JP2002209881A - X-ray diagnostic apparatus, control method thereof, and storage medium - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To detect with high accuracy whether or not a metal is contained in a subject. In an X-ray CT system, a scout image of a subject is obtained by stopping the rotation of a gantry apparatus, performing X-ray irradiation and detection, and transporting the subject (S).
1). Then, the low-frequency component or the background component is removed from the scout image (S2, S3), the data of the removed image is subtracted from the scout image (S4), and binarized using a predetermined threshold (S5). . After the region numbering (labeling) process (S6), feature parameters are extracted for continuous regions having a certain area equal to or larger than "1" after binarization (S6).
7) It is determined whether the corresponding area is a metal object based on the characteristic parameter (S10). Alternatively, in a line sensor X-ray system or the like in the industrial field, an X-ray fluoroscopic image is obtained (S1), and the above S2, S3, S4, S5,
After S6 and S7, it is determined whether the object is a metal object, foreign matter, or defect (S10), and the product, material, or food having the metal object, foreign matter, or defect is hit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an X-ray image diagnostic apparatus, a control method thereof, and a storage medium.

[0002]

2. Description of the Related Art When an X-ray image of a subject is obtained for diagnosis or examination, the presence of a substance such as a metal in the subject hinders the diagnosis. The presence of metal in the subject
There are several factors. In particular, when the subject is a human body, a typical example is a case where a device for implanting a bone is embedded, or a metal denture or food contains metal. In the field of industrial X-ray inspection, it is also used for detecting metal, foreign matter, or defects from formed materials, foods, products, materials flowing on conveyors, and foods.

[0003]

SUMMARY OF THE INVENTION X-ray CT (Computerize)
d Tomography) system includes a device called a gantry device in which an X-ray tube and an X-ray detector rotate around a subject. By this rotation, an X-ray transmitted through the subject at different X-ray irradiation angles is detected by the X-ray detector, so that an X-ray tomographic image is reconstructed.

In such a system, when a substance having an extremely high X-ray absorptivity such as a metal is present in a subject, it appears as a noise called an artifact on a reconstructed X-ray tomographic image and greatly hinders diagnosis. become.

[0005] Therefore, if it is possible to grasp in advance whether or not a metal exists in the subject, and if so, where it is, it will be useful not only for diagnosis but also for X-ray tomographic images. It is possible to perform optimal reconstruction processing by using the reconstruction processing, which is very useful. In the field of industrial X-ray inspection, it is useful for detecting metals, foreign substances, and defects in materials, foods, and products.

The present invention has been made in view of the above problems, and an X-ray diagnostic apparatus or X-ray foreign matter / defect detecting apparatus capable of detecting with high accuracy whether or not a subject contains a metal. And a control method thereof.

[0007]

In order to solve this problem, for example, an X-ray diagnostic apparatus of the present invention has the following arrangement. That is, an X-ray diagnostic apparatus that detects X-rays that have passed through a subject and diagnoses the presence or absence of a metal object in the subject. Input means for inputting, removing means for removing a low-frequency component or a background component of the input two-dimensional X-ray image by using a predetermined filter, and removing the two-dimensional X-ray image from the input means. Binarizing means for subtracting the two-dimensional X-ray image obtained by the means and comparing it with a predetermined threshold to binarize;
For each continuous region of significant bits of the binary image obtained by the binarizing unit, a parameter extracting unit that extracts a characteristic parameter of the region, and each region is extracted based on the characteristic parameter obtained by the parameter extracting unit. Determining means for determining whether the object is a metal object.

[0008]

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

In the embodiment, an X-ray diagnostic apparatus is an X-ray diagnostic apparatus.
An example applied to a line CT system will be described.

FIG. 1 is a block diagram of an X-ray CT system according to the embodiment. As shown, the system comprises:
A gantry device 100 for irradiating the subject with X-rays and detecting X-rays transmitted through the subject, various operation settings are performed on the gantry device 100, and based on data output from the gantry device 100. The operation console 200 is configured to reconstruct and display an X-ray tomographic image.

The gantry apparatus 100 has the following configuration, including the main controller 1 that controls the entire system.

Reference numeral 2 denotes an interface for communicating with the operation console 200. Reference numeral 3 denotes a gantry having a hollow portion for transporting a subject (a subject) lying on the table 12. X-ray tube 4 (X
A collimator 6 having a slit for defining an X-ray irradiation range is provided.

