JP2017169904A - X-ray imaging apparatus and mark display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray imaging apparatus and a mark display method in which an image can be displayed in a display unit without detaching a positioning mark even when performing calibration.SOLUTION: An X-ray photographing apparatus includes: a high voltage image storage unit 32 for storing a high voltage image obtained by photographing a positioning mark with a first flat panel detector 23 while a high tube voltage is applied to a first X-ray tube 25 to perform X-ray irradiation; a low voltage image storage unit 33 for storing a low voltage image obtained by photographing the positioning mark with the first flat panel detector 23 while a low tube voltage is applied to the first X-ray tube 25 to perform X-ray irradiation; and an image processing unit 31 for displaying the positioning mark using a pixel value obtained by adding a difference of the pixel value between an area corresponding to the positioning mark in the high voltage image and an area other than the area corresponding to the positioning mark to a difference of the pixel value between an area corresponding to the positioning mark in the low voltage image and an area other than the area corresponding to the positioning mark.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an X-ray imaging apparatus and a mark display method, and more particularly to an X-ray imaging apparatus and a mark display method for displaying a positioning mark for positioning an X-ray tube and an X-ray detector on a display unit. .

  In radiation therapy in which radiation such as X-rays or proton beams is irradiated to an affected area such as a tumor, it is necessary to accurately irradiate the affected area with radiation. However, not only the subject may move the body, but the affected part itself may move. For example, a tumor near the lung moves greatly based on respiration. For this reason, a radiotherapy apparatus having a configuration in which a gold marker having a spherical shape is placed near the tumor, the position of the marker is detected by an X-ray fluoroscopic imaging apparatus, and irradiation of therapeutic radiation is controlled is proposed. (See Patent Document 1).

  In the X-ray fluoroscopic apparatus used in such a radiotherapy apparatus, X-rays such as an X-ray tube that irradiates the subject with X-rays and a flat panel detector that detects X-rays that have passed through the subject are used. It is necessary to position the detector at a position aligned with each other. For this reason, a positioning mark such as a cross wire for positioning the X-ray tube and the X-ray detector is attached to the X-ray tube, and the positioning mark is attached to the X-ray detector by the X-ray detector. It is conceivable that the X-ray tube and the X-ray detector are positioned at positions aligned with each other by detecting whether the center of the positioning mark and the center of the X-ray detector coincide with each other. .

  On the other hand, an X-ray detector such as a flat panel detector used in such an X-ray imaging apparatus needs to execute calibration every certain period in order to correct the sensitivity for each pixel. When performing this calibration, uniformly irradiate the flat panel detector with X-rays without any obstruction on the surface of the flat panel detector, and examine the variation in sensitivity of each pixel on the entire flat panel detector at that time. Thus, the sensitivity is corrected so as to be constant.

  At this time, the positioning marks such as the cross wires described above are fixed to the X-ray tube. For this reason, when calibration is performed with such a positioning mark present, sensitivity adjustment is performed in a state including the positioning mark image, so that the positioning mark image is visible. The problem of disappearing arises. For this reason, it is necessary to remove a positioning mark such as a cross wire from the X-ray tube every time calibration is executed.

  In Patent Document 2, when calibration is performed on a flat panel detector having a positioning target disposed on the front surface thereof, the pixel value of the target image captured by the flat panel detector is obtained during X-ray fluoroscopy. By changing the pixel value so that the target image is displayed and creating the gain characteristic map of the flat panel detector with the pixel value of the target image changed, the positioning target is placed on the surface of the flat panel detector. There is disclosed a radiation imaging apparatus that can execute calibration without erasing an image of a target even if it is disposed.

Japanese Patent No. 3053389 Japanese Patent No. 5347554

  The radiological fluoroscope described in Patent Document 2 described above performs calibration without erasing the target image even when calibration is performed on a flat panel detector on which a positioning target is disposed. Although it is an excellent thing that can be done, there is a problem that it is necessary to perform special image processing.

  The present invention has been made to solve the above-described problems, and displays an image of a positioning mark on the display unit without removing the positioning mark even when calibration of the X-ray detector is executed. An object of the present invention is to provide an X-ray imaging apparatus and a mark display method capable of performing the above.

