JPH0732769B2 - Adjustment device for CT scanner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT scanner adjusting apparatus for adjusting the focus position of an X-ray source constituting a CT scanner with respect to an X-ray detector.

[0002]

2. Description of the Related Art In a CT scanner (computer tomography apparatus), the focal position of the X-ray source with respect to the X-ray detector and the mechanical section is constant in order to obtain an appropriate cross-sectional image without causing false images. Must be

Generally, it is difficult to stably manufacture an X-ray tube, which is an X-ray source, so that the X-ray focal point is always in the correct and same position with respect to the housing. Therefore, CT
Not only when the scanner is manufactured, but also the focus position must be adjusted each time the X-ray tube is replaced.

However, the conventional adjustment is to take a cross-sectional image of a pin phantom (pin-shaped test object) and empirically determine the adjustment amount and the adjustment direction from the artifact of the cross-sectional image, or scan the pin phantom. Then
An empirical method has been used in which raw data of the X-ray detector is output and plotted to obtain the adjustment amount. For this reason, there is a problem that the adjustment takes time, the accuracy is not improved, and it depends on the skill level of the adjuster, so that no one can easily perform the adjustment.

[0005]

As described above, the conventional adjusting method has drawbacks in terms of adjusting time, accuracy, and easiness.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a CT scanner adjusting apparatus which enables anyone to easily perform highly accurate focus position adjustment of an X-ray source in a short time. To provide.

[0007]

In order to achieve the above object, a CT scanner that obtains a cross-sectional image by moving an object so as to cross a fan beam emitted from an X-ray source toward an X-ray detector. In the present invention, the reference object arranged on the mounting table on which the object is mounted is arranged at a constant interval in the direction perpendicular to the moving direction, and the mounting table on which the reference object is arranged is moved in the moving direction. Adjustment amount calculation means for obtaining a focus position adjustment amount of the X-ray source with respect to the X-ray detector, based on the movement distance when the X-ray detector is moved to and the output of the X-ray detector for each reference subject with respect to the movement distance. Having it is the gist.

[0008]

In the CT scanner adjusting apparatus according to the present invention, the subject is placed on the mounting table on which the subject is placed against the fan beam emitted from the X-ray source in order to obtain a sectional image. Reference objects are arranged in the direction perpendicular to the moving direction at regular intervals, and a moving distance when the mounting table is moved in the moving direction and an X-ray detector for each reference object with respect to the moving distance. Based on the output of
The focus position adjustment amount for the X-ray detector of the radiation source is calculated.

[0009]

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

FIG. 1 is a diagram showing a configuration example of a CT scanner having an adjusting device according to the present invention. This CT scanner is of a so-called TR (traversal rotation) type that obtains a cross-sectional image by scanning the subject by rotation and traverse movements. That is, in this CT scanner, an X-ray tube 5 and an N-channel X-ray detector 7 are arranged opposite to each other on a U-shaped frame 3 supported and fixed by a column 1, and from the X-ray tube 5 X-ray detector 7
The frame 3 is provided with a traverse mechanism 13 that moves (traverses) the subject 11 so as to traverse the fan beam 9 radiated toward. The traverse mechanism 13 includes a mounting table 15 on which the subject 11 is mounted, a rotation mechanism section 17 for rotating the mounting table 15, and a moving mechanism section 19 for moving the mounting table 15 and the rotation mechanism section 17. Thus, with such a configuration, the subject 11 is moved a plurality of times at different angles so as to traverse the fan beam 9, and based on the output from the X-ray detector 7 caused by each movement, the data acquisition unit 21 and The cross-sectional image of the subject 11 is obtained in the configuration unit 23.

In FIG. 1, 25 and 27 are collimators, 29 is an X-ray source position adjusting knob, 31 is an X-ray source drive control unit, 33 is a drive control unit of the traverse mechanism 13, 3
5 is a central control unit for controlling the operation of the entire CT scanner, 3
7 is a CRT.

On the other hand, in FIG. 1, reference numeral 39 denotes an adjustment amount calculation unit for obtaining the adjustment amount of the focal position of the X-ray tube 5, which is an interface 41, a CPU 43, a memory 45 and a display 4.
This is a configuration having 7.

The operation of the adjustment amount calculating section 39 will be described below by setting the xy coordinate system as shown in FIG. 2 so that the focus position O'of the X-ray tube 5 is Δx and Δy with respect to the correct focus position O. An example will be described where there is a deviation.

As a premise, the adjustment amount calculation unit 39 obtains the adjustment amount based on the output from the X-ray detector 7 due to the scanning of the reference object. The reference object for that purpose will be described with reference to FIG. In FIG. 3, 49a, 49
Reference numeral b denotes a pin phantom which constitutes a reference subject, which is symmetrically arranged at a distance R with respect to the rotation center axis H of the support base 51 and is mounted on the mounting base 15 via the support base 51.

The adjustment amount calculation unit 39 is thus arranged on the mounting table 1
The pin phantoms 49a and 49b mounted on the No. 5 are moved once across the fan beam 9 in the arrangement shown in FIG. 2, and the moving distance (traverse distance) X and each pin phantom in the X-ray detector 7 From the detection result, the relationship between the two is obtained as shown in FIG.

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

[0017]

[Equation 1]

In this equation, FDD, FCD, xcenter
Is a length defined by the geometric setting of the system as shown in FIG.

Further, the adjustment amount Δy is obtained by the following procedure.
First, Δx ₁ and Δx ₂ are calculated from the following equations.

[0020]

[Equation 2]

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

[0022]

[Equation 3]

Then, the average value M _o of the obtained magnification values M is calculated, and finally the adjustment amount Δy is calculated from the following equation.

