JPH05329143A - Ct scanner - Google Patents

Abstract

(57) [Summary] [Object] To provide a CT scanner capable of varying the size of the X-ray focus so that an appropriate tomographic image can be obtained according to the subject and the purpose. [Configuration] When the X-ray tube 5 capable of emitting X-rays having a large focal point and a small focal point is controlled by the X-ray control unit 31 to switch the size of the X-ray focal point and the X-ray focal point is switched. In addition, the X-ray tube 5 so that the position of the X-ray focus does not change.
Is adjusted by the focus position control unit 60 via the focus position adjusting mechanism 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT scanner which irradiates an object with X-rays and detects X-rays transmitted through the object to form a tomographic image of the object.

[0002]

2. Description of the Related Art CT scanners are widely used, from those used for medical purposes to take a tomographic image of a human body to those used for industrial purposes to take a tomographic image inside an object. Various scanning systems such as the second generation and the third generation have been developed.

In the various CT scanners that have been developed in this way, the size of the X-ray focus irradiated to the subject is changed depending on the type of the subject to be inspected to improve the resolution or shorten the scanning time. There are many cases where it is desired to inspect the subject. For example, in the case of a subject that does not easily transmit X-rays, or when high-speed imaging is desired, it is advantageous to inspect the subject using X-rays with a large focus, and high resolution is required. In some cases, it may be advantageous to examine the subject using X-rays of small focus.

However, there is no conventional CT scanner capable of varying the size of the X-ray focus in this way.
This is because if the size of the X-ray focal point radiated in the X-ray tube is changed, the position of the X-ray focal point shifts.

By the way, there are many ordinary industrial X-ray tubes in which the size of the X-ray focus can be switched in two steps. For example, the 160MZ type X from Seiffert GmbH (Germany)
The X-ray tube can be used by switching between a small focal point of 0.4 × 0.4 mm and a large focal point of 1.5 × 1.5 mm, and the maximum rating of this X-ray tube is the tube voltage and tube current at the small focal point. Each one
It is 60 kV and 4 mA, and the tube voltage and the tube current at the large focus are 160 kV and 10 mA, respectively.

13 and 14 show the structure of an industrial X-ray tube and the structure of a filament of the industrial X-ray tube which can be used by switching the size of the X-ray focal point as described above. It is a figure. 14 (a) is a plan view of the filament, and FIG. 14 (b) is a plan view of FIG.
FIG. 14C is a sectional view taken along line B, and FIG. 14C is a sectional view taken along line AA in FIG.

In the X-ray tube shown in FIG. 13, an anode 102 and a cathode 103 are arranged so as to face each other, and on the cathode 103, a filament for large focus 104a and a filament for small focus 104b are formed, as can be seen from FIG. It has a filament 104. Then, the thermoelectrons generated from the filament 104 are accelerated by the high voltage applied between the cathode 103 and the anode 102, become the electron gun 105, and hit the anode (target), thereby emitting the X-ray 106. To do.

A large focal point filament 104a and a small focal point filament 104 constituting the filament 104.
The high focus generator b can switch between the large focus and the small focus by switching the filament to be turned on from the high voltage generator 107. Both filaments are surrounded by the wall of the cathode cap 110, which serves as a lens together with the anode and the like, and the electrons generated from the filaments are converged and hit the X-ray focal point, which is a narrow range on the anode. , X-rays are generated.

By the way, the filament for large focus 104a
Since the small-focus filament 104b and the small-focus filament 104b are separated from each other by a predetermined distance as shown in FIG. 14, electrons from both filaments strike different positions on the target of the anode that are offset from each other. That is, the position of the X-ray focal point is displaced.

[0010]

As described above, none of the conventional CT scanners can change the size of the X-ray focus, and the conventional industrial X-axis that can switch the size of the focus. Even if a CT scanner is constructed using a ray tube, the position of the X-ray focal point will shift if the size of the X-ray focal point is switched. Accurate positioning with respect to the detector and mechanism is an important point for forming a high-quality tomographic image. Therefore, if the X-ray focal point shifts, a high-quality tomographic image is formed. There is a problem that you cannot do it.

The present invention has been made in view of the above,
It is an object of the invention to provide a CT scanner capable of varying the size of the X-ray focus so that an appropriate tomographic image can be obtained according to the subject and the purpose.

Another object of the present invention is to obtain a tomographic image of good quality by preventing saturation of the X-ray detector when the size of the X-ray focus is switched.
To provide a T-scanner.

