JP2002238885A - Method and program for controlling position of x-ray focal point, and x-ray ct apparatus and x-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always obtain an optimum X-ray fan beam in a radiography system with a simple structure without regard to the displacement of an element (especially a rotary anode of an X-ray tube) constituting the radiography system. SOLUTION: The radiography system comprises an X-ray tube 40 capable of deflecting an electronic beam for generating X-rays, a collimator for restricting the width (w) of the generated X-rays in the direction of the body axis of a subject 100, and an X-ray detector 70 having at least two detector rows A and B in the direction of the body axis for detecting the dose of the X-ray fan beam XLFB passing the collimator. In the method of controlling the position of the focal point of the X-rays in the radiography system, the electronic beam is controlled to be deflected, based on prescribed detection signals (a) and (b) of at least two detector rows of the X-ray detector 70, in the direction where the amplitudes of the prescribed detection signals (a) and (b) are the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a program for controlling an X-ray focal position, an X-ray CT apparatus and an X-ray tube, and more particularly, to a structure capable of deflecting an electron beam for generating X-rays. An X-ray tube, a collimator for limiting a line width of a subject in a body axis direction for generated X-rays, and an X-ray detector capable of detecting a dose of an X-ray fan beam passing through the collimator, comprising: The present invention relates to an X-ray focus position control method for an X-ray imaging system having at least two detector rows in directions, a program thereof, an X-ray CT apparatus, and an X-ray tube.

[0002]

2. Description of the Related Art FIG. 7 is a view for explaining the prior art, and shows a side view of a main part of a scanning gantry (X-ray imaging system) in a conventional X-ray CT apparatus. In the figure, reference numeral 40 'denotes a rotating anode type X-ray tube, and an electron gun 42 for generating an electron beam.
A convex rotating anode 41 made of tungsten or the like which generates X-rays by irradiation with an electron beam, a motor rotor 47 integrally supporting the rotating anode 41, a motor rotor 47.
And an anode shaft 48 rotatably supported by bearings. A rotating magnetic field is applied to the motor rotor 47 from an external motor stator (not shown), so that the motor rotor 47 (rotating anode 41) is provided. At high speed.

Further, reference numeral 50 denotes an X-ray irradiation range (mainly the body axis C).
Lb) collimator, 100 is the object, 2
Reference numeral 0 denotes an imaging table on which the subject 100 is placed and moved in the body axis direction. Reference numeral 70 denotes a large number (n = 1000) arranged in the channel direction.
X-ray detectors (twin detectors) in which the X-ray detection elements are arranged in, for example, two rows A and B in an arc shape, and 80 is projection data g of the subject 100 based on a detection signal of the X-ray detector 70. A data collection unit (D which generates and collects (X, θ)
AS). Here, X represents a detection channel of the X-ray detector 70, and θ represents a view angle.

In an X-ray CT apparatus provided with a twin detector 70, an X-ray fan beam X passing through a collimator 50 is used.
By uniformly (equally) irradiating the detector rows A and B with the LFB, two rows of projection data g _A (X, θ) and g _B (X, θ) are obtained per rotation of the scanning gantry. Since they are obtained at the same time, the scanning efficiency is good.

However, during scanning, the X-ray tube 40 '
Is generally the operating temperature of the X-ray tube 40 '(i.e., thermal expansion / contraction of the mechanism), other scanning conditions {tilt angle of the scanning gantry, rotation speed of the scanning gantry, large / small focal size, etc. It is known that the X-ray fan beam XLFB is displaced in the z-axis (body axis) direction by｝.
Is not evenly (equally) irradiated, so that the resulting C
Artifacts and a reduction in the S / N ratio occur in the T tomographic image.

In this regard, conventionally, the movement of the focal point F has been covered by sliding the collimator 50 in the z-axis direction according to the movement of the X-ray focal point F by a mechanical linear motion mechanism. That is, the collimator 50 includes two parallel plates 50 a and 50 b arranged in the z-axis direction, and is screwed through a common support member 54 that supports them and a nut member 53 fixed to the support member 54. Rotating shaft 52 having a groove
It is connected to.

