JP2003139724A - Ct unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce spreading of radiation beams caused by a definite size of a radiation source, and to provide a CT image of high spatial resolution and good quality with reduced fogging. SOLUTION: A post collimator 4 having through-holes for passing the radiation beams corresponding to respective detectors 5 in a radiation source 2 side of the plurality of detectors 5 is arranged, and an intermediate collimator 7 having through-holes for limiting the radiation beams in positions shifts from the center of the radiation source 2 in the radiation beams, and for passing the beams in the central part is arranged between the post collimator 4 and the radiation source 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a CT apparatus,
In particular, the present invention relates to a CT apparatus provided with a post collimator which is arranged on the radiation source side of a plurality of detectors and has a through hole so as to guide a radiation beam to each detector.

[0002]

2. Description of the Related Art Generally, a CT apparatus is constructed so that a radiation source irradiates an object and the radiation transmitted through the object is detected by a plurality of detectors. In addition to the radiation that passes through the sample and enters the detector, scattered rays from various directions enter. In order to obtain a good tomographic image based on the radiation incident on the detector, it is necessary to prevent such scattered rays from entering the detector as much as possible. In the conventional CT apparatus, the detector side near the radiation source is required. One collimator, also called a precollimator or a postcollimator, is provided on the radiation side near the detector. These collimators are usually made of heavy metals such as lead and tungsten, which have high radiation shielding ability, and the post-collimator is installed immediately before the detector to prevent radiation scattered by the subject from entering the detector. In addition, the pre-collimator limits the radiation generated radially from the radiation source to a desired range including the subject. This pre-collimator can reduce the leakage radiation to the outside of the CT apparatus, and the shape of the guide hole of the pre-collimator is changed according to the shape of the radiation beam to be formed. When it is desired to obtain a fan-shaped beam, a conical guide hole is formed as a parallel plate guide hole that allows passage only in a desired angular range.

[0003]

However, in the conventional CT apparatus, an X-ray tube or a linear accelerator is generally used as a radiation source, and the X-ray tube accelerates an electron beam at a high voltage and serves as an anode target. X-rays are generated by colliding with an electron beam, and are used as a radiation source with a relatively low energy of several hundred keV. A linear accelerator accelerates electrons by a high-frequency electric field and collides with a target to generate X-rays. However, these radiation sources use X-rays generated by the bremsstrahlung of electrons that collide with the target, but the incident electrons interact with the electric field created by the target nuclei and undergo multiple scattering, which causes Since the radiation source spreads over a certain angular range, the radiation source does not become an ideal point light source and has a certain spread. Therefore, no matter how small the cross-sectional area of the post-collimator through-hole is, radiation from a certain solid angle, which corresponds to the spread of the light source, is incident on the detector, which contributes to a reduction in spatial resolution. Usually, this spread is on the order of 0.1 to 1 mm in diameter, but when spatial resolution on the order of more than this is required, it is necessary to reduce this solid angle.

Now, focusing on only the radiation beam incident on a certain detector among the radiation radially emitted from the radiation source, when the radiation source has a spread, for example, only r from the center of the radiation source. A part of the radiation beam from the distant position is blocked by the end face of the post collimator, but the remaining part is incident on the detector through the through hole. Assuming that the distances from the detector to the radiation source and from the detector to the subject are t and αt (α ≦ 1), this radiation beam passes through a place near the subject and deviated from the central axis by αr. When the radius of the radiation source is about ro, blurring of about αro occurs, so that the closer the subject position is to the radiation source, the larger the blurring becomes. On the other hand, since the radiation beam is emitted radially from the radiation source, the pitch of the radiation beam becomes smaller as it gets closer to the radiation source, which is advantageous for improving the spatial resolution. On the contrary, the spatial resolution decreases. For example, if the detector pitch is 1 mm and ro is 0.5 mm,
When α is set to 2/3, the beam pitch in the vicinity of the subject becomes 0.33 mm and the blur becomes 0.33 mm, and even if the subject is brought closer to the radiation source, the blur becomes larger, which is meaningless. In recent years, the demand for spatial resolution of 0.1 mm level has been increasing in the field of industrial high-energy X-ray CT apparatus, and the conventional C that is greatly affected by the spread of the radiation source.
This is difficult to achieve with a T-apparatus.

An object of the present invention is to reduce the spread of the radiation beam due to the radiation source having a finite size, and to provide a CT apparatus capable of obtaining a high-quality tomographic image of high spatial resolution with less blurring. To provide.