[0013]

In order to achieve the above object, the CT scanner of the present invention according to claim 1 irradiates an object with X-rays, detects the X-rays transmitted through the object, and detects the object. A CT scanner for forming a tomographic image of a specimen, wherein an X-ray source capable of emitting X-rays having a plurality of focal points and a size of a focal point of X-rays emitted from the X-ray source are switched. X-ray focus switching control means for controlling the X-ray source, and the X-ray focus switching control means.
The gist is to have focus position adjusting means for adjusting the position of the X-ray focus so as not to change when the X-ray focus is switched by the line focus switching control means.

The CT scanner of the present invention according to claim 2 is a CT scanner which irradiates an object with X-rays and detects X-rays transmitted through the object to form a tomographic image of the object. An X-ray source having a plurality of electron generating means coaxially arranged on the cathode so as to generate thermoelectrons that emit X-rays having a plurality of focal points by hitting the anode by being accelerated by a high voltage; X-ray focus control means for selectively driving and controlling a plurality of electron generating means of the X-ray source, and controlling the selector to generate X-rays having different focal points. ..

Further, the CT scanner of the present invention according to claim 3 is a CT scanner which irradiates an X-ray to a subject and detects the X-ray transmitted through the subject to form a tomographic image of the subject. X, which can emit X-rays having multiple focal points
The X-ray focus is controlled by the X-ray focus switching control unit that controls the X-ray source so as to switch the size of the X-ray focus emitted from the X-ray source. The gist of the present invention is to have an X-ray detector whose gain changes according to the size of the switched X-ray focus when switched.

The CT scanner of the present invention according to claim 4 is
A CT scanner for irradiating a subject with X-rays, detecting X-rays transmitted through the subject, and forming a tomographic image of the subject,
A gist having a scanning speed switching means for switching a scanning speed of X-rays passing through a subject, and an X-ray detector whose gain changes according to the scanning speed of the X-rays switched by the scanning speed switching means. To do.

[0017]

According to the CT scanner of the present invention as defined in claim 1, the X-ray focal point is switched by controlling the X-ray source capable of emitting X-rays having a plurality of focal points. The position is adjusted so that the position of the X-ray focal point does not change when is switched.

Further, in the CT scanner of the present invention as defined in claim 2, there are provided a plurality of electron generating means coaxially arranged on the cathode so as to generate thermoelectrons which emit X-rays having a plurality of focal points. The drive is selectively controlled so that X-rays having focal points of different sizes are selectively generated.

Further, in the CT scanner of the present invention as defined in claim 3, when the X-ray focal point is switched, the gain of the X-ray detector is varied according to the size of the switched X-ray focal point. ..

The CT scanner of the present invention according to claim 4 is
When the X-ray scanning speed is switched by irradiating the subject with X-rays, X-ray scanning is performed according to the switched X-ray scanning speed.
The gain of the line detector is changed.

[0021]

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

FIG. 1 is a diagram showing the configuration of a CT scanner according to an embodiment of the present invention. In the same figure, the mechanical section shown in the upper part is a plan view of the present CT scanner installed on the floor as seen from above, and the lower part shows the respective control parts in a block diagram.

The CT scanner shown in FIG. 1 is of a so-called TR (traverse-rotation) system (second generation system) which obtains a tomographic image of the subject by scanning the subject by rotating and traversing the subject. An X-ray tube 5 and an N-channel X-ray detector 7 are arranged opposite to a U-shaped frame 3 supported by a support 1 so as to be movable in the vertical direction.

A subject 11 is placed on a mounting table 15 between the X-ray tube 5 and the X-ray detector 7, and a fan beam radiated from the X-ray tube 5 toward the X-ray detector 7. 9 for subject 1
1 crosses. The mounting table 15 on which the subject 11 is mounted is designed to be rotated by the rotating mechanism section 17 and is also connected to the moving mechanism section 19 controlled by the traverse mechanism 13, whereby the mounting table 15, that is, the The subject 11 is configured to move along the moving mechanism unit 19, that is, traverse.
In addition, 25 and 27 are collimators.

The CT scanner having such a structure is
While moving the subject 11 a plurality of times at different angles so as to cross the fan beam 9, the X-ray detector 7 in each movement is moved.
The output signal from the object is collected by the data collecting unit 21, and the collected data is reconstructed by the reconstructing unit 23.
One tomographic image can be displayed on the CRT 37.

