JPH1127568A - X-ray image tube system and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray tube system in which the image distortion due to external magnetic field is prevented with a simple configuration, and to provide its control method. SOLUTION: This system is provided with an X-ray image tube 11 that receives X-ray through an input window 11a and a television camera 13 that converts an output of the X-ray image tube 11 into an electric signal. In this case, a turning angle of the television camera 13 from a reference position, that is a position of the television camera 13 in the case that a direction of an external magnetic field Y is orthogonal to an axis O of the X-ray image tube 11, corresponding to a cross angle between the direction of the external magnetic field Y and the axis O of the X-ray image tube 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an X-ray image tube apparatus for correcting an image distortion caused by a peripheral external magnetic field such as terrestrial magnetism, and a control method thereof.

[0002]

2. Description of the Related Art An X-ray image tube is an electron tube that converts X-rays into, for example, visible light, and is widely used in medical X-ray diagnostic apparatuses and the like. The X-ray image tube is entirely composed of a vacuum envelope, and an input unit is provided at one end in the vacuum envelope.
An output section is provided at the other end in the vacuum envelope. A focusing electrode and an anode are provided between the input unit and the output unit.

In the above configuration, X-rays that pass through a subject and are input to an X-ray image tube are converted into electrons at an input unit. Electrons output from the input unit are accelerated and focused by an electron lens formed of a focusing electrode and an anode, and input to the output unit, where they are converted into visible light and the like.

[0004]

The inside of a vacuum envelope constituting an X-ray image tube is maintained at a high vacuum state.
In this, the electrons output from the input unit are accelerated and focused by the electron lens, and reach the output unit. At this time, when an external magnetic field enters the inside of the vacuum envelope, Lorentz force due to the external magnetic field acts on the electrons, and the trajectories of the electrons are bent.

In the X-ray image tube, the Lorentz force acts more on electrons output from the periphery than on the center of the input section. For this reason, when an external magnetic field enters, the output image of the X-ray image tube rotates as shown in FIG. 6A shows the case where there is no influence of the external magnetic field, FIG. 6B shows the case where the influence of the external magnetic field is present, and FIG. 6C shows the case where the influence of the external magnetic field becomes stronger. .

As a method of preventing the influence of the above-mentioned external magnetic field, there is a method of installing a magnetic shield on the front surface of the vacuum envelope to shield the external magnetic field. The magnetic shield is made of a ferromagnetic material having a high magnetic permeability and a small coercive force, and is made as thin as about 50 μm to about 100 μm. However, since the magnetic shield is made of a substance having a large atomic number, the transmittance of X-rays is low. Therefore, when the magnetic shielding plate is provided, there is a problem that the amount of X-ray exposure given to the subject increases.

For this reason, there is a method in which a correction coil is used in place of a magnetic shielding plate to cancel an external magnetic field penetrating an X-ray image tube (see Japanese Patent Application Laid-Open No. 63-121239). However, the correction by the correction coil is only a small part of the image distortion due to the external magnetic field, and it is difficult to effectively correct the image distortion.

In view of this, a method has been considered in which a magnetic shield plate for shielding an external magnetic field and a correction coil are used together (Japanese Patent Laid-Open No. Hei 8-3).
No. 15575). This publication discloses that the correction coil has a large effect of correcting the rotation of the output image due to the external magnetic field. However, the amount of rotation of the output image due to the external magnetic field around the X-ray image tube is not uniform. Therefore, if the current flowing through the correction coil is fixed at a certain value,
In some cases, the rotation of the output image cannot be corrected.

In order to solve such a problem, a method of arranging a sensor for detecting an external magnetic field inside or around an X-ray image tube, and adjusting a current flowing through a correction coil according to the magnitude of the external magnetic field. (For example, see JP-A-7-99)
033, JP-A-2-210744).
In the case of this method, for example, a Hall element is used as a sensor. However, the Hall element has a property that the zero magnetic field is easily drifted. Therefore, it is difficult to accurately measure an external magnetic field as small as about 0.3 to 0.5 Gauss existing around the X-ray image tube. Further, an electric circuit for controlling the current flowing through the correction coil based on the external magnetic field detected by the Hall element is required, and there is a problem that the system configuration is complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray image tube apparatus capable of preventing image distortion due to an external magnetic field with a simple configuration and a control method therefor.

