JP2000107162A - Tomograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a ring-shaped artifact in an X-ray imager such as a third generation computerized tomograph, permit correct tomography, modify a data transmission system and permit fast scanning. SOLUTION: The tomograph 10 comprises a radiation source 3 that rotates around a subject and irradiates radiation to the subject 2, ring-shaped detection element rows 50 where a plurality of detection elements 5 that detect radiation from the radiation source 3 are arranged in series on the circumference surrounding the subject 2, and a detector cylinder 11 where a plurality of the detection element rows 50 are arranged in the direction of the rotating axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation imaging apparatus for imaging a radiation characteristic distribution in a subject using general radiation such as an X-ray CT apparatus for taking an image using radiation such as X-rays. Related to the device.

[0002]

2. Description of the Related Art Conventionally, X-rays are emitted to a subject, and X-rays transmitted through or scattered by the subject are detected by an X-ray detector. An X-ray CT apparatus that captures a fluoroscopic image, a tomographic image, or a three-dimensional image of a subject based on the number of photons) is known.

As such an X-ray CT apparatus, a cone beam CT apparatus has been developed. In a normal X-ray CT device,
The X-ray beam is thinly cut out in the Z direction and is called a fan beam, but the cone beam CT uses an X-ray beam that also spreads in the Z direction, and this X-ray beam is called a cone beam.

[0004] As the cone beam CT,
At present, in a conventional CT (that is, a row having only one row), a so-called third generation type or R / R
Only forms corresponding to the type called type are considered. The third generation CT scans (collects projection data) a pair of an X-ray source and a detector while rotating around the subject.

FIG. 16 shows an example of a cone beam CT apparatus. Cone beam CT device 1 shown in FIG.
Also belongs to the third-generation type CT apparatus, in which the detector 4 rotates together with the X-ray source 3 around the subject 2 around the Z axis as a rotation axis, and the scan of the region of interest is completed in one rotation. It is.

In an ordinary X-ray CT apparatus, detection elements are arranged in one line in the ch direction for sampling in the ch direction, and each element is identified by a channel number (ch). On the other hand, in the cone beam CT apparatus 1,
As shown in the drawing, the detection elements 5 are further arranged in the Z direction (row direction). That is, cone beam CT
The detector 4 in the device 1 is configured such that the detection elements 5 are two-dimensionally arranged in an orthogonal lattice.

According to such a cone beam CT apparatus 1, the detecting element 5 is moved in two directions of the z direction (row direction) and the ch direction.
The detector 4 is arranged in a grid in the direction
By irradiating the radiation with a thickness in the z direction and in a cone shape, projection data for a plurality of rows can be collectively obtained.

[0008]

However, the above-mentioned third method
In the cone beam CT apparatus 1 belonging to the generation X-ray CT apparatus, there is a problem that a so-called ring-shaped artifact occurs. This ring-shaped artifact refers to a characteristic variation of each channel in a detector and a system for electrically processing data of the detector such as A / D conversion (hereinafter, referred to as a “DAS (Data Acquisition System)”). It forms concentric artifacts on the image and hinders accurate diagnosis.

This ring-shaped artifact is an important problem peculiar to the third generation type CT apparatus, and can occur not only in a cone beam CT apparatus but also in a conventional CT apparatus. Great care must be taken in designing and manufacturing detectors and DASs.

By the way, in the cone beam CT,
Since the number of rows goes up to several hundreds, the number of elements of the detector has been about 1000 at most in the conventional CT.
00 times. Therefore, in the cone beam CT, it is practically difficult to manage the characteristics of such a large number of circuits and detector elements to a satisfactory level in terms of ring artifacts.

Here, as a signal reading method of the detector in the conventional CT apparatus, in order to achieve dense mounting,
For example, see “Amorphous Semiconductors Usher In Digit
al X-ray Imaging, Rowlands et.al., November 1997
Physics Today, pp 24-30 "is generally assumed.

This method is to read out electric charges stored in a minute capacitance (capacitance) formed in a semiconductor circuit by a TFT matrix array, and is a technique originally developed for liquid crystal display, and suppresses ring artifacts. Does not have the necessary stability and linearity. Therefore, if the apparatus is of such a degree that it is sufficient to distinguish between human bone and soft tissue, there is no problem even if there is a little ring artifact, but it is a general method to observe the contrast difference between soft tissues. When CT applications are required, use may be difficult.