The gantry 3 has an X-ray detector having a plurality (approximately 1000) of detecting elements for detecting X-rays transmitted through the subject along the circumference of the cavity of the gantry as shown in the figure. And a data collection unit 9 for collecting data obtained from the detection unit 8. The X-ray tube 4 and the detection unit 8 are provided at positions facing each other with a hollow portion therebetween, and are held and rotated by the gantry 3 in a state where the relationship is maintained. This rotation is performed by a rotation motor 10 driven by a drive signal from a motor controller 11. The table 12 on which the subject is placed is transported in the body axis direction (Z-axis direction) of the subject, and is driven by a table motor 13. Note that the detection unit 8 may have either one row or multiple rows of detection elements. A system composed of one row of detection element groups is called a single-slice X-ray CT system, and a multi-row system is called a multi-slice X-ray CT system. In the embodiment, a single paper slice X-ray CT system will be described for simplicity.

The main controller 1 analyzes various commands received via the I / F 2, and based on the analyzed commands, the X-ray tube controller 5 and the motor controller 1
1. Various control signals are output to the table motor controller 14. Further, the main controller 1 transmits the data collected by the data collection unit 9 to the I / F 2
Also, processing for sending to the operation console 200 via the.

On the other hand, the operation console 200 is a so-called workstation, as shown in the figure, a CPU 51 for controlling the entire apparatus, a ROM 52 for storing a boot program and a BIOS, and an RA for functioning as a main storage.
Including M53, the following configuration is provided.

The HDD 54 is a hard disk drive, which provides an OS, various instructions to the gantry device 100, and a diagnostic program for reconstructing an X-ray tomographic image based on data received from the gantry device 100. A condition table, which will be described in detail later, is stored.

The VRAM 55 is a memory for expanding the image data to be displayed. The image data and the like can be expanded on this memory and displayed on the CRT 56. 57 and 58 are a keyboard and a mouse for performing various settings. An interface 59 communicates with the gantry device 100.

In the X-ray CT system having the above configuration, the subject is laid on the table 12 and a set schedule (how to reconstruct a range of tomographic images with respect to the transport direction of the subject). ), The rotation of the gantry 3, the X-ray tube 4
In general, before that, a process for obtaining an X-ray image for positioning, called a scout scan for determining the schedule, is performed.

A scout scan is a gantry device 10.
This is a scan in which the X-ray tube 4 is moved in the Z-axis direction while the X-ray tube 4 is positioned directly above the subject, for example, while the gantry 3 is fixed.
More specifically, while the table 12 is moving, the X-ray tube 4 is driven, the one-dimensional transmitted X-ray intensity is sequentially obtained from the detection unit 8, and the one-dimensional transmitted X-ray intensity is obtained continuously to obtain a two-dimensional X-ray transmitted image of the subject. Say get scan.

In this embodiment, the scout scan is used to detect a metal portion in the subject.

FIG. 2 is an example of an X-ray transmission image (called a scout image) of the subject obtained by the scout scan (stored on the RAM 53 of the operation console 200). In the drawing, the vertical axis is the Z axis (the direction in which the subject is transported)
The horizontal axis corresponds to the position of each detection element of the X-ray detection unit 8. However, since a signal is usually obtained for each channel when a signal is obtained from the detection element, it is indicated by a channel ch in the drawing. Also, since the signal obtained from the detection element is an analog signal, the signal is A / D converted to digital data, and the digital data of each channel is quantized to, for example, 8 bits. That is, each pixel of the illustrated two-dimensional X-ray transmission image has a value in the range of 0 to 255.

FIG. 3A shows data at a position Zi in the Z-axis direction in FIG. 2 (the vertical axis is the X-ray attenuation rate,
The horizontal axis is the above channel).

In the drawing, A and B indicate that the X-ray attenuation rate is higher than other portions. However, in the case of a living body, bone has a higher X-ray attenuation rate than other tissues,
If they happen to overlap, it will appear as a larger damping rate, so the part with the larger damping rate will be
The presence of metal objects cannot be determined.

In the present embodiment, several characteristic parameters are extracted based on a two-dimensional X-ray image obtained by a scout scan, and when each characteristic parameter matches a preset condition, the part is made of metal. Was certified as

In order to realize this processing, in the embodiment,
First, a process of generating a binary image for discriminating a portion having a large X-ray attenuation rate from a portion having a small X-ray attenuation rate is performed. Then, part 2
A process of extracting a feature parameter from the value image is performed. Finally, the obtained feature parameters are collated with preset conditions to determine the presence or absence of metal. The details will be described below step by step.