[0006]

In order to achieve the above object, the present invention provides a radiation source for irradiating a subject with radiation, and a post-collimator having a plurality of through holes for allowing the radiation transmitted through the subject to pass therethrough. , Using a plurality of detectors arranged to face the through holes of the post collimator and juxtaposed to detect the radiation beams passing through the through holes, and the signals obtained from the detectors. In a CT apparatus provided with a tomographic image reconstruction means for reconstructing a tomographic image for one transverse section of the subject, between the radiation source and the post collimator, the radiation beams of the radiation beams respectively corresponding to the plurality of detectors are provided. It is characterized in that at least one intermediate collimator for limiting the cross-sectional area is provided.

In the CT apparatus according to the present invention, since an intermediate collimator for limiting the cross-sectional area of each radiation beam corresponding to each of a plurality of detectors is installed between the post collimator and the radiation source, it has been deviated from the center of the radiation source so far. The radiation beam that was incident on the detector is mostly shielded by the intermediate collimator and the useless spread is limited, so that only the radiation beam emitted from near the center is incident on the detector. When a tomographic image reconstructing means reconstructs a tomographic image for one cross-section of the subject based on the beam, a high-quality tomographic image with high spatial resolution and less blurring can be obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a plan view and a front view of a CT apparatus according to an embodiment of the present invention.
The CT device includes a radiation source 2 that irradiates the subject 1 with radiation.
A pre-collimator 3 provided on the irradiation side of the radiation source 2 for shaping the radiation into a desired beam shape; a post-collimator 4 having a plurality of through holes for passing the radiation transmitted through the subject 1; A plurality of detectors 5 arranged to face each through hole of the collimator 4 to detect the radiation beam passing through each through hole, and a slice for reconstructing a tomographic image by using each signal of each detector 5 The image reconstructing means 6 is provided. Between the radiation source 2 and the post collimator 4, an intermediate collimator 7 having a plurality of through holes that allow only a necessary part of the radiation beam incident on the post collimator 4 to pass therethrough is installed. This intermediate collimator 7 is installed at the radiation source 2 and the post collimator 4
However, as will be described later, the radiation source 2 is more preferable than the first sample stage 9 on which the subject 1 is placed.
It is desirable to be on the side.

The radiation source 2 is, for example, an electron linear accelerator or X
The radiation source control device 8 controls the emission and stoppage of radiation using a line tube. When an electron linear accelerator is used as the radiation source 2, generally, the electron linear accelerator can generate higher-energy radiation, so that a large subject can be imaged, and when an X-ray tube is used,
Although the size of the subject that can be imaged is reduced, the size and cost of the device can be reduced.

Radiation emitted radially from the radiation source 2 is shaped into a desired beam shape by a precollimator 3 which is usually made of a heavy metal such as tungsten or lead. Usually, the pre-collimator 3 is shaped into a thin fan-shaped beam that falls within a predetermined angle range so that it hits only the intermediate collimator 7 and the post-collimator 4, so that the leakage radiation to the outside of the CT apparatus is reduced. Most of the radiation that hits the wall surfaces other than the through-holes of the intermediate collimator 7 and the post-collimator 4 is absorbed by the collimator itself, the leaked radiation is significantly reduced, and the scattered radiation entering each detector 5 is also reduced. Decrease.

Each detector 5 uses a combination of a scintillator and a photodiode, a semiconductor detector or the like, and is arranged side by side in an array so as to detect fan-shaped radiation. The smaller the juxtaposed interval of the detectors 5 and the more the detectors 5 are arranged, the finer the sampling pitch and the higher the spatial resolution of the tomographic image. Therefore, the semiconductor detectors are smaller in size and can be densely arranged. As the semiconductor, Si, GaAs, CdTe, HgI2 or the like is used.

A first sample table 9 for fixing the subject 1 is arranged between the intermediate collimator 7 and the post collimator 4, and a second sample table 10 is arranged between the precollimator 3 and the intermediate collimator 7. When the subject 1 is imaged, the first sample table 9 and the second sample table 10 are selectively used according to the size and the required spatial resolution. Since the radiation beam spreads radially, the first sample table 9 has a wider imaging range than the second sample table 10, but the sampling pitch becomes coarser.
On the contrary, when the second sample table 10 is used, the imaging pitch becomes narrower but the sampling pitch becomes finer. The subject 1 is firmly fixed on the first sample table 9 or the second sample table 10 so as not to move during imaging.