Further, in a third-generation CT apparatus, data collected from a detector and a DAS in a rotating unit to a fixed unit (such as a unit for performing image reconstruction calculation) must be transmitted. In this transmission, transmission of data from several hundred thousand elements requires a very wide transmission path.

However, when a scan as fast as CT or higher is required, a transmission bandwidth of about 1 GB / sec may be required. This requires a large number of broadband coaxial cables, for example, even if they are connected by cables, and since the coaxial cables are not very flexible, the rotating part is restricted from free rotation.

In the cone beam CT, continuous rotation by a slip ring may be considered. In this case, data transmission from the rotating part to the fixed part cannot be performed by cable connection.

On the other hand, since the slip ring does not have a sufficient bandwidth, it is conceivable to drive an extremely large number of slip rings in parallel, but this is not practical because the mounting spacers and costs increase. In this regard, transmission by light has been conventionally performed in CT, but the positional relationship between the light source and the light receiving unit is not constant, so that an infinite number of light propagation paths are generated, and the light beam is transmitted due to a propagation phase difference. There is a possibility that the bandwidth cannot secure a sufficient value.

Accordingly, the rotating part is restricted in this state, and only low-speed scanning can be performed. A problem is expected that the compensation is required for both the spatial resolution in the body axis direction and the size of the visual field in the body axis direction by sampling in the body axis (Z) direction.

Accordingly, the present invention has been made in view of the above-mentioned problems, and eliminates ring-like artifacts in a radiation imaging apparatus such as a third-generation CT apparatus, thereby enabling more accurate radiation imaging. It is an object of the present invention to provide a radiation imaging apparatus capable of improving a data transmission method and performing higher-speed scanning.

[0019]

In order to achieve the above object, a radiation imaging apparatus according to the present invention comprises: a radiation source which rotates around a subject and radiates the subject with radiation; A large number of detection elements for detecting radiation from the radiation source are arranged in series on a circumference around the subject, and a plurality of detection elements are arranged in the rotation axis direction. And detectors arranged in rows.

According to the present invention, a detector is constructed by arranging a plurality of annular detection element rows, and during scanning, the detector does not rotate and only the radiation source rotates. To perform cone beam exposure. Therefore, the cone beam irradiated in the present invention moves sequentially on the detection elements arranged in a grid.

Thus, according to the present invention, even if there are slight variations in the characteristics of a large number of detection elements, the occurrence of ring artifacts can be prevented by performing mutual correction.

In the invention according to claims 4 to 10, the "ch direction" refers to the fourth generation type C in which the detector forms an annular shape.
In the case of the T apparatus, the direction is the circumferential direction around the center of rotation of the radiation source, and in the case of the third generation CT apparatus in which the detector forms an arc, the direction of the circumference around the radiation source is Third generation type C in which the detector is in the circumferential direction and the detector is a flat type
In the case of the T device, the direction is the tangential direction of the circumference around the radiation source.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, a radiation imaging apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view schematically illustrating the entire configuration of the radiation imaging apparatus 10 according to the present embodiment.

In FIG. 1, a radiation imaging apparatus 10 is a so-called fourth-generation type CT apparatus.
While rotating around the subject 2 in the plane, the subject 2
And an annular detector cylinder 11 formed by arranging a large number of detection elements 5 for detecting radiation from the radiation source 3 in a grid pattern. The detector cylinder 11 does not rotate, and only the radiation source 3 rotates around the subject 2.

In the radiation imaging apparatus 10, a cone beam is used as the X-ray beam emitted from the radiation source 3. That is, in the present embodiment, the X-rays make a fan-shaped fan beam having a spread in the xy plane also have a spread in the z direction, and have a conical or pyramid shape as a whole.

The detecting element 5 accumulates the X-ray beam from the radiation source 3 as electric charge and outputs the electric charge to a data processing means or the like as an electric signal. It has a layer for performing charge conversion, and has a TFT matrix array thereunder.

In the present embodiment, the detection elements 5 are arranged in series along the ch direction on a circumference centered on the rotation center (Z axis) of the radiation source 3 to form an annular detection element row 50. (Parts indicated by oblique lines in the figure), and a plurality of detection element rows 50 are arranged in the rotation axis direction (z-axis direction or row direction). Thus, the detection elements 5 are arranged in a lattice as a whole.

Then, such a large number of detection elements 5,
As the readout circuit and X-ray / electric signal conversion,
For example, “Amorphous Semiconductors Usher In Digital
X-ray Imaging, Rowlands et.al., November 1997 Phy
It is preferable to employ a technology related to a so-called flat detector (two-dimensional radiation detector) such as sics Today, pp 24-30 ”.