On the other hand, the collimator control unit 50A outputs projection data g _A (Xn, θ) of each predetermined (reference channel n) of the detector rows A and B extracted from the data collection unit 80.
g _B (Xn, θ) are compared to detect these difference signals (error signals), and generate a slide control signal of the collimator 50 such that the difference signal is set to 0. Add to The motor drive unit 50B amplifies the input control signal and adds it to the pulse motor PM. The pulse motor 51 which receives the signal amplifies the rotation shaft 52 according to the control signal, thereby moving the collimator 50 in the moving direction of the focal point F. Is displaced.

That is, assuming that the rotating anode 41 (X-ray focal point F) has moved from its reference position z0 to the side of -z1 (dotted line), the collimator 50 is accordingly moved to its reference position Z.
The X-ray fan beam XLFB is evenly applied to the detector rows A and B by moving from 0 to −Z1. Further, if the rotating anode 41 moves from the reference position z0 to the side of + z2 (broken line), the collimator 50 is moved from the reference position Z0 to the side of + Z2 in response to this.
The detector rows A and B are evenly irradiated with the X-ray fan beam XLFB.

A method of uniformly irradiating the X-ray fan beam XLFB to the detector rows A and B by moving the X-ray detector 70 in the z-axis direction instead of moving the collimator 50 is also available. Are known.

[0010]

However, according to the above-mentioned method using a mechanical linear motion mechanism, the sliding operation of the collimator 50 is caused by play (play) in a screwing portion between the rotary shaft 52 and the nut member 53 or the like. And its positioning operation becomes unstable. In addition, an electric circuit unit and a motor mechanism unit for controlling the movement of the collimator 50 are required,
These configurations are large and expensive.
In addition, the linear motion mechanism complicates the configuration of the scanning gantry section, increases the weight by that amount, and places a burden on the rotating operation of the scanning gantry section. This problem is caused by the X-ray detector 7.
The same applies when moving 0.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art.
X-ray focal position control method, program, and X-ray CT apparatus capable of always obtaining an optimal X-ray fan beam for the imaging system regardless of displacement of elements constituting the X-ray imaging system (particularly, the rotating anode of the X-ray tube) And an X-ray tube.

[0012]

The above-mentioned problem is solved, for example, by referring to FIG.
Is solved. That is, the X-ray focal position control method of the present invention (1) includes an X-ray tube 40 configured to deflect an electron beam for generating X-rays, and a body axis of the subject 100 for the generated X-rays. Collimator for limiting line width w in the direction, and X-ray fan beam XLF passing through the collimator
An X-ray detector 70 capable of detecting the dose of B, having at least two detector rows A and B in the body axis direction, comprising:
Based on at least two predetermined detection signals a and b in at least two rows of the X-ray detector 70, deflection control of the electron beam is performed in a direction in which both signal amplitudes are the same.

According to the present invention (1), based on at least two rows of the predetermined detection signals a and b of the X-ray detector 70, the deflection of the electron beam is controlled in a direction in which both signal amplitudes become the same. In a simple method of controlling the deflection of the electron beam, the system can detect a component of the X-ray imaging system (particularly, the rotating anode 41 of the X-ray tube 40) regardless of displacement in the body axis (z-axis) direction. An always optimal X-ray fan beam is obtained such that the rows A and B are evenly irradiated (distributed).

The program of the present invention (2) is a program for causing a computer to execute the X-ray focal position control method described in the present invention (1). That is, a control signal for deflecting the electron beam in a direction in which both signal amplitudes are the same is generated by using the predetermined detection signals a and b in at least two columns of the X-ray detector 70 as inputs. Such a program is provided on a recording medium such as a CD-ROM or online through a wired / wireless communication line.

In the X-ray CT apparatus according to the present invention (3), the X-ray tube 40 and the X-ray detector 70 face each other with the subject 100 interposed therebetween. 100
An X-ray CT apparatus for reconstructing a CT tomographic image of: an electron gun 42 and a rotating anode 41 that generates X-rays by irradiating an electron beam from the electron gun and has a slope in the direction of the rotation axis thereof; An X-ray tube 40 including an electron beam deflecting unit 43 interposed therebetween and configured to deflect an electron beam from the electron gun 42 toward the rotating anode 41.
A collimator 50 for limiting a line width w of the subject 100 in the body axis direction with respect to the generated X-rays, and at least two rows in a body axis direction capable of detecting a dose of the X-ray fan beam XLFB passing through the collimator 50. An X-ray detector 70 having detector rows A and B, and an electron beam deflecting unit 43 based on at least two predetermined detection signals a and b of the X-ray detector 70 in a direction in which both signal amplitudes are the same. And a deflection control unit 60A for controlling the deflection of the light.

