JP2020014801A - X-ray imaging device - Google Patents

Abstract

To improve measurement accuracy and measurement efficiency of the body thickness of a subject used for acquiring an X-ray image.SOLUTION: An X-ray imaging device 1 comprises: body thickness detectors 220 which are arranged at a plurality of different positions to acquire body thickness data of a subject 100 from a plurality of directions; and a body thickness calculator 240 which generates a body thickness map by using the respective body thickness data acquired by the body thickness detectors 220.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an X-ray imaging apparatus, and more particularly to a technique for performing imaging according to body thickness information of a subject.

  In fluoroscopic imaging using an X-ray imaging apparatus, a subject is irradiated with X-rays, and the X-rays transmitted through the subject are detected by an X-ray detector. When the irradiated X-rays are reflected and scattered in the body of the subject, secondary X-rays (scattered X-rays) are generated. When the amount of the scattered X-rays increases, the image quality (contrast) of the captured image decreases. Therefore, for the purpose of improving the image quality, there is a method of arranging a grid for absorbing scattered X-rays between the subject and the detector to take an image. In this method, since the irradiated X-rays are attenuated by the grid, It is necessary to perform imaging by increasing the output of X-rays, and an increase in exposure dose becomes a problem.

  In order to reduce the exposure dose and improve the image quality, image processing for removing scattered X-rays (for example, scattered X-ray correction processing and gridless processing) is generally performed to solve the above-mentioned problems.

  The scattered X-ray correction process focuses on the fact that the main component of the scattered X-ray is a low-frequency component, estimates the scattered X-ray by applying the original image to a low-frequency filter (scattered X-ray estimation filter), and estimates the scattered X-ray. This is a method of subtracting scattered X-rays from an original image. Since the amount of scattered X-rays is affected by the thickness of the subject and the size of the irradiation field, accurate scattered X-ray correction processing requires accurate information on the thickness of the subject and the size of the irradiation field. Need to get to.

Specifically, as shown in FIG. 15, in the scattered X-ray correction processing, a unique body thickness is obtained from the gradation for each pixel, the distance between the X-ray tube focal point and the image receiving surface (SID), and the X-ray irradiation conditions. Thus, a table showing the relationship between these factors and the body thickness is created based on the experimental data, and the pixel value (f _{pixel value} ) of the body thickness is estimated (f means a function). Then, the body thickness pixel value calculated from the X-ray condition is subtracted from the original image pixel value to estimate the body thickness (f _{body thickness} ). Then, a low-frequency filter (LPF) is created from the estimated value of the body thickness, and an estimated scattered X-ray image is drawn using the low-frequency filter.

  However, in the conventional scattered X-ray correction processing, the X-ray reflection from other than the subject (for example, a metal object arranged around the subject) or a decrease in the irradiation X-ray dose due to the secular change of the X-ray tube. In some cases, differences between the estimated value and the actual value of the body thickness may occur because the considerations are not taken into account.

  On the other hand, Patent Literature 1 discloses a method of pattern matching using a human body pattern and a method of measuring a body thickness using an optical sensor and a distance sensor. In this method, the body thickness is measured from the difference between the distance between the optical sensor and the body surface of the subject and the distance between the optical sensor and the table.

JP-A-2017-136300

  In the body thickness measurement method of Patent Document 1 described above, the body thickness information that can be obtained at one time is the distance from the optical sensor to a certain location. However, since the body thickness of the subject varies from site to site, it is desirable to obtain an image. It was difficult to measure the body thickness of the entire site at once.

  An object of the present invention is to improve measurement accuracy and measurement efficiency of a body thickness of a subject used for acquiring an X-ray image.

  An X-ray imaging apparatus according to the present invention includes a body thickness detector arranged at a plurality of different positions to acquire body thickness data of a subject from a plurality of directions, and body thickness data acquired by the plurality of body thickness detectors. And a body thickness calculation unit that generates a body thickness map using

  According to the present invention, since a three-dimensional body thickness map is generated, it is possible to improve the measurement accuracy and the measurement efficiency of the body thickness of the subject used for acquiring the X-ray image.