[0011]

SUMMARY OF THE INVENTION The present invention provides an X-ray image tube having an X-ray image tube for inputting X-rays through an input window, and a television camera for converting an output of the X-ray image tube into an electric signal. The apparatus is characterized in that a relative rotation position of the television camera with respect to the X-ray image tube is changed according to an angle between a direction of an external magnetic field and a tube axis of the X-ray image tube.

Further, the present invention provides an X-ray image tube apparatus provided with an X-ray image tube for inputting X-rays through an input window and a television camera for converting an output of the X-ray image tube into an electric signal. The case where the direction of the magnetic field is orthogonal to the tube axis of the X-ray image tube is defined as the reference position of the television camera. The smaller the angle between the direction of the external magnetic field and the tube axis of the X-ray image tube, the smaller the TV camera Is characterized in that the rotation angle from the reference position is increased.

According to the present invention, there is provided an X-ray image tube apparatus comprising an X-ray image tube for inputting X-rays through an input window and a television camera for converting an output of the X-ray image tube into an electric signal. The case where the direction of the magnetic field and the tube axis of the X-ray image tube are orthogonal to each other is set as the reference position of the TV camera, and corresponding to the change in the angle between the direction of the external magnetic field and the tube axis of the X-ray image tube, The rotation angle of the television camera from the reference position is changed.

Further, a thin ferromagnetic plate is arranged in front of the input window of the X-ray image tube.

Further, according to the control method of the X-ray image tube apparatus of the present invention, the direction of the image reproduced on the monitor at the first position where the direction of the external magnetic field and the tube axis of the X-ray image tube are orthogonal to each other. A change from the first position to the second position when the direction of the screen reproduced on the monitor is matched at the second position where the direction of the external magnetic field matches the tube axis of the X-ray image tube. Measuring the rotation angle of the television camera connected to the X-ray image tube; and, based on the rotation angle of the television camera measured in this step, the first position and the second position. Determining a predetermined function approximating a rotation angle of the television camera from the first position at a third position between the X-ray image tube and the third position; The rotation angle of the TV camera It consists a step of setting the approximated value function.

According to the above configuration, the relative rotation position of the television camera with respect to the X-ray image tube is changed according to the angle between the direction of the external magnetic field and the tube axis of the X-ray image tube. In this case, even if the angle at which the direction of the external magnetic field intersects with the tube axis of the X-ray image tube changes and image distortion occurs in the X-ray image tube, the image distortion is corrected by rotating the television camera. Therefore, an image without image distortion is reproduced on the monitor screen. According to this configuration, a complicated structure or an electric circuit for correcting image distortion is not required,
The configuration is simplified.

A case where the direction of the external magnetic field is orthogonal to the axis of the X-ray image tube is defined as a reference position of the television camera,
The smaller the angle between the direction of the external magnetic field and the axis of the X-ray image tube, the greater the angle of rotation of the television camera from the reference position. For example, when the direction of the external magnetic field is orthogonal to the tube axis of the X-ray image tube, when the tube axis of the X-ray image tube changes, the image distortion increases as the angle between them decreases, and the rotation of the output image increases. Become. Therefore, image distortion can be corrected by increasing the rotation angle of the television camera from the reference position as the angle between them decreases.

Further, a predetermined function for determining the rotation angle of the television camera is obtained, and the rotation angle of the television camera is set using the predetermined function. In this case, even if the direction of the X-ray image tube changes, the rotation angle of the television camera is controlled by a predetermined function set in advance, and image distortion is corrected.

