JP2013088265A - Radiation collimator and method for manufacturing the radiation collimator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture a fine radiation collimator having one or more deep hole openings in which an opening interval is about 0.2 to 0.3 mm and an opening diameter is ten times or more as long as a fine hole diameter of about 0.1 mm.SOLUTION: Openings and positioning holes are formed in a plate-like material by etching, press working or laser processing, one or more plate-like materials are laminated by allowing positioning pins previously installed on a fixture to pass through or are laminated while being positioned by putting an edge of a material plate onto a positioning holder.

Description

  In medical and industrial X-ray fluoroscopy devices and X-ray detectors of X-ray CT devices, scattered X-rays generated in the subject are detected in channels other than the specified channels of the X-ray detector and the resolution of the image is reduced. It is related with the collimator used in order to prevent.

In fluoroscopic imaging using X-rays or the like, it is known that X-rays are irregularly reflected by a subject and the resolution of the image is lowered. As X-ray energy increases, it is becoming a fatal problem in spatial resolution. This is especially true for electron linear accelerator-based X-ray sources.
In Patent Document 1, an attempt is made to avoid this problem by using a detector having X-ray energy selectivity.

  In order to remove such scattered radiation, a collimator may be installed between or in front of the radiation detector elements so as to separate the channels of the radiation detector.

Various shapes of collimators have been devised. For example, there are slits for arranging a large number of thin plates as shown in Patent Document 2, Patent Document 3, and FIG. Most of them are plate-like ones installed perpendicular to the radiation incident direction.
Patent Document 4 discloses a method of manufacturing an X-ray collimator for industrial X-ray inspection.

  In Patent Document 5, a collimator is manufactured by casting.

  In addition, a bundle of thin glass tubes (microchannel plate: MCP) and a multicapillary tube are used as a collimator.

In radionuclide medicine, SPECT (Single Photon Emission Computer Tomography) has traditionally used collimators in gamma cameras. According to Non-Patent Document 1, the specific specifications of a parallel porous collimator for SPECT are as follows: a low energy collimator for ^99m Tc (140keV), etc., has a hole diameter of about 2 to 3mm and a partition wall thickness. The length is about 0.3mm and the number of holes is about 1 to 50,000.

  According to Non-Patent Document 2, an X-ray grid is used in an X-ray fluoroscopic inspection using a relatively low energy X-ray lamp. In the old days, a device called a moving grid or a bucky blende is used, but a fine grid called Lisholm blende is also used. This is a plate (foil) thickness of 0.03-0.05 mm, height (length with respect to the radiation incident direction) of 1.5 mm-3.0 mm, and lattice spacing (dot pitch) of 0.2 mm-0.3 mm.

These structures are not much different from those shown in FIG. When constructing a fine grid, the two sets of slits are overlapped 90 degrees apart.
If the foil is thick, it can be cut and integrated with each other, but it is very difficult with a thin foil, and it is simply placed one on top of the other.

  There is no problem when the radiation is a parallel beam (parallel), but in the case of a fan beam (fan shape) or cone beam (conical shape), the foil constituting the slit must be tilted and supported in accordance with the radiation source. In the case of a fan beam, it is not impossible to engage two sets of slits, but in the case of a cone beam, it seems extremely difficult.

The biggest difficulty of these slits and grids is the structure that supports the thin plate in a state perpendicular to the radiation detector. X-rays can be scattered by the support above or below the slit or grid.
Patent Document 6 proposes that a low-density foam material (high resistance foam) is filled between slits and used as a support for the slit. However, low-energy X-rays may be absorbed even by these foam materials.

  The slits also have manufacturing difficulties. The plates constituting the slit must be precisely arranged at equal intervals and fixed to the support with an adhesive or the like. When there is a slight error in the interval, it becomes a change in the size of the opening on the radiation detector side, resulting in sensitivity variations.

Further, the above-mentioned slits and grids also cause a problem that the user cannot freely change the height according to the use situation.
A plurality of slits and grids must be prepared, which is complicated and expensive.