The X-ray tube 5 is capable of changing the size of the X-ray focal point between a small focal point and a large focal point, and by changing the X-ray focal point in this way, the X-ray tube is changed. Since the focus position is variable, a focus position adjusting mechanism 29 is provided near the X-ray tube 5 so as to adjust such a change in the X-ray focus position. The focus position adjusting mechanism 29 includes a vertical movement motor, a horizontal movement motor, and a front and rear movement motor so that the X-ray tube 5 can be driven in the vertical, horizontal, and front-back directions to adjust the X-ray focal point position. To have. The focus position adjusting mechanism 29 is controlled by the focus position control unit 60. The focus position control unit 60 includes a motor driver 61, an interface 62, an interface 63, a CPU 64, a memory 65.
It consists of

Further, the X-ray tube 5 is controlled by the X-ray control unit 31 such as its start-up and the size of the X-ray focus, and the X-ray control unit 31 controls the overall operation of the CT scanner. Is controlled by. The traverse mechanism 13 and the rotation mechanism unit 17 are provided in the central control unit 35.
Is controlled via the drive control section 33.

The data collecting section 21 for collecting the data from the X-ray detector 7 is connected to the central control section 35 and also to the adjusting position calculating section 39 for obtaining the adjusting position of the X-ray focus of the X-ray tube 5. The data collected by the data collection unit 21 is also supplied to the adjustment position calculation unit 39. The adjustment position calculation unit 39 includes an interface 41 connected to the data collection unit 21, a CPU 43 that calculates the adjustment position of the X-ray focus from the collection data supplied via the interface 41, a memory 45 that stores various data, and a display. Have 47.

Next, the operation of the CT scanner configured as above will be described.

This CT scanner has a focus position measurement mode for measuring the position of the X-ray focus by changing the size of the X-ray focus of the X-ray tube 5, and the measured position after measuring the position of the X-ray focus. And a scan mode for scanning the subject using the data.

The focus position measuring mode is a mode in which the adjustment positions of the focus position adjusting mechanism 29 at the small focus and the large focus are measured and stored in the memory 65 of the focus position control unit 60 as digital values.

First, a method of selecting a small focus and measuring the adjustment position in the vertical (Z) direction will be described with reference to FIGS. 2 and 3.

First, when the operator issues a command from the panel of the central control unit 35, this command is issued by the focus position control unit 6.
0, the motor driver 61 of the focus position control unit 60 causes the vertical movement motor of the focus position adjusting mechanism 29 to return the X-ray tube 5 to the lower limit position, and from this lower limit position, the X-ray tube 5
Is increased at a constant speed and the X-ray is started to be emitted from the X-ray tube 5 under the control of the X-ray controller 31. At this lower limit position, the focus position of the X-ray tube 5 is located below the correct focus position O, as indicated by O'in FIG.

When the X-ray tube 5 starts to emit X-rays, the X-ray detector 7 detects the X-rays from the X-ray tube 5, and the data acquisition unit 2
Supply to 1. The data collector 21 collects data from the X-ray detector 7 and supplies it to the adjusted position calculator 39.

An encoder for detecting the vertical movement position is attached to the vertical movement motor of the focus position adjusting mechanism 29, and the vertical movement position from this encoder is used as the digital data during data collection and the focus position control unit 60 is provided.
Are supplied to the adjustment position calculation unit 39 from the focus position control unit 60.

As described above, the measurement is completed by moving the X-ray tube 5 from the lower limit position to the upper limit position. The adjustment position calculation unit 39 receives the output data (I) from the X-ray detector 7 corresponding to the vertical movement position data (Z) of the X-ray tube 5 having the relationship shown in FIG. The correct position Zo in the vertical (Z) direction is calculated from the above relationship. This calculation is performed by calculating Z0, where Z is the same value on the left and right areas of the output data I (Z) of the X-ray detector 7, as shown in FIG. The correct position Zo in the vertical (Z) direction calculated in this way is calculated by the adjustment position calculation unit 3
9 is supplied to the focus position control unit 60, and the focus position control unit 60 stores it in the memory 65 and moves the X-ray tube 5 up and down to this position Zo via the focus position adjusting mechanism 29 to stop it.

Next, regarding the method of measuring the adjustment position in the horizontal direction, that is, the adjustment position in the horizontal plane (x, y), the xy coordinate system is set as shown in FIG. 4, and the focus position of the X-ray tube 5 is set. A case where O ′ is deviated from the correct focus position O by Δx and Δy will be described as an example.

The measurement of the adjustment position in this horizontal plane is as follows.
The reference object is used instead of the object 11. That is, the adjustment position calculation unit 39 calculates the adjustment position based on the output signal detected by the X-ray detector 7 by scanning the reference object with X-rays from the X-ray tube 5.