In fact, a two-dimensional radiation detector of this kind is known as X
It is currently being put to practical use as a replacement for an image intensifier or a film in a line device. Although there are various types of such detectors, most of them can be manufactured in a cylindrical shape. However, if it is difficult to integrally manufacture a complete cylinder, it is also possible to manufacture a plurality of one-half or one-fourth rounds.

Of course, this is not the case, as in the case of a conventional CT, a large number of scintillators and photodiodes are densely mounted, and a preamplifier and an integrating circuit are arranged for each detection element 5 as in the conventional technique. Good.

The radiation imaging apparatus 10 according to the present embodiment employs a cone beam system in a so-called fourth-generation CT apparatus. Therefore, the cone beams to be exposed are arranged in a grid. It moves sequentially over a large number of detected elements 5. As a result, even if there is slight variation in the characteristics of the detection elements, ring-shaped artifacts do not occur. 4th generation type C
The reason that ring-shaped artifacts at T do not arise from the detector is that it is already known to the relevant technicians in the fan beam and will not be described in detail here,
For the same reason, ring-shaped artifacts do not occur in the cone beam due to the detector.

Further, the radiation imaging apparatus 1 according to the present embodiment
In the case of 0, the detector 11 does not rotate. Therefore, when data is transmitted from the detector 11 to the image reconstructing device or the like via the DAS or the like, all of these devices can be connected by a cable.

Moreover, in this case, there are no restrictions on mounting even if a large number of cables are used. Therefore, there is no problem in transmitting a large amount of data at a high speed. For example, the data transmission from the DAS to the image reconstructing apparatus can use a non-contact system such as light instead of a cable. Even in this case, since the detector 11 according to the present embodiment does not rotate, the positional relationship between the light source (laser) and the light receiver can be fixed, the optical path can be limited, and data can be transmitted over a wide band.

Second Embodiment Next, a second embodiment of the present invention will be described.
The radiation imaging apparatus according to the embodiment will be described. The overall configuration of the radiation imaging apparatus according to the second embodiment is the same as that of the radiation imaging apparatus 1 according to the first embodiment described above.
Same as 0. That is, as shown in FIG. 1, the radiation imaging apparatus 20 according to the present embodiment employs a cone beam system in a fourth-generation CT apparatus, and the detector cylinder 11 does not rotate and the radiation source 3 Only the detector element 5 rotates, and the detection elements 5 are arranged in an annular shape along the channel direction to form a detection element row 50, and the detection element rows 50 are arranged in a plurality of rows in the row direction.

In particular, the radiation imaging apparatus 20 according to the present embodiment includes, in addition to the configuration of the above-described first embodiment,
It is characterized by having a blade 12 as shown in FIGS. 2 (a) to 2 (c).

The blade 12 is for shielding scattered radiation, is formed of a radiation absorbing member such as tungsten or molybdenum, and has a plurality of blades on the inner peripheral surface of the detector cylinder 11 along the direction ch. Be placed.

As shown in FIG. 3, these blades 12 have a circle C1 centered on a point P1 on the rotation axis (z-axis), or points P2 to P5 and the like as vertices, and each detecting element row 50 has a bottom surface. Each of the cones C1 to C5 has a shape obtained by cutting out a part of each conical surface.

More specifically, the blade 12a provided in correspondence with the detection element row 50a located at the center of the plurality of detection element rows 50 has a rotation center of the radiation source 3, that is, a point P1 on the z-axis. It forms an annular shape obtained by cutting out the outer periphery of the circle C1.

The blades 12b to 12e located outside the blade 12a are connected to the radiation source 3
Each of the intersections P2 to P5 of a line connecting the lines 0a to 50e and a line connecting the radiation source 3 'and each of the detection element arrays 50a to 50e at the opposing position are set as vertices to detect each ring. Cones C1 to C5 having element rows 50a to 50e as bottom surfaces
Is formed in a substantially annular shape obtained by cutting out the outer peripheral portion of the conical surface.

Here, when scanning is performed by rotating the radiation source 3, as shown in FIG. 4A, the relative distance between each detection element and the radiation source 3 is long at a position immediately below the radiation source 3. , Near the distant position (viewing end) away from the position immediately below. FIG. 4B shows a cross section of the cone beam at the position immediately below, and FIG. 4C shows a cross section of the cone beam at the separation position.