According to the present invention (3), a rotating anode having a slope in the body axis direction, and a simple and highly reliable configuration for changing and controlling the electron beam applied to the slope in the direction of the slope,
Since the influence of the displacement of the elements constituting the X-ray imaging system (particularly, the rotating anode 41 of the X-ray tube 40) can be effectively corrected (avoided), an optimal X-ray fan beam can always be obtained for the X-ray imaging system.

The X-ray tube 40 of the present invention (4) is an electron gun 42 and a rotating anode 41 for generating X-rays by irradiating an electron beam from the electron gun, and has a slope in the direction of the rotation axis. An electron beam deflecting unit 43 interposed between the electron gun 42 and the rotary anode 41 and configured to deflect an electron beam from the electron gun 42 toward the rotary anode 41. Things.

[0018]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the same reference numerals indicate the same or corresponding parts throughout the drawings.

FIG. 2 is a structural view of a main part of the X-ray CT apparatus according to the embodiment. In the drawing, reference numeral 30 denotes an X-ray fan beam XL.
A scanning gantry unit for performing axial / helical scanning / reading of the subject 100 by FB, and 20 is a subject 100
A shooting table on which is mounted and moved in the direction of the body axis CLb,
Reference numeral 10 denotes a remote operation console unit for an engineer or the like to operate.

In the scanning gantry section 30, reference numeral 40 denotes a rotating anode type X-ray tube, and 40A denotes a dose (tube voltage k) of the X-ray tube 40.
V, tube current mA, etc.), 41 is a rotating anode of the X-ray tube 40, 42 is an electron gun for irradiating the rotating anode 41 with an electron beam, and 43 is a connection between the electron gun 42 and the rotating anode 41. An electron beam deflecting unit 60A interposed therebetween to deflect the electron beam is a deflection control unit 60A.

Further, reference numeral 50 denotes an X-ray irradiation range (mainly the body axis C).
Lb direction) collimator, 70 is channel C
An X-ray detector (twin detector) in which a large number (about n = 1000) of X-ray detection elements arranged in the H direction are arranged in, for example, two rows A and B in the body axis CLb direction.
Projection data g of the subject 100 based on the 0 detection signal
_A data collection unit (DAS) for generating and collecting _A (X, θ) and g _B (X, θ), and 30A is a rotation control unit for rotating the scanning gantry (X-ray imaging system) around the body axis CLb. .

In the operation console unit 10, X is X
A central processing unit for performing main control and processing (scan control, CT tomographic image reconstruction processing, etc.) of the X-ray CT apparatus;
PU, 11b are RAM, ROM used by CPU 11a
A memory (MM) 12 for inputting commands and data including a keyboard, a mouse, and the like; 13, a display device (CRT) for displaying scan plan information and CT tomographic images reconstructed; Reference numeral 14 denotes a control interface for exchanging various control signals CS, monitor signals MS, and the like between the CPU 11a and the scanning gantry unit 30 and the imaging table 20, and reference numeral 15 denotes data collection for temporarily storing projection data from the data collection unit 80. A buffer 16 is a hard disk that finally stores and stores projection data from the data collection buffer 15 and stores various application programs necessary for operation of the X-ray CT apparatus, various calculation / correction data files, and the like. Device (HDD).

In this collimator 50, only the opening slit width w in the direction of the body axis CLb is variable if necessary, and the collimator 50 is assumed to be fixed in its entire sliding operation.

With this configuration, the X-ray fan beam XLFB that has passed through the collimator 50 from the X-ray tube 40 is
00 and simultaneously enter the detector rows A and B of the X-ray detector 70. The data collection unit 80 projects data g _A (X, θ) and g _B (X, θ) corresponding to each detection output of the X-ray detector 70.
θ) are generated and stored in the data collection buffer 15. Further, X-ray imaging similar to the above is performed at each view angle θ at which the scanning gantry is slightly rotated, and thus projection data for one rotation of the scanning gantry is collected and accumulated.