FIG. 1 is a block diagram illustrating an overall configuration of an X-ray imaging apparatus 1 according to a first embodiment. FIG. 2 is a plan view showing a configuration example of a body thickness detector. FIG. 2 is a side view showing a configuration example of the X-ray imaging apparatus 1. FIG. 2 is a plan view showing a configuration example of the X-ray imaging apparatus 1 as viewed from above. 9 is a flowchart illustrating a method of generating a body thickness map of a subject performed by the X-ray imaging apparatus. FIG. 4 is an explanatory diagram of acquisition of body thickness data (image) of a subject by a body thickness detector. FIG. 4 is an explanatory diagram of acquisition of body thickness data (image) of a subject by a body thickness detector. 5 is a flowchart of a scattered X-ray correction process performed by the X-ray imaging apparatus 1. 9 is a flowchart illustrating a method of generating a body thickness map of a subject according to the second embodiment. FIG. 2 is a side view showing a configuration example of the X-ray imaging apparatus. FIG. 4 is an explanatory diagram showing a radiation angle of X-rays. Explanatory drawing which shows the body thickness calculation at the time of oblique perspective imaging | photography. FIG. 9 is a side view showing a configuration example of an X-ray imaging apparatus according to a third embodiment. Explanatory drawing which shows the body thickness calculation of a modification. 9 is a flowchart of a scattered X-ray correction process performed by a conventional X-ray imaging apparatus.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the X-ray imaging apparatus 1 includes a table 102 on which a subject 100 is placed, an X-ray irradiator 104 that irradiates the subject 100 with X-rays, and a position facing the X-ray irradiator 104. An X-ray detector 112 that detects X-rays that have been transmitted through the subject 100 and is located in the X-ray detector; an image processor 114 that performs image processing on the X-ray signal output from the X-ray detector 112; An image storage unit 116 stores the X-ray image output from the unit 114, and a display unit 118 displays the X-ray image.

  Further, the X-ray imaging apparatus 1 includes an X-ray aperture 106 having a plurality of aperture blades on the subject 100 side of the X-ray irradiating unit 104 to set an X-ray irradiating area for the subject 100, And a high voltage generator 110 for supplying power to the power supply 104. Further, the X-ray imaging apparatus 1 includes a control unit 120 that controls each component, and an operation unit 122 that performs various commands to the control unit 120 by operation of an operator.

  The X-ray detection unit 112 includes, for example, a plurality of detection elements that detect X-rays arranged in a two-dimensional array. The X-rays emitted from the X-ray irradiation unit 104 and transmitted through the subject 100 are used. Is detected, and an X-ray signal corresponding to the detected X-ray dose is generated. Specifically, the X-rays detected by the X-ray detection unit 112 are stored as charges in a storage capacitor (not shown) for each pixel. Then, an X-ray signal based on the electric charge accumulated for each pixel is output to the image processing unit 114.

  Further, the X-ray imaging apparatus 1 is disposed at a plurality of different positions and acquires body thickness data of the subject 100 from a plurality of directions, and each body acquired by the plurality of body thickness detectors 220. A body thickness calculation unit 240 that generates a body thickness map using the thickness data.

  The body thickness detector 220 is fixed at a position where the subject 100 can be detected from a plurality of directions, and acquires an infrared image of the subject 100 from each direction. A specific arrangement example of the body thickness detector 220 will be described later in detail.

  As shown in FIG. 2, each body thickness detector 220 includes an infrared detector 221 for receiving an infrared image, a lens 222 for protecting the infrared detector 221, and a cover 223. The lens 222 is disposed on the light receiving surface side of the infrared detector 221, the cover 223 is disposed on the surface opposite to the light receiving surface of the infrared detector 221, and the lens 222 and the cover 223 sandwich the infrared detector 221. Are located.

  The infrared detector 221 is, for example, an infrared array sensor in which a plurality of detection elements for detecting infrared light are arranged in a two-dimensional array, and detects infrared light emitted by the subject 100 and detects a detected two-dimensional infrared image. Is transmitted to the body thickness calculator 240.

  The body thickness calculation unit 240 generates a three-dimensional body thickness map of the subject 100 using each two-dimensional image received from the plurality of body thickness detectors 220 arranged at each position.

  The image processing unit 114 performs image processing on the X-ray signal output from the X-ray detection unit 112, and outputs an X-ray image subjected to the image processing. The image processing includes gamma conversion, gradation conversion processing, enlargement / reduction of an X-ray image, and the like.

  The image processing unit 114 performs a scattered X-ray correction process using the body thickness map of the subject 100 calculated by the body thickness calculation unit 240. Specifically, the image processing unit 114 creates a scattered X-ray estimation filter from the body thickness map of the subject 100, and uses the scattered X-ray estimation filter to extract the scattered X-ray estimation image. Generate Furthermore, the image processing unit 114 obtains an X-ray scattering correction image in which the scattered X-rays have been corrected (removed) by calculating the difference between the pixel value of the X-ray image and the pixel value of the scattered X-ray estimation image.

  In the present embodiment, the function of the control unit 120 can be realized by a computer including a CPU and a memory. The calculation and control programs may be stored in a storage device in advance, or may be fetched from outside and uploaded and executed by the CPU. Part of the function of the arithmetic unit can be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

  Hereinafter, an installation example of the body thickness detector 220 will be described with reference to FIGS. First, details of the mechanism of the X-ray imaging apparatus 1 will be described. The X-ray imaging apparatus 1 has a stand unit 10 installed on the floor, a support frame 30 also functioning as a bed on which the subject 100 is placed, and the support frame 30 movably supported by the stand unit 10. It includes a support arm 20 and a column 50 movably connected to the support frame 30. A table 102 on which the subject 100 is placed is provided above the support frame 30. In the following drawings, the short direction of the table 102 is defined as an X direction, and the longitudinal direction of the table 102 is defined as a Y direction. A direction perpendicular to the XY plane, that is, a direction perpendicular to the mounting surface of the subject 100 on the table 102 is defined as a Z direction.