  According to a first aspect of the present invention, there is provided an X-ray imaging apparatus comprising: an X-ray tube; and an X-ray detector that detects X-rays emitted from the X-ray tube and passed through the subject. The X-ray detector is used to photograph a positioning mark for positioning the X-ray tube and the X-ray detector in a state in which the X-ray is irradiated by applying a tube voltage of 1, and a first voltage image is obtained. The X-ray detection is performed on the positioning mark in a state in which a first voltage image generation unit to be generated and a second tube voltage lower than the first tube voltage is applied to the X-ray tube and X-rays are irradiated. A second voltage image generation unit that generates a second voltage image photographed by the instrument, and image processing for displaying an image of the positioning mark on the image display unit based on the first voltage image and the second voltage image And a section.

  According to a second aspect of the invention, the image processing unit includes a pixel value difference between a region corresponding to the positioning mark and a region other than the region corresponding to the positioning mark in the first voltage image, and the second voltage. The positioning mark is displayed on the image display unit with a pixel value obtained by adding a pixel value difference between a region corresponding to the positioning mark in the image and a region other than the region corresponding to the positioning mark.

  According to a third aspect of the present invention, in the image processing unit, an area other than an area corresponding to the positioning mark in the first voltage image and an area other than an area corresponding to the positioning mark in the second voltage image are the same. Weighting processing for weighting the pixel values to be equal to each other, and subtraction processing for performing subtraction between the first voltage image and the second voltage image.

  According to a fourth aspect of the present invention, there is provided an X-ray imaging apparatus comprising: an X-ray tube; and an X-ray detector that detects X-rays emitted from the X-ray tube and passed through the subject. In a mark display method for displaying an image of a positioning mark for positioning an X-ray detector on an image display unit, the positioning mark is applied to the X-ray tube by applying a first tube voltage to the X-ray. A first voltage imaging step of imaging with the X-ray detector in an irradiated state to obtain a first voltage image; and a second tube having the positioning mark on the X-ray tube lower than the first tube voltage. Based on a second voltage imaging step of obtaining a second voltage image by imaging with the X-ray detector in a state where a voltage is applied and irradiating X-rays, and the first voltage image and the second voltage image An image processing process for displaying an image of the positioning mark on the image display unit Characterized in that it comprises a and.

  According to a fifth aspect of the present invention, in the image processing step, a difference in pixel value between a region corresponding to the positioning mark and a region other than the region corresponding to the positioning mark in the first voltage image, and the second voltage A calculation step of calculating a pixel value representing the positioning mark by adding a pixel value difference between a region corresponding to the positioning mark in the image and a region other than the region corresponding to the positioning mark; And a display step of displaying the positioning mark on the image display unit using a pixel value representing the positioning mark calculated in the step.

  According to the first and fourth aspects of the present invention, the positioning mark image is displayed on the image display unit using the first voltage image and the second voltage image. Even when the calibration of the line detector is executed, an image of the positioning mark can be displayed on the display unit without removing the positioning mark.

  According to the second, third, and fifth inventions, the pixel value difference between the region corresponding to the positioning mark in the first voltage image and the other region and the positioning mark in the second voltage image are supported. Since the positioning mark is displayed by adding the pixel value difference between the area and the other area, the slight difference in pixel value that occurs when the positioning mark is photographed with different voltages is emphasized. Even when the X-ray detector is calibrated, it is possible to display an image of the positioning mark on the display unit.

1 is a schematic view showing an X-ray fluoroscopic apparatus as an X-ray imaging apparatus according to the present invention, together with a horizontal irradiation port 21 and a vertical irradiation port 22 in a radiation irradiation apparatus 40. It is a block diagram which shows the control system of a X-ray fluoroscope with a radiation irradiation apparatus. 3 is a schematic diagram of positioning marks 28 and 29. FIG. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention. It is explanatory drawing which shows the mark display process in the mark display method which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an X-ray fluoroscopic apparatus as an X-ray imaging apparatus according to the present invention, together with a horizontal irradiation port 21 and a vertical irradiation port 22 in a radiation irradiation apparatus 40. FIG. 2 is a block diagram showing the control system of the X-ray fluoroscopic apparatus together with the radiation irradiation apparatus. The X-ray fluoroscopic apparatus and the radiation irradiation apparatus 40 constitute a radiotherapy apparatus.

  The radiation irradiation apparatus 40 includes a horizontal irradiation port 21 and a vertical irradiation port 22 that emit radiation such as X-rays and electron beams toward the patient 20 on the treatment table 27. The treatment table 27 can move and rotate in six axis directions.