At the same time, the imaging table 20 is intermittently / continuously moved in the direction of the body axis CLb in accordance with the axial / helical scan method. Thus, all projection data on a required imaging area of the subject 100 is collected and accumulated. These are finally stored in the hard disk drive 16. The CPU 11a reconstructs a CT tomographic image of the subject 100 based on the obtained projection data after the end of all the scans or following (in parallel with) the execution of the scan, and displays this on the display device 13. . Hereinafter, the X-ray focal position control according to the present invention will be described in detail.

FIG. 3 is a view for explaining an X-ray focal position control method according to the first embodiment. The electrostatic electron gun 42E controlled by the X-ray control unit 40A and the deflection control unit 60A control the electron gun 42E. And an electrostatic type electron beam deflecting unit 43E. In the following description, the symbol <
> Represents a vector. Vectors in the figure are represented by bold characters. Further, projection data g _A (X) of each predetermined (reference channel n) of the detector rows A and B in the X-ray detector 70
n, θ) and g _B (Xn, θ) are referred to as reference signals a and b.

The electron gun 42E includes a heater H driven by a tube current mA, a cylindrical cathode (cathode) C, a grid (grid) G, and a first anode A1, and a tube voltage k.
Rotating anode 41 (second anode A
Together with 2), an electron beam is formed so as to be focused on the surface of the rotating anode 41.

That is, the electron flux heated by the heater H and emitted from the cathode C is accelerated by the first lens system including the surface of the cathode C, the limiting holes of the lattice G, and the first anode A1. • Focused and concentrated on a small axial point (first crossover point) on the cathode surface. Further, the electron flux passing through the crossover point (which can be regarded as an electron source) is accelerated by the second lens system formed by the voltage ratio of the first and second anodes A1 and A2 (the action of the equipotential surface). The light is focused and finally focused (imaged) on the surface (second crossover point) of the rotating anode 41.

The electron beam deflecting unit 43E is connected to the axis (z
An upper and lower plate electrodes 43a and 43b provided so as to sandwich an electron beam traveling in the (axial) direction, and by applying a voltage ± V to these, a uniform electric field is applied to the space between the plate electrodes 43a and 43b. ± <E> is formed. Then, electrons (beams) traveling in this space in the z-axis direction generate an electric field <
<F>, <f> = q <E>
q: As a result of receiving the electron charge, the second crossover point (X-ray focal point F) is displaced in the y-axis direction.

On the other hand, the deflection control unit 60A includes a detector array A,
A calculation unit 61 for comparing the reference signals a and b of B to detect a difference signal (error signal) ve between them;
cumulative addition section (ADD) 62 that cumulatively adds (integrates) e to generate a control signal vc for controlling the deflection of the electron beam.
And a differential amplifier (DVA) 63 that generates a control voltage V corresponding to the control signal vc.

The calculation unit 61 obtains an error signal ve based on, for example, ve = k ・ (ab) / (a + b) based on the reference signals a and b of each view. Here, k is a coefficient that determines the detection sensitivity of the error signal ve.

FIG. 3A shows the detection characteristics of the error signal ve. The error signal ve depends on the slit width w of the collimator 50 (that is, the total line energy received by the detector rows A and B) due to the effect of the normalization term {× 1 / (a + b)} included in the above equation. Instead, it changes linearly in the range of -k ≦ ve ≦ k.

Further, the accumulative adder 62 accumulatively adds (integrates) the error signals ve generated in time series (for each view) from the calculator 61 to generate the control signal vc at each time point.
Then, the differential amplifier 63 amplifies the input control signal vc to generate a control voltage V, which is used to deflect the electron beam deflector 43E.
To the flat plate electrodes 43a and 43b.

By forming a feedback loop for controlling the X-ray focal position by using such a configuration, the rotating anode 4
X regardless of the movement in the z-axis direction due to thermal expansion / contraction
The line focus F can always be positioned directly above the boundary line CLd between the detector rows A and B. Hereinafter, this will be described in detail.

Now, the rotating anode 41 is at its reference position (solid line).
If it is at z0, the focal point F0 at this time is located directly above the boundary line CLd between the X-ray detector rows A and B, so that the X-ray fan beam XLFB that has passed through the collimator 50 passes through each of the detector rows A and B. The reference signals a and b in this case have a relationship of a = b. Therefore, in this state, the control signal vc = 0 and the control voltage V = 0 due to the error signal ve = 0 generated each time, and the electron beam in this case goes straight on the axis of the system without being deflected. Then, an image is continuously formed on the focal point F0.