  The stand unit 10 is a housing that supports the entire imaging stand (the support arm unit 20, the support frame 30, the support unit 50, and the like). Since an elevating mechanism for raising and lowering the support arm 20 with respect to the stand 10 and a rotating mechanism for rotating the support arm 20 with respect to the stand 10 are housed inside the stand 10, the support arm is provided. The support frame 30 supported by 20 can move up and down in the Z direction, and can rotate around a predetermined X direction axis. Further, the support frame 30 is movable in the Y direction with respect to the support arm 20 by a slide mechanism provided on the support arm 20.

  The support 50 can be slid in the Y direction and the X direction with respect to the support frame 30 by an X-ray irradiation unit moving mechanism provided inside the support frame 30. Further, an oblique insertion portion 51 for rotating the support portion 50 about an axis in a predetermined X direction is fixed to the X-ray irradiation unit moving mechanism. The oblique insertion part 51 and the support part 50 can slide integrally.

  Since the X-ray irradiator 104 is provided at the tip of the column 50, the X-ray irradiator 104 can be moved in the Y and X directions together with the column 50 by the X-ray irradiator moving mechanism. The X-ray irradiator 104 has an X-ray tube that receives power from the high voltage generator 110 and generates X-rays. The X-ray irradiator 104 may include an X-ray filter or the like that selectively transmits X-rays of a specific energy.

  Inside the oblique insertion portion 51, a support portion oblique insertion mechanism for rotating the support portion 50 about a predetermined X-direction axis with respect to the support frame 30 is provided. The rotation of the column 50 is controlled by a column rotation controller 132 (FIG. 1) provided in the controller 120.

  An X-ray irradiator rotating unit 105 that connects the X-ray irradiator 104 to the support 50 is provided at the tip of the support 50. An X-ray irradiating unit oblique insertion mechanism for rotating the X-ray irradiating unit 104 about the predetermined Y-direction axis with respect to the support 50 is provided inside the X-ray irradiating unit rotating unit 105. The rotation of the X-ray irradiator 104 is controlled by an X-ray irradiator rotation controller 130 (FIG. 1) provided in the controller 120.

  A compression section 90 is provided on the side of the support section 50 facing the support frame 30. The compression unit 90 performs imaging while compressing the region of interest of the subject 100.

  Further, an X-ray detection unit moving mechanism (not shown) that slides the X-ray detection unit 112 in the X direction and the Y direction with respect to the support frame 30 is installed inside the support frame 30.

  Although not shown, each of the above-described mechanisms for sliding or rotating each member includes a known mechanism such as a motor, a sprocket, and a chain connecting the sprockets.

  Here, an example of an attachment position of the body thickness detector 220 will be described. In the present example, three body thickness detectors 220a to 220c are provided in the X-ray imaging apparatus 1, and the front (the surface viewed from the abdomen) of the subject 100 from three directions orthogonal to each other. Acquire infrared images of the side and top (viewed from the head). The body thickness calculation unit 240 calculates the body thickness of a region R (FIG. 4) where the ranges in which the body thickness detectors 220a to 220c acquire infrared images overlap, and the X-ray irradiation unit 104 irradiates this region R with X-rays. Is done.

  The body thickness detector 220a that detects the front of the subject 100 is attached to a frame provided around the X-ray aperture 106 so that the light receiving surface faces the table 102. As described above, since the X-ray irradiator 104 can slide in the X and Y directions, the body thickness detector 220a can also slide in the X and Y directions integrally with the X-ray irradiator 104 and the X-ray aperture 106. It is. In addition, since the column 50 can rotate about the axis in the X direction with respect to the support frame 30, the body thickness detector 220 a attached to the X-ray aperture 106 can also rotate with the column 50. Further, since the X-ray irradiating unit 104 can be rotated about the Y-direction axis with respect to the support 50 by the X-ray irradiating unit rotating unit 105, the body thickness detector 220a is also integrated with the X-ray irradiating unit 104. And can be rotated.

  The body thickness detector 220b that detects the side surface of the subject 100 is attached to the column 50 so that the light receiving surface faces the subject 100 placed on the table 102. The body thickness detector 220c that detects the upper surface of the subject 100 is fixed to the table 102 by the detector fixture 250 such that the light receiving surface faces the subject 100 placed on the table 102. The height at which the body thickness detectors 220b and 220c are arranged is preferably a height from the table 102 at which the body thickness of the subject 100 can be detected. In addition, it is preferable that the body thickness detector 220c is installed at the end on the side where the head of the subject 100 is arranged so that the thickness of the foot can be measured. When a step platform for receiving the subject 100's foot is arranged at one end of the table 102, the body thickness detector 220c is preferably provided at the other end of the table 102 opposite to the step platform.