  On the other hand, the X-ray fluoroscopic apparatus measures the X-rays irradiated from the first X-ray tube 25, the second X-ray tube 26, and the first X-ray tube 25 and the second X-ray tube 26 and passing through the patient 20. A first flat panel detector 23 and a second flat panel detector 24 are provided. A positioning marking member 28 is disposed in the X-ray irradiation direction of the first X-ray tube 25, and a positioning marking member 29 is disposed in the X-ray irradiation direction of the second X-ray tube 26. . These positioning marking members 28 and 29 may be directly connected to the first X-ray tube 25 and the second X-ray tube 26, or may be connected via a collimator or the like not shown.

  FIG. 3 is a schematic diagram of the positioning marking members 28 and 29.

  The positioning marking members 28 and 29 are for positioning the first X-ray tube 25 and the first flat panel detector 23, and the second X-ray tube 26 and the second flat panel detector 24 at positions aligned with each other. And includes a marked line L made of an X-ray absorbing member that functions as a positioning mark according to the present invention. This marked line L may be comprised with the wire etc. which absorb an X-ray, and may be comprised by attaching X-ray non-transmissive material with respect to translucent boards, such as an acryl. Positioning mark line so that the intersection of the cross-shaped mark line L in the positioning mark line members 28 and 29 coincides with the optical axis of the X-rays irradiated from the first X-ray tube 25 and the second X-ray tube 26. The member 28 is connected to the first X-ray tube 25, and the positioning marking member 29 is connected to the second X-ray tube 26. The intersection of the cross mark L in the positioning mark member 28 and the center of the first flat panel detector 23 coincide, and the cross point of the cross mark L in the positioning mark member 29 and the second flat. When the center of the panel detector 24 coincides, the first X-ray tube 25 and the first flat panel detector 23 are positioned at positions where the second X-ray tube 26 and the second flat panel detector 24 are aligned with each other. That's right.

  1 and 2 again, the horizontal irradiation port 21 and the vertical irradiation port 22 in the radiation irradiation apparatus 40 described above are fixed in the examination room. The first flat panel detector 23 can move between the imaging position on the front surface of the vertical irradiation port 22 facing the first X-ray tube 25 via the patient 20 and the retracted position separated from the vertical irradiation port 22. It has become. Further, the second flat panel detector 24 can move between the imaging position on the front surface of the horizontal irradiation port 21 facing the second X-ray tube 26 via the patient 20 and the retracted position separated from the horizontal irradiation port 21. It has become.

  The X-ray fluoroscopic apparatus includes a control unit 30 that controls the entire apparatus. The control unit 30 includes an image processing unit 31, a high voltage image storage unit 32, and a low voltage image storage unit 33 which will be described later. The control unit 30 is connected to the radiation irradiation apparatus 40 described above directly or via a network.

  Further, the X-ray fluoroscopic apparatus includes a display unit 35. The display unit 35 functions as a graphical user interface (GUI), and includes, for example, a liquid crystal display panel. In addition to displaying X-ray images, the display unit 35 positions the first X-ray tube 25 and the second X-ray tube 26 and the first flat panel detector 23 and the second flat panel detector 24, respectively. Images of the positioning marking members 28 and 29 are displayed.

  When performing radiotherapy using the X-ray fluoroscopic apparatus and the radiation irradiation apparatus 40 having such a configuration, a marker is placed near the tumor in the patient 20, and the position of the marker is detected by the X-ray fluoroscopic imaging apparatus. By executing the moving body tracking for tracking the position of the tumor, the irradiation position of the therapeutic radiation irradiated from the radiation irradiation apparatus 40 is controlled.

  In this X-ray fluoroscopic apparatus, it is necessary to position the first X-ray tube 25 and the first flat panel detector 23 and the second X-ray tube 26 and the second flat panel detector 24 at positions aligned with each other. . In order to perform this positioning, the marking line L in the positioning marking members 28 and 29 is used. Even when the first and second flat panel detectors 23 and 24 are calibrated, the images of the marked lines L on the positioning marked members 28 and 29 are displayed on the display unit 35. There is a need.

  Hereinafter, a mark display method according to the present invention for displaying the images of the positioning marking members 28 and 29 will be described. 4 to 10 are explanatory views showing mark display steps in the mark display method according to the present invention. The following operations are similarly performed on the first flat panel detector 23 and the second flat panel detector 24. In the following description, a case will be described in which an image of the positioning marking member 28 photographed by the first flat panel detector 23 is displayed.