<Generation of Binary Image> X-ray attenuation rate (absorption rate)
In the embodiment, the following is performed in order to distinguish a portion (pixel) having a large size from a portion (pixel) that is not so.

First, the scout image created on the RAM 53 is subjected to a filtering process using a minimum value filter. The minimum value filter is, for example, a filter of a 5 × 5 pixel block size, and sets the minimum value among the 25 pixels as the output value of the target pixel (the center pixel of the 5 × 5 pixel block). In the filtering process, the filtering process is performed by shifting one pixel at a time in the raster scan order in the image.

This filtering process is performed on the entire scout image to obtain a first-order minimum value filtered image. Next, the primary minimum value filtered image is again subjected to the minimum value filtering process to obtain a secondary minimum value filtered image. Hereinafter, this minimum value filter processing is repeated a predetermined number of times (n times).

When this processing is performed, FIG.
Data of the nth-order minimum value filtered image as shown in (b) can be obtained, and a portion having a large X-ray attenuation rate can be removed.

Next, the maximum value filter processing is performed n times on the nth-order minimum value filter processing image. The maximum value filter uses the maximum value in a 5 × 5 pixel block as the output value of the pixel of interest (center pixel), and performs raster scanning within the image while shifting it one pixel at a time. . It can be easily understood that the data at the Z-axis position Zi of the n-th maximum value filtered image is in the state shown in FIG. That is, the change of the high frequency component of the X-ray attenuation rate of the scout image is removed.

In the present embodiment, the n-th order maximum value filter image generated as described above is subtracted from the scout image stored in the RAM 53. For example, FIG.
When the one-dimensional data of FIG. 3C is subtracted from the one-dimensional data at the Zi position of the scout image of FIG. 3A, data as shown in FIG. 4 is obtained, that is, a low-frequency component or a background image is removed. High-frequency components can be left.

In response to this result, a preset threshold Th
Is applied, the pixel exceeding the threshold value Th is set to “1”, and the pixel below the threshold value is set to “0”. By performing this for all scout images, it is possible to successfully extract only a portion having a large X-ray absorptance (its pixel value is significant, that is, “1”) as shown in FIG. That is, the generation of a binary image including a continuous region of pixels having a large X-ray absorption rate is completed.

<Extraction of Feature Parameters> An area numbering (labeling) process for extracting a continuous area from significant (pixel value is “1”) in the binary image obtained as described above is performed. FIG. 5 shows that four areas are generated. Labeling is performed in raster scan order.

Each labeling area (label "1")
To “4”), the area, feret diameter,
The area ratio, the sum of the pixel values, the circularity, the Feret diameter ratio, and the elliptical approximation of the major and minor parameters are extracted (calculated).
The meaning of each parameter will be described below with reference to FIG. In the following, the “continuous region” indicates a “labeled region”. Area: number of pixels S in the continuous area, Feret diameter: two adjacent sides (height and width) of the circumscribed rectangle of the continuous area, Lx, Ly Area ratio: S / (Lx · Ly) (area of the continuous area with respect to the area of the circumscribed rectangle) ), Sum of pixel values: sum of each pixel value in the scout image corresponding to the continuous area Circularity: 4πS / (perimeter ² ) (perimeter is histogram measurement after “contour detection” logical filter processing) Feret diameter ratio: Lx / Ly Elliptical approximation major axis / minor axis: major axis and minor axis at the time of elliptical approximation In the above, the method of calculating “circumferential length” in circularity corresponds to a binary image. This can be realized by performing a “contour extraction” logical filter process on the area and measuring the histogram. As the logical filter processing, for example, when the size is 3 × 3 pixels, “the central pixel is“ 1 ”, and at least one of the surrounding eight pixels is“ 0 ”.
Is satisfied, the value of the central pixel is set to "1" (if the condition is not satisfied, the value of the central pixel is set to "0"). By performing this logical filter processing,
As a result, only the pixels on the outer periphery of the area of the binary image that is "1" are "1", and both inside and outside the area are "0". Therefore, the perimeter can be obtained by counting the number of pixels that are “1”. As a method for calculating the perimeter, reference can be made to “Digital Image Processing”, 9.2, “Area and Perimeter” in Chapter 9 of Rosonfeld, Kak Modern Science Publishing Company.

