JP6240951B2 - X-ray imaging apparatus and X-ray image selection method - Google Patents

Description

  The present invention relates to an X-ray imaging apparatus, and more particularly to an X-ray imaging apparatus that generates a plurality of X-ray images including a specific part of a subject in an imaging region. The present invention also relates to an X-ray image selection method, and more particularly to an X-ray image selection method for selecting one X-ray image from among a plurality of X-ray images in which a specific part of a subject is included in an imaging region.

  Conventionally, in a dental panoramic X-ray imaging apparatus, a panoramic image is created on the assumption that a plurality of tomographic planes are parallel to a detection plane of a detector. For this reason, when the subject's dentition is located on the reference tomographic plane, an image without distortion could be created for the center of the front tooth, but the subject's dentition from the reference tomographic plane was The image was always distorted when it came off. In addition, if the subject's dentition was not positioned along the reference tomographic plane, the image was also blurred horizontally.

  Therefore, in recent years, as a dental panoramic X-ray imaging apparatus capable of obtaining an image with little blur even when the subject's dentition is deviated from the reference tomographic plane, a tomography having an arbitrary cutting height can be obtained by one tomography. A dental panoramic X-ray imaging apparatus that performs tomosynthesis for reconstructing an image has been proposed.

JP 2013-85667 A (paragraphs 0071 to 0087)

  However, among the plurality of tomosynthesis tomographic images, the image that is most focused on the front tooth portion and the image that is most focused on the molar portion do not necessarily match. For this reason, conventionally, it has been necessary for the user to select an image that is most focused on the region of interest while the user himself / herself confirms the degree of focus of the region of interest, which places a burden on the user (see, for example, Patent Document 1). . In addition, even when the region of interest is the entire region of the tomosynthesis tomographic image, which tomosynthesis tomographic image becomes the most focused image depends on the deviation of the subject's dentition and the reference tomographic plane, The user himself / herself has to confirm the degree of focus of the region of interest.

  In view of the above situation, an object of the present invention is to provide an X-ray imaging apparatus capable of automatically selecting one X-ray image having the best focus in a predetermined region (for example, a region of interest). is there. In addition, in view of the above situation, the present invention provides a predetermined area including at least a part of an area in which a specific part is imaged from among a plurality of X-ray images in which the specific part of the subject is included in the imaging area ( For example, the present invention relates to an X-ray image selection method capable of selecting one X-ray image having the best focus in a region of interest.

  In order to achieve the above object, an X-ray imaging apparatus according to the present invention includes an X-ray irradiation unit that irradiates a subject with X-rays, an X-ray detection unit that detects X-rays transmitted through the subject, and the X-ray detection unit. An image processing unit that generates an X-ray image based on a detection result of the line detection unit, wherein the image processing unit generates a plurality of the X-ray images in which a specific part of the subject is included in an imaging region, and With respect to each of the X-ray images in which a specific part of the subject is included in the area, a first-order differential image is calculated by differentiating a predetermined area including at least a part of the area obtained by imaging the specific part, Further, the second-order differential image is calculated by differentiating the first-order differential image, and the average of the pixel values of the second-order differential image is calculated from all the X-ray images in which the specific region of the subject is included in the imaging region. Configuration to select one X-ray image that maximizes (first It is of the configuration) and.

  In the X-ray imaging apparatus having the first configuration, a swiveling unit that moves around the subject in a state where the pair of the X-ray irradiation unit and the X-ray detection unit face each other with the subject interposed therebetween. The image processing unit includes, as frame data, a signal output by the X-ray detection unit as the turning unit moves the X-ray irradiation unit and the X-ray detection unit around the subject. It is desirable to have storage means for sequentially storing and to reconstruct a tomosynthesis tomographic image from the frame data (second configuration).

  In the X-ray imaging apparatus having the second configuration, it is preferable that the image processing unit reconfigures the tomosynthesis tomographic image from the frame data using a shift addition method (third configuration).

  In the X-ray imaging apparatus according to any one of the first to third configurations, when the specific part of the subject is a dentition of the subject, the image processing unit at least includes a region where the specific part is imaged. The first-order differential image is calculated by differentiating a predetermined region including a part only in the horizontal direction, and the second-order differential image is calculated by differentiating the first-order differential image only in the horizontal direction. Also good.