  The arrangement of the body thickness detectors 220a to 220c described above is a configuration common to the following first to third embodiments. Note that the body thickness detector is not limited to an example in which three are arranged orthogonally to each other, and it is sufficient that two or more body thickness detectors are arranged in different positions. As described above, since the X-ray thickness detectors 220a to 220c acquire the body thickness data of the subject 100 from a plurality of directions, the three-dimensional body thickness of the entire region R of the subject 100 to be acquired is calculated. Measurement can be performed at once, and measurement accuracy and measurement efficiency of the body thickness of the subject used for acquiring the X-ray image are improved.

<First embodiment>
[Generation method of body thickness map Z]
Hereinafter, a method of generating the body thickness map Z of the subject 100 will be described with reference to FIGS. In the present embodiment, a body thickness map Z is obtained as a three-dimensional map of the region R using body thickness data acquired by the plurality of body thickness detectors 220a to 220c. The body thickness map Z of the subject 100 is generated by irradiating the subject 100 with X-rays by the X-ray irradiating unit 104 and performing image processing on the X-ray signal output from the X-ray detecting unit 112 by the image processing unit 114. This is performed in parallel with the operation of generating the X-ray image I1 (FIG. 8). In the description, the body thickness detector 220 of the present example uses the 8 × 8 two-dimensional array infrared detector 221 to measure the body thickness of the subject 100.

[Step S11]
As shown in FIG. 5, when the generation of the body thickness map Z is started, the body thickness detector 220 acquires data obtained by detecting the body thickness of the subject 100 from a plurality of directions. The detection region R of the body thickness detector 220 does not necessarily have to be the whole body of the subject 100, and the body thickness detector 220 only needs to detect at least a range in which the subject 100 is irradiated with X-rays. In this example, the body thickness detector 220a acquires the body thickness data (image) A from the front (abdominal side) of the subject 100, and the body thickness detector 220b acquires the body thickness data from the side of the subject 100. (Image) B is acquired, and the body thickness detector 220c acquires body thickness data (image) C from the upper surface (head side) of the subject 100.

  The body thickness data A, B, and C are pixel arrays corresponding to the detection element array of the infrared detector 221. As shown in the following formulas (1-1) to (1-3), m columns × n rows, respectively. (M and n are natural numbers, and as shown in FIGS. 6 and 7, in this example, m = 8 and n = 8).

  When the body thickness data is binarized, the body thickness detectors 220a to 220c set the pixel value of the pixel that has detected the subject 100 to “1” and the pixel value of the pixel that has not detected the subject 100 to be “1”. The body thickness data is acquired as “0”. In that case, the body thickness data A, B, and C of the subject 100 as shown in FIGS. 6 and 7 can be expressed by the following equations (2-1) to (2-3), respectively.

[Step S12]
Next, the body thickness calculation unit 240 calculates body thickness data (map) X of the subject 100 viewed from the side and body thickness of the body viewed from the top based on the body thickness data A, B, and C. Calculate the data (map) Y.

  The body thickness data X and Y of the detection region R of the subject 100 are derived from the following equations (3-1) and (3-2), respectively.

  In this example, since each pixel is binarized with m = n = 8, each pixel value of body thickness data X and Y is calculated as in the following equations (4-1) and (4-2), respectively. can do.

  The body thickness data X, Y derived from the body thickness data A, B, C of the subject 100 shown in the equations (2-1) to (2-3) are respectively expressed by the following equations (5-1), It can be shown as (5-2).

[Step S13]
Next, the body thickness calculator 240 obtains final three-dimensional body thickness data (map) Z from the body thickness data X and Y. The body thickness map Z can be represented by the following equation (6). For each pixel of the body thickness map Z, a smaller pixel value is adopted by comparing the pixel values of the pixels of the body thickness data X and Y. In this example, since m = n = 8, each pixel of the body thickness map Z can be derived from Expression (7).

(Equation 7)
z _ij = min {x _ij , y _ij }
(1 ≦ i ≦ 8, 1 ≦ j ≦ 8) (7)

  Then, the body thickness data Z derived from the body thickness data X and Y of the subject 100 shown in the equations (5-1) and (5-2) can be expressed as the following equation (8). .

  As described above, from the body thickness data A, B, and C detected by the body thickness detector 220 from three directions orthogonal to each other, the three-dimensional body thickness map Z of the detection region R of the subject 100 is calculated by the body thickness calculation unit 240. Generated.

[Imaging method]
Hereinafter, an overall flow of the X-ray imaging method using the body thickness map Z in the first embodiment will be described with reference to FIG. The body thickness map Z is used for correcting the scattered X-rays of the captured X-rays.

[Step S1]
First, the operator operates the operation unit 122 to instruct the X-ray imaging apparatus 1 to start scattered X-ray correction processing. In the scattered X-ray correction processing, a scattered X-ray estimation filter that estimates scattered X-rays is generated by cooperation of the body thickness detector 220, the body thickness calculation unit 240, and the image processing unit 114 (details in the following steps). S1A and S1B will be described). The generated scattered X-ray estimation filter is used to correct the X-ray image I1 and remove the influence of the scattered X-ray on the X-ray image I1. The X-ray image I1 is obtained after the operator instructs the start of the scattered X-ray correction processing. Specifically, first, the operator operates the operation unit 122 to instruct the start of the fluoroscopic imaging processing. The X-ray irradiating unit 104 irradiates the subject 100 with X-rays in accordance with the instruction to start the fluoroscopic imaging process, and the X-ray transmitted through the subject 100 is detected by the X-ray detecting unit 112. The X-rays detected by the X-ray detection unit 112 are processed by the image processing unit 114, and an X-ray image I1 is obtained. The operator may instruct the acquisition of the X-ray image I1 at the same time as the instruction to start the scattered X-ray correction processing.