A method for calculating the elliptical approximate major axis and minor axis will be described with reference to FIG.

First, the center of gravity G (G _x , G _y ) of the continuous area (tentatively named Rs) is obtained as follows.

G _x = Σx · Rs (x, y) / N (x
Product _{sum) G y = Σy · Rs (} x about, y) / N (product sum) where for y, Rs (x, y) is the pixel value in the region Rs after binarization (region Rs ( x, y) = “1”), and N is the number of pixels in the area.

Next, when this region Rs is approximated to an ellipse, the angle θ between the main axis (the direction of the major axis) and the horizontal axis due to the second moment is obtained. The method of obtaining the angle θ between the main axis and the horizontal axis of the ellipse is described in, for example, the document “Image Analysis Handbook”.
(Supervised by Takagi and Shimoda; University of Tokyo Press) may be used. Thus, centering on the center of gravity G obtained earlier,
The principal axis and the horizontal axis are made to coincide by reversely rotating the approximate ellipse by the obtained angle θ. After rotation of the coordinate system (* 1 expression shown), a pixel having a pixel value has become "1" Rs (x ', y') and is expressed, the major axis L _l and minor axis L _s is as follows Is required.

L _l = (Σx ′ ² · Rs (x ′, y ′) / N) ^1/2
L ₂ = (積 y ′ ² · Rs (x ′, y ′) / N) ^1/2 (sum of y ′) <Judgment of presence or absence of metal> After the extraction of the region having a high X-ray absorptivity from the scout image and the extraction (calculation) of the characteristic parameters for each of the continuous regions having a certain area or more, the respective regions are extracted according to the obtained characteristic parameters. The determination of the presence or absence of a metal object is performed.

However, it is necessary to appropriately adjust the criterion for determining whether or not a metal object is present in accordance with the type of the metal object to be detected.
For example, when the subject is a living body and an X-ray tomographic image of the head is to be obtained, a metal denture is a main target, and in the case of an abdomen, minute dentures contained in food or the like are used. A piece of metal is the subject.

Therefore, in this embodiment, the main scan (X
In the setting of a scan for obtaining a line tomographic image), conditions for determining the presence or absence of a metal object are switched according to which part of the subject is to be scanned.

FIG. 6 shows a condition table for this determination, which is stored as a file in the HDD 54. As shown in the figure, there are a plurality of types of condition tables, and a scout image is displayed and a technician (or a doctor)
When a user designates a region to be scanned (a scanning range on the Z axis), any one of the condition tables is selected.

When the main scan schedule is set and which part is to be determined, one of the condition tables is read from the HDD 54 in accordance with the determined part. For example, if the frontmost condition table is read in FIG. 6, as follows (shown T ₀ through T ₁₂ is preset to a site (or each target to be scanned).

First, it is determined whether the feature parameters (seven in this embodiment) of one labeled area satisfy all the conditions of the read condition table. For example, the area S obtained from a labeled region is T ₀ ≦ S
≦ T ₁ , and the Feret diameter Lx (and Ly) is T ₂ ≦ L
It is determined whether x (and Ly) ≦ T ₃ is satisfied,..., and all seven conditions are satisfied. Then, when all the conditions are satisfied, it is determined that the noted labeled area is a metal object. This process is performed for all labeled areas.

When a labeling area determined to be a metal object is included in a certain fixed scan range in the Z-axis direction performed in the setting of the main scan schedule,
X using the metal artifact removal algorithm
Reconstruction processing of a line tomographic image is performed.

It should be noted that the present invention has a feature in the detection processing of a metal object. That is, the metal artifact removal algorithm itself is not directly related to the present invention, and merely shows an application example of the present invention. However, as for the technology relating to the metal artifact removal algorithm, the one already proposed by the present applicant as Japanese Patent Application No. 2000-83946 is adopted.

<Overall Process Flow> As described above, the specific procedure of the above process is shown in the flowchart of FIG. The program according to the flowchart is stored in the HDD 54 in the operation console 200, and is loaded into the RAM 53 and executed.

First, in step S1, the X-ray tube 4 is positioned directly above the subject (the detection unit 8 is positioned immediately below) with respect to the gantry apparatus 100, and the table 1 is positioned at that position.
An instruction command for performing a scout scan is issued and started by carrying out the conveyance of the X-ray tube 2 and driving the X-ray tube 4. As a result, two-dimensional scout image data (8 bits per pixel) is sent from the gantry device 100, and is received and stored in a predetermined area of the RAM 53.