[0019]

Embodiments of the present invention will be described with reference to FIG. Reference numeral 11 denotes an X-ray image tube incorporated in an X-ray diagnostic apparatus or the like. The position of the X-ray image tube 11 changes from A to C in accordance with the situation in which the subject T is imaged. It shows how it changes. Reference numeral O denotes a tube axis, for example, an X-ray image tube 1
1 passes through the centers of the input section and the output section. The X-ray image tube 11 is housed in a tube container 12, and the X-ray image tube 11
Is provided with an input window 11a for inputting X-rays. The tube container 12 is made of a magnetic material, and has a function of magnetically shielding the X-ray image tube 11. Reference numeral 13 denotes a television camera, the output of the X-ray image tube 11,
For example, a visible image is converted into an electric signal. The television camera 13 is configured to rotate about the axis with respect to the X-ray image tube 11. TV camera 13
Is connected to a monitor 14 for reproducing an electric signal into an image. The arrow Y indicates an external magnetic field around the X-ray image tube 11, and in this case, the external magnetic field is directed upward from the bottom of the figure.

In the case of the above configuration, the X-ray image tube 11
The relationship between the positions A to C and the rotation angle of the output image of the X-ray image tube 11 due to the external magnetic field Y is, for example, as shown in FIG. The horizontal axis in FIG. 2 indicates the positions A to C of the X-ray image tube 11, and the vertical axis indicates the rotation angle of the output image.

At the position A (FIG. 1), the axis of the X-ray image tube 11 is perpendicular to the direction of the external magnetic field Y. At this time, the external magnetic field Y is shielded by the tube container 12, and almost no image distortion occurs in the X-ray image tube 11. In FIG.
The rotation angle of the output image in this state is set to 0.

At the position C (FIG. 1), the direction of the external magnetic field Y and the axis of the X-ray image tube 11 coincide. At this time, X
Since there is no tube container 12 in front of the X-ray image tube 11, the external magnetic field Y enters the X-ray image tube 11. As a result, X
Image distortion occurs in the line image tube 11, and the rotation angle θ2 of the output image increases.

At the position B, the direction of the external magnetic field Y and the axis of the X-ray image tube 11 are shifted, and the axis of the X-ray image tube 11 is inclined with respect to the direction of the external magnetic field Y. In this case, the rotation angle θ1 of the output image is smaller than that at the position C.

As described above, the rotation angle of the output image changes according to the angle between the direction of the external magnetic field Y and the axis of the X-ray image tube 11. For example, as the angle decreases, the rotation angle of the output image increases. In the present invention,
Utilizing the above relationship, for example, the television camera 13 connected to the X-ray image tube 11 is rotated (for example, arrow R in FIG. 1) in accordance with the rotation angle of the output image of the X-ray image tube 11, and The distortion has been corrected.

Here, an example of the image distortion correcting method according to the present invention will be described with reference to FIG. The horizontal axis in FIG. 3 indicates the positions A to C of the X-ray image tube 11 (see FIG. 1),
The vertical axis indicates the rotation angle of the television camera 13.

For example, the X-ray image tube 11 is placed at a position A (FIG. 1). Then, in a state where image distortion due to the external magnetic field Y hardly occurs, the positions of the X-ray image tube 11 and the television camera 13 are adjusted so that the image is reproduced on the screen of the monitor 14 in a correct direction. The position of the television camera 13 at this time is set as a reference position, and the rotation angle of the television camera 13 is set to 0, and the point P is determined.

Next, the X-ray image tube 11 is placed at the position C (FIG. 1). In this case, the external magnetic field Y is applied to the X-ray image tube 1
Invade 1 Therefore, image distortion occurs in the X-ray image tube 11, and the output image rotates. At this time, the television camera 13 is rotated about its axis so that the image is reproduced on the screen of the monitor 14 in the same direction as the position A. At this time, the rotation angle θ1 of the television camera 13 is measured, and the point Q is determined based on the measurement.

Then, an approximate expression connecting the points P and Q is set. For example, the symbol a approximates the point P and the point Q with a straight line. The symbol b approximates the points P and Q by a cosine function. The symbol c is used to reproduce an image in the correct direction on the screen of the monitor 14 at positions c1, c2, c3,... Where the point P and the point Q are equally divided, for example.
The rotation angle of the television camera 13 at that time is measured, and the rotation angles of the positions c1, c2, c3,... Are approximated by a polynomial connecting straight lines. Also, a curve connecting the points P, c1, c2, c3,..., Point Q may be approximated by a quadratic or higher polynomial.