As shown in FIG. 4, particularly in FIG. 5, this reference object is separated by a distance R from the rotation center axis H of the support base 51.
Pair of pin phantoms 49 symmetrically arranged with
It is composed of a and 49b. Then, the pin phantoms 49 a and 49 b are mounted on the mounting table 15 via the support table 51.

The adjusting position calculating section 39 detects the pin phantoms 49a and 49b mounted on the mounting table 15 in this manner as shown in FIG.
In the arrangement shown in FIG. 6, the fan beam 9 is moved once so as to cross it, and the moving distance (traverse distance) X and the detection results from the X-ray detector 7 for each of the pin phantoms 49a and 49b are shown in FIG. Seek a relationship.

Then, the adjustment amount Δx is obtained from this relationship by the following equation.

[0042]

[Equation 1] Note that FDD, FCD, and xcenter in this equation are lengths determined by the geometric setting of the system as shown in FIG.

Further, the adjustment amount Δy is obtained by the following procedure. First, Δx1 and Δx2 are calculated from the following equations.

Δx ₁ (1, N) = x ₁ (1) −x ₁ (N) Δx ₁ (2, N−1) = x ₁ (2) −x ₁ (N−1) Δx ₁ (k, N−k + 1) = x ₁ (k) −x ₁ (N−k + 1) Δx ₂ (1, N) = x ₂ (1) −x ₂ (N) Δx ₂ (2, N−1) ) = X ₂ (2) −x ₂ (N−1) ········ Δx ₂ (k, N−k + 1) = x ₂ (k) −x ₂ (N−k + 1) In the above equation, , Kf use a value of about N / 4.

Then, based on the result obtained by the above equation, the magnification value M is obtained from the following equation.

[0046]

[Equation 2] Then, the average value Mo of the obtained magnification values M is calculated, and finally the adjustment amount Δy is obtained from the following equation.

[0047]

[Equation 3] Since Δx and Δy are obtained as described above, the adjustment position calculation unit 39 further receives the current position x and y in the horizontal plane of the X-ray tube 5 from the focus position control unit 60, and Calculate the correct positions xo and yo.

Xo = x + Δx yo = y + Δy Correct position xo in the horizontal plane thus calculated,
yo is supplied to the focus position control unit 60. The focus position control unit 60 stores the correct positions xo and yo in the memory 65 and moves the X-ray tube 5 to the correct positions xo and yo in the horizontal plane via the focus position adjusting mechanism 29.

When the measurement of the focal position with respect to the small focal point is completed as described above, the large focal point is then selected and the same measurement is performed to calculate the positions xo, yo and zo at the large focal point, and the focal point is calculated. Position adjustment is also performed. And the adjustment position xo,
Yo and zo are stored in the memory 65 of the focus position control 60 separately for the small focus and the large focus.

As described above, the focus position measurement mode ends, and the adjustment positions xo and yo for the small focus and the large focus are obtained.
, Xo are stored, the scan mode is performed next based on this adjusted position.

In this scan mode, the subject 11 is placed on the placing table 15, and the operator selects the size of the focus on the panel of the central control unit 35. The X-ray control unit 31 switches the size of the focus in the X-ray tube 5 according to the selected focus size, and the focus position control unit 6
0 is the memory 6 corresponding to the size of the selected focus.
The focus position is adjusted so that the X-ray tube 5 is focused on the adjustment position stored in 5. When the focus position adjustment is completed, the CT scanner is ready to scan.
When the operator starts scanning, the scanning is performed in the same manner as a normal CT scanner to create a tomographic image of the subject 11.

The CT scanner described above is normally used in the scan mode, and the focus position measurement mode is used during the manufacture of the apparatus, the replacement of the X-ray tube, the periodic inspection, and the like.

Although the above embodiment has described the case where the size of the focal point is set in two steps, that is, the small focal point and the large focal point, this is not limited to two steps, and any number of steps is possible.

Further, in the above embodiment, the adjustment position calculation unit 3
Although the adjustment position of the X-ray tube is calculated by using 9, the position adjustment of the X-ray tube is performed even without using the adjustment position calculation unit 39, which is a sectional image of a pin phantom that is a pin-shaped test object. Taking an image and empirically determining the adjustment amount and the adjustment direction from the artifact of this cross-sectional image, or scanning the pin phantom, outputting the raw data of the X-ray detector, and plotting etc. to obtain the adjustment amount. It is also possible to obtain the adjustment position for each of the small focus and the large focus by an empirical method such as. Then, the adjustment position thus obtained may be manually input to the focus position control unit 60.

Further, in the above embodiment, the focus position control unit 6
The position of the X-ray tube 5 is mechanically adjusted from 0 via the focal position adjusting mechanism 29. Instead of performing the mechanical operation in this way, for example, a current is passed through a coil to bend the electron beam and focus position. Can also be adjusted.