  In order to achieve the above object, an X-ray image selection method according to the present invention includes an acquisition step of acquiring a plurality of X-ray images including a specific part of a subject in an imaging region, and a specific part of the subject in the imaging region. For each of the X-ray images included, a first-order differential image is calculated by differentiating a predetermined region including at least a part of the region obtained by imaging the specific part, and further, the first-order differential image is differentiated. A calculation step of calculating a second-order differential image, and the X-ray that maximizes the average of the pixel values of the second-order differential image among all the X-ray images in which the specific region of the subject is included in the imaging region And a selection step for selecting one image.

  According to the X-ray imaging apparatus of the present invention, a focus in a predetermined area including at least a part of an area in which a specific part is imaged from among a plurality of X-ray images in which the specific part of the subject is included in the imaging area. Can automatically select the best X-ray image. Therefore, it is not necessary for the user to select the image with the best focus, and the user is not burdened. Further, according to the X-ray image selection method according to the present invention, the predetermined region including at least a part of the region in which the specific region is imaged from among the plurality of X-ray images in which the specific region of the subject is included in the imaging region. One X-ray image with the best focus in the region can be selected based on a clear criterion. Therefore, it is not necessary for the user himself / herself to visually select the most focused image and select it based on subjective criteria, and the user is not burdened.

It is a block diagram explaining the basic composition of the dental X-ray imaging apparatus concerning one embodiment of the present invention. It is a figure which shows the orbit figure of panoramic imaging. It is a figure which shows the example of an external appearance of a standing type X-ray imaging apparatus main body. It is a functional block diagram for demonstrating the image processing means of the dental X-ray imaging apparatus which concerns on one Embodiment of this invention. It is a figure which shows the tomographic plane of five layers. 5 is a flowchart illustrating an image processing operation according to an embodiment of the present invention. It is a figure which shows the tomosynthesis tomographic image (panoramic image) based on the inner 14th tomographic plane. It is a figure which shows the tomosynthesis tomographic image (panoramic image) based on the tomographic plane containing a standard dentition. It is a figure which shows the tomosynthesis tomographic image (panoramic image) based on the outer 15th tomographic plane. It is a figure which shows the panoramic image on which the designation | designated frame for designating a predetermined area | region is superimposed. It is a figure which shows the various operators used when differentiating an image.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating a basic configuration of a dental X-ray imaging apparatus according to an embodiment of the present invention. The dental X-ray imaging apparatus according to this embodiment can perform dental panoramic X-ray imaging and head and neck X-ray CT imaging. The dental X-ray imaging apparatus according to this embodiment includes an X-ray imaging apparatus main body 1 and an X-ray image display apparatus 2 and is configured to transmit and receive data via a communication cable or the like.

  The X-ray imaging apparatus body 1 includes an X-ray irradiation unit 110 that irradiates a subject (patient) with X-rays, an X-ray detection unit 120 that detects X-rays transmitted through the subject O, and an X-ray irradiation unit. 110 and the swivel arm 3 which has the X-ray detection part 120 facing each other.

  In panoramic imaging, tomographic imaging is performed while the swivel arm 3 is horizontally moved and swiveled so that the X-ray irradiation unit 110 and the X-ray detection unit 120 draw a predetermined locus along the shape of the dental arch.

  The X-ray imaging apparatus main body 1 includes a subject holding means (head fixing part) 4 that holds the maxillofacial surface of the subject O, a drive unit 160 that drives the turning arm 3, and an imaging apparatus main body control unit 170. And further. An operation panel 71 a is added to the photographing apparatus main body control unit 170.

  The X-ray irradiation unit 110 includes an X-ray generator 112 including an X-ray tube or the like that irradiates X-rays, and a collimator 111 including a slit or the like that controls the spread of the X-ray beam. The collimator 111 is composed of, for example, a mask in which a plurality of slits having different shapes are formed. The collimator 111 selects one of the slits and spreads the X-ray beam irradiated from the X-ray generator 112 by the selected slit. It has become a mechanism to limit. For example, in panoramic imaging, a panoramic slit is selected, and an X-ray slit beam corresponding to the selected shape of the panoramic slit is irradiated toward the X-ray detector 121 of the X-ray detector 120.