Next, assuming that the rotating anode 41 is slightly displaced to the -z1 side, since the collimator 50 is fixed, the reference signals a and b have a relationship of a <b. As a result, the error signal ve <0, the control signal vc <0, and the control voltage V <0. In this case, the electron beam is slightly deflected in the direction opposite to the y-axis and travels straight, and slightly moves at the focal point F0. An image is formed on the lower side. Since the rotating anode 41 at this time is slightly displaced to the side of -z1, the X-ray focal point F generated at this time is located immediately above the boundary line CLd. XLF
B is also equally (equally) distributed over the detector rows A and B.

Next, when the rotating anode 41 further slightly displaces to the -z1 side, the error signal ve <0 generated at this time is cumulatively added to the immediately preceding (up to) control signal vc <0. The control voltage V becomes further negative, and in this case, the electron beam receives a stronger deflection in the direction opposite to the y-axis, travels straight, and forms an image further below the focal point F0. Since the rotating anode 41 at this time is further slightly displaced to the side of -z1, the X-ray focal point F generated at this time is also located immediately above the boundary line CLd. Beam XL
FB is also equally distributed on each of the detector rows A and B.

Thereafter, the process proceeds in the same manner, and eventually the rotating anode 4
When 1 is shifted to the position of -z1 (dotted line), the error signal ve <0 generated at this time is cumulatively added to the immediately preceding (up to) control signal vc <0, so that the control voltage V is further negative. In this case, the electron beam receives a stronger deflection in the direction opposite to the y-axis, travels straight, and forms an image just at the position F1. And the rotating anode 41 at this time is exactly -z1.
(Dotted line), the X-ray focal point F1 generated at this time is also located directly above the boundary line CLd.
Therefore, the X-ray fan beam XLFB in this case is also equally distributed on the detector rows A and B. When the rotating anode 41 is displaced to the side of + z2 (broken line), the above operation is reversed.

Strictly speaking, the electron beam forms an image on an arc R having a radius r from the substantial center of deflection in the electron beam deflecting unit 43E. At each position reaching F1 or F2, the image may be blurred. However, this blur is the reference position F
Although not shown, since it can be handled as a function of the beam deflection amount (control signal vc) from 0, for example, the convergence control of the first and / or second lens system is corrected based on the control signal vc at each time. This makes it possible to effectively avoid (correct) image blurring. Preferably, the correction value used at that time is obtained in advance by an experiment or a simulation and stored in a ROM or the like.

Thus, according to the first embodiment,
Regardless of the movement of the rotating anode 41 in the z-axis direction, the X-ray focal point F can always be positioned directly above the boundary line CLd between the detector rows A and B.

FIGS. 4 and 5 are views (1) and (2) for explaining an X-ray focal position control method according to the second embodiment, in which an electromagnetic electron gun 42M controlled by an X-ray controller 40A.
And an electromagnetic type electron beam deflecting unit 43M controlled by the deflection control unit 60A.

FIG. 4 shows the configuration of the X-ray focal position control system. The inclination angle θ of the inclined surface of the rotating anode 41 in the X-ray tube 40 is the same as the inclination angle θ of the rotating anode 41 shown in FIG.
Is bigger than. Therefore, the amount of displacement of the X-ray focal point F in the y-axis direction can be reduced.
Can be made closer to a more constant one.

The electron gun 42M includes a heater H driven by a tube current mA and a cylindrical cathode (cathode).
C and a focusing coil FOC (or a permanent magnet) that generates a uniform magnetic field <B> (= μ ₀ <H>) in the cylinder, which is parallel to the axis (z-axis) of the system. Including tube voltage k
Together with the rotating anode 41 biased by V, it forms an electron beam that is focused on the surface of the rotating anode 41.

That is, of the electron beam heated by the heater H and emitted from the cathode C, the component traveling parallel to the axis (z-axis) of the system is only the tube voltage kV without being affected by the magnetic field <B>. Therefore, it is accelerated and travels straight to reach the rotating anode 41. on the other hand,
Paraxial electrons that travel at an angle with the axis of the system {magnetic field <B>} receive a force in a direction perpendicular to the axis due to the interaction with the magnetic field <B>, resulting in a helical motion along the axis. And the magnetic field <B> is adjusted so that the magnetic field <B> reaches the rotating anode 41 when returning to just on the axis. In this way, an electron beam that is finally focused on the surface of the rotating anode 41 is formed.