That is, at the time of irradiation, the incident angle of the X-ray slightly changes depending on the position of the detection element. The length, angle, and interval of the blade 12 according to the present embodiment are set so as to allow the change in the incident angle of the X-ray. The arrangement and dimensional design of the blade 12 are performed according to the following procedure.

First, the distance FDD 'between the detecting element 5 and the radiation source 3' when observing the visual field end is obtained using the following equation according to the axial field size.

[0043]

(Equation 1) In the above equation, φ _d is the angle between a straight line from the detector to the center of the visual field and a straight line connecting the detector to the visual field end, and R
_d is the radius of the detector cylinder and R _fov is the radius of the field of view.

At this time, it is assumed that the blade 12 is made to face the radiation source 3 when the radiation source 3 is at the opposing position.

Next, using the value of FDD ', blade 1
Find the spacing and height of 2. At this time, the source 3 ′ is substantially located at the distance of FDD ′ when observing the end of the visual field, and the length W _{s of the} shadow formed by the blade 12 at that time is larger than the extension W _d of the sensitivity area of the detection element 5. If it is not too small, the detection element 5 cannot measure the X-ray that has passed through the subject 2 at the end of the visual field. Similarly, if there is no pitch P _b of the blades 12 is greater than W _s, the detection element between the blade 12 can not detect the X-rays passing through the field of view edge. Therefore, to satisfy W _s <W _d, and so as to satisfy W _s <P _b, defining a pitch P _b and the blade height h of the blades 12.

By approximation of FDD >> h, FDD ′ >> h,

(Equation 2) Defines h as the W _s is less than W _d, and align the blade 12 than the W _s at larger pitch P _b.

Note that, in this design guideline, for the detection element row at the end in the z direction, X
The lines are considerably absorbed by the blades 12. However, the decrease in the detected dose in the peripheral part does not significantly affect the overall image quality, and furthermore, if necessary, the X near the radiation source
The design of the line attenuator (wedge) can be modified to slightly increase the radiation dose in the peripheral area.

When more accurate imaging is required, the focal point of the inclination angle of the blade is set slightly before the radiation source at the opposing position in order to somewhat reduce the absorption of X-rays around the visual field. Such a design may be adopted.

According to the radiation imaging apparatus 20 having such a collimator (configured by the blade 12), the surface of the blade 12 is substantially orthogonal to the row direction,
In addition, when the radiation source 3 is located at the opposing position, it is substantially along the line connecting the radiation source 3 and the blade 12, so that the X-rays that have proceeded normally reach the detection element 5 without being blocked by the blade 12. . On the other hand, the scattered rays that are refracted in the subject 2 and travel at an irregular angle are blocked by the blade 12, so that the deterioration of the image due to the scattered rays can be prevented.

At this time, depending on the angle, the blade 1
Some X-rays are shielded by the X-rays 2, but typically, there is a slight radiation dead zone in the detector elements between the element rows, and the blade 12 viewed from the source 3.
If the shadow is positioned so that it just falls into the dead zone, radiation can be detected without waste.

In this embodiment, a large number of blades 1
2 are drawn at the same pitch in the Z-axis direction, but the ends in the Z-axis direction may be coarse and the center may be densely arranged. Also,
The blade near the center may be taller (h is larger). These deformations are useful for obtaining as large a scattered radiation removing capability as possible near the center while relaxing the design constraints by Equations 1 and 2.

(Operation of scattered radiation detecting element) In this embodiment, as shown in FIGS. 4B and 4C, X-rays are directly applied to the outermost detecting element row 50f. By eliminating them, these are scattered ray detecting element rows 5
0f is provided. This causes the outermost detection element row 50f to detect only scattered radiation, and from the outputs of the other detection element rows,
This is intended to be used for the purpose of correcting the output from the scattered ray detection element array 50f, that is, the scattered ray component.

Also in this case, it is preferable to perform collimation by providing a blade in the detection element array for detecting the scattered radiation. That is, more accurate data can be obtained by matching the conditions of the other detection element rows 50 performing collimation with the scattered radiation detection element rows.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
The radiation imaging apparatus according to the embodiment will be described. As shown in FIGS. 7A and 7B, the radiation imaging apparatus 30 according to the present embodiment is obtained by providing the above-described blade 12 in a normal fourth-generation CT apparatus.