  In order to display the image of the positioning marking member 28 with respect to the image taken by the first flat panel detector 23 that has been calibrated, first, a high tube voltage (that is, the first X-ray tube 25) X-rays are emitted from the first X-ray tube 25 in a state where a high-voltage image (that is, a first voltage image) is detected by the first flat panel detector 23. ). This high voltage image is stored in the high voltage image storage unit 32 in the control unit 30 shown in FIG. FIG. 4 shows a pixel value of a region corresponding to the marked line L of the positioning marking member 28 in the high voltage image at this time, and a pixel value of a region other than the region corresponding to the marked line L of the positioning marking member 28. It shows. In this high voltage image, the pixel value of the area corresponding to the marked line L of the positioning marking member 28 is B2, and the pixel value of the area other than the area corresponding to the marked line L of the positioning marking member 28 is It is A2. In FIG. 4, the difference between the pixel value B2 of the area corresponding to the marked line L of the positioning marking member 28 and the pixel value A2 of the area other than the area corresponding to the marked line L of the positioning marking member 28 is T2. It is said.

  Next, X-rays are emitted from the first X-ray tube 25 in a state where a low tube voltage (that is, a second tube voltage lower than the first tube voltage) is applied to the first X-ray tube 25, and a positioning mark is obtained. An image of the member 28 is detected by the first flat panel detector 23 and a low voltage image (that is, a second voltage image) is taken. This low voltage image is stored in the low voltage image storage unit 33 in the control unit 30 shown in FIG. FIG. 5 shows a pixel value in a region corresponding to the marking line L of the positioning marking member 28 and a pixel value in a region other than the region corresponding to the marking line L of the positioning marking member 28 in the low voltage image at this time. It shows. In this low voltage image, the pixel value of the area corresponding to the marked line L of the positioning marking member 28 is B1, and the pixel value of the area other than the area corresponding to the marked line L of the positioning marking member 28 is It is A1. In FIG. 5, the difference between the pixel value B1 of the area corresponding to the marked line L of the positioning marking member 28 and the pixel value A1 of the area other than the area corresponding to the marked line L of the positioning marking member 28 is T1. It is said.

  In general, in the case where the standard line L of the positioning standard marking member 28 is photographed by the first flat panel detector 23 that has been calibrated, the standard line L in the positioning standard marking member 28 is detected from the image by calibration. The image disappears. However, when the tube voltage applied to the first X-ray tube 25 is changed, the quality of the X-ray irradiated from the first X-ray tube 25 changes, whereby the mark L in the positioning mark member 28 is changed. The pixel value of the region corresponding to In the present invention, the tube voltage applied to the first X-ray tube 25 is changed to irradiate the first flat panel detector 23 with X-rays having different radiation qualities. A slight change in the pixel value of the region is used, and both the high-voltage image and the low-voltage image are used to enhance them, thereby generating an image of the marking line member 28 for positioning. These processes are executed by the image processing unit 31 in the control unit 30 shown in FIG.

  Next, A2 which is a pixel value in a region other than the region corresponding to the marked line L of the positioning marked line member 28 in the high voltage image is subtracted from each pixel value in the high voltage image shown in FIG. FIG. 6 shows the pixel values of the area corresponding to the marked line L of the positioning marking member 28 and the areas other than the area corresponding to the marked line L of the positioning marking member 28 in the image subjected to such processing. The pixel value is shown. In this image, the pixel value of the area corresponding to the marked line L of the positioning marking member 28 is-(A2-B2), and other than the area corresponding to the marked line L of the positioning marking member 28. The pixel value of the area is 0.

  Next, the sign of the pixel value of the image shown in FIG. 6 is inverted. That is, each pixel value in this image is multiplied by (−1). FIG. 7 shows the pixel values of the area corresponding to the marked line L of the positioning marking member 28 and the areas other than the area corresponding to the marked line L of the positioning marking member 28 in the image subjected to such processing. The pixel value is shown. In this image, the pixel value of the area corresponding to the marking line L of the positioning marking member 28 is (A2-B2), and the area other than the area corresponding to the marking line L of the positioning marking member 28 The pixel value of is 0.