  The X-ray detection unit 120 includes a cassette 122 provided with an X-ray detector 121 including a CCD sensor spread in two dimensions, an X-ray indirect conversion method (FPD: flat panel detector) sensor, and the like. Although the cassette 122 is detachable from the X-ray detection unit 120, the X-ray detector 121 may be fixedly provided on the X-ray detection unit 120 without using the cassette 122. Since the dental X-ray imaging apparatus according to the present embodiment employs the tomosynthesis method, the X-ray detector 121 has a plurality of X-ray detection elements also in the lateral (width) direction. For example, the X-ray detector 121 can collect incident X-rays as image data having a digital electrical quantity corresponding to the amount of X-rays at a frame rate of 300 fps (one frame is, for example, 64 × 1500 pixels). it can. Hereinafter, this collected data is referred to as “frame data”.

  The drive unit 160 includes a turning axis position setting unit 161 that moves the turning shaft 3 c along the dental arch during panoramic photography, and a turning shaft rotating unit 162 that rotates the turning arm 3. The turning axis position setting means 161 includes an XY table for moving the turning axis 3c in the XY direction (horizontal direction), an X axis motor, and a Y axis motor. The turning shaft rotating means 162 includes a turning motor provided on the XY table of the turning axis position setting means 161. The turning motor is a hollow motor that has a highly accurate positioning function by a direct drive system in which a load is directly connected to the motor without using a reduction gear. The pivot axis 3c is set to coincide with the midline of the subject O at the start of imaging.

  The X-ray imaging apparatus main body 1 further includes turning arm position setting means 31 for moving the turning arm 3 straight in the horizontal direction. The turning arm position setting means 31 includes a turning table that can turn and a slide table that can move directly on the turning table.

  At the time of panoramic imaging, the pair of the X-ray irradiation unit 110 and the X-ray detection unit 120 is positioned so as to face each other across the oral cavity of the subject O, and the pair rotates together around the oral cavity. To be driven. However, this rotation is not a rotation that draws a simple circle. That is, the pair of the X-ray generator 112 and the X-ray detector 121 is rotationally driven so that the rotational center RC of the pair moves along the Y axis as shown in FIG. The Y axis is an axis of symmetry of a substantially horseshoe-shaped standard dentition SS. In FIG. 2, one trajectory of the swivel arm 3 is shown every predetermined number of frames (for example, every 30 frames) in the right half of the page, and is not shown in the left half of the page. In addition, the X-ray irradiation unit 110 and the X-ray detection unit 120 are illustrated only for one trajectory, and illustration is omitted for the other trajectories.

  The imaging apparatus main body control unit 170 includes a control device (for example, a CPU) 171 that executes various control programs including a control program that controls the drive unit unit 160, and an X-ray generation unit control unit 172 that controls the X-ray irradiation unit 110. And X-ray detection unit control means 173 for controlling the X-ray detection unit 120. The operation panel 71a is composed of a small liquid crystal panel and a plurality of operation buttons. In addition to the operation buttons, input means such as a keyboard, a mouse, and a touch panel can also be used. In addition, the operation panel 71a may include display means including a display such as a liquid crystal monitor.

  For example, information such as characters and images necessary for operating the X-ray imaging apparatus main body 1 may be displayed on the display means provided on the operation panel 71a. Further, the display means connected to the X-ray image display device 2 for displaying the X-ray panoramic image or the X-ray CT image, and the display content displayed on the display means 26 of the X-ray image display device 2 is provided on the operation panel 71a. In addition, various commands may be issued to the X-ray imaging apparatus main body 1 through a pointer operation with a mouse or the like on characters or images displayed on the display means 26.

  The X-ray imaging apparatus main body 1 performs panoramic imaging of a dental arch in accordance with a command from the operation panel 71a or the X-ray image display apparatus 2. In addition, various commands, coordinate data, and the like are received from the X-ray image display device 2, while photographed image data is sent to the X-ray image display device 2. Further, the base of the imaging region (imaging target region) rr is based on the lower edge line of the cone beam emitted from the X-ray irradiation unit 110.