Then, the process proceeds to a step S2, wherein the RAM 53
Is subjected to the minimum value filter processing n times. Next, in step S3, the maximum value filter processing is performed n times. These minimum filtering,
The maximum value filter processing is as described above.

In step S4, the filtered image data obtained as described above is subtracted from the scout image, and in step S5, is binarized by comparing it with a threshold value.
In step S6, the binarized image data (2
Area numbering (labeling) processing is performed on the areas that are continuously present as “1” in the value image data), and step S
At step 7, feature parameters (seven in this embodiment) are extracted (or calculated) from each labeled area.

Next, the process proceeds to step S8, in which the main scan schedule is set (setting for obtaining an X-ray tomographic image by rotating the gantry 3). Steps S2 to S2
Until step S7 is an internal process of the operation console 200, the operator (technician or doctor)
When a scout scan start instruction is issued (step S1),
The resulting scout image is displayed in step S8, and it looks as if the user proceeds to the schedule setting screen. The operator designates a part to obtain an X-ray tomographic image by setting the schedule (for example, head, chest, abdomen, hands, feet, etc.).
Then, the range on the Z axis is specified.

When the setting of the schedule is completed and the start of the main scan is instructed, the process proceeds to step S9.
The corresponding table in the condition table group stored in the HDD 54 is read.

Then, the process proceeds to step S10, in which the presence / absence of metal for each labeled region is determined with reference to the read table, and the region determined to be a metal object is subjected to the main scan. Is determined to be included in the range.

If it is determined that a metal object is included in the range of the main scan, the process proceeds to step S11, and a setting is made to perform X-ray tomographic image reconstruction processing using a metal artifact removal algorithm. If it is determined that a metal object is not included in the range of the main scan, the process of step S11 is skipped to perform a normal reconstruction process.

In step S12, the gantry device 1
At step S13, an X-ray tomographic image reconstruction process is performed based on the data transferred from the gantry device 100 in order to perform scanning according to the set schedule. After step S11, this reconstruction processing is performed in accordance with the metal artifact removal algorithm.

As described above, according to the present embodiment,
It is possible to detect the presence or absence of a metal object under optimal conditions for each part of the subject. Therefore, the X-ray C for obtaining the X-ray tomographic image
If applied to the T system, the processing for removing metal artifacts can be applied to an appropriate site, and the reliability of a reconstructed X-ray tomographic image can be increased.

In the above embodiment, the number of repetitions of the minimum value filter processing and the maximum value filter processing is set to n. However, the number may be appropriately set by the operator. Also, the threshold value for binarization may be set freely by the operator.

In any case, the image after one scout scan can be corrected any number of times, and no burden is imposed on the subject. As an example, the scout image and the binary image may be displayed side by side, and the number of times and the threshold may be adjusted until the intended binary image is obtained.

The contents of the condition table can be freely edited.
Addition and deletion may be performed. For example, when detecting metal dentures, for example, the difference is large between adults and children, so it is desirable to be able to appropriately correct the criterion values (T1 to T14).

Further, in the above-described embodiment, an example in which the present invention is applied to an X-ray CT system as a device for detecting a metal object has been described. However, other systems (for example, an angio device) may be used without departing from the spirit of the present invention. But it doesn't matter. In particular, if a product, material, or food containing a metal object, a foreign substance, or a defect is inspected in a line sensor X-ray system for food inspection, material inspection, or product inspection in the industrial field, it is rejected (removed). It is also effective in systems.

Most of the processing in the embodiment is performed on the operation console 200 side, and most of the processing can be realized by software. Therefore, the present invention can be realized by incorporating software into the device.

Furthermore, in the embodiment, the size of the filter in the filter processing is described as 5 × 5 pixel size, but may be 3 × 3 or any other size.

[0063]

As described above, according to the present invention, it is possible to detect with high accuracy whether or not a subject contains a metal.

[Brief description of the drawings]

FIG. 1 is a block diagram of an X-ray CT system according to an embodiment.

FIG. 2 is a diagram illustrating an example of a scout image according to the embodiment.

FIG. 3 is a diagram illustrating the concept of filter processing in the embodiment.