That is, the radiation imaging apparatus 30 is a radiation source 3 that rotates around the subject 2 and radiates radiation to the subject.
An annular detector 14 having only one detection element row;
Blade 12 located on the radiation source side of the detector
And

The structure of the blade 12 is similar to that of the second embodiment. However, the shadow of the blade 12 in the present embodiment falls into the detection element (the row has only one row, and the detector element is long in the Z-axis direction).

According to such a radiation imaging apparatus 30,
Since the scattered radiation can be cut by the blade 12, deterioration of noise statistics due to the scattered radiation can be prevented. More specifically, as shown in FIG. 8, X-rays often encounter the Compton scattering process in the subject 2 and are partially absorbed by the photoelectric effect, as shown in FIG. Direct rays that are not scattered or absorbed reach detector 14 linearly. X-rays that have undergone Compton scattering can be redirected in random directions. Some X-rays undergo this Compton scattering many times. The X-ray whose path is bent in the Z-axis direction like B or C may be cut by the blade 12, although there are cases where the X-ray passes through between the blades 12 as shown in FIG.

As a modified example of the blade 12, for example, the blade can be only one at the center.

(Modification of Third Embodiment) The third embodiment described above
In the embodiment of the present invention, the usual fourth generation, ie, stationary / R
It is assumed that the rotation orbit of the radiation source 3 is inside the detector cylinder 14 of the otate type, but the present invention is not limited to this. For example, the present invention can be implemented in a fourth generation type called a Nutate / Rotate system in which the rotation trajectory of the radiation source 3 is located outside the detector.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.
The radiation imaging apparatus 40 according to the embodiment will be described. Note that the radiation imaging apparatus 4 according to the fourth embodiment
0 is the same as that of the radiation imaging apparatus 10 according to the first embodiment described above. That is, as shown in FIG. 9, the radiation imaging apparatus 40 according to the present embodiment adopts a cone beam method in the fourth generation CT apparatus.
The detector cylinder 11 does not rotate but only the radiation source 3 rotates, and the detection elements 5 are arranged in a grid.

In particular, in the radiation imaging apparatus 40, the above-described blade is formed in an arc shape, and is provided movably on the inner surface of the detector cylinder 11, and rotates about the subject 2 together with the radiation source 3. It is characterized by doing.

That is, as shown in FIG. 10A, the blade 15 in the present embodiment is not disposed over 360 degrees around the circumference of the detector cylinder 11 and is cut into an arc shape. This faces the source 3 and rotates together with the source 3.

The blade 15 is mounted on a rigid base (not shown), and the radiation source 3 is also mounted on the base. By rotating the base, the blade 15 always rotates while facing the radiation source 3.

A major advantage of such a configuration is that since the blade and the radiation source are always in a facing position relationship, there is no design restriction as described in the equations (1) and (2). In addition, the blade height can be increased as long as it does not collide with others, so that the ability to remove scattered radiation can be increased. In other words, since the surface of each blade can be along the surface connecting the lower end of the blade and the radiation source,
This is because the shadow created by the blade is only the thickness of the blade and does not increase with the position of the source.

(First Modification of Fourth Embodiment) In the above-described fourth embodiment, the fourth generation type cone beam has been described, but the present invention is not limited to this. . For example, an apparatus having a third-generation cone beam CT or a flat detector can also be used. Further, the present invention can be applied to a third-generation or fourth-generation ordinary CT apparatus that does not use a cone beam.

(Modification 2 of Fourth Embodiment) Modifications of the blade 15 described above include the following.
That is, as shown in FIG. 10B, for example, in the fourth generation cone beam method, the surface of the blade 17 is Z
It can also be parallel to the direction.

According to such a blade 17, when the cone beam is thin in the Z direction, the ability to remove scattered radiation can be improved.

(Third Modification of the Fourth Embodiment) Further, as a modification of the blade, there is one shown in FIG. 10C. The blade 18 according to this modified example is a hybrid type of the above-mentioned two examples, in which blades parallel to the ch direction and the z direction are assembled in a lattice shape, and high scattering positive removal ability can be expected.

(Fifth Embodiment) Furthermore, the fifth embodiment of the present invention
The radiation imaging apparatus 40 according to the embodiment will be described. The radiation imaging apparatus 5 according to the fifth embodiment
0 is the same as that of the radiation imaging apparatus 10 according to the first embodiment described above. That is, as shown in FIG. 11, the radiation imaging apparatus 50 according to the present embodiment employs a cone beam method in a fourth-generation CT apparatus, and the detector cylinder 11 does not rotate and the radiation source 3 Only the detector rotates, and the detection elements are arranged in a grid.