  The X-ray image display device 2 connected to the X-ray imaging device main body 1 includes a display device main body 20. The display device main body 20 is provided with display means 26 composed of a display device such as a liquid crystal monitor, and operation means 25 composed of a keyboard, a mouse, and the like. An X-ray image is displayed on the display means 26. Various commands can be given through a pointer operation with a mouse on characters or images displayed on the display means 26. Since the display means 26 can be constituted by a touch panel, the display means 26 also serves as the operation means 25 in this case.

  The image display device main body 20 includes a control device (for example, CPU) 21 that executes various programs, a storage unit 22 that is configured by a hard disk or the like and stores various types of shooting data, images, and the like, and an image generation unit 23 that performs image reconstruction. It has. The control device 21, the storage unit 22, and the image generation unit 23 constitute an image processing unit. The storage unit 22 also stores dentition coordinates and the like which will be described later. The control device 21 controls various operations according to a program stored in the storage unit 22 and operates so as to fulfill the function of the image generation means 23 according to the program. That is, the control device 21 also serves as the image generation unit 23.

  The storage unit 22 can store frame data, tomosynthesis tomographic images, and the like.

  FIG. 3 is a diagram showing an example of the appearance of the standing type X-ray imaging apparatus main body 1. Although the standing type will be described here, the present invention can be applied to a dental X-ray imaging apparatus including a sitting type X-ray imaging apparatus main body. 3A is a top view, FIG. 3B is a front view, and FIG. 3C is a side view.

  The X-ray imaging apparatus main body 1 includes a base 5 placed on the floor, a lower pole 6 erected in the vertical direction from the base 5, and an upper pole 7 connected to the lower pole 6 so as to be slidable in the vertical direction. A fixed arm 8 fixed to the upper end of the upper pole 7, a revolving arm 3 rotatably connected to the fixed arm 8, and a subject (for example, a tooth) fixed to the center of the upper pole 7 And a head holding portion 9 that holds the head of the human body including the head. The swivel arm 3 has an X-ray irradiation unit 110 and an X-ray detection unit 120, and the head holding unit 9 has a subject holding means (head fixing unit) 4. In the embodiment, the fixed arm 8 is fixed to the upper pole 7. However, for example, the fixed arm 8 is directly or directly on the wall or ceiling of the room where the X-ray imaging apparatus main body 1 is installed. The aspect attached with the adjustment mechanism which can be adjusted may be sufficient.

  FIG. 4 shows a block diagram for control and processing of the X-ray imaging apparatus according to the present embodiment. As shown in the figure, data from the X-ray imaging apparatus main body 1 is given to the X-ray image display apparatus 2 via a communication line.

  The X-ray image display device 2 is configured by, for example, a personal computer or a workstation capable of storing a large amount of image data in order to handle a large amount of image data. That is, the X-ray image display apparatus main body 20 includes a control device 21, a storage unit 22, an image generation unit 23, and interfaces 24 and 27 as main components, and these are the internal bus 28. Are connected so as to be able to communicate with each other. The control device 21 includes a CPU 21a and a ROM 21b in which a control program such as an OS is stored. The storage unit 22 includes a buffer memory 22a, an image memory 22b, and a frame memory 22c. An operation unit 25 and a display unit 26 are connected to the control device 21 via an interface 24.

  The interface 27 is connected to the X-ray imaging apparatus main body 1 and mediates communication of control information and collected data exchanged between the control device 21 and the X-ray irradiation unit 110 and the X-ray detection unit 120. Accordingly, the control device 21 can transmit a panoramic image taken by the X-ray imaging apparatus main body 1 to an external server according to, for example, DICOM (Digital Imaging and Communications in Medicine) standard.

  The buffer memory 22 a temporarily stores the digital electrical quantity frame data received from the X-ray detection unit 120 via the interface 27.

  The image generation unit 23 is placed under the control of the control device 21 and operates a process for creating a panoramic image using the standard dentition SS provided by the device and a process for using the panoramic image. Has a function to execute interactively with a person. A program for realizing this function is stored in advance in the ROM 21b. This program may be stored in the ROM 21b in advance. However, in some cases, the program may be installed in the ROM 21b or another non-illustrated non-volatile recording medium via a communication line or a portable memory. May be.

  In the present embodiment, the standard tooth row SS described above is prepared in advance on the apparatus side. The standard dentition SS may be selected from a plurality of tomographic planes.