  Next, the pixel value A1 of an area other than the area corresponding to the marked line L of the positioning marked line member 28 in the low voltage image shown in FIG. 5 is added to each pixel value of the image shown in FIG. In other words, the pixels other than the region corresponding to the marking line L of the positioning marking member 28 in this image and the region other than the region corresponding to the marking line L of the positioning marking member 28 in the low voltage image are the same pixel. A weighting process for weighting is executed so as to obtain a value. FIG. 8 shows the pixel values of the area corresponding to the marked line L of the positioning marking member 28 and the areas other than the area corresponding to the marked line L of the positioning marking member 28 in the image subjected to such processing. The pixel value is shown. In this image, the pixel value of the area corresponding to the marking line L of the positioning marking member 28 is (A2−B2 + A1), and the area other than the area corresponding to the marking line L of the positioning marking member 28. The pixel value of is A1.

  Thereafter, subtraction is performed between the image shown in FIG. 8 and the low voltage image shown in FIG. That is, each pixel value in the low voltage image shown in FIG. 5 is subtracted from each pixel value in the image shown in FIG. FIG. 9 shows the pixel values of the area corresponding to the marked line L of the positioning marking member 28 and the areas other than the area corresponding to the marked line L of the positioning marking member 28 in the image subjected to such processing. The pixel value is shown. In this image, the pixel value of the area corresponding to the marking line L of the positioning marking member 28 is (A2−B2) + (A1−B1). The pixel value of the area other than the corresponding area is 0.

  In the image shown in FIG. 9, the pixel value of the area corresponding to the marked line L in the positioning marking member 28 is the same as the area corresponding to the marked line L of the positioning marked member 28 in the high-voltage image and the positioning marking. The pixel value difference (A2-B2, that is, T2) from the region other than the region corresponding to the marked line L of the member 28 and the region corresponding to the marked line L of the positioning marked member 28 in the low voltage image are positioned. The pixel value is obtained by adding the difference (A1-B1, that is, T1) of the pixel value from the area other than the area corresponding to the marked line L of the marked line member 28. For this reason, it becomes possible to emphasize the pixel value of the area | region corresponding to the marked line L of the marking line member 28 for positioning.

  An image in which the pixel value in the region corresponding to the marking line L of the positioning marking member 28 is emphasized by the action of the image processing unit 31 is displayed on the display unit 35 shown in FIG. At this time, it is possible to emphasize and display the image of the marking line L of the positioning marking member 28. Since the center portion of the marking line L of the positioning marking member 28 having a cross shape coincides with the optical axis of the X-ray irradiated from the first X-ray tube 25, this position is set to the first position. By making it coincide with the center position of the flat panel detector 23, the first X-ray tube 25 and the first flat panel detector 23 can be positioned at positions aligned with each other.

  In the above-described embodiment, the pixel value A1 of an area other than the area corresponding to the marked line L of the positioning marked line member 28 in the low voltage image is added to each pixel value of the image shown in FIG. Thus, the region other than the region corresponding to the marking line L of the positioning marking member 28 in this image is the same as the region other than the region corresponding to the marking line L of the positioning marking member 28 in the low-voltage image. After performing the weighting process to be a pixel value, the low voltage image is subtracted from the processed image.

  However, the positioning mark in the image shown in FIG. 7 is obtained by subtracting the pixel value A1 in a region other than the region corresponding to the mark L of the positioning mark member 28 in the low voltage image from the low voltage image. A weighting process is performed such that a region other than the region corresponding to the marked line L of the member 28 and a region other than the region corresponding to the marked line L of the positioning marked member 28 in the low voltage image have the same pixel value. After execution, the low voltage image may be subtracted.

  In the embodiment described above, as shown in FIGS. 4 and 5, the pixel value of the region corresponding to the marking line L of the positioning marking member 28 is the region corresponding to the marking line L of the positioning marking member 28. It is smaller than the pixel value in the other area. In particular, in a low-voltage image, the pixel value of the area corresponding to the marked line L of the positioning mark member 28 is smaller than the pixel value of the area other than the area corresponding to the marked line L of the positioning mark member 28. It is common to become. However, in the high-voltage image, depending on the state of the calibration performed before that, the pixel value of the region corresponding to the marked line L of the positioning marked member 28 becomes the marked line L of the positioning marked member 28. May be larger than the pixel value of the region other than the region corresponding to.