The first sample table 9 and the second sample table 10 are provided with vertical moving devices 13 and 14 and horizontal moving devices 15 and 16, respectively, and these vertical moving devices 13 and 14 and horizontal moving devices, respectively. Device 15,
Since it is possible to move to any position by 16,
This CT device can image a cross section of the subject 1 at an arbitrary height. The vertical movement devices 13 and 14, the horizontal movement devices 15 and 16, the first sample table 9 and the second sample table 10 are respectively the movement and rotation control device 1
It is controlled by signals sent from 7, 18. However, it is not always necessary to have a plurality of sample tables, and only one of the first sample table 9 and the second sample table 10 may be provided. Both sample tables 9, 1
Instead of moving 0 up and down, both sample tables 9, 10
The radiation source 2, the pre-collimator 3, the post-collimator 4, and the intermediate collimator 7 may be moved up and down in a fixed state, as long as they are relatively movable. In this case, the radiation source 2, the pre-collimator 3, the post-collimator 4, and the intermediate collimator 7 need to keep the relative position among them always constant.

CT devices include those called the first generation method, the second generation method, the third generation method, and the fourth generation method from the historical background of development. In the present embodiment, the second generation method and the third generation method are used. Use the method. In the case of shooting with the second generation method,
The first sample table 9 or the second sample table 10 on which the subject 1 is placed translates from the outer side of the fan-shaped beam to the outer side of the opposite side, rotates by a predetermined angle and then translates again in the opposite direction, and this is repeated. While collecting measurement data. In the case of the third generation method, the subject 1 is always included in the fan beam, and the measurement data is collected by rotating the first sample table 9 or the second sample table 10.

The post-collimator 4 is formed with through-holes through which the radiation beam passes as many as the detectors 5 located behind it. All the through holes are linearly cut at an angle such that the center of the radiation source 2 is seen. The cross-sectional shape of the through hole is usually circular or rectangular, but other shapes may be used. The cross-sectional area of the through hole of the post collimator 4 is determined according to the light receiving area of each detector 5 installed behind the post collimator 4, and is set smaller than the light receiving area of each detector 5. On the other hand, the intermediate collimator 7 arranged closer to the radiation source 2 than the post collimator 4 is formed with a plurality of through holes corresponding to the radiation beams reaching the respective detectors 5, and each of the through holes looks into the center of the radiation source 2. It is cut straight at an angle like this. Since the width of the radiation beam becomes narrower as it gets closer to the radiation source 2, it is desirable to make the cross-sectional area of the through hole of the intermediate collimator 7 smaller than the cross-sectional area of the through hole of the post collimator 4, and at least that of the through hole of the post collimator 4. The cross-sectional area is below.

Like the post collimator 4, the through holes of the intermediate collimator 7 are linearly cut so as to look into the center of the radiation source 2, and when it is attempted to form the same number of through holes as the post collimator 4, it goes without saying. Intermediate collimator 7
The pitch of the through holes is smaller than the pitch of the post collimator 4. The thickness of the wall between the through holes is determined by the pitch and the cross-sectional area, but if the wall between the through holes becomes too thin, the radiation scattered on the wall surface of the through hole will penetrate the wall and enter the adjacent through hole, causing blurring. Therefore, it is necessary to secure a certain thickness of the wall between the through holes. For example, when the cross-sectional areas of the through holes of the post collimator 4 and the intermediate collimator 7 are the same, the number of through holes of the intermediate collimator 7 is set to half the number of through holes of the post collimator 4, and the wall thickness between the through holes is secured.

Further, the post collimator 4 and the intermediate collimator 7 are respectively moved in the vertical direction moving device 1 as shown in FIG.
9 and 20, each of which has a plurality of through holes having different cross-sectional areas in the vertical direction. Therefore, by controlling the position switching means shown by the vertical movement devices 19 and 20, it is possible to select the cross-sectional area of each through hole through which each radiation beam passes, and to achieve the required spatial resolution. Accordingly, the cross-sectional areas of the through holes of the post-collimator 4 and the intermediate collimator 7 can be variously combined and photographed.