In the radiation imaging apparatus 50 according to the present embodiment, the blade described above
It is characterized by being arranged at a predetermined angle with respect to the h direction. That is, as shown in FIG.
Numeral 9 is spirally arranged on the inner peripheral surface of the detector cylinder 11 and has a shape obtained by cutting out a curved surface including the radiation source 3 and the bottom of the spiral blade 19.

Specifically, when viewed from the z-axis direction, FIG.
As shown in FIG. 2A, the blades 19 are spirally arranged so as to be sequentially stacked. Also,
When viewed from the x direction (or the y direction), as shown in FIG. 12B, the blade 19 is arranged at a predetermined angle γ with respect to the ch direction (the rotation direction of the radiation source 3). I have.

The blade 19 according to the present embodiment as described above
According to the present invention, by adjusting the size of the predetermined angle γ, the blade has an intermediate effect between a blade perpendicular to the Z direction and a blade parallel to the Z direction, that is, a ring derived from the scattered radiation removal ability and the shadow of the blade. The balance with the ability to remove artifacts can be adjusted.

This embodiment can be used not only in the fourth-generation cone beam CT but also in a radiation imaging apparatus having a third-generation cone beam CT or a flat detector.

(Sixth Embodiment) The above-described second to second embodiments will be described.
In the fifth embodiment, the blades 12, 15, 17, 1
8 and 19 have been described as being always within the radiation exposure range. However, the present invention is not limited to these, and these blades 12, 15, 17, 18,
19 can be provided movably so as to escape from the radiation exposure range.

As a structure for retracting the blade, for example, a function of moving the blade assembly in the Z-axis direction and moving the blade assembly to the outside of the cone beam may be provided.

If the blade 15 moves together with the radiation source 3 (such as the above-described fourth embodiment), it is not limited to the movement in the Z-axis direction, but is moved in the rotation angle direction and positioned outside the cone beam. You can also.

According to such a retractable blade, a small field of view with little influence of scattered radiation, that is, an image of a subject with small radiation attenuation, or an ordinary CT apparatus without a cone beam is used. When imaging, the SNR can be improved by increasing the geometric efficiency as needed. That is, in such a case, collimation by the blade can be omitted as appropriate when imaging an object in which the influence of the shadow of the blade is greater than the effect of scattered radiation.

(Seventh Embodiment) Next, the seventh embodiment of the present invention will be described.
The radiation imaging apparatus according to the embodiment will be described. The radiation imaging apparatus according to the present embodiment is characterized in that a monitor detector 20 is provided on the blade 15 in the above-described fourth embodiment.

The monitor detector 20 is a detection element for calibration constituted by an element for detecting radiation that does not pass through the subject out of the radiation emitted by the radiation source 3. As shown in the figure, the upper part of each blade 15 which rotates in pairs with the radiation source 3 (inward of the rotation plane)
Are arranged in series in the z-axis direction.

In the present embodiment, the monitor detector 20 is arranged before and after the blade 15 (forward and backward in the rotational direction) in consideration of the fact that the X-ray output fluctuation is not isotropic. If the situation is not different, one may be used. In addition, the monitor detector 20 is placed above the blade 15 (on the X-ray incidence side), because strong X-rays that do not attenuate can be applied, so that there is no need to worry about the effects of scattered radiation. If you want to do so on mounting, it can be near the lower end of the blade. Further, the monitor detectors 20 may be attached to all the blades 15, may be attached every other blade, or may be attached in any number in the Z direction.

The radiation imaging apparatus according to this embodiment can be based on either a fourth-generation CT apparatus or a third-generation CT apparatus, and can use a cone beam system or a normal fan beam system. It can be used for any of them.

According to the radiation imaging apparatus having the monitor detector 20 according to the present embodiment, the monitor detector 20 accurately monitors the time variation of the X-ray output, and collects the data based on the monitor result. Can be corrected. In particular, the monitor detector 20 according to the present embodiment
Are arranged in series in the z direction, so that X in the z direction
Fluctuations in line output can be accurately detected.

(Eighth Embodiment) Further, an eighth embodiment of the present invention will be described.
The radiation imaging apparatus according to the embodiment will be described. In the radiation imaging apparatus according to the present embodiment, the radiation imaging apparatus according to each of the above-described embodiments is provided with a measuring device that measures the intensity distribution of the radiation that the radiation source 3 emits before passing through the subject among the radiation that is emitted. It is characterized by the following.