[Step S1A]
In the scattered X-ray correction processing, first, the body thickness detector 220 and the body thickness calculation unit 240 perform the body thickness estimation (generation of the body thickness map Z) of the subject 100 as described above. The body thickness calculation unit 240 transmits the information of the generated body thickness map Z to the control unit 120, and the control unit 120 transmits X information according to the body thickness information of the subject 100 received from the body thickness calculation unit 240. The irradiation condition of the line may be determined. Accordingly, the image processing unit 116 can generate the X-ray image I1 corresponding to the body thickness of the subject 100. The generated X-ray image I1 is stored in the image storage unit 116.

[Step S1B]
Next, a scattered X-ray estimation filter (f _LPF (f _{body thickness} )) corresponding to the _{body thickness} map Z is generated. Specifically, when the calculation of the body thickness map Z is completed, the body thickness calculation unit 240 sends the body thickness map Z to the image processing unit 114. The image processing unit 114 uses the calculated body thickness map Z as the estimated _{body thickness} (f _{body thickness} ) and generates a scattered X-ray estimation filter based on the estimated body thickness in the same manner as the known method shown in FIG. I do. The body thickness calculation unit 240 may display a three-dimensional body thickness image generated from the body thickness map Z, a numerical value of the body thickness of the subject 100, and the like on the display unit 118.

[Step S2]
The image processing unit 114 reads the X-ray image I1 stored in the image storage unit 116, multiplies the generated scattered X-ray estimation filter by the X-ray image I1, and acquires the scattered X-ray estimated image I2.

[Step S3]
The image processing unit 114 obtains the difference between the pixel value of the X-ray image I1 and the pixel value of the scattered X-ray estimation image I2, thereby correcting the X-ray scattered according to the body thickness of the subject 100. The scatter correction image I3 is obtained. The X-ray scattering correction image I3 is displayed on the display unit 118 and stored in the image storage unit 116. Note that the stop instruction of the correction processing is performed by an instruction of the operator from the operation unit 122, and the body thickness measurement may be continued until the stop instruction is issued after the processing is started, or the start / stop instruction of the body thickness measurement may be performed. , May be linked with the start / stop of X-ray fluoroscopy.

  As described above, according to the X-ray imaging apparatus 1 of the present embodiment, the X-ray obtained by removing the scattered X-ray from the three-dimensional body thickness map Z generated by detecting the subject 100 from a plurality of directions. Images can be drawn. Further, in the X-ray imaging apparatus 1, by using the body thickness map Z, it is possible to detect the body thickness of the subject 100 from a plurality of directions, measure the body thickness of the entire part to be acquired at a time, and render an image. Therefore, measurement accuracy and measurement efficiency of the body thickness of the subject used for acquiring the X-ray image are improved.

<Embodiment 2>
In the second embodiment, based on the first embodiment, a case where an X-ray image of the subject 100 is acquired in a state where the support 50 is rotated about the X-direction axis with respect to the stand 10 (hereinafter, the table 102 The method of generating the body thickness map Z2 in the case of oblique perspective imaging in the longitudinal direction will be described with reference to FIGS. FIG. 9 shows a flowchart of generating a body thickness map to which the calculation of the body thickness at the time of oblique insertion is applied, FIG. 10 shows the entire configuration of the X-ray imaging apparatus 1 at the time of oblique perspective radiography in the longitudinal direction, and FIG. 12 shows the relationship between the radiation angle of the X-ray emitted from the X-ray irradiator 104 and the X-ray detector 112, and FIG. 12 shows a method of calculating the body thickness when obliquely inserted.

As shown in FIG. 9, in the second embodiment, the inclination θ _s of the support portion 50 with respect to the support frame 30 with respect to the body thickness map Z (steps S11 to S13) of the subject 100 calculated by the method of the first embodiment are shown. Then, the body thickness map Z2 is calculated by correcting the radiation angle of the X-ray (step S14). A specific flow of the second embodiment will be described later.

First, the relationship between the inclination θ _s of the support 50 and the radiation angle of X-rays and the body thickness of the subject 100 will be described with reference to FIGS. As described in the configuration of the apparatus, the body thickness detector 220a is rotatable about the axis in the X direction integrally with the support 50. X-rays are emitted radially from an X-ray irradiator 104 through an X-ray aperture 106.