  FIG. 10 shows pixel values in a region corresponding to the marking line L of the positioning marking member 28 in the high voltage image in such a case, and regions other than the region corresponding to the marking line L of the positioning marking member 28. The pixel value is shown. In this high voltage image, the pixel value of the area corresponding to the marked line L of the positioning marking member 28 is B2, and the pixel value of the area other than the area corresponding to the marked line L of the positioning marking member 28 is A case where A2 is smaller than B2 is shown.

  In such a case, as in the case shown in FIG. 4, the pixel values in the region other than the region corresponding to the marked line L of the positioning marked line member 28 in the high voltage image are obtained from the pixel values in the high voltage image. When A2 is subtracted, the pixel value of the area corresponding to the marked line L of the positioning marked line member 28 in the image after the subtraction is a positive value. For this reason, by multiplying each pixel value in this image by (1) without reversing the positive / negative of the pixel value, the same process as the above-described process is performed, whereby the positioning marking member 28 is obtained. It is possible to emphasize and display the image of the marked line.

  In the above-described embodiment, the present invention is applied to an X-ray fluoroscopic apparatus that constitutes a radiotherapy apparatus together with the radiation irradiation apparatus 40. However, the present invention may be applied to other X-ray imaging apparatuses.

DESCRIPTION OF SYMBOLS 20 Patient 21 Horizontal irradiation port 22 Vertical irradiation port 23 1st flat panel detector 24 2nd flat panel detector 25 1st X-ray tube 26 2nd X-ray tube 27 Treatment table 28 Marking member for positioning 29 Marking member for positioning 30 Control part 31 Image processing unit 32 High voltage image storage unit 33 Low voltage image storage unit 35 Display unit 40 Radiation irradiation device L Mark line

Claims (5)

In an X-ray imaging apparatus comprising: an X-ray tube; and an X-ray detector that detects X-rays emitted from the X-ray tube and passed through the subject.
The X-ray detector is used to image a positioning mark for positioning the X-ray tube and the X-ray detector in a state in which the X-ray tube is irradiated with the first tube voltage applied to the X-ray tube. A first voltage image generation unit for generating a first voltage image;
A second voltage image is generated by photographing the positioning mark with the X-ray detector in a state where a second tube voltage lower than the first tube voltage is applied to the X-ray tube and the X-ray is irradiated. A second voltage image generator that
An image processing unit that displays an image of the positioning mark on an image display unit based on the first voltage image and the second voltage image;
An X-ray imaging apparatus comprising: The X-ray imaging apparatus according to claim 1,
The image processing unit includes a pixel value difference between a region corresponding to the positioning mark in the first voltage image and a region other than a region corresponding to the positioning mark, and the positioning mark in the second voltage image. An X-ray imaging apparatus that displays the positioning mark on the image display unit with a pixel value obtained by adding a pixel value difference between an area corresponding to 1 and an area other than the area corresponding to the positioning mark. The X-ray imaging apparatus according to claim 2,
The image processing unit is configured such that an area other than an area corresponding to the positioning mark in the first voltage image and an area other than an area corresponding to the positioning mark in the second voltage image have the same pixel value. An X-ray imaging apparatus that executes a weighting process for weighting and a subtraction process for performing a subtraction between the first voltage image and the second voltage image. An X-ray imaging apparatus comprising: an X-ray tube; and an X-ray detector that detects X-rays emitted from the X-ray tube and passed through the subject. The X-ray tube and the X-ray detector In a mark display method for displaying an image of a positioning mark for positioning on an image display unit,
A first voltage imaging step of obtaining a first voltage image by imaging the positioning mark with the X-ray detector in a state in which a first tube voltage is applied to the X-ray tube and irradiated with X-rays;
The positioning mark is imaged by the X-ray detector in a state in which a second tube voltage lower than the first tube voltage is applied to the X-ray tube and irradiated with X-rays, and a second voltage image is obtained. Obtaining a second voltage imaging step;
An image processing step of displaying an image of the positioning mark on the image display unit based on the first voltage image and the second voltage image;
The mark display method characterized by including. The mark display method according to claim 4,
The image processing step includes
A difference in pixel value between a region corresponding to the positioning mark in the first voltage image and a region other than a region corresponding to the positioning mark; a region corresponding to the positioning mark in the second voltage image; A calculation step of calculating a pixel value representing the positioning mark by adding a pixel value difference with an area other than the area corresponding to the positioning mark;
A display step of displaying the positioning mark on the image display unit using a pixel value representing the positioning mark calculated in the calculation step;
Mark display method including

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