When the intermediate collimator 7 is added between the radiation source 2 and the post collimator 4, it is necessary to accurately match the center lines of the through holes of the post collimator 4 and the intermediate collimator 7. For this reason, as shown in FIG. 1, position adjusting through holes 31 and 32 are formed at both ends of the post collimator 4 and the intermediate collimator 7 in the direction of fan radiation spreading and outside the fan radiation, respectively. A laser irradiation device 33 such as HeNe is arranged behind.

A laser beam 34 is emitted from the rear of the adjusting through hole 31 using a laser irradiating device 33, and passes through the position adjusting through hole 31 of the post collimator 4 and then the position adjusting through hole 32 of the intermediate collimator 7. At the same time, the post-collimator 4 and the intermediate collimator 7 are arranged so that the passed laser beam 34 strikes the center of the radiation source 2.
Is adjusted by the vertical movement devices 19, 20 or the mounting position for the vertical movement devices 19, 20 is adjusted. This adjustment is performed on both sides of the post collimator 4 and the intermediate collimator 7 so that the laser beam 34 will hit the center position of the same radiation source 2 no matter which one is irradiated with the laser beam 34. In this way, the center lines of the through holes of the post collimator 4 and the intermediate collimator 7 can be accurately matched.

FIG. 3 comprises only a post collimator 4,
FIG. 6 is a cross-sectional view of the main parts of the CT apparatus when there is no intermediate collimator 7. Here, only the radiation beam incident on one detector 5a is shown, and the cross-sectional shape of the post collimator 4 is square. Since the post-collimator 4 has a square cross-sectional shape, the radiation beam 22 obliquely incident has a rectangular cross-sectional shape. However, when the distance d between the post-collimator 4 and the radiation source 2 is sufficiently larger than the height 2a of the through hole, the beam cross-sectional shape can be regarded as a square. The radiation beam 21 emitted from the center of the radiation source 2 is not shielded by the end face 24 of the post collimator 4 at all, and all enters the detector 5a. However, the radiation beam 22 from the off-center position depends on the distance r from the center and the angle θ about the central axis shown in FIG.
Is partially shielded by the end face 24 of the, and is completely shielded by the end face 24 when r becomes large to some extent.

FIG. 4 is a through hole 4a of the post collimator 4.
Is a perspective view showing the geometrical relationship between the radiation beam cross section and
The surface 24 is seen from the radiation source 2 side. Through hole 4a
The length of one side is 2L1, the length of one side of the cross section of the radiation beam incident on the detector 5a on the surface 24 is 2L2, and the distance between the centers thereof is δ. That is, a large square having a side 2L1 of FIG.
A small square L2 indicates a cross section on the surface 24 of the radiation beam incident on the detector 5a. An amount obtained by integrating the area A1 ′ obtained by projecting the overlapping portion 25 of the two squares on the detector light receiving surface 26 with respect to r and θ corresponds to the intensity of the incident beam on the detector 5a. Therefore, the incident beam intensity
I is given by the formula shown in step S1 of FIG. Here, I0 is a constant and A1 (r, θ) is the area of the overlapping portion 25 on the surface 24, which is given by the formula shown in step S2 of FIG.

On the other hand, FIG. 5 is a cross-sectional view of a main part of the CT apparatus shown in FIG. 1, showing a radiation beam incident on a certain detector 5a. The through holes of the post collimator 4 and the intermediate collimator 7 each have a square cross-sectional shape. When r is very small, the radiation beam is shielded not in the surface 27 but in the through hole of the intermediate collimator 7, but it is negligible. Therefore, here, the radiation beam is shielded only at the end surface 27 of the intermediate collimator 7. By installing the intermediate collimator 7 between the post-collimator 4 and the radiation source 2, an off-center beam such as the radiation beam 28 hits the detector 5a in the related art, but is almost shielded by the intermediate collimator 7. Therefore, only the radiation beam 29 emitted from the vicinity of the center is incident on the detector 5a. Therefore, the radiation beam 2 incident on the detector 5a
When the tomographic image reconstructing means reconstructs the tomographic image for one cross section of the subject based on 9, a clear image with less blurring can be obtained.