Further, not only the X-ray tube but also a linac (linear accelerator) can be applied.

Further, the CT scanner system is a traverse-type.
Not only the second generation rotation type, but also the third generation
The present invention can be similarly applied to other types such as generation and fourth generation.

FIG. 7 is a diagram showing the structure of a cathode having an X-ray tube filament applicable to a CT scanner according to another embodiment of the present invention, and FIG. 7A is a front view thereof, 7B is a sectional view taken along the line BB of FIG. 7A, and FIG. 7C is a sectional view taken along the line AA of FIG. 7A.

The X-ray tube having the cathode 83 shown in FIG. 7 has the structure shown in FIG. 13 as a whole and has two kinds of filaments for the small focus and the large focus. Only the structure of the filament is changed so that the focal position does not change even when is switched between the small focus and the large focus.

Specifically, in FIG. 7, a small-focus filament 80b is provided in the center of the cathode cap 81, and a large-focus filament 80a is provided parallel to both sides so as to surround the small-focus filament 80b. It is provided. Therefore, the center position of the filament when the filament is switched to only the small focus filament 80b and the center position of both filaments when the filament is switched to the large focus filament and the large focus filament 80a and the small focus filament 80b are turned on. Are the same, and the focal position does not change even if the filament is switched.

The periphery of the filament composed of the small-focus filament 80b and the large-focus filament 80a is covered with the wall of the cathode cap 81, and this serves as an electron lens together with other electrodes such as an anode.

More specifically, when the small focus is selected, only the small focus filament 80b is turned on, and when the large focus is selected, both the large focus filament 80a and the small focus filament 80b are turned on. Thus, the X-ray controller operates. In this case, the center position of the small focus when only the small focus filament 80b is turned on is the center of the small focus filament 80b, or both the large focus filament 80a and the small focus filament 80b are turned on. Since the central position of the large focal point at the time is also the center of the filament 80b for the small focal point, the central position at the small focal point and at the large focal point does not change.

Then, the small focus filament 80b selected so as to form the small focus or the large focus in this way.
The thermoelectrons generated from the filament composed of the filament for large focus 80a are converged by the electron lens system composed of the cathode cap 81 and the anode and are accelerated by the electric field between the cathode and the anode to focus on the anode. To generate X-rays. In the case of a large focal point, the filament becomes large and the focal point also becomes large.
Since a is disposed so as to surround the small-focus filament 80b, a large focal point is formed so as to surround the small focal point, and the X-ray focal point position is prevented from shifting.

In the above embodiment, the filament is formed into a coil, but the filament is not limited to this, and it may be formed into a plate-shaped resistor, for example.

FIGS. 8A, 8B and 8C show the structure of the cathode having the filament of the X-ray tube applicable to the CT scanner according to another embodiment of the present invention. ，
It is a figure similar to (b), (c).

The embodiment shown in FIG. 8 has the same filament as that shown in FIG.
0a and the small focus filament 80b are arranged in separate recesses in the cathode cap. With this configuration, it is possible to design a cathode cap that places importance on the convergence property at the time of small focus.

FIGS. 9 (a), 9 (b) and 9 (c) show the structure of the cathode having the filament of the X-ray tube which can be applied to the CT scanner according to still another embodiment of the present invention.
It is a figure similar to (a), (b), (c).

The embodiment shown in FIG. 9 is constructed such that the large-focus filament 82a is completely surrounded by the small-focus filament 82b, and is made one round.

FIG. 10 is a diagram showing the structure of a CT scanner according to still another embodiment of the present invention. In the figure,
The mechanical section shown in the upper part is a plan view of the present CT scanner installed on the floor as seen from above, and the lower part shows each control section in a block diagram.

In the CT scanner shown in FIG. 10, the gain of the X-ray detector, which is the ratio of the input current to the output voltage in the conventional X-ray detector circuit, is fixed and cannot be switched. When the focus of the X-ray is increased as in each of the embodiments shown in FIG. 9, there is a problem that the output of the X-ray detector is saturated, and therefore the X-ray is prevented in order to prevent such saturation. While setting the gain of the detector to the large focal point, and also when switching the focal point from the large focal point to the small focal point, the output of the X-ray detector becomes too small and the dynamic range of the data acquisition unit is not fully utilized. The first purpose is to control so as to set the gain of the X-ray detector in accordance with a small focus so as to prevent it, and as described above, enables high-speed CT scan and high-speed fluoroscopy, and It is possible to perform a so-called fine scan in which the scanning time is extended instead of increasing the focus of X-rays in order to increase the X-ray dose and reduce the noise in the image. If the fine scan is performed with the fine scan, the problem that the output of the X-ray detector is saturated occurs as described above. Therefore, in order to prevent such saturation, the gain of the X-ray detector is adjusted to the fine scan. The normal scan prevents the output of the X-ray detector from becoming too small when the fine scan is switched to the short scan, that is, the normal scan, and the dynamic range of the data acquisition unit is not fully utilized. The second purpose is to control so as to set the gain of the X-ray detector in accordance with the above.