FIG. 4 is a diagram illustrating an example in which data of one line of an image after filter processing has been subtracted from one line of scout image data.

FIG. 5 is a diagram illustrating an example of a binary image according to the embodiment.

FIG. 6 is a diagram illustrating a storage state of a condition table in the embodiment.

FIG. 7 is a flowchart illustrating an operation processing procedure in the embodiment.

FIG. 8 is a diagram showing an area of a feature parameter and a Feret diameter in the embodiment.

FIG. 9 is a diagram illustrating a method of calculating a major axis and a minor axis by elliptic approximation in the embodiment.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihiko Nishiide 4-7-1, Asahigaoka, Hino-shi, Tokyo 127 G-F Yokogawa Medical System Co., Ltd. F-term (reference) 4C093 AA22 BA03 CA13 EA02 EB17 FD01 FD08 FE18 FF15 FF18 FF23 FF28

Claims (7)

[Claims] 1. An X-ray diagnostic apparatus which detects X-rays transmitted through a subject and diagnoses the presence or absence of a metal object in the subject, wherein the two-dimensional X-ray of the subject indicates an X-ray absorption rate. An input unit for inputting a line image, and a low-frequency component or a background component of the input two-dimensional X-ray image.
A removing unit that removes by using a predetermined filter; and a two-dimensional X-ray image obtained by subtracting the two-dimensional X-ray image obtained by the removing unit from the two-dimensional X-ray image input by the input unit. Binarizing means for converting, for each continuous area of significant bits of the binary image obtained by the binarizing means, parameter extracting means for extracting feature parameters of the area, X-ray diagnostic apparatus comprising: a determination unit configured to determine whether each region is a metal object based on the obtained characteristic parameter. 2. The image processing apparatus according to claim 1, wherein the removing unit outputs a minimum value in an area of n × n pixels as a value of a central pixel, and a maximum value in an area of n × n pixels. 2. The method according to claim 1, further comprising: a maximum value filtering unit that outputs the value of the center pixel; and a control unit that repeatedly executes each of the minimum value filtering unit and the maximum value filtering unit a predetermined number of times. An X-ray diagnostic apparatus according to the item. 3. The characteristic parameter includes at least one of an area of each significant bit continuous area, a Feret diameter, an area ratio, a sum of pixel values, a circularity, a Feret diameter ratio, and an elliptical approximate major axis / minor axis. The X-ray diagnostic apparatus according to claim 1, wherein the X-ray diagnostic apparatus is included. 4. The X-ray diagnostic apparatus according to claim 1, wherein said determining means changes a criterion according to a diagnosis site of the subject. 5. The X-ray CT system, wherein the input unit inputs a two-dimensional X-ray image of the subject showing the X-ray absorptivity by transporting the subject in a state where the rotation of the gantry is stopped in the X-ray CT system. The X-ray diagnostic apparatus according to claim 1, wherein: 6. A control method of an X-ray diagnostic apparatus for detecting X-rays transmitted through a subject and diagnosing the presence or absence of a metal object in the subject, the control method comprising: An input step of inputting a two-dimensional X-ray image, and a low-frequency component or a background component of the input two-dimensional X-ray image
A removing step of removing by using a predetermined filter, and a two-dimensional X-ray image obtained by subtracting the two-dimensional X-ray image obtained in the removing step from the two-dimensional X-ray image input in the input step, and comparing with a predetermined threshold value A parameter extraction step of extracting, for each successive region of significant bits of the binary image obtained in the binarization process, a feature parameter of the region; A determination step of determining whether or not each area is a metal object based on the obtained characteristic parameter. 7. A storage medium for storing a program code for an X-ray diagnostic apparatus for detecting X-rays transmitted through a subject and diagnosing the presence or absence of a metal object in the subject, the program comprising: And a program code of an input step of inputting a two-dimensional X-ray image of the subject, and a program code of a removal step of removing low-frequency components of the input two-dimensional X-ray image by using a predetermined filter. A program code for a binarizing step of subtracting the two-dimensional X-ray image obtained in the removing step from the two-dimensional X-ray image input in the inputting step and comparing it with a predetermined threshold to binarize; For each continuous area of significant bits of the binary image obtained in the binarizing step, a program code of a parameter extracting step for extracting a characteristic parameter of the area, and a characteristic parameter obtained in the parameter extracting step, Storage medium characterized by storing a program code for a determining step of regions to determine whether a metal object.