It should be noted that which of the above-described approximate expressions is used is appropriately selected according to the place where the X-ray diagnostic apparatus is installed. Then, the above-described approximate expression is incorporated as a control program for adjusting the rotation angle of the television camera, and the rotation of the X-ray diagnostic apparatus around the subject, and therefore, the rotation of the X-ray image tube, The rotation angle of the TV camera connected to the camera is adjusted.

According to the above configuration, when the position of the X-ray image tube 11 with respect to the direction of the external magnetic field changes and the output image is rotated, the television camera rotates in accordance with the rotation of the output image. Therefore, in the example of the lattice image,
As shown in FIGS. 4A to 4C, an image without rotation is reproduced on the monitor screen regardless of the positions A to C.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 5, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In this embodiment, a thin magnetic shielding plate 51 made of a ferromagnetic material is arranged in front of a human-powered window of the X-ray image tube, and shields an external magnetic field coming from the front of the X-ray image tube.
In this case, the influence of the external magnetic field is smaller than in the case of FIG. 1, and the rotation angle of the output image is smaller. Therefore, although the rotation angle of the television camera becomes small, the image distortion is corrected as in the previous embodiment.

[0032]

According to the present invention, it is possible to realize an X-ray image tube apparatus capable of preventing image distortion due to an external magnetic field with a simple configuration and a control method thereof.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for describing an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of the embodiment of the present invention.

FIG. 3 is a characteristic diagram for explaining the operation of the embodiment of the present invention.

FIG. 4 is a diagram showing a reproduced image for explaining the operation of the embodiment of the present invention.

FIG. 5 is a schematic configuration diagram for explaining another embodiment of the present invention.

FIG. 6 is a diagram showing a reproduced image for explaining a conventional example.

[Description of Signs] 11 ... X-ray image tube 11a ... Input window of X-ray image tube 12 ... Tube container 13 ... TV camera 14 ... Monitor P ... Subject O ... Tube axis of X-ray image tube

Claims (5)

[Claims] 1. An X-ray image tube apparatus comprising: an X-ray image tube into which X-rays enter through an input window; and a television camera for converting an output of the X-ray image tube into an electric signal. An X-ray image tube apparatus, wherein a relative rotation position of the television camera with respect to the X-ray image tube is changed according to an angle of the X-ray image tube with a tube axis. 2. An X-ray image tube apparatus comprising: an X-ray image tube for inputting X-rays through an input window; and a television camera for converting an output of the X-ray image tube into an electric signal. The case where the tube axis of the X-ray image tube is perpendicular to the reference position of the television camera, the smaller the angle between the direction of the external magnetic field and the tube axis of the X-ray image tube, the smaller the reference position of the television camera. An X-ray image tube device characterized by increasing the rotation angle from the camera. 3. An X-ray image tube apparatus comprising: an X-ray image tube into which X-rays are input through an input window; and a television camera for converting an output of the X-ray image tube into an electric signal. The case where the tube axis of the X-ray image tube is orthogonal to the reference position of the TV camera, and corresponding to the change in the angle between the direction of the external magnetic field and the tube axis of the X-ray image tube, An X-ray image tube apparatus, wherein a rotation angle from the reference position is changed. 4. The X-ray image tube apparatus according to claim 1, wherein a thin ferromagnetic plate is arranged in front of the input window of the X-ray image tube. 5. A direction of an image reproduced on a monitor at a first position where a direction of an external magnetic field and a tube axis of the X-ray image tube are orthogonal to each other, the direction of the external magnetic field and the tube axis of the X-ray image tube. When the orientation of the image reproduced on the monitor at the second position where
Measuring the rotation angle at which the television camera connected to the X-ray image tube is rotated at the change to the position of the X-ray image tube. Based on the rotation angle of the television camera measured at this step, the first Determining a predetermined function that approximates a rotation angle of the television camera from the first position at a third position between the position and the second position;
Setting the rotation angle of the television camera to a value approximated by the predetermined function when the X-ray tube moves to the third position.