In the CT scanner shown in FIG. 10, the adjustment position calculation unit 39 and the focus position control unit 60 are removed from the configuration of the CT scanner shown in FIG. 1, and instead the X-ray focus switching unit 38 and the scanning speed switching unit 40 are used. Only the difference is provided and the other configurations are the same, and thus the same reference numerals are given. The X-ray focus switching device 38 and the scanning speed switching device 40 output switching information as digital signals.

FIG. 11 is a detailed circuit diagram of the N-channel X-ray detector 7 used in the CT scanner shown in FIG. The X-ray detector 7 shown in the figure has N channel parts 100 from 1 channel to N channel, and the output signals from the N channel parts 100 are input to the multiplexer 75 and switched to time division. And is supplied to the data collection unit 21,
In the figure, the internal structure of only one channel is shown in detail.

First, the channel section 100 of one channel
The configuration of will be described. The channel portion 100 is an X-ray tube 5
Scintillator 71 which emits light when exposed to X-rays from
The light from the scintillator 71 is detected by the photodiode 72 and converted into a current i. The current i from the photodiode 72 is the current I in the current amplifier 76.
Is amplified to. The current amplifier 76 is the operational amplifier 11
1, resistor 112, capacitor 113, resistor 114, X-ray focus switching switch 173, scanning speed switching switch 1
74, resistors 121, 122, 131 and 132. The X-ray focus switching switch 173 and the scanning speed switching switch 174 are connected to the gain switching signal A from the X-ray focal switching device 38 and the scanning speed switching device 40, respectively. Is controlled by the integration constant switching signal B.

The current I amplified by the current amplifying section 76 is integrated by the integrator 79 and then sampled and held by the sample and hold section 150.
The integrator 79 includes an operational amplifier 141 and an integrating capacitor 14
2, a transistor switch 143, and a resistor 145. The sample-and-hold unit 150 includes a transistor switch 151, resistors 152 and 154, and a capacitor 1.
55 and an operational amplifier 153.

Transistor switch 143 of integrator 79
Is controlled by the reset / integration signal C from the X-ray control unit 31, and when the switch is on, the integration capacitor 142
The current integrated into is discharged and reset. Also,
The transistor switch 151 of the sample-and-hold unit 150 is controlled by the sample / hold signal D from the data collection unit 21, and the integrator 7 is turned off when the switch is off.
The output of 9 is held as the charge of the capacitor 155, and the output of the operational amplifier 153 is held at the same value as the output of the integrator at the moment when it is turned off.

The above is the channel section 10 for one channel.
Although the configuration is 0, the configurations of the other channel units 100 from 2 channels to N channels are exactly the same. The output signal of the sample-and-hold section 150 of each channel section 100 is supplied to the data collection section 21 switched by time division via the multiplexer 75. In FIG. 11, the X-ray focus switching switch 173 and the scanning speed switching switch 174 are schematically shown as mechanical switches.
Actually, a semiconductor switch or the like is used.

The operation of the CT scanner configured as above will be described.

First, prior to the scanning operation, the gain switching signal A and the integration constant switching signal B output from the X-ray focus switching unit 38 and the scanning speed switching unit 40 are used to switch the X-ray focus switching switch 173 and the X-ray focus switching unit 173 of the current amplifier 76. The scanning speed switching switch 174 is switched. The X-ray focus switching switch 173 has a resistance 12 when the focus is small.
1, the switching control is performed so as to be connected to the resistor 122 in the case of a large focal point, and the scanning speed switching switch 174 is connected to the resistor 131 in the case of normal scanning, which is a high speed scan, and is a low speed scan. It is switched to be connected to the resistor 132 in the case of fine scan.

As described above, the X-ray focus switching switch 17
When the scanning operation is started after the switch 3 and the switch 174 for switching the scanning speed are switched and connected, the X-ray tube 5 starts emitting X-rays, and the X-ray detector 7 and the data acquisition unit 21 start data acquisition. .. This scan is the CT of FIG.
Since it is of the same traverse-rotation type as the scanner, detailed description thereof will be omitted, and the operation inside the X-ray detector 7 shown in FIG. 11 will be described.