[0024]

[Equation 4]

Since this result is displayed and output on the display 47, the operator may operate the X-ray source position adjusting knob 29 in accordance with this display for adjustment.

Therefore, according to the present embodiment, the focus position of the X-ray tube may be adjusted according to the calculation result of the adjustment amount calculation section, and it is not based on the empirical method as in the prior art. It can be performed accurately and in a short time.

The present invention is not limited to the above embodiment, and various modes are conceivable in order to improve the adjustment accuracy. Specifically, for example, the number of traverse operations may be increased, or the number of pin phantoms 49 may be increased as shown in FIG. In addition, after one traverse operation, the mounting table 15 is rotated 180 ° and the traverse operation is performed again, and the adjustment amounts Δx and Δ obtained by the respective operations are performed.
It is also conceivable to use the average value of y as the adjustment amount. According to this aspect, as shown in FIG.
Even if there is a deviation in the deployment position of 9b, an error due to this deviation can be corrected to obtain an accurate correction amount.

Further, in the above embodiment, the focus adjustment of the X-ray tube 5 is adjusted by the X-ray source position adjusting knob 29, but the adjustment amount calculation unit 39 does not actually adjust the focus adjustment result. Certain Δx and Δy may be used as parameters for reconstruction. Specifically, for example, a value obtained by subtracting Δy from the values of FCD and FDD is used as a new FCD and FDD.
DD or as the value of xcenter

[0029]

[Equation 5]

Is used. Alternatively, the data collection start point of the traverse operation, that is, the traverse distance and the reference point of X may be shifted so that the value of xcenter becomes the value of the above equation. This can be done by changing the control parameter of the drive control unit 33. The parameters can be changed manually, but the changed amount can also be transferred from the adjustment amount calculation unit 39 and automatically changed. Here, in the above embodiment, the X-ray detector 7 and the mounting table 15 are used.
And that the collimators 25 and 27 have already been adjusted to the correct position by another mechanical adjustment not shown, and the adjustment of the X-ray tube in the vertical direction is such that the X-rays pass through the collimators 25 and 27 and the X-ray detector. Note that it is assumed that the light has been adjusted so that it is incident on. Here, if the distance between the detector 7 and the mounting table 15 is adjusted so as to deviate from the design value (FDD-FCD), correct adjustment can be performed by changing the calculation formula of the above embodiment as follows. is there. Δy
Is calculated by the following formula.

[Equation 6] Here, the values obtained in the above embodiment are used as Δx ₁ and Δx ₂ . A value of about N / 4 is used for k. θ (i) is the installation angle of the i channel, that is, i channel − with reference to FIG.
Point O-means the angle formed by the center channel and is a design value. When the X-ray tube is adjusted by Δy in the y direction and Δx obtained in the above embodiment in the x direction, the focal position is adjusted to the front of the center channel in the x direction and to the position of the distance FDD from the detector in the y direction. . At this time, the focus is adjusted to a correct position relative to the X-ray detector 7, but the detector 7
And the mounting table 15 are still displaced. That is, the distance between the focal point O and the mounting table 15 is a value FCD ′ deviated from the FCD. FCD 'can be calculated by the following formula.

[Equation 7] Here, the value calculated by the above equation is used as Δy. By inputting the FCD ′ obtained here to the reconstruction unit and using it as a reconstruction parameter, the cross-sectional image can be accurately reconstructed. Alternatively, Δy _c is calculated by the formula Δy _c = FCD′−FCD, and the mounting table 15 is moved and adjusted by Δy _{c in the} y direction together with the rotation mechanism portion 17 and the movement mechanism portion 19, or alternatively, the X-ray tube 5 and the X-ray detection are performed. -7 in the y direction
Move and adjust by y _c .

[0031]

As described above, according to the present invention, the subject is moved with respect to the fan beam radiated from the X-ray source in order to obtain a sectional image on the stage on which the subject is placed. The reference object is arranged at a constant interval in the direction perpendicular to the moving direction, and the moving distance when the mounting table is moved in the moving direction and the X-ray detector for each reference object with respect to the moving distance. Since the focus position adjustment amount of the X-ray source with respect to the X-ray detector is calculated based on the output, anyone can easily perform highly accurate focus position adjustment of the X-ray source in a short time. .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining an adjusting operation of the embodiment.

FIG. 3 is a diagram showing a configuration of a reference object for adjustment operation in the embodiment.

FIG. 4 is a diagram for explaining a process of an adjusting operation in the embodiment.

FIG. 5 is a diagram showing another configuration example of a reference subject.

FIG. 6 is a diagram for explaining another example of the adjusting operation.

[Explanation of symbols]

 5 X-ray tube 7 X-ray detector 9 Fan beam 11 Subject 13 Traverse mechanism 15 Mounting table 21 Data collection unit 23 Reconstruction unit 29 X-ray source position adjustment knob 35 Central control unit 39 Adjustment amount calculation unit 41 Interface 43 CPU 45 memory 47 display 49a, 49b pin phantom

Claims (1)

[Claims] 1. A CT scanner for obtaining a cross-sectional image by moving a subject so as to cross a fan beam emitted from an X-ray source toward an X-ray detector, on a mounting table on which the subject is mounted. A reference object arranged at a constant interval in the direction perpendicular to the moving direction, a moving distance when the mounting table on which the reference object is arranged is moved in the moving direction, and each reference for the moving distance. Based on the output of the X-ray detector for the subject, X
An adjusting device for a CT scanner, comprising: an adjusting amount calculating means for obtaining an adjusting amount of a focus position of an X-ray detector of a radiation source.