The electron beam deflecting unit 43M includes two right and left deflecting coils DFCa and DFCb provided so as to sandwich an electron beam traveling in the axial direction of the system. Coil DFCa,
A uniform magnetic field <B> (= μ ₀ <H>) is formed between the DFCs. Then, electrons (beams) traveling in this space in the z-axis direction have forces <f>, <f> = q <v> × <B> acting in the y-axis direction due to the magnetic field <B>, where q: As a result of receiving the electric charge <v>: the velocity of the electron x: the vector product <B>: the magnetic flux density, the focal point (X-ray focal point F) of the electron beam in this case is displaced in the y-axis direction. FIG. 5 shows the image (perspective view).

Returning to FIG. 4, the deflection control unit 60A
Is a calculation unit 61 that compares the reference signals a and b of the detector rows A and B to detect a difference signal (error signal) ve therebetween, and accumulates (integrates) the error signal ve to obtain an electron beam. And a current amplifier (FET) Q that generates a control current vc for generating a control current vc corresponding to the control signal vc.

The operation unit 61 may be the same as that described with reference to FIG. Further, a constant β for applying a constant bias to the control current I is added to the cumulative addition unit 62. The current amplifier Q is composed of a constant current source circuit using, for example, an FET, and controls the control voltage vc (= Σve + β) of the gate terminal G.
Flows between the source S and the drain D.

The output characteristics of the control current I are shown in FIG. A constant bias current _Iβ is added to the control current I. Now, when the control current is assumed to be deflected to the position of the focal point F0 when I _beta, rotating anode 41 is the reference position z0
When displacement in the range of + z2 or -z1 from the control current I varies from up / down I _beta.

By forming a feedback loop for controlling the X-ray focal position using the above configuration, the rotating anode 4
The X-ray focal point F can always be positioned directly above the boundary line CLd between the detector rows A and B, regardless of the movement of 1. Hereinafter, this will be described in detail.

Now, the rotating anode 41 is at its reference position (solid line).
If it is at z0, the focal point F0 at this time is located directly above the boundary line CLd between the X-ray detector rows A and B, so that the X-ray fan beam XLFB that has passed through the collimator 50 passes through each of the detector rows A and B. The light is incident evenly (equally) on the upper side, and therefore, the reference signals a and b have a relationship of a = b. Accordingly, in this state, the error signal ve = 0 which occurs every time the control signal vc = beta, becomes the control current I = I _beta, electron beam in this case is subsequently imaged on the focus F0.

Next, assuming that the rotating anode 41 is slightly displaced to the -z1 side, since the collimator 50 is fixed, the reference signals a and b have a relationship of a <b. As a result, due to the error signal ve <0 at this time, the control signal vc = β−ve and the control current I <I
_β , and the electron beam in this case forms an image slightly below the focal point F0. The rotating anode 41 at this time is −z1
Is slightly displaced to the side of
The line focus F is located immediately above the boundary line CLd separating the detector rows A and B, and thus the X-ray fan beam X in this case is
The LFB is also equally (equally) distributed on each of the detector rows A and B.

Thereafter, the process proceeds in the same manner, and eventually the rotating anode 4
When 1 is displaced to the position of -z1 (dotted line), the error signal ve <0 generated at this time is cumulatively added to the immediately preceding (up to) control signal vc, so that the control current I further decreases. In this case, the electron beam forms an image just at the position of F1. And the rotating anode 41 at this time is exactly -z
1 (dotted line), the X-ray focal point F1 generated at this time is also located immediately above the boundary line CLd. Therefore, in this case, the X-ray fan beam XLFB also has the detector rows A and B. Evenly distributed on top. In addition, the rotating anode 41 has +
When it is displaced to the side of z2 (broken line), the above operation is reversed.

Thus, according to the second embodiment,
Regardless of the movement of the rotating anode 41 in the z-axis direction, the X-ray focal point F can always be positioned directly above the boundary line CLd between the detector rows A and B.