When the X-rays from the X-ray tube 5 are incident on the scintillator 71, the scintillator 71 generates light, which is detected by the photodiode 72, converted into a current i and output. This current i is the operational amplifier 111 of the current amplifier 76, the resistor 112, the capacitor 113, the resistor 114,
The output of the operational amplifier 111 is converted into a voltage V _B represented by the following equation through a current-voltage conversion unit including an X-ray focus switching switch 173 and resistors 121 and 122.

V _B = -Rf (R1 + R2) i / R2 where Rf, R1 and R2 are resistors 112 and 11, respectively.
The resistance value is 4,121.

This voltage V _B passes through the voltage / current conversion unit consisting of the scanning speed switching switch 174 and the resistors 131 and 132 of the current amplification unit 76, and the current I at the input of the integrator 79.
Is converted to. This current I is expressed by the following equation.

I = V _B / R3 Here, R3 is the resistance value of the resistor 131.

The current I can be considered to be the current i amplified by the current amplifying section 76. In this case, the current I is expressed by the following equation.

I = −Rf · (R1 + R2) · i / R2 · R3 This current I is converted into the voltage V _D via the integrator 79. This voltage V _D is expressed by the following equation.

V _D = −I · T ′ / C2 where T ′ is the integration time and C2 is the capacitor 14
2 capacity.

The integrator 79 is reset by the reset / integration signal C from the data collection unit 21 for each collection, and the data integrated for the time T'is collected. The above-mentioned equation of the voltage V _D is the above-mentioned equation of the current I I = V _B / R3
Can be transformed into

V _D = −T ′ · V _B / R3 · C2 This voltage V _D is switched by the multiplexer 75 for each channel and collected in the data collecting section 21.

Since the input current to the X-ray detector 7 is i and the output voltage is V _D , the gain V of the X-ray detector 7 is V.
_D / i is given by the following equation.

V _D / i = Rf · (R1 + R2) · T '/
R2, R3, C2 By the way, saturation inside the X-ray detector 7 occurs when the voltage of each part deviates from the range of -10 to + 10V.
Therefore, in order to prevent saturation from occurring in the output of the operational amplifier 111 of the current amplification unit 76, the above-mentioned voltage V _B
As can be seen from the equation, when the focus is small, the voltage V _B is increased by switching with the switch 173 for switching the X-ray focus and using the small resistor 121, and when the focus is large, the switch for switching the X-ray focus is used. It is sufficient to reduce the voltage V _B by switching with the switch 173 and using the large resistance 122.

On the other hand, the above-mentioned formula of the voltage V _D V _D = -T '
In V _B / R3 · C2, R3 · C2 is selected so as to have almost the same value as the integration time T ′, which causes | V _D | to have almost the same value as | V _B | 79
Saturation of the output of will not occur. In addition, R3 ・ C
2 is called the integration constant of the circuit.

Therefore, when the scanning speed is increased and the integration time T'is shortened, the scanning speed switching switch 17 is used.
4 and a small resistor 131 is used to slow down the scanning speed and when the integration time T ′ becomes long, the scanning speed switching switch 174 is used to switch to a large resistor 13.
2 should be used.

FIG. 12 is an operation waveform diagram of the X-ray detector 7 described above. As shown in the figure, the reset / integration signal C
The integrator 79 starts integration from the moment when is switched to integration. Then, the output signal of the integrator 79 at the moment when the sample / hold signal D is held is held, and the time T ′ during this time becomes the integration time. The held output signal is switched between channels by the multiplexer 75 while being held, and the data collection unit 21
Are sequentially supplied.

In the above embodiment, the switching is performed in two steps by the X-ray focus switching switch 173 and the scanning speed switching switch 174. However, the number of switching is not limited to this, and more switching is possible. Also, the resistors 121, 1
Instead of switching 22 and 131, 132, respectively, resistor 114 or 112 and capacitor 142 respectively.
Can also be switched. Furthermore, the present invention can be applied not only when switching the size of the focus, but also when switching the tube voltage and tube current of the X-ray tube.

[0095]

As described above, according to the present invention as set forth in claim 1, the size of the X-ray focal point is switched, and when the X-ray focal point is switched, the X-ray focal point position does not change. Since the position is adjusted as described above, for example, in the case of an object in which X-rays are difficult to transmit or when high-speed scanning is desired, inspection can be performed using large-focus X-rays, and when resolution is required, small-focus X-rays can be used. The size of the X-ray focal point can be easily and reliably switched according to the subject and the purpose such that the examination can be performed using X-rays.