  Frame data and image data processed by the image generating means 23 or being processed are stored in the image memory 22b so as to be readable and writable. For the image memory 22b, a large-capacity recording medium (nonvolatile and readable / writable) such as a hard disk is used. The frame memory 22c is used for displaying reconstructed panoramic image data, post-processed panoramic image data, and the like. The image data stored in the frame memory 22 c is given to the display means 26 via the interface 24 and displayed on the screen of the display means 26.

  The CPU 21a of the control device 21 controls the overall operation of the components of the device in accordance with a program responsible for overall control and processing stored in the ROM 21b. Such a program is set so as to interactively receive operation information for each control item from the operator. Therefore, the CPU 21a is configured to be able to execute collection (scanning) of frame data and the like, as will be described later.

  When the subject O places his / her chin on the head holding portion 9 in a standing posture, the position of the head (jaw portion) of the subject O is fixed at substantially the center of the rotation space of the swivel arm 3. . In this state, the turning arm 3 rotates around the head of the subject O along the XY plane.

  While the revolving arm 3 is rotating, pulsed X-rays are emitted from the X-ray irradiation unit 110 at a predetermined cycle. The X-rays pass through the jaw (dentation portion) of the subject O located at the imaging position and enter the X-ray detection unit 120. As described above, the X-ray detection unit 120 detects incident X-rays at a very high frame rate (for example, 300 fps), and outputs corresponding two-dimensional digital data (for example, 64 × 1500 pixels) of digital electricity. Output sequentially in frame units. As described above, the frame data is temporarily stored in the buffer memory 22a via the communication line and the interface 27 of the X-ray image display apparatus 2. The temporarily stored frame data is then transferred and stored in the image memory 22b.

  In this embodiment, the tomosynthesis method is used to obtain a panoramic image. In the tomosynthesis method, X-rays are irradiated from the X-ray irradiation unit 110 to the subject O at a plurality of different angles, and X-rays transmitted through the subject O are detected by the X-ray detection unit 120, A photographed image (frame data) is photographed and stored in the image memory 22b. The image generation unit 23 reconstructs a tomosynthesis tomographic image based on an arbitrary tomographic plane from a plurality of captured images (frame data) stored in the image memory 22b. The tomosynthesis tomographic image is stored in the storage unit 22 as a panoramic image or displayed on the display means 26. In this embodiment, as a cross section necessary for setting an arbitrary tomographic plane, a cross section including the standard tooth row SS and a 1 mm pitch in the positive direction (inward direction) of the Y axis with respect to the cross section including the standard tooth row SS A total of 31 cross sections are set, including the 15 cross sections set at 1 and the 15 cross sections set at a 1 mm pitch in the negative direction (outward direction) of the Y axis with respect to the cross section including the standard dentition SS. ing. FIG. 5 illustrates five of the 31 cross sections. A solid line indicates a cross section including the standard tooth row SS, and four dotted lines indicate a cross section set 1 mm inside the cross section including the standard tooth row SS and a cross section including the standard tooth row SS 2 mm. The cross section set to the inner side, the cross section set to the outside of 1 mm with respect to the cross section including the standard tooth row SS, and the cross section set to the outside of 2 mm with respect to the cross section including the standard tooth row SS are shown.

  In this embodiment, a tomosynthesis tomographic image is reconstructed from the frame data using the shift addition method. In the shift addition method, among frame data (pixel data) collected at a constant rate by scanning, a plurality of pieces of frame data determined for each position of a locus projected on the XY plane, for example, by an amount corresponding to the position are mutually connected. This is a process of shifting and mutual addition.

  The panoramic image stored in the image memory 22b is displayed on the display means 26 in various ways. The display mode is set based on a user instruction given from the operation means 25, for example.

  Next, processing executed by the control device 21 and the image generation unit 23 will be described with reference to the flowchart of FIG.

  First, when the preparation for imaging such as positioning of the subject O is completed, the control device 21 responds to the operator's instruction given through the operation means 25 and commands a scan for data collection (step S1). . Thereby, the turning arm 3 and the X-ray irradiation unit 110 are instructed to be driven along a preset control sequence. Therefore, while rotating the pair of the X-ray irradiation unit 110 and the X-ray detection unit 120 around the jaw of the subject O, the X-ray irradiation unit 110 emits X-rays during the rotation operation. . X-rays exposed from the X-ray detection unit 110 pass through the subject O and are detected by the X-ray detection unit 120. Therefore, as described above, the digital electric quantity frame data (pixel data) reflecting the X-ray transmission quantity is output from the X-ray detector 121 at a rate of 300 fps, for example. This frame data is stored in the image memory 22b.