Specifically, as shown in FIG. 14, an X-ray sensor 26 is provided two-dimensionally on a thin substrate 25. Then, the substrate 25 is placed at a position where X-rays before passing through the subject can be detected, that is, closer to the radiation source 3 than the subject.

The X-ray sensor 26 detects only a small part of the incoming X-ray and converts it into an electric signal.
For example, it can be constituted by a thin semiconductor detector. The semiconductor detector does not need to have particularly high sensitivity, and for example, a bulk silicon can be used. Also,
The semiconductor detector needs to apply a high voltage as a bias, but the bias electrode is omitted in FIG.

The output from the X-ray sensor 26 is
Via the printed circuit pattern 27, it is sent to an electric circuit such as an amplifier. The printed circuit pattern 27 is made of a conductor having a low X-ray source weak coefficient, such as aluminum, which is made very thin and thin, so that the X-ray distribution is not affected.

According to the radiation imaging apparatus provided with such an X-ray sensor 26, it is possible to monitor a two-dimensional fluctuation of the source output. The X-ray sensor 26 according to the present embodiment can be used not only for the fourth-generation cone beam CT but also for the third-generation cone beam CT.

(Modification of the Eighth Embodiment) The X-ray sensor described above, when there is no significant difference in the source output fluctuation state in the x direction, as shown in FIG. The shape may be continuous in the direction.

Further, as shown in FIG. 9B, when there is a difference in the source output fluctuation situation in the X direction and there is not much difference in the Z direction, the shape may be continuous in the z direction. Good. In the case of a fan beam, since there is no fluctuation in the Z-axis direction, it is preferable to adopt this mode.

[0090]

According to the radiation imaging apparatus of the present invention,
For example, effective scattered ray collimation can be performed even in the fourth generation CT, and the image quality of the fourth generation CT can be improved. Further, if the fourth-generation type system and the present collimation are applied to the cone beam CT, it is possible to realize radiation imaging without ring artifacts.

Further, if the fourth-generation cone beam CT system and the present collimation are applied, the band limitation of the slip ring and other data transmission systems that do not depend on the cable can be eliminated, and a large amount of data from the detector can be quickly transmitted. Processing
Can be transmitted. As a result, high resolution in the body axis direction, a long field of view in the body axis (Z) direction, high resolution in the XY directions, and X
A wide field of view in the Y direction and high-speed scanning can be simultaneously realized.

Further, the two-dimensional source output fluctuation can be easily and accurately monitored by the cone beam CT, and the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall structure of a radiation imaging apparatus according to a first embodiment to which a radiation imaging apparatus according to the present invention is applied.

FIGS. 2A and 2B are diagrams showing a radiation imaging apparatus according to a second embodiment, in which FIG. 2A is a perspective view, FIG. 2B is a front view seen from a z direction, and FIG. It is the side view seen from.

FIG. 3 is a sectional view of a detector cylinder of the radiation imaging apparatus according to the second embodiment.

FIG. 4A is an explanatory diagram showing a relationship between a cone beam and a detector cylindrical visual field range in the second embodiment, and FIG. 4B is a diagram illustrating a cone at a position immediately below in FIG. It is sectional drawing of a beam, (c) is sectional drawing of the cone beam in the separation position in (a).

FIG. 5 is an explanatory diagram showing a procedure for designing a blade according to a second embodiment.

FIG. 6 is an explanatory diagram showing a procedure for designing a blade according to a second embodiment.

FIG. 7 is a sectional view of a detector in a radiation imaging apparatus according to a third embodiment to which the radiation imaging apparatus according to the present invention is applied.

FIG. 8 shows a blade according to a third embodiment,
It is explanatory drawing which shows the state in which a line is shielded.

FIG. 9 is a perspective view of a radiation imaging apparatus according to a fourth embodiment to which the radiation imaging apparatus according to the present invention is applied.

FIG. 10 is an explanatory diagram showing a modified example of the radiation imaging apparatus according to the fourth embodiment.

FIG. 11 shows a fifth embodiment to which the radiation imaging apparatus according to the present invention is applied.
It is a perspective view of a radiation imaging device concerning an embodiment.

FIG. 12B is a front view of the blade according to the fifth embodiment viewed from the z direction, and FIG. 12B is a top view viewed from the y direction.

FIG. 13 shows a seventh example to which the radiation imaging apparatus according to the present invention is applied.
FIG. 4 is a perspective view showing a monitor detector of the radiation imaging apparatus according to the embodiment.