Strictly speaking, the electron beam forms an image on an arc R having a radius r from the substantial center of deflection in the electron beam deflecting unit 43M. Therefore, the position of the focal point F0 in FIG. At each position reaching F1 or F2, the image may be blurred. However, this blur is the reference position F
Since it can be handled as a function of the beam deflection amount (control signal vc) from 0, although not shown, for example, the control signal vc at each time point
By correcting the current applied to the focusing coil FOC based on the above, blurring of the image can be effectively avoided (corrected). Preferably, for the correction value used at that time,
This is obtained in advance by experiments or simulations and stored in a ROM or the like.

FIG. 6 is a diagram for explaining an X-ray focus control system according to another embodiment, and shows an example of application to an X-ray detector (multi-detector) 70 having three or more detector rows. In the figure, the X-ray detector 70 includes, for example, four detector rows A1, A2, B1, and B2 arranged in the body axis direction.
A boundary line CL separating the central detector rows A2 and B1
The X-ray focal point F can be controlled at a position directly above d.

That is, the data collection unit 80 generates the projection data g of the subject 100 based on the detection signal of the X-ray detector 70.
_A1 (X, θ), g _A2 (X, θ), g _B1 (X, θ), g _B2
Assuming that (X, θ) are generated all at once and the reference signals of the respective columns are a1, a2, b1, and b2, the arithmetic unit 61 calculates the reference signal a of each view.
1, a2, b1, b2, based on each error signal ve,
For example, ve = k ｛{(a1 + a2)-(b1 + b2)} / (a
1 + a2 + b1 + b2). Here, k is a coefficient that determines the detection sensitivity of the error signal ve. In this case, the X-ray focal point F is fixedly controlled to a position where the reference signals (a1 + a2) = (b1 + b2) on both sides.

Alternatively, although not shown, the operation unit 61
Based on the reference signals a1 and b2 at both end rows, an error signal ve for each time is obtained by, for example, ve = k ・ (a1−b2) / (a1 + b2). In this case, the X-ray focal point F is controlled to be at least at a position where the reference signals a1 = b2 at both end rows.

In each of the above embodiments, the case where the deflection control of the electron beam covers the displacement of the rotary anode 41 has been mainly described, but the present invention is not limited to this. For example, in the configuration shown in FIG. 3, if the collimator 50 is slightly moved to the right side (z-axis direction) in the figure for some reason when the X-ray focal point F is at the reference position F0, In this case, the reference signals a and b have a relationship of a <b, and the error signal ve <0 and the control signal vc <0,
In addition, the control voltage V <0. As a result, the electron beam in this case is slightly deflected below the original position F0. At this time, since the rotating anode 41 is at the reference position z0 by the above assumption, a new X-ray focal point F is thereby set to the rotating anode 41.
Is moved slightly lower right than the original focal point F0 along the slope of the X-ray fan beam XLF.
B is evenly distributed on the detector rows A and B of the X-ray detector 70 via the displaced collimator 50.

Alternatively, if the X-ray detector 70 slightly moves to the left (in the direction opposite to the z-axis) in the figure for some reason when the X-ray focal point F is at the reference position F0, Have a relationship of a <b, the error signal ve <0 and the control signal v
c <0 and control voltage V <0. As a result, the electron beam in this case is slightly deflected below the original position F0. At this time, the rotating anode 41 is at the reference position z0 by the above assumption, so that the new X-ray focal point F moves slightly lower right than the original focal point F0 along the slope of the rotating anode 41, Thereby, the subsequent X-ray fan beam XLFB is evenly distributed on the detector rows A and B of the X-ray detector 70 shifted in position. Note that the above is also true for the configuration in FIG.

In the above case, in the practical apparatus, the collimator 50 and / or the X-ray detector 70 move slightly in the z-axis direction (playback, distortion, etc.) in addition to the movement of the rotating anode 41 in the z-axis direction. It is quite possible that this is caused by the influence of X), but according to the present embodiment, X
Despite the complicated combination of displacements of each element in the X-ray imaging system, the X-ray fan of the imaging system is always controlled by a simple control that only controls the deflection of the electron beam in the direction in which the reference signals a and b are always the same. The beam XLFB can always be evenly distributed over the detector rows A and B.

The electron gun 42 and the electron beam deflecting unit 43
In addition to the above, any combination of an electrostatic type and an electromagnetic type is possible. Also, the electron gun 42
However, various other structures may be used. For example, a heater (filament) H having a structure exposed to the anode may be used.