  When this scan command is completed, the processing instruction is transferred to the image generation means 23. The image generation means 23 reconstructs a 30-layer tomosynthesis tomographic image from the frame data stored in the image memory 22b using the shift addition method (step S2). The 30-layer tomosynthesis tomographic image obtained in step S2 is stored in the image memory 22b as a 30-layer panoramic image. Specifically, the image generation means 23 reconstructs a 30-layer tomosynthesis tomographic image as follows.

  The image generating means 23 is set to be 1 mm inside the tomographic plane including the standard dentition SS (the cross section including the standard dentition SS, the cross section including the standard dentition SS, and the cross section including the standard dentition SS). A tomosynthesis tomographic image is reconstructed on the basis of a tomographic plane comprising a region outside the cross section.

  Further, the image generating means 23 is set to the inner P-th tomographic plane (a cross section set Pmm inside with respect to the cross section including the standard dentition SS and a Pmm inner side with respect to the cross section including the standard dentition SS. A tomosynthesis tomographic image is reconstructed based on a tomographic plane including a region outside the cross-section that is set inside (P + 1) mm with respect to the cross-section that is inside the cross-section and includes the standard dentition SS. However, P is a natural number of 1 or more and 14 or less.

  Further, the first outer tomographic plane (a region including the standard dentition SS and a region inside the cross section set outside the cross section including the standard dentition SS and outside the cross section including the standard dentition SS by 1 mm) A tomosynthesis tomographic image is reconstructed on the basis of a tomographic plane comprising a cross section set to the outside of 1 mm.

  In addition, the image generating means 23 is arranged on the outer Q-th tomographic plane (outside the cross section set outside (Q-1) mm with respect to the cross section including the standard dentition SS) and the cross section including the standard dentition SS. The tomosynthesis tomographic image is reconstructed on the basis of the area inside the cross section set outside Qmm and the tomographic plane consisting of the cross section set outside Qmm with respect to the cross section including the standard dentition SS. However, Q is a natural number of 2 or more and 15 or less.

  The 30-layer tomosynthesis tomographic images (panoramic images) described above are all X-ray images in which the dentition of the subject is included in the imaging region. Here, as an example of the tomosynthesis tomographic image reconstructed by the image generating means 23, a tomosynthesis tomographic image (panoramic image) based on the inner 14th tomographic plane is shown in FIG. A tomographic image (panoramic image) is shown in FIG. 8, and a tomosynthesis tomographic image (panoramic image) based on the outer fifteenth tomographic plane is shown in FIG.

  Next, the image generation means 23 displays one of 30 panoramic images (for example, a tomosynthesis tomographic image based on a tomographic plane including the standard dentition SS) on the display screen 26a of the display means 26 (step S3).

  In step S4 following step S3, the image generation means 23 determines whether or not a predetermined area including at least a part of an area where the subject's dentition is photographed is specified. When a predetermined area is designated by a mouse pointer operation or the like on the panoramic image displayed on the display screen 26a of the display means 26 (YES in step S4), the process proceeds to step S5. As a specification mode of the predetermined area, for example, a mode in which the predetermined area is specified using a specification frame (white line frame in the drawing) as shown in FIG.

  In step S5, the image generation means 23 selects a panoramic image that maximizes the average pixel value of the second-order differential image obtained by second-order differentiation of the predetermined area, and the selected panoramic image is displayed on the display screen 26a of the display means 26. Display and finish the process. Specifically, the image generation means 23 differentiates a predetermined area of the panoramic image of one layer, and calculates the gradient of the predetermined area (the horizontal differential and the vertical differential are combined into a vector). Calculate the first-order differential image showing the norm, (ii) differentiate the first-order differential image obtained in (i) above, and further calculate the second-order differential image showing the norm of the gradient of the first-order differential image (Iii) Similarly, the above calculations (i) and (ii) are performed for the remaining 29 layers of panoramic images, and (iv) the average of the pixel values of the second-order differential image is selected from all 30 panoramic images. One maximum panoramic image is selected, the selected panoramic image is displayed on the display screen 26a of the display means 26, and the process ends. In addition, when there are a plurality of panoramic images in which the average of the pixel values of the second-order differential image is maximum, a plurality of panoramic images may be displayed, and a predetermined rule (for example, a tomosynthesis tomographic image based on the innermost tomographic plane is selected. (Single rule) may be displayed.