FIG. 14 is an eighth diagram to which the radiation imaging apparatus according to the present invention is applied;
It is a perspective view showing the X-ray sensor of the radiation imaging device concerning an embodiment.

FIG. 15 is an eighth view to which the radiation imaging apparatus according to the present invention is applied.
It is a perspective view which shows the example of a change of the radiation imaging device which concerns on embodiment.

FIG. 16 is a perspective view showing a conventional X-ray imaging apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Radiation imaging apparatus, 2 ... Subject, 3 ... Source, 5 ... Detection element, 11 ... Detector cylinder, 50 ... Detection element row

Claims (10)

[Claims] 1. A radiation source which rotates around a subject and irradiates the subject with radiation, and a large number of detection elements which detect radiation from the radiation source are arranged around the subject. A radiation imaging apparatus comprising: an annular array of detection elements arranged in series on a circumference; and a detector having a plurality of arrays of the detection elements arranged in the rotation axis direction. 2. A circle centered on a point on the rotation axis of the radiation source or a cone of a cone having a vertex at a point on the rotation axis of the radiation source and a bottom face at each of the annular detection element rows. The radiation imaging apparatus according to claim 1, further comprising a shielding plate disposed on an inner peripheral surface of the detector so as to extend along the surface. 3. A radiation source for rotating around a subject and exposing the subject to radiation, and a detecting element for detecting radiation from the radiation source.
An annular detector having an array of detection elements arranged in series on a circumference centered on the rotation center of the radiation source; and a circle centered on a point on the rotation axis of the radiation source, or the radiation And a shielding plate disposed on an inner peripheral surface of the detector so as to follow a conical surface of a cone having a point on a rotation axis of a source as a vertex and the circumference as a bottom surface. apparatus. 4. A radiation source that rotates around a subject and irradiates the subject with radiation, and a detecting element that detects radiation from the radiation source is c.
a detector having a row of detection elements arranged in series in the h direction, and a circle movably provided on the radiation source side of the detector so as to be along a plane including the radiation source and the row of detection elements. And an arc-shaped shield plate, wherein the shield plate rotates around the subject together with the radiation source so as to be arranged to face the radiation source with the subject interposed therebetween. Radiation imaging device. 5. A radiation source for rotating around a subject and exposing the subject to radiation, and a detecting element for detecting radiation from the radiation source.
a detector having a detection element array arranged in series in the channel direction; and a circle movably provided on the radiation generation source side of the detector so as to be along a surface including the radiation generation source and the detection element array. A radiation imaging apparatus comprising: an arc-shaped shielding plate; wherein the shielding plate is arranged at a predetermined angle with respect to a circumferential direction of the circumference. 6. A radiation source that rotates around a subject and irradiates the subject with radiation, and a detection element that detects radiation from the radiation source.
a detector having a detection element array arranged in series in the channel direction; and a circle movably provided on the radiation generation source side of the detector so as to be along a surface including the radiation generation source and the detection element array. A radiation imaging apparatus, comprising: an arc-shaped shielding plate, wherein the shielding plate is movably provided so as to be retracted from the radiation exposure range. 7. A radiation source that rotates around a subject and irradiates the subject with radiation, and a detection element that detects radiation from the radiation source.
a detector having a detection element array arranged in series in a channel direction, and a measuring device for measuring an intensity distribution of the radiation emitted by the radiation source before passing through the subject, A radiation imaging apparatus characterized by the above-mentioned. 8. The radiation imaging apparatus according to claim 4, wherein the detector is configured by arranging a plurality of the detection element rows in the rotation axis direction. 9. A radiation source that rotates around a subject and irradiates the subject with radiation, and a detection element that detects radiation from the radiation source.
a detection element array arranged in series in the channel direction, a detector arranged in a plurality of the detection element arrays in the rotation axis direction, and a radiation transmitted through the subject among radiations emitted by the radiation source. An element for detecting radiation that is not to be detected, and a calibration detection element row in which the elements are arranged in series in the rotation axis direction. The calibration detection element row is arranged to face the radiation source with the subject interposed therebetween. Thus, the radiation imaging apparatus rotates around the subject together with the radiation generation source. 10. The detection element array according to claim 4, wherein the detection element array has an annular shape in which the detection elements are arranged in series on a circumference centered on a rotation center of the radiation source.
A radiation imaging apparatus according to claim 1.