustrated in FIG. 13, moving image shooting when viewing the movement of the knee joint is illustrated. The knee joint is composed of a femur, a patella, a rib, and a tibia, and it is confirmed whether the knee can be bent and stretched smoothly. In this case, the doctor causes the subject to bend and stretch the knee while applying a load, and observe the state with a moving image. FIG. 13 is an image obtained by imaging the knee joint with the radiation imaging apparatus 104, but what is actually displayed on the display apparatus 105 is an area of a visual field area 1301 of a predetermined size. The visual field region 1301 may be limited by being limited by a diaphragm, may be limited by a preset virtual fixed collimator size, or may be trimmed on an image. Here, it is assumed that the visual field size is set in advance. In any case, the image of the visual field is output to the image server 108 as moving image data. In this photographing, since it is necessary to see the movement of the subject, the relative positional relationship between the subject and the visual field region changes every moment.

FIG. 14 is a flowchart showing the operation of the imaging control apparatus 103 according to the third embodiment. Similar to the first embodiment, the image separation unit 202 calculates the effective atomic number and the surface density from the low energy image and the high energy image acquired by the image acquisition unit 201 (step S1401). The image separation unit 202 further generates an image (bone surface density image) in which the bone is emphasized using the effective atomic number and the surface density image, and the effective atomic number of the bone (step S1402). The substance extraction unit 203 extracts the femur from the generated surface density image of the bone, and sets a portion to be displayed at the center of the visual field region. The user may designate a part to be displayed at the center of the visual field area on the GUI, but a characteristic part of the bone may be set in advance. In this embodiment, since it is desired to observe the knee joint, that is, the contact portion between the femur and the tibia, the lowermost portion 1302 of the femur is a portion that is displayed at the center of the visual field region. The visual field determination unit 221 automatically detects the specific position (the lowest part of the femur) of the specific material (bone) from the femur extracted by the material extraction unit 203 by a method such as pattern matching, and obtains the coordinates ( Step S1403).

The visual field determination unit 221 acquires the visual field size from the visual field size holding unit 213, and sets the visual field region so that the detected lowermost part of the femur is at the center of the visual field region (step S1404). The display position adjustment unit 222 calculates a movement amount for moving the visual field region to the center of the display region (step S1405). The image display unit 205 cuts out the visual field region determined by the visual field determination unit 221 from the fluoroscopic image, moves it according to the movement amount calculated by the display position adjustment unit 222, and displays it on the display device 105 (step S1406). Thus, the display position of the visual field area is adjusted and displayed on the display device 105. The image output unit 206 transmits the image of the visual field area cut out from the fluoroscopic image to the image server 108 (step S1407). Note that the transmission of the moving image by the image output unit 206 may be executed after the moving image has been shot. As described above, the region of interest is displayed at the center of the visual field region even when the subject moves.

The image separation unit 202 calculates the effective atomic number and the surface density, and creates the surface density image of the bone from the effective atomic number of the bone, but is not limited thereto. As described above, it is possible to create a monochromatic radiation image when a virtual single-wavelength radiation having a wavelength with a high bone absorption rate is irradiated from the effective atomic number and surface density, and to extract the femur from the image. . In the third embodiment, the image of the visual field region 1301 is extracted from the fluoroscopic image, but the present invention is not limited to this. For example, using the movable diaphragm, the movable diaphragm is moved according to the detection result of the lowermost part of the femur, the irradiation field is detected as described in the second embodiment, and the display position is adjusted and displayed. You may do it.

Also, instead of bone, a target part, organ, or organ may be recognized by energy subtraction, and as a result, display control may be performed so that the target object is in the center of the visual field region. For example, a region of a predetermined organ (for example, stomach) may be detected based on an image obtained by energy subtraction, and display control may be performed so that the center of the region becomes the center of the visual field region.

As described above, although the present invention has been described with respect to a moving image system capable of energy subtraction with a single irradiation and capable of acquiring a fluoroscopic image, the present invention is not limited thereto. That is, even if it is not a moving image system but a still image system, it can be applied even to a system that cannot simultaneously acquire energy subtraction and a fluoroscopic image by one irradiation, and the same effectiveness can be obtained.

The first embodiment and the second embodiment have been described above. According to the first embodiment, the surface density image of the diaphragm is generated from the images of a plurality of radiation distributions with different radiation energies, the diaphragm area of the radiation generator is extracted, and applied to the radiation image. It becomes possible to recognize the irradiation field well. Further, according to the second embodiment, the irradiation field can be displayed at an appropriate position with an appropriate display magnification. Furthermore, according to the third embodiment, since the visual field region can be appropriately maintained following the movement of an appropriate subject, a moving image that is easy to observe is obtained particularly in a fluoroscopic image (moving image).

If an areal density image for an effective atomic number of 13 or more is created, an image in which aluminum, enamel, iron, and lead, which are substances having an effective atomic number of 13 or more, are emphasized, that is, an areal density image of a metal is obtained. . In the above embodiment, not only the irradiation field, but by obtaining a metal surface density image that is an image in which a substance having an effective atomic number of 13 or more (aluminum, enamel, iron, lead) is emphasized, the region of the metal is determined. It is also possible to identify or generate an image excluding metal areas.