The area of the integration region
When the above processes (i) to (iv) are expressed by mathematical formulas, the following formula (1) is obtained. In the following equation (1), the coordinates of the panoramic pixel are expressed as (x, y), and a predetermined area in the panoramic image of the nth layer is represented.
It expresses. Then, the image generation means 23
Select the panoramic image of the layer.

  Various methods for differentiating an image which is a collection of pixel values have been known. FIG. 11 shows a part of operators used in these differentiation methods as an example of lateral differentiation. In the case of differentiation in the vertical direction, the operator shown in FIG. 11 may be rotated 90 degrees clockwise and the top and bottom and the left and right may be switched.

  In each operator, the numerical value at the upper left is multiplied by the pixel value of the pixel located one pixel above the differentiation target pixel, and the numerical value at the center is the value of the pixel located immediately above the differentiation target pixel. The pixel value is multiplied, the numerical value in the upper right is multiplied by the pixel value of the pixel located one right above the differentiation target pixel, and the numerical value in the left center is the pixel located one left to the left of the differentiation target pixel. The value in the center is multiplied by the pixel value of the pixel to be differentiated, the value in the center right is multiplied by the pixel value of the pixel located one right to the right of the differentiation target pixel, and the value in the lower left Is multiplied by the pixel value of the pixel located one pixel left below the differentiation target pixel, and the numerical value at the lower center is multiplied by the pixel value of the pixel located immediately below the differentiation target pixel. The numerical value is multiplied by the pixel value of the pixel located one pixel below the differentiation target pixel, and the sum of each multiplication value is differentiated. The differential value of the elephant pixels. The operator shown in FIG. 11 is a 3 × 3 operator. However, the operator is not limited to this, and an operator of M × N (M is an odd number of 3 or more, N is an odd number of 3 or more). Can be used.

  Further, unlike the above-described specific example, instead of (i) above, (i ′) a predetermined area of the panoramic image of one layer is differentiated and squared to indicate the square of the norm of the gradient of the predetermined area. A first-order differential image is calculated, and instead of (ii) above, (ii ′) the first-order differential image obtained in (i ′) above is differentiated and squared, and the gradient of the first-order differential image is further calculated. A second-order differential image indicating the square of the norm may be calculated.

  Also, unlike the above-described specific example, instead of (i) above, (i ″) differentiating a predetermined area of the panoramic image of one layer, the absolute value of the horizontal component of the gradient of the predetermined area and its First-order differential image showing the sum of the absolute value of the vertical component of the gradient of the predetermined area is calculated, and instead of (ii) above, (ii ″) the first-order differential obtained in (i ″) above Differentiating the image, and further calculating a second-order differential image indicating the sum of the absolute value of the horizontal component of the gradient of the first-order differential image and the absolute value of the vertical component of the gradient of the first-order differential image Good.

  In addition, when the specific part of the subject is the dentition of the subject as in this embodiment, the horizontal focus is more important than the vertical focus in consideration of the dentition direction. Alternatively, only the horizontal differentiation may be performed without performing the vertical differentiation.

  Further, if the number of pixels belonging to the predetermined region of the panoramic image of each layer is the same, even if the sum of the pixel values of the second-order differential image is compared, the average of the pixel values of the second-order differential image is compared. Comparison results can be obtained. Conversely, if the number of pixels belonging to the predetermined area of the panoramic image of each layer is not the same, the number of pixels belonging to the predetermined area of the panoramic image of each layer is taken into account, and the average of the pixel values of the second-order differential image is obtained. It is necessary to compare the average pixel values of the second-order differential images.

  The predetermined area may be a partial area of the panoramic image or the entire area of the panoramic image. Further, the position of the predetermined area is not limited to that specified by the user as in the present embodiment, and the position of the predetermined area may be set in advance and stored in the storage unit 22.