In each of the above embodiments, an example of application to the X-ray detector 70 having two or more detector rows has been described.
Not limited to this. The present invention can be applied to an X-ray detector (single detector) 70 having a single detector row. However, although not shown, the deflection control unit 60A in this case slightly changes the previous signal amplitude (or a predetermined reference value) and the current deflection amount for a single reference signal a generated every time, for example. Compare with the signal amplitude at the time,
The deflection control of the electron beam is performed in a direction in which the signal amplitude is constant (or the difference is 0).

Although a plurality of preferred embodiments of the present invention have been described, it is to be understood that various changes in the configuration, control, processing, and combinations thereof can be made without departing from the spirit of the present invention. Not even.

[0064]

As described above, according to the present invention, with a simple structure, the optimum X-ray for the imaging system is always obtained regardless of the displacement of the elements constituting the X-ray imaging system (particularly, the rotating anode of the X-ray tube). Since the X-ray fan beam can be obtained, it greatly contributes to miniaturization, cost reduction, and improvement in reliability of the X-ray imaging system.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a main part configuration diagram of an X-ray CT apparatus according to an embodiment.

FIG. 3 is a diagram illustrating an X-ray focal position control method according to the first embodiment.

FIG. 4 is a diagram (1) illustrating an X-ray focal position control method according to a second embodiment.

FIG. 5 is a diagram (2) illustrating an X-ray focal position control method according to a second embodiment.

FIG. 6 is a diagram illustrating an X-ray focus control method according to another embodiment.

FIG. 7 is a diagram illustrating a conventional technique.

[Description of Signs] 10 Operation console unit 11 Central processing unit 11a CPU 11b Main memory (MM) 12 Input device 13 Display device (CRT) 14 Control interface 15 Data collection buffer 16 Hard disk device (HDD) 20 Imaging table 30 Scanning gantry unit Reference Signs List 30A Rotation control unit 40 X-ray tube 40A X-ray control unit 41 Rotating anode 42 Electron gun 43 Electron beam deflection unit 50 Collimator 60A Deflection control unit 70 X-ray detector 80 Data acquisition unit (DAS)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Hayakawa Inside 127 Gee Yokogawa Medical System Co., Ltd., 4-7 Asahigaoka, Hino-shi, Tokyo (72) Inventor Akira Izumihara 4-7-7 Asahigaoka, Hino-shi, Tokyo 127 GE Yokogawa Medical Systems Corporation F-term (reference) 4C093 AA22 CA13 CA32 EA13 EA20 FA15 FA45 FA60

Claims (4)

[Claims] 1. An X-ray tube configured to deflect an electron beam for generating X-rays, a collimator for limiting a line width of the generated X-ray in a body axis direction of a subject, and passing through the collimator. An X-ray detector capable of detecting the dose of the X-ray fan beam, wherein the X-ray detector has at least two detector rows in the body axis direction. An X-ray focal position control method, comprising: controlling deflection of an electron beam in a direction in which both signal amplitudes are the same based on at least two predetermined detection signals in at least two columns of an X-ray detector. 2. A program for causing a computer to execute the X-ray focal position control method according to claim 1. 3. An X-ray tube and an X-ray detector are opposed to each other across a subject, and CT of the subject is detected based on a detection signal of the X-ray detector.
An X-ray CT apparatus for reconstructing a tomographic image, comprising: an electron gun; and a rotating anode that generates X-rays by irradiating an electron beam from the electron gun, the rotating anode having an inclined surface in a rotation axis direction thereof, An X-ray tube having an electron beam deflecting unit configured to deflect an electron beam from the electron gun toward the rotating anode interposed therebetween, and a line width in the body axis direction of the subject with respect to the generated X-rays A X-ray detector having at least two detector rows in the body axis direction capable of detecting a dose of an X-ray fan beam passing through the collimator; and a predetermined each of at least two X-ray detector rows. An X-ray CT apparatus comprising: a deflection control unit that controls the deflection of an electron beam deflection unit in a direction in which both signal amplitudes are the same based on the detection signal. 4. An X-ray tube comprising: an electron gun; and a rotary anode that generates X-rays by irradiating an electron beam from the electron gun, the X-ray tube having an inclined surface in a rotation axis direction thereof. An X-ray tube comprising an electron beam deflector interposed between a rotating anode and an electron beam deflector configured to deflect an electron beam traveling from an electron gun toward the rotating anode.