  In recent years, two-dimensional high-resolution (hundreds of thousands to millions of pixels and pixel size 0.2 mm) large area flat panel type two-dimensional radiation detectors are widely used for the medical industry. The demand for the kind is getting stricter.

  MCP can be configured as a fine collimator, but it is difficult to increase the area.

  On the other hand, an X-ray collimator for shaping a cone beam of an X-ray source has been proposed as in Patent Document 7, but a specific manufacturing method is not shown.

Japanese Patent No. 3569227 Japanese Patent Publication No. 05-312956 Japanese Patent Publication No. 2003-116646 Japanese Patent No. 4393793 Japanese Patent No. 4630541 Japanese Patent No. 4644385 Japanese Patent No. 4421327

Koichi Ogawa “IV Collimator Opening” Video Information Medical July 2002 p.884 Takehiro Saijo Radiation medical physics 2nd edition 2001

  There is a manufacturing difficulty with a slit or a combination of slits, and the shape of a collimator that can be configured is limited.

  An object of this invention is to provide the radiation collimator which can shape | mold easily the micro deep hole of arbitrary shapes 10 times or more of a hole diameter.

A ray collimator is formed by laminating thin collimator plates that have been processed with fine holes to form fine deep holes in a desired shape.
Specifically, fine holes are formed in a thin material plate by etching, press working, laser processing, or the like, and these are laminated.

Etching, especially photoetching, is a technique for making holes in thin metal plates, which is the same as the shadow mask manufacturing method for cathode ray tubes (CRT), and can be used as it is, forming minute deep holes that were difficult with conventional methods. The manufactured collimator can be easily manufactured.
In particular, tungsten and tungsten alloys are substances that are considered to be most useful as radiation shielding materials, but their use has been limited due to their difficulty in processing. However, according to the present invention, use as a collimator in which fine deep holes are formed is facilitated.

  Since the shadow mask for a cathode ray tube forms openings at intervals (dot pitch) of about 0.2 mm to 0.3 mm, it is obvious that a collimator having the same opening can be formed. Further, it can be directly applied to a two-dimensional detector. Since the cathode ray tube has 29 inches, etc., it can handle large areas.

The radiation collimator according to the present invention can be applied to photon beams (X-rays, γ-rays), charged leptone rays (electrons, etc.), α-rays, ion (heavy ion) particle beams, hadron particle beams (protons, neutrons, etc.).
It is also possible to collimate the radiation emitted from the radiation generator rather than the detector side. For example, it is like patent 4421327 gazette. The radiation collimator disclosed in Patent Document 6 can also be manufactured by the method according to the present invention.

The perspective view which showed the example of the conventional radiation collimator. The top view (a) and AA sectional drawing (b) which showed the implementation method of the fine radiation collimator (Example 1). The schematic diagram about the positioning method of a material board (thin collimator board). It is a schematic diagram about the thinning of the opening part of a thin collimator board. Fig. 4 is a schematic view of positioning a thin collimator plate by molding the unevenness that meshes with each other. These are the schematic diagrams which showed the Example with respect to the curved X-ray detector for X-ray CT (Example 2). (Example 3) about the optimization about the collimator opening part with respect to a cone beam or a fan beam. The schematic diagram shown about the setting of the molding angle in the case of shape | molding a collimator opening part diagonally. The schematic diagram shown about the expansion ratio of the opening part when shape | molding a collimator opening part perpendicular | vertical. The schematic diagram shown about the optimization of the collimator opening part of the collimator which reduces an image. The schematic diagram which showed the function and effect of the collimator which reduces an image. In Equations 1 and 2, a graph showing the beam size σ (s) for each βw when emittance ε is 1 A graph showing the beam size σ (s) for each ε when β _w is 1 in Equation 1 and Equation 2. The schematic diagram which showed the effect at the time of increasing the thickness of a fine radiation collimator. The schematic diagram which showed the difference in the radiation incident angle of a pinhole collimator and the expansion / contraction system by this invention. The schematic diagram which showed SPECT and its imaging range using a parallel collimator. The schematic diagram which showed SPECT using the reduction system collimator and its imaging range.