The distance d between the intermediate collimator 7 and the radiation source 2
When 2 is sufficiently larger than the height 2a2 of the through hole, the beam cross-sectional shape can be regarded as a square. As in the conventional case, when the area A2 ′ obtained by projecting the overlapping portion of the through hole of the intermediate collimator 7 and the beam cross section on the detector light receiving surface 30 is obtained, FIG.
It is represented by the formula of step S3 shown in FIG. s1 and s2 are given by equations 38 and 39 in step S2 of FIG. However, d, L1, and L2 in this case are given by the formula of step S4. d1 is the distance from the radiation source 2 to the post collimator 4, d2 is the distance from the radiation source 2 to the intermediate collimator 7, and 2a1 and 2a2 are the heights of the through holes of the post collimator 4 and the intermediate collimator 7, respectively.

Here, equation 4 in step S1 shown in FIG. 8 is used.
0 and the equation 41 of step S3 shown in FIG. 9 are used to compare the amount of the radiation beam entering the detector 5a between the conventional CT apparatus shown in FIG. 3 and the CT apparatus shown in FIG. Figure 6
Is a plot of A1 ′ and A2 ′ with respect to r when θ = 0 °. As can be seen from the figure, in the CT apparatus shown in FIG. 5, the radiation beam emitted from the position where r is large is almost blocked by the intermediate collimator 7, and only the radiation beam emitted from the vicinity of the center is incident on the detector 5a. As a result, even if the radiation source 2 has a finite size, FIG.
If the CT apparatus shown in FIG. 2 is used, it is possible to obtain a clear sectional image with less blurring by using only the beam from the vicinity of the center of the radiation source 2.

FIG. 7 shows a C according to another embodiment of the present invention.
It is a top view which shows T device. The same parts as those of the previous embodiment are designated by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described. An intermediate second collimator 35 is added between the intermediate collimator 7 and the radiation source 2, and a third sample table 36 is provided between the intermediate second collimator 35 and the precollimator 3. As will be understood from this description, at least one intermediate collimator may be provided between the post collimator 4 and the radiation source 2 or between the post collimator 4 and the precollimator 3. This intermediate second collimator 35
Also in the above, through holes are formed so as to satisfy the relationship between the post collimator 4 and the intermediate collimator 7 described above, and the intermediate second collimator 35 is provided at both ends in the spreading direction of the fan-shaped radiation beer. A position adjusting through hole 37 for adjusting the position by the laser irradiation device 33 is formed.

Like the first and second sample tables 9 and 10, the third sample table 36 is also provided with a vertical moving device and a horizontal moving device, respectively. Since this CT device can be moved to any position,
It is possible to take a cross-section at any height. Further, the third sample table 36 and its vertical movement device and horizontal movement device are also controlled by signals sent from the movement rotation control device 42. Both sample tables 9, 1
Instead of vertically moving 0 and 36, the radiation source 2, the pre-collimator 3, the post collimator 4, and the intermediate collimators 7 and 35 may be vertically moved while the sample tables 9 and 10 are fixed. It should be movable.

When the intermediate second collimator 35 is installed, a laser beam 34 is emitted from a laser irradiation device 33 arranged behind the adjusting through hole 31, and the position adjusting through hole 31 of the post collimator 4 and then the intermediate collimator 7 are provided. Of the post-collimator 4 and the intermediate collimators 7, 3 so that the laser beam 34 passing through the position-adjusting through hole 32 and the position adjusting through-hole 37 of the second intermediate collimator 35 hits the center of the radiation source 2.
The position of 5 is adjusted by the vertical movement device or the mounting position with respect to the vertical movement device is adjusted. This adjustment is performed on both sides of the post collimator 4 and the intermediate collimator 7 so that the laser beam 34 will hit the center position of the same radiation source 2 no matter which one is irradiated with the laser beam 34. Thus, even if the intermediate second collimator 35 is added, the post collimator 4 and the intermediate collimators 7, 35
It is possible to accurately and easily match the center lines of the respective through holes.

Also in this embodiment, as in the previous embodiment, the radiation beam emitted from the position away from the center of the radiation source 2 can be almost blocked by the intermediate collimators 7 and 35, and the radiation emitted from the vicinity of the center. Only the beam will be incident on the detector. Therefore, the radiation source 2
Even if has a finite size, it is possible to obtain a clear sectional image with less blurring by using only the beam from the vicinity of the center of the radiation source 2.