  Note that the X-ray imaging apparatus according to the present invention is not limited to a dental X-ray imaging apparatus, but can be applied to all X-ray imaging apparatuses that generate a plurality of X-ray images including a specific part of a subject in an imaging region. it can. For example, the present invention can also be applied to a medical X-ray imaging apparatus in which a specific part of a subject is a subject's rib.

  Further, the method of generating a plurality of X-ray images in which a specific part of the subject is included in the imaging region is not limited to the above-described embodiment. For example, a method of reconstructing a tomosynthesis tomographic image using an FBP (Filtered Back Projection) method, a method of performing normal panoramic imaging a plurality of times while changing imaging conditions, and the like may be used.

  The X-ray imaging apparatus according to the present invention selects an X-ray image having the maximum average pixel value of a second-order differential image obtained by second-order differentiation of a predetermined area, thereby obtaining an X-ray image with the best focus. Selected. Thereby, it is difficult to select an X-ray image with the best focus only by the first-order differentiation, and an X-ray image with the best focus can be selected from a plurality of X-ray images with unclear edges. Therefore, the present invention is particularly applicable to an X-ray imaging apparatus capable of generating a plurality of X-ray images with unclear edges by one imaging by reconstructing a tomosynthesis tomographic image using the shift addition method. Is suitable.

DESCRIPTION OF SYMBOLS 1 X-ray imaging apparatus main body 2 X-ray image display apparatus 3 Turning arm 110 X-ray irradiation part 120 X-ray detection part 20 Image display apparatus main body 21 Control apparatus 22 Memory | storage part 25 Operation means 26 Display means

Claims (4)

An X-ray irradiation unit that irradiates the subject with X-rays;
An X-ray detector that detects X-rays transmitted through the subject;
An image processing unit that generates an X-ray image based on a detection result of the X-ray detection unit,
The image processing unit
Generating a plurality of X-ray images in which a specific part of the subject is included in an imaging region;
A first-order differential image is calculated by differentiating a predetermined area including at least a part of an area obtained by imaging the specific part with respect to each of the X-ray images in which the specific part of the subject is included in the imaging area. Further, the second-order differential image is calculated by differentiating the first-order differential image,
An X-ray imaging apparatus that selects one X-ray image that maximizes an average of pixel values of the second-order differential image from all the X-ray images in which a specific part of the subject is included in an imaging region. And
The X-ray image is a panoramic image;
The specific part of the subject is the subject's dentition,
The image processing unit
A first area differential image is calculated by differentiating a predetermined area including at least a part of an area where the specific part is imaged only in a lateral direction of the panoramic image, and the first order differential image is further converted into the panoramic image. An X-ray imaging apparatus, wherein the second-order differential image is calculated by differentiating only in the lateral direction. Swiveling means for moving the X-ray irradiation unit and the X-ray detection unit around the subject in a state of facing each other with the subject interposed therebetween,
The image processing unit sequentially stores, as frame data, signals output by the X-ray detection unit as the turning unit moves the X-ray irradiation unit and the X-ray detection unit around the subject. The X-ray imaging apparatus according to claim 1, further comprising a storage unit configured to reconstruct a tomosynthesis tomographic image from the frame data.   The X-ray imaging apparatus according to claim 2, wherein the image processing unit reconstructs the tomosynthesis tomographic image from the frame data using a shift addition method. An acquisition step of acquiring a plurality of X-ray images including a specific part of the subject in the imaging region;
A first-order differential image is calculated by differentiating a predetermined area including at least a part of an area obtained by imaging the specific part with respect to each of the X-ray images in which the specific part of the subject is included in the imaging area. And a calculation step for differentiating the first-order differential image to calculate a second-order differential image;
A selection step of selecting one X-ray image in which the average of the pixel values of the second-order differential image is maximized from all the X-ray images in which a specific part of the subject is included in the imaging region. A line image selection method comprising:
The X-ray image is a panoramic image;
The specific part of the subject is the subject's dentition,
In the calculation step,
A first area differential image is calculated by differentiating a predetermined area including at least a part of an area where the specific part is imaged only in a lateral direction of the panoramic image, and the first order differential image is further converted into the panoramic image. A method for selecting an X-ray image, wherein the second-order differential image is calculated by differentiating only in the horizontal direction.