As shown in FIG. 10, at the time of oblique penetration fluoroscopic imaging in which the column 50 is inclined by an angle θ _s with respect to the direction orthogonal to the mounting surface of the subject 100 on the table 102, the irradiation surface of the X-ray irradiation unit 104 As compared with the case where the image is taken in a state of facing the mounting surface of the subject 100 on the table 102 in parallel (hereinafter, referred to as vertical imaging), the transmission distance of the X-ray that passes through the body of the subject 100 is longer. Become. That is, it is necessary to calculate the body thickness on the assumption that the body thickness is longer in oblique perspective imaging than in vertical imaging. On the other hand, as shown in FIG. 11, the X-rays radially emitted have different transmission distances through the subject 100 for each angle, and thus the transmission distance of the X-rays depends on the radiation angle. The value is different from the measured body thickness distance.

In other words, at the time of oblique perspective radiography in the longitudinal direction, the transmission distance of the X-ray that passes through the body of the subject 100 changes depending on two factors, the inclination θ _s of the column 50 and the radiation angle of the X-ray. Therefore, in the second embodiment, the body thickness calculation unit 240 reflects the two elements of the inclination θ _s and the radiation angle of the X-ray on the body thickness map Z, and transmits the X-ray transmitted through the body of the subject 100. A map (body thickness map Z2) indicating Z2 _ij (1 ≦ i ≦ m, 1 ≦ j ≦ n) is calculated.

  Hereinafter, returning to FIG. 9, the flow of the second embodiment will be described in detail. In the second embodiment, the steps of the entire X-ray imaging process using the calculated body thickness map Z2 are the same as the steps S1 to S3 (FIG. 8) of the entire X-ray imaging process using the body thickness map Z. As described above, the method of generating the body thickness map Z in steps S11 to S13 is the same as in the first embodiment.

[Step S14]
In step S14, the body thickness map Z2 corresponding to the X-ray irradiation angle with respect to the subject 100 is recalculated from the body thickness map Z using the inclination θ _s of the support portion 50 and the angle of the X-ray radiation angle. .

Note when tilting the column portion 50 slope only theta _s, struts rotation control section 132 of FIG. 1, strut to tilt with respect to a direction orthogonal struts 50 on the mounting surface of the subject 100 of the table 102 An instruction is given to an oblique insertion mechanism (not shown). The support part oblique insertion mechanism rotates the support part 50 with respect to the support frame 30 in response to an instruction from the support part rotation control unit 132. Struts rotation control section 132, the information of the inclination theta _s control strut unit 50, and transmits to the body thickness arithmetic unit 240.

Regarding the X-ray irradiation angle, the X-ray emission angle is divided for each predetermined angle range, and the transmission distance is calculated for each of the divided emission angles in order to obtain the transmission distance that passes through the subject 100 for each angle. . Number of divisions is not particularly limited, wherein the angle of the X-rays emitted is, as shown in FIG. 11, n aliquoted according to the resolution n of the body thickness detector 220, the respective radiation angle theta ₁ ~ It is defined as θ _n. The body thickness calculator 240 stores the angles of the radiation angles θ _{1 to} θ _n in advance.

In step S14, specifically, the body thickness calculation unit 240 determines, for each pixel of the body thickness map Z generated in step S13, the inclination θ _s of the support 50 and the radiation angle θ _{N of the} X-ray ( An X-ray transmission distance Z2 _ij during oblique perspective imaging is calculated by Expression (11) using 1 ≦ N ≦ n (described in detail later), and a body thickness map Z2 of the subject 100 is calculated. Generate. The map indicating the transmission distance Z2 _ij is the body thickness map Z2, and the body thickness map Z is a map indicating the body thickness distance Z _ij of the subject 100 detected by the body thickness detector 220. During oblique perspective imaging, the X-ray transmission distance Z2 _ij has a value different from the body thickness distance Z _ij due to the inclination θ _s and the radiation angle θ _N.

Next, a calculation formula for calculating the transmission distance _Z2ij from the body thickness distance _Zij will be described with reference to FIG. In this example, the body thickness detector 220 generates a body thickness map Z2 of the subject 100 in a region R where the body thickness of the subject 100 is detected.

Here, when the relational expression between the body thickness distance Z _mn and the transmission distance Z2 _mn is derived from the triangle indicated by the thick line in the region R, the relational expression can be expressed by the following expression (9) (−90 ° < θ _s <90 °). When this equation (9) is generalized, each pixel value z2 _ij of the body thickness map Z2 can be obtained from each pixel value z _{ij of} the body thickness map Z using the inclination θ _s and the radiation angle θ _N ( Equation (10)).

(Equation 9)
Z _mn : Z2 _mn = π / 2- (θ _s + θ _n ): π / 2 (9)

(Equation 10)
z2 _ij = π · z _ij / (π−2 (θ _s + θ _N )) (10)

  From the pixel value obtained from the equation (10), the body thickness map Z2 can be expressed as the following equation (11).

As described above, in the second embodiment, the transmission distance Z2 _ij that passes through the body of the subject 100 is calculated for each radiation angle of the X-rays emitted from the X-ray irradiation unit 104 and each rotation angle of the support unit 50. The body thickness map Z2 can be calculated. If X-ray imaging is performed using the body thickness map Z2, scattered X-ray correction is performed in consideration of the difference in the distance of X-rays transmitted through the body of the subject 100 due to the difference in the X-ray irradiation angle. Can be.