According to the second aspect of the present invention, a plurality of electron generating means coaxially arranged on the cathode are selected so as to generate thermoelectrons that emit X-rays having a plurality of focal points. Drivingly controlled to selectively generate X-rays having focal points of different sizes, the position does not change even if the focal point of X-rays is changed. Accordingly, the size of the X-ray focus can be switched easily and surely.

Further, according to the present invention as set forth in claims 3 and 4, when the X-ray focal point is switched, the gain of the X-ray detector is changed according to the size of the switched X-ray focal point. In addition, when the X-ray scanning speed is switched, the gain of the X-ray detector is changed according to the switched X-ray scanning speed, so that even if the X-ray focus size is changed, Since saturation does not occur inside the X-ray detector and the output of the X-ray detector can be increased,
By fully utilizing the dynamic range of the line detector and the data acquisition unit, it is possible to obtain a tomographic image with good image quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a CT scanner according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method of measuring an adjustment position in a vertical (Z) direction in the CT scanner shown in FIG.

3 is a diagram showing a relationship between an output I of an X-ray detector and a vertical position Z in a method of measuring an adjustment position in a vertical (Z) direction in the CT scanner shown in FIG.

FIG. 4 is an explanatory diagram showing a method of measuring an adjustment position in the horizontal direction in the CT scanner shown in FIG.

5 is a diagram showing a pin phantom used in the CT scanner shown in FIG. 1. FIG.

6 is an explanatory diagram showing a relationship between a channel of an X-ray detector used in the CT scanner shown in FIG. 1 and a pin phantom at a traverse distance.

FIG. 7 is a view showing a structure of a cathode having an X-ray tube filament applicable to a CT scanner according to another embodiment of the present invention.

FIG. 8 is a view showing a structure of a cathode having an X-ray tube filament applicable to a CT scanner according to another embodiment of the present invention.

FIG. 9 is a view showing a structure of a cathode having an X-ray tube filament applicable to a CT scanner according to still another embodiment of the present invention.

FIG. 10 is a diagram showing a configuration of a CT scanner according to still another embodiment of the present invention.

11 is a detailed circuit configuration diagram of an N-channel X-ray detector 7 used in the CT scanner shown in FIG.

12 is a timing chart showing operation waveforms of the X-ray detector shown in FIG.

FIG. 13 is a diagram showing the structure of an industrial X-ray tube.

14 is a diagram showing a structure of a filament of the X-ray tube shown in FIG.

[Explanation of symbols]

 5 X-ray tube 7 X-ray detector 11 Subject 21 Data acquisition unit 23 Reconstruction unit 29 Focus position adjustment mechanism 31 X-ray control unit 35 Central control unit 39 Adjustment position calculation unit 60 Focus position control unit

Claims (4)

[Claims] 1. A CT scanner which irradiates an X-ray to a subject and detects the X-ray transmitted through the subject to form a tomographic image of the subject, the X-ray having focal points of a plurality of sizes. And an X-ray focus switching control unit that controls the X-ray source so as to switch the size of the focus of X-rays emitted from the X-ray source, and the X-ray focus switching control unit. A CT scanner comprising: focus position adjusting means for adjusting the position of the X-ray focus so that the position of the X-ray focus does not change when the focus is switched. 2. A CT scanner which irradiates an object with X-rays, detects the X-rays transmitted through the object, and forms a tomographic image of the object, wherein the CT scanner is accelerated by a high voltage and hits a plurality of anodes. Selecting an X-ray source having a plurality of electron generating means coaxially arranged on the cathode so as to generate thermoelectrons that emit X-rays having a focal point of And a X-ray focal point control means for controlling so as to selectively generate X-rays having focal points of different sizes. 3. A CT scanner, which irradiates an object with X-rays, detects X-rays transmitted through the object, and forms a tomographic image of the object, the X-ray having focal points of a plurality of sizes. And an X-ray focus switching control unit that controls the X-ray source so as to switch the size of the focus of X-rays emitted from the X-ray source, and the X-ray focus switching control unit. A CT scanner, comprising: an X-ray detector whose gain changes in accordance with the size of the switched X-ray focus when the X-ray focus is switched. 4. A CT scanner for irradiating a subject with X-rays, detecting the X-rays transmitted through the subject, and forming a tomographic image of the subject, wherein the scanning speed of X-rays transmitted through the subject. And a scanning speed switching means for switching the scanning speed and an X-ray detector whose gain changes according to the scanning speed of the X-rays switched by the scanning speed switching means.
Scanner.