<Other embodiments>
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

This application claims priority on the basis of Japanese Patent Application No. 2018-078626 filed on Apr. 16, 2018, the entire contents of which are incorporated herein by reference.

Claims

Acquisition means for acquiring images of a plurality of radiation distributions with different radiation energies from the radiation imaging apparatus;
Generating means for generating a processed image in which a specific substance is emphasized based on the plurality of radiation distribution images;
A radiographic image processing apparatus comprising: a determining unit that determines an area to be set in a radiographic image based on information on the specific substance in the processed image.
The radiographic image processing apparatus according to claim 1, wherein the processed image is generated based on a result of energy subtraction performed on the plurality of radiation distribution images.
3. The radiographic image processing apparatus according to claim 1, wherein the generation unit generates an area density image with respect to an effective atomic number within a predetermined value range as the processed image.
4. The radiation image processing apparatus according to claim 3, further comprising setting means for a user to arbitrarily set a range of the predetermined value.
The radiation imaging apparatus is capable of acquiring images of the plurality of radiation distributions by performing sampling a plurality of times during a single irradiation of radiation,
5. The acquisition unit according to claim 1, wherein the acquisition unit acquires images of the plurality of radiation distributions including an image that is a source of a radiation image for each single irradiation of radiation. The radiation image processing apparatus described.
The generation unit generates an area density image of an effective atomic number of the specific substance as the processed image from an image of an effective atomic number and an area density image generated by performing energy subtraction on the plurality of radiation distribution images. The radiographic image processing apparatus according to claim 1, wherein the radiographic image processing apparatus is a radiographic image processing apparatus.
The generating means irradiates monochromatic radiation having a wavelength at which the radiation absorption rate of the specific substance has a peak from an image of an effective atomic number and an image of surface density generated by performing energy subtraction on the images of the plurality of radiation distributions. The radiographic image processing apparatus according to claim 1, wherein a monochromatic radiographic image is generated as the processed image.
The radiographic image processing apparatus according to any one of claims 1 to 7, wherein the specific substance is a substance or metal constituting a diaphragm in a radiation generating apparatus.
9. The radiation image processing apparatus according to claim 8, wherein the determining unit determines an irradiation field as the region.
The specific substance includes a substance that constitutes a human body and air but does not include a substance that constitutes an aperture, and the determining means determines an irradiation field as the region. The radiation image processing apparatus according to item.
The determining means determines a geometric shape that applies to the shape defined by the specific substance from the processed image, and detects an irradiation field from the radiographic image using the determined geometric shape, The radiation image processing apparatus according to claim 8, wherein an irradiation field region is determined.
The radiation image processing apparatus according to claim 11, wherein the geometric shape is a circle or a rectangle.
The determining means determines an irradiation field based on a binarized image obtained by binarizing the processed image when a geometric shape applicable to the shape defined by the specific substance cannot be determined. The radiographic image processing apparatus according to claim 11 or 12.
11. The radiographic image processing apparatus according to claim 8, wherein the determining unit determines an irradiation field based on a binarized image obtained by binarizing the processed image.
The generation means generates an image in which a void region is emphasized with the specific substance as air,
The radiographic image processing apparatus according to claim 1, wherein the determining unit determines an irradiation field based on a geometric shape that is applicable to a shape defined by the blank region. .
16. The radiographic image processing apparatus according to claim 15, wherein the determining unit determines an irradiation field in the radiographic image so as to include the blank region at a predetermined ratio or more.
The radiographic image processing according to any one of claims 9 to 16, further comprising an adjusting unit that adjusts a position so that a center of the irradiation field coincides with a center of a display area of the radiographic image. apparatus.
The radiographic image processing apparatus according to claim 17, wherein the adjusting means further enlarges the size of the irradiation field within a range that does not become a digital zoom.
The radiation according to claim 9, further comprising display means for displaying an image in which a region excluding the irradiation field determined by the determination means is masked in the radiation image. Image processing device.
The radiation according to any one of claims 9 to 19, further comprising output means for outputting an image cut out by a rectangle circumscribing the irradiation field determined by the determination means from the radiation image. Image processing device.
The radiographic image processing apparatus according to any one of claims 1 to 7, wherein the determining unit determines an area of a predetermined size centered on a specific position of the specific substance as a visual field area.
The radiographic image processing apparatus according to claim 21, further comprising display means for extracting and displaying the visual field region determined by the determining means from the radiographic image.
A radiation image processing method comprising:
An acquisition step of acquiring images of a plurality of radiation distributions with different radiation energies;
Generating a processed image in which a specific substance is emphasized based on the plurality of radiation distribution images;
A radiation image processing method comprising: a determination step of determining a region to be set in the radiation image based on information on the specific substance in the processed image.
The radiation image processing method according to claim 23, wherein, in the generation step, the processed image is generated based on a result of energy subtraction performed on the images of the plurality of radiation distributions.
A program for causing a computer to function as each unit of the radiation image processing apparatus according to any one of claims 1 to 22.