<Embodiment 3>
In the third embodiment, based on the first embodiment, a case in which an X-ray image of the subject 100 is acquired in a state where the X-ray irradiating unit 104 is rotated about the Y-direction axis with respect to the support unit 50 (hereinafter, referred to as an X-ray image) A method of generating the body thickness map Z3 in a case where oblique perspective imaging is performed in the short direction of the table 102) will be described with reference to FIG. FIG. 13 shows the entire configuration of the X-ray imaging apparatus 1 at the time of oblique perspective fluoroscopy.

In the third embodiment, the body thickness map is corrected using the inclination from the body thickness map Z, as in the second embodiment, but the direction of the inclination used at the time of calculation is different. Specifically, in the third embodiment, the radiation angle of the X-ray to the subject 100 is determined in consideration of the radiation angle of the X-ray and the inclination θ _e of the X-ray irradiator 104 with respect to the support 50. The body thickness map Z3 is calculated. That is, in the third embodiment, the body thickness map Z2 in step S14 of the flow illustrated in FIG. 9 can be read as the body thickness map Z3. The body thickness map Z3 is calculated using Expression (13) described later.

The inclination θ _e of the X-ray irradiator 104 with respect to the support 50 will be described. As described in the configuration of the apparatus, the rotation of the X-ray irradiating unit 104 is controlled by the X-ray irradiating unit rotation control unit 130, and the X-ray irradiating unit 104 can rotate around the axis in the Y direction. The body thickness detector 220a is rotatable integrally with the X-ray irradiation unit 104.

Further, as shown in FIG. 11, the X-ray is inclined toward the subject 100 with respect to the direction orthogonal to the mounting surface of the subject 100 on the table 102 (here, the radiation angles θ _{1 to} θ _n ). Is irradiated.

Therefore, at the time of oblique perspective imaging in the short direction, the body thickness calculation unit 240 reflects the two elements of the inclination θ _e and the X-ray radiation angle θ _N (1 ≦ N ≦ n) on the body thickness map Z. Then, a map (body thickness map Z3) indicating the transmission distance Z3 _ij (1 ≦ i ≦ m, 1 ≦ j ≦ n) of the X-ray transmitted through the body of the subject 100 is generated. During oblique perspective imaging, the X-ray transmission distance Z3 _ij has a value different from the body thickness distance Z _ij due to the inclination θ _e and the X-ray emission angle θ _N.

The X-ray irradiation unit rotation control unit 130 in FIG. 1 tilts the X-ray irradiation unit 104 by an angle θ _e with respect to the direction orthogonal to the mounting surface of the subject 100 on the table 102. When instructed to 105, the X-ray irradiation unit rotation unit 105 rotates the X-ray irradiation unit 104 with respect to the support 50. The X-ray irradiation unit rotation control unit 130 transmits information on the controlled inclination θ _e of the X-ray irradiation unit 104 to the body thickness calculation unit 240.

In step S14, the body thickness calculation unit 240 generates a body thickness map Z3 of the subject 100 in the region R illustrated in FIG. In this example, the inclination theta _s of X-ray in the region R read as inclination theta _e, transmission distance _{Z2 ij} of the subject 100 may be replaced with transmission distance _{Z3 ij.}

Further, relation between each pixel value _{z3 ij} of body thickness maps each pixel value _{z ij} and body thickness map of Z Z3 is read as _e a theta _s Equation (10) theta, were read as the _{z2 ij z3 ij} It can be represented by the following equation (12) (-90 ° <θ _e <90 °).

(Equation 12)
z3 _ij = π · z _ij / (π-2 (θ _e + θ _N )) (12)

  From the pixel value obtained from the equation (12), the body thickness map Z3 can be expressed as the following equation (13).

As described above, in the third embodiment, the transmission distance Z3 _ij that passes through the body of the subject 100 is considered for each radiation angle of the X-ray emitted from the X-ray irradiation unit 104 and each rotation angle of the X-ray irradiation unit 104. The calculated body thickness map Z3 can be calculated. If X-ray imaging is performed using the body thickness map Z3, scattered X-ray correction can be performed in consideration of the difference in the distance of X-rays transmitted through the body of the subject 100 due to the difference in the incident angle of the X-rays. Can be.

<Modification>
A body thickness map considering both the inclination θ _s described in the second embodiment and the inclination θ _e described in the third embodiment, and a body thickness considering a radiation angle θ _N in addition to the inclination θ _s and the inclination θ _e. A map may be generated. When generating the inclination theta _s and inclination theta _e in addition the body thickness map Z4 Considering radiation angle theta _N, the pixel values _{z mn} of transmission distance _{Z4 mn} pixel values _{z4 mn} and body thickness distance _{Z mn} shown in Figure 14 Can be expressed by the following equation (14). When this equation (14) is generalized, each pixel value z4 _ij of the body thickness map Z4 is obtained from each pixel value z _ij of the body thickness map Z using the inclinations θ _s and θ _e and the radiation angle θ _N. (Equation 15).