In each of the above-described embodiments, at least one intermediate collimator is provided between the pre-collimator 3 and the post-collimator 4, and a through-hole having a size smaller than the through-hole of the post-collimator 4 is formed in this intermediate collimator. Then, only the beam from the vicinity of the center of the radiation source 2 is used. The closer the intermediate collimator is to the radiation source 2, the more effective it is, but the through hole becomes finer and the processing becomes difficult. . Therefore, a means for limiting the radiation from the radiation source 2 which is displaced in the vertical direction is added to the pre-collimator 3 or its immediate vicinity, and in the intermediate collimator provided between the pre-collimator 3 and the post-collimator 4, each detector is provided with The horizontal direction of each incoming radiation beam,
That is, the same effect can be obtained by limiting the displacement of the detectors in the juxtaposition direction.

[0030]

As described above, according to the CT apparatus of the present invention, a clear sectional image with less blurring can be obtained by using only the radiation beam from the vicinity of the center of the radiation source with a relatively simple structure. be able to.

[Brief description of drawings]

FIG. 1 is a plan view of a CT device according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional front view of the CT apparatus shown in FIG.

FIG. 3 is an enlarged cross-sectional view showing a main part of a conventional CT device.

FIG. 4 is a perspective view showing a geometrical relationship between a through hole of a collimator and a cross section of a radiation beam.

5 is an enlarged cross-sectional view showing a main part of the CT apparatus shown in FIG.

6 is a characteristic diagram showing the relationship between the incident radiation intensity and the radiation source position of the CT apparatus shown in FIG.

FIG. 7 is a plan view of a CT device according to another embodiment of the present invention.

FIG. 8 is a flowchart for obtaining a radiation beam amount in a conventional CT device.

9 is a flowchart for obtaining a radiation beam amount in the CT apparatus shown in FIG.

[Explanation of symbols]

1 subject 2 Radiation source 3 Pre-collimator 4 post collimator 5 detectors 6 tomographic image reconstruction means 7 Intermediate collimator 9 First sample table 10 Second sample table 21,22 radiation beam 33 Laser irradiation device 34 laser beam 35 Intermediate Second Collimator 37 Position adjustment through hole

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G001 AA01 AA07 BA11 CA01 DA01                       DA08 JA07 PA11 PA14 QA01                       SA02 SA10 SA30                 2G088 EE02 FF02 JJ15

Claims (9)

[Claims] 1. A radiation source for irradiating a subject with radiation,
A post collimator having a plurality of through holes that allow the radiation that has passed through the subject to pass through, and juxtaposed so as to detect the radiation beams that have respectively passed through the through holes and are arranged to face the through holes of the post collimator. A CT apparatus comprising a plurality of detectors, and a tomographic image reconstructing means for reconstructing a tomographic image for one cross section of the subject using each signal obtained from each of the detectors. At least one intermediate collimator for limiting the cross-sectional area of each radiation beam corresponding to each of the plurality of detectors is provided between the post collimators. 2. The one according to claim 1, wherein the intermediate collimator has a plurality of through holes that define at least the apposition direction of each of the radiation beams corresponding to each of the plurality of detectors. Characteristic CT device. 3. The CT apparatus according to claim 1, wherein the intermediate collimator is arranged closer to the radiation source than the subject. 4. The precollimator according to claim 1, wherein the precollimator is disposed on the radiation source side and passes radiation only in a desired range including the subject, and the intermediate collimator is the precollimator and the post. A CT device characterized by being provided between collimators. 5. The moving means according to claim 1, further comprising a moving means capable of moving the radiation source, the post collimator and the intermediate collimator in a vertical direction while keeping their relative positions constant. Characteristic CT device. 6. The cross-sectional area perpendicular to the axial direction of the through hole of the intermediate collimator according to claim 1, wherein the cross-sectional area perpendicular to the axial direction of the through hole of the post collimator is equal to or less than the cross-sectional area of the through hole of the post collimator. CT device. 7. The post collimator and the intermediate collimator according to claim 1, wherein the post collimator and the intermediate collimator each have a plurality of sets of the through-holes having different cross-sectional areas in a moving direction thereof, and switch for switching a position in each moving direction. A CT apparatus having means. 8. The device according to claim 1, wherein position adjusting through holes are formed at both ends of the post collimator and the intermediate collimator, respectively, and both of the post collimator and the intermediate collimator are provided behind the post collimator. A CT device comprising a laser irradiation device for irradiating a laser beam passing through a position adjusting through hole toward the radiation source. 9. The intermediate collimator according to claim 1, wherein the intermediate collimator is arranged at a position where the radiation beam deviating from the center of the radiation source is shielded before hitting a wall surface near the through hole of the post collimator. Characteristic C
T device.