  An embodiment of the present invention will be described.

In the present invention, a deep hole opening is formed by photoetching on a thin plate-like material having a thickness of about 0.10 to 0.25 mm, and the material plate thus manufactured is laminated to a required thickness as shown in FIG. Features.
Since positioning is required when stacking, positioning holes 6 through which positioning pins 4 pass are formed in the material plate at the same time. Alternatively, it is conceivable that the edge is precisely processed in advance and positioned while being pressed against a positioning jig 21 (also called a V-shaped block) as shown in FIG.
The laminated material plates can be integrated by diffusion bonding, adhesion, welding, brazing, or the like. If the plate thickness is 1mm or more, welding and brazing are considered effective. If it is 1 mm or less, diffusion bonding or adhesion is preferable.

The thickness of the thin collimator plate is not limited to 0.10 mm to 0.25 mm. If finer processing is required, an optimum thickness is selected. Depending on the material, it is possible to form an opening of several μm in a plate having a thickness of 5 μm or less.
Conversely, it is possible to have a thickness of 1 mm and an opening of 2 mm. The collimator having the dimensions described in Non-Patent Document 1 can be manufactured by the method according to the present invention.

  Moreover, it can also be used in the state which the positioning pin penetrated, without performing adhesive joining. In the fine radiation collimator which is the main object of the present invention, the laminated material plates (thin collimator plates 2) are brought into close contact with the radiation detector 1 with a plate-like collimator holder 5. The collimator holder may be made of metal with a shape in which the opening of the collimator is hollowed or a material with a high radiation transmittance that covers the entire collimator.

  In the drawings in the present application, the drawing is performed so that there is a gap between the thin collimator plates 2 for the sake of convenience.

The material is preferably a material for which photo-etching technology has been established and has a high radiation shielding ability. Materials for copper, iron and CRT shadow masks are also an option. Tungsten is the best shielding material, but pure tungsten is very hard and difficult to process, and therefore it is difficult to cut into complex shapes. Generally, formation by sintering is performed. In order to improve workability, a tungsten alloy (such as heavy alloy) may be used. Fortunately, however, methods for etching tungsten-based metals have also been disclosed (Japanese Patent Publication Nos. 05-175170, 2008-258395, and 2011-151287).
Although the shielding ability is inferior, silicon is also an option in the soft X-ray region.

  There is press working as a technology that can perform the same processing, but a mold is necessary, and initial investment tends to be large. However, press processing is an effective processing method for processing materials such as lead that are not suitable for etching.

  High molecular compounds such as polyethylene and paraffin are often used to shield neutron beams. In some cases, boron that easily traps neutrons is added. However, these are not suitable for etching. If it is press working, these materials can be processed and used as a collimator.

JP-A-60-233154 has high heat resistance and hot water resistance selected from the group consisting of polyimide resin, epoxy resin, polyphenylene sulfide resin, polyetheretherketone resin, polyamideimide resin and polyetherimide resin. There is disclosed a neutron absorption shielding material composition characterized in that one or more kinds are used as a matrix and a neutron absorbing material is mixed and dispersed. The publication also discloses that the neutron absorbing material is a gadolinium-containing material, a boron-containing material, a lithium-containing material, or the like.
The polyimide etching method is disclosed in Japanese Patent No. 3251515. This is mainly used for forming through-holes in flexible printed circuit boards for electronic circuits. Fine processing with a film thickness of 25 μm and hole sizes of 50 μm to several hundred μm is also possible. Therefore, a fine neutron collimator made of polyimide can be constructed.

When it can be assumed that the radiation to be detected is a parallel beam (parallel), thin collimator plates using the same mask may be prepared for the required thickness. This is a SPECT that does not scale.
In this case, if the material can be pressed such as iron or lead, pressing is an option as a processing method.

  However, the actual radiation is often a fan beam or a cone beam. In this case, since the thin collimator plate needs to have different dot pitches and aperture diameters in each layer in accordance with the incident angle of the beam to each detection element, in the case of the collimator for fan beam and cone beam, the mold is Since a large amount is required, pressing is not suitable.

When a large number of thin collimator plates are stacked, depending on the state of the collimator opening, there is a possibility that each thin collimator plate rises without being in close contact.
In order to prevent this, it is conceivable to install a plate having a certain degree of rigidity after laminating the collimator plates and press down the thin collimator plates.
As another method, before forming the opening, as shown in FIG. 4, the thickness of the collimator opening is slightly thinner than the edge of the thin collimator plate (several percent to 10%). (Thinning) is also considered. Only one side may be thinned, or both sides may be thinned.
If half etching is applied, this thinning process is possible.

  On the contrary, the same effect can be obtained by sandwiching a thin film (less than 10%) sufficiently thinner than the thin collimator plate between the edges of the thin collimator.

Another method is a lift-off method in which a thin foil is added to the edge portion by film formation (vacuum deposition, sputtering, CVD) and the collimator opening is removed using a photomask.
As shown in FIG. 5, it is possible to form an uneven structure that meshes with the upper and lower thin collimators by thinning the thin collimator plate, and to position it. This is especially effective for thick plate-like materials of about 1 mm.

  A plurality of openings need not be formed, and a radiation collimator having a single opening can be manufactured.

  When it can be assumed that the radiation to be detected is a parallel beam (parallel), thin collimator plates using the same mask may be prepared for the required thickness as shown in FIG. This is the collimator used for SPECT without magnification.

The actual radiation is often a fan beam (fan shape) or a cone beam (cone shape).
In this case, the thin collimator plate needs to have a different dot pitch and opening diameter in each layer in accordance with the incident angle of the radiation to each detection element.

In the case of X-ray CT, since the detector is bent in a concave shape, the collimator also optimizes the dot pitch and aperture diameter as shown in FIG.
When the distance from the radiation source to the detector is R and the distance from the radiation source to each thin collimator plate is r, with the collimator opening at the radiation detector position as a reference, the opening of each thin collimator plate The shape is r / R times that at the radiation detector position.
The distance r _n from the radiation detector to the radiation source of the n th thin collimator can be expressed as r _n = Rdt (n−1). Here, d is the distance between the radiation detector and the center of the first thin collimator plate, and t is the distance between the centers of the collimator plates.
The reason why t is not the thickness of the thin collimator plates is that the distance between the thin collimator plates may change due to bonding or joining of the thin collimator plates, and t is a distance that takes this into account. Should.

For a fan beam or cone beam, the dot pitch and aperture diameter may be optimized as shown in FIG.
Optimization can be done by scaling the collimator opening shape at the radiation detector position with respect to each thin collimator plate.
When the distance from the radiation source 33 to the radiation detector 1 is L, and the distance from the nth thin collimator plate to the radiation source 33 from the bottom is l _n , _n with respect to the thin collimator plate 2 at the radiation detector position. The magnification of the opening shape of the second thin collimator plate is l _n / L. When the distance from the radiation detector to the first thin collimator plate is d and the distance between each collimator plate is t, the distance between the nth thin collimator plate and the radiation detector is t (n-1). Since + d can be written, l _n = Lt (n-1) -d.
That is, the magnification of the aperture shape of the nth thin collimator from the detector side is (Lt (n−1) −d) / L (& lt1). That is, in reality, the dot pitch and the aperture diameter of the thin collimator plate are reduced.

  Needless to say, enlargement / reduction is performed in only one direction in the case of a fan beam and in two directions in the case of a cone beam.

  However, since forming the optimal aperture shape for all thin collimator plates will lead to increased costs, it is possible to shape every multiple sheets, such as every second or every third, as required by the collimator user. It is also possible to change.

The fan beam or cone beam collimator has strict requirements on the shape, and even if the holes in each thin collimator plate should be machined diagonally, the half-etching method is applied and separate masks are used from both the front and back sides. It is also possible to form an opening that is inclined with respect to the plate surface by etching.
The angle in this case is also in the explanatory diagram of FIG. 8, but the inclination from the vertical direction of the plate surface is θ, and the perpendicular (substantially) drawn from the radiation source of the corresponding opening to the radiation detector and the collimator. When the distance from the central axis of the radiation detector is m, θ = arctan (m / l). Naturally, in the case of a cone beam, the direction of inclination is the direction toward the perpendicular. In the case of a fan beam, the direction is from the source line toward the vertical surface drawn to the detector.

  In the above method, each collimator opening has the same opening diameter with respect to the radiation source. However, this is an elliptical shape on the surface of the radiation detector. When θ is large, problems such as affecting the pixels adjacent to the radiation detector may occur.

As another idea, a collimator opening in which the shape on the surface of the radiation detector becomes a shape having no distortion such as a circle or a square can be considered.
The opening shape on the surface of the radiation detector is determined, and the opening shape is formed by a solid (slanted column) that can be formed by moving it toward the radiation source along the oblique line having the relationship of 1 / m.
As another method, a pyramid with a radiation source at the top and an oblique cone shape or a quadrangular pyramid shape with an opening shape (circular, square, or arbitrary shape) on the surface of the radiation detector or an arbitrary bottom surface is formed. Simple openings are also conceivable. FIG. 6 is drawn based on this method.

However, in the above method, the opening area as viewed from the radiation source decreases as θ increases, and is not necessarily the same in all openings.
Therefore, the actual sensitivity of the radiation detector depends on θ, and some correction is necessary.
In the first place, since the radiation source itself such as X-ray soot is not ideal, the radiation intensity often has θ dependence (it is highly likely that the radioisotope shows a radiation intensity distribution close to ideal). Therefore, it is essential to perform correction on the radiation detector side, and the above correction may be performed in that category. Therefore, the non-uniformity of the opening area is not a fatal problem.

In order to completely avoid this problem, it is appropriate to make the radiation detector always face the front of the radiation detector with respect to the radiation source as shown in FIG. This is feasible when the fan beam is the target.
If a cone beam is the object, the detector and collimator must be shaped to form part of a sphere.

  Example 6 is another method.

  When half-etching cannot be used or when the opening cannot be formed diagonally, such as by pressing, as shown in FIG. 9, the vertical line or vertical surface drawn from the radiation source or virtual focus to the radiation detector and collimator is used. It can also be dealt with by enlarging in the direction of heading.

In the fan beam collimator according to the third embodiment, the relationship between the radiation incident side and the detector side can be switched as shown in FIGS. 10 and 11 to reduce the image. In this way, a wide range of radiation sources can be visualized.
In short, the position of the radiation source 33 in FIG. 7 is read as the virtual focal point 71 of radiation.

If the distance from the virtual focus 71 to the radiation detector 1 is L, and the distance from the nth thin collimator plate to the virtual focus from the detector side is l _n , the thin collimator plate 2 at the radiation detector position is The magnification of the opening shape of the nth thin collimator plate is l _n / L. When the distance from the radiation detector to the first thin collimator plate is d and the distance between each collimator plate is t, the distance between the nth thin collimator plate and the radiation detector is t (n-1). Since + d can be written, l _n = L + t (n-1) + d.
That is, the magnification of the aperture shape of the nth thin collimator from the detector side is (L + t (n−1) + d) / L (& gt1). In other words, in reality, the dot pitch of the thin collimator plate increases as the distance from the detector increases.

Like the fan beam or cone beam collimator, there are strict requirements for the shape, and even if the holes in each thin collimator plate should be machined diagonally, the half-etching method is applied and etched separately from the front and back sides. Accordingly, it is possible to form an opening that is inclined with respect to the plate surface.
In this case, as shown in FIG. 10, the inclination from the vertical direction of the plate surface is θ, and the perpendicular from the virtual focus of the corresponding opening to the radiation detector and the collimator, that is, the distance from the center axis of the detector Where m is θ = arctan (m / l). Naturally, the direction of inclination is the direction against the center axis of the detector.

  However, if the opening diameter of the opening is enlarged on the subject side, the image may be blurred. It is desirable that the opening diameter of the opening is constant for each thin collimator plate, and only the opening interval (dot pitch) is enlarged. In other words, the shape of the opening is a column whose center axis passes through the virtual focus.

Alternatively, the opening at the radiation detector position is the bottom surface, the center of the opening at the radiation radiation detector position and the central axis that passes through the virtual focus, and the apex at any position in the subject direction (oblique) The pituitary gland is considered.
The position of the apex of the (slanted) body must be closer to the subject than the collimator surface.
The closer to the collimator, the narrower the collimator field of view. The farther away, the wider the field of view. When the focal position is at infinity, it is asymptotic to a (slanted) cylinder with the same base.

As a developed form of the fourth embodiment, a radiation detector and a radiation collimator may be convex.
In the fourth embodiment, as described in detail in the third embodiment, the radiation collimator opening area at the center and the end of the radiation detector is different. In order to avoid this, referring to the second embodiment, the radiation source position of the second embodiment is regarded as a virtual focus, the radiation detector is arranged in a convex shape, and the radiation collimator is configured accordingly.
In this way, since radiation can be made to enter the radiation detector perpendicularly, the problem of position dependency of radiation sensitivity described in the third embodiment can be avoided.

Considering in the same manner as in Example 2, the distance r from the virtual focal point of the thin collimator plate from a radiation detector in the n-th becomes _{r n = R + d + t} (n-1).
However, as described in the fourth embodiment, it is preferable that the shape of the opening is not a vertical body having a virtual focus as a vertex, but a column body having a central axis passing through the virtual focus or a vertical body having a vertex on the subject side.

  As described in the third embodiment, the X-ray source such as an X-ray tube does not have a uniform air dose distribution, shows a strong dose distribution near the center, and becomes weaker toward the outside of the field of view.

According to the present invention, the size of the collimator opening can be arbitrarily determined within a range that does not interfere with the adjacent opening. Using this fact, it is possible to easily correct the dose distribution in the radiation detector.
That is, the dose entering the radiation detector can be reduced by making the collimator opening area smaller than that at the end near the center where the dose is high.

  As a result, the dose distribution in the radiation detector can be made close to uniform, and the correction of the dose distribution in the radiation detector-side signal processing device or the like is facilitated. As a result, the substantial dynamic range of the radiation detector is improved.

It should be noted that this method does not improve the sensitivity at the end portion but reduces the sensitivity at the center portion.
Since it is inevitable that the sensitivity of the entire detector is reduced, it is a point to consider that this is a trade-off with securing the dynamic range.

  According to the present invention, the shape of the opening of the radiation collimator can be arbitrarily determined within a range that does not interfere with the adjacent opening. In the above embodiment, a collimator opening having a shape like a (slanting) pit or a (slanting) column was considered, but other shapes can also be realized.

  For example, an opening having a shape represented by Equations 5.138 (p.164) and (Equation 1) of “Particle Accelerator Physics I” Second Edition by H. Wiedemann is also conceivable.

(Equation 1)
β (ss _w ) = β _w + (ss _w ) ² / β _w

In Equation 1, β (s) is a value called a beta function in the field of accelerator beam physics. s _w is the position on the s-axis of the beam waste (focal point), and β _w is β in the beam waste. This equation shows how the beam size changes on the s-axis (beam motion direction axis) in the process from convergence to divergence when the particle beam is converged.
In the present application, s may be read as r to l in the second embodiment, the third embodiment, or the fourth embodiment.

Since the particle beam actually has a finite spread and divergence angle (emittance), it has a finite spread at the focal point. As expressed by Equation 2, the square root of β (s) multiplied by emittance ε corresponds to the beam size σ (s).

(Equation 2)
σ ² (s) = εβ (s)

  There are various definitions of the beam size σ (s) and emittance ε. For example, when defining the beam size with a standard deviation assuming that the beam profile is a normal distribution, when using the full width at half maximum (FWHM), when defining as a range that includes a certain percentage of beam particles (for example, 90%), etc. It is.

The graph of the change with respect to s of beam size (sigma) (s) using the relationship of Numerical formula 1 and Numerical formula 2 is shown in FIG.12 and FIG.13. In both figures, s _w = 0 was set.
In FIG. 12, ε = 1 is plotted, and β _w is 0.5, 1, and 2. It can be seen that when the beam waste is small, the beam converges and diverges rapidly.
In FIG. 13, β _w = 1 and ε is plotted as 0.5, 1, and 2. It can be seen that if the emittance ε is small, the beam waste can be reduced without sudden convergence and divergence.

This is generally true for radiation sources. When the radiation is collimated to a certain position (focal point), the collimated radiation passes through a space that satisfies Equations 1 and 2.
Therefore, it is possible to collimate radiation by using a radiation collimator having an aperture shape according to Equation 1 and Equation 2.

In Examples 3, 4 and 5, the shape of the opening of the radiation collimator was assumed to be a (slanted) pit or a (slanted) column, but an opening shape using Formulas 1 and 2 is also conceivable.
The position of the focal point does not need to be the position of the intermediate layer of the radiation collimator, and may be located in the forefront of the radiation collimator.

  The field of view of the radiation collimator having the aperture shape expressed by Equation 1 and Equation 2 is expressed by Equation 1 and Equation 2. However, the opening shape must include the beam waste of Equation 1.

On the contrary, this means that the shape of the collimator opening is the most in the field of view when detecting radiation emitted from a radiation source having a finite size by a radiation detector having a finite size. It suggests whether it is efficient.
However, it is probably difficult to provide a radiation collimator opening shape including the beam waste of Equation 1 in terms of spatial arrangement.
In reality, it is approximated by the shape of a (slanted) pituitary body while taking this into consideration.

Another way of thinking is to ignore the spread of the radiation source and emittance and to have the narrowest field of view near the subject. This way of thinking seems better to increase the resolution of radiographic images.
However, the narrowest field of view near the subject means that a beam waste must exist near the subject. This is not realistic.

  Actually, the beam waste is moved from the ideal arrangement to the radiation collimator side so that the beam waste is positioned near the forefront of the collimator. Alternatively, it can be considered that the beam waste is present in the radiation collimator.

  Although realization is not practical, it can be used to design an actual radiation collimator with reference to the optimal configuration. In that sense, Formula 1 and Formula 2 are useful.

  On the other hand, Equation 1 and Equation 2 also apply to the convergence of a Gaussian (Gaussian) beam of laser light. This shape can also be used for a spatial filter used for forming laser light.

  Moreover, Formula 1 and Formula 2 can also be applied to shaping of a charged particle beam as in the eighth embodiment.

For example, as a collimator for forming a charged particle beam such as a proton beam or an electron beam, a collimator in which copper and tungsten are alternately laminated can be considered. The heat generated by the collimator can be dispersed by copper. The copper plate can be made larger than the tungsten plate, and copper can be used as a cooling fin. Of course, it is not always necessary to alternate, and it is also possible to sandwich copper every two or more pieces of tungsten.

Further, the interval at which the copper plate is inserted need not be constant. For example, since the heat generation is large on the side where the electron beam is incident, the insertion interval of the copper plate is narrowed, and on the opposite side, the heat generation is small, so that the insertion interval of the copper plate is wide.
Specifically, it is considered that the present invention can be applied to the production of the X-ray target of Japanese Patent No. 4650642.

  It is not necessary that the copper plate and the tungsten plate have the same thickness. Nevertheless, it is likely that the same thickness will inevitably be the same due to the convenience of etching.

  Since diffusion bonding technology has been established, each tungsten plate can be bonded and integrated. Copper-tungsten bonding has also been put into practical use.

  If the radiation collimator manufactured by the method described in the present application is applied to an X-ray detector used for X-ray CT or the like, the spatial resolution is improved, so that a finer lesion can be found. In industrial applications, it will also be possible to detect defects that could not be found by electronic board inspection. The same applies to non-destructive inspections and baggage inspections at airport ports.

  As described above, in SPECT, a collimator has been conventionally used in a gamma camera. However, according to the present invention, the user can freely change the length of the collimator in the γ-ray incident direction. The γ-ray incident direction length is changed by changing the number of thin collimator plates. As shown in FIG. 14, by increasing the number of thin collimator plates, the field of view 63 of the detector with respect to the radiation source 61 becomes narrower, or the collimator wall through which the penetration line 64 from another radiation source 62 must pass. The number of sheets increases. Accordingly, the detection efficiency of γ rays decreases. This is a trade-off relationship, but this can be determined by the user.

  Actually, the collimator holder 5 may be easily removed. If all the thin collimator plates are independent, the handling becomes troublesome. For example, every 10 sheets are bonded and joined every 100 sheets for easy handling. It will be easier to handle if you put a tab on the collimator plate you made in this way.

  In SPECT, an enlargement / reduction imaging system is also used, but a pinhole collimator is generally used. It is also conceivable to use Example 3 or Example 4 instead of the pinhole collimator.

The problem with the enlargement / reduction imaging system using the pinhole collimator is that the distance between the subject and the radiation detector must be increased in order to enlarge the image once again through the radiation through the pinhole portion. This leads to a reduction in the final radiation detection efficiency.
If this distance is made extremely short, the incident angle of radiation at the radiation detector becomes extremely large, and the difference in radiation sensitivity between the central portion and the end portion becomes extremely large. Of course, correction is possible, but if appropriate correction is not performed, artifacts may appear in the final reconstructed image.

By using the third embodiment, the fourth embodiment, or the fifth embodiment instead of the pinhole collimator, this problem can be somewhat alleviated.
As shown in FIG. 15, when the radiation source as a subject and the radiation detector are at the same distance, the radiation incident angle is smaller in Example 3 in the right diagram than in the pinhole collimator in the left diagram.

  Furthermore, by applying the sixth embodiment, it is possible to easily correct the sensitivity distribution.

  In particular, recent high-resolution large-area semiconductor radiation detectors are not large enough to cover the entire human body even though the area is large. However, by combining the reduced imaging system according to Example 4 or Example 5 and the existing high-resolution large-area semiconductor radiation detector, it is possible to configure a gamma camera that is smaller and has higher resolution than the conventional one and can cover the entire human body. .

Currently, SPECT is trending to increase the number of gamma cameras for imaging. This is because the SPECT shooting time can be shortened if the number of gamma cameras increases. However, in practice, as shown in FIG. 16, the number of gamma cameras is limited by the external dimensions of the gamma cameras. In order to increase the number of gamma cameras, gamma cameras are installed away from the human body. This means an increase in the size of the device.
Since the gamma camera using the reduced imaging system according to the fourth embodiment or the fifth embodiment may be smaller than the object to be photographed, this limitation may be relaxed as shown in FIG.

Following the Great East Japan Earthquake that occurred on March 11, 2011, a nuclear disaster occurred at TEPCO's Fukushima Daiichi Nuclear Power Station. Since the gamma camera to which the fourth or fifth embodiment is applied can visualize the radiation source, it can be used to collect information for reducing the exposure of accident recovery workers.
It can also be used to visualize contaminated areas in areas contaminated with radioactive materials.

DESCRIPTION OF SYMBOLS 1 Radiation detector 2 Thin collimator board 3 Collimator main body 4 Positioning pin 5 Collimator holding 6 Positioning hole 7 Collimator opening part 8 Radiation incident direction 11 Slit-type collimator 21 Positioning jig 33 Radiation source 44 Radiation (cone beam or (Fan beam)
45 Subject 52 Thinning part 61 Radiation source 62 Radiation source 63 Field of view of detector 64 Penetration line 65 Radiation that can be incident on radiation detector 71 Virtual focus 81 Radiation source or virtual focus 82 Pinhole collimator 91 SPECT imaging range

Claims (5)

  A radiation collimator characterized in that one or a plurality of fine deep holes are formed