(Equation 14)
z4 _mn = √ (a _mn ² + b _mn ² + z _mn ² )
= √ (z _mn ²・ tan (θ _s + θ _n ) ² + z _mn ²・ tan (θ _e + θ _n ) ² + z _mn ² ) (14)
= z _mn √ (tan (θ _s + θ _n ) ² + tan (θ _e + θ _n ) ² +1)

(Equation 15)
_{z4 ij = z ij · √ (} tan (θ s + θ N) 2 + tan (θ e + θ N) 2 +1) (15)

  From the pixel value obtained from the equation (15), the body thickness map Z4 can be expressed as the following equation (16).

Modification There are other example, in the embodiment 2, may be taking into consideration either the inclination theta _s and the radiation angle theta _N only generates a body thickness map. In that case, it is possible to calculate the inclination theta _s towards not considered as 0 to either the value of the emission angle theta _N, each pixel value z2 _ij body thickness map from the above equation (10). Furthermore, in embodiment 3, it may generate a body thickness map Z3 in consideration of either one of the inclination theta _e and the radiation angle theta _N only. In that case, it is possible to calculate the inclination theta _e of those who do not consider either the value of the emission angle theta _N as 0, each pixel value z3 _ij body thickness map from the formula (12).

The slope theta _s and inclination theta _e, by arranging the inclination sensor inside the periphery and the support frame 30 of the X-ray irradiation unit 104 may be detected.

  As described above, in the X-ray diagnostic apparatus 1, the support frame 30 can be slid in the longitudinal direction with respect to the support arm 20, but the table 102 can be slid in the longitudinal direction with respect to the support frame 30. It may be.

DESCRIPTION OF SYMBOLS 1 ... X-ray imaging apparatus, 10 ... Stand part, 20 ... Support arm part, 30 ... Support frame, 50 ... Support part, 51 ... Oblique insertion apparatus, 90 ... Compression device, 100: subject, 102: table, 104: X-ray irradiation unit, 105: rotating unit of X-ray irradiation unit, 106: X-ray diaphragm, 110: high Voltage generation unit, 112: X-ray detection unit, 114: Image processing unit, 116: Image storage unit, 118: Display unit, 120: Control unit, 122: Operation unit, 130 ... X-ray irradiation unit rotation control unit, 132 ... column rotation control unit, 220 ... body thickness detector, 221 ... infrared detector, 222 ... lens, 223 ... cover , 240 ... body thickness calculation unit, 250 ... detector fixture

Claims (9)

A body thickness detector arranged at a plurality of different positions to acquire body thickness data of the subject from a plurality of directions,
A body thickness calculation unit that generates a body thickness map using each body thickness data obtained by the plurality of body thickness detectors,
An X-ray imaging apparatus comprising: The X-ray imaging apparatus according to claim 1,
An X-ray imaging apparatus, further comprising: an image processing unit that creates a scattered X-ray estimation filter using the body thickness map generated by the body thickness calculation unit and executes a scattered X-ray correction process. The X-ray imaging apparatus according to claim 1,
An X-ray imaging apparatus, wherein the body thickness detector includes an infrared detector in which a plurality of detection elements for detecting infrared light are arranged in a two-dimensional array. The X-ray imaging apparatus according to claim 1,
An X-ray imaging apparatus, wherein the body thickness calculation unit generates a three-dimensional body thickness map of a subject using a two-dimensional image acquired by the body thickness detector at each position. The X-ray imaging apparatus according to claim 1,
The said body thickness detector is arrange | positioned at three places of the said X-ray imaging apparatus, The said body thickness calculation part uses the body thickness data from three mutually orthogonal directions of a test subject, The X-ray imaging characterized by the above-mentioned. apparatus. The X-ray imaging apparatus according to claim 1,
An X-ray imaging apparatus, wherein the body thickness calculating unit generates a body thickness map according to an X-ray irradiation angle with respect to a subject. The X-ray imaging apparatus according to claim 1,
An X-ray irradiator;
A rotatable column supporting the X-ray irradiator;
Further, a strut portion oblique insertion mechanism for rotating the strut portion,
The X-ray imaging apparatus, wherein the body thickness calculation unit generates a body thickness map for each rotation angle of the support. The X-ray imaging apparatus according to claim 1,
An X-ray irradiator;
A column supporting the X-ray irradiator;
An X-ray irradiation unit oblique insertion mechanism that rotates the X-ray irradiation unit with respect to the support unit,
The X-ray imaging apparatus, wherein the body thickness calculation unit generates a body thickness map for each rotation angle of the X-ray irradiation unit with respect to the support unit. The X-ray imaging apparatus according to claim 1,
An X-ray detector that detects an X-ray transmitted through the subject and generates an X-ray signal;
The body thickness calculation unit divides an X-ray irradiation angle according to the resolution of the body thickness detector and generates a body thickness map according to the divided X-ray irradiation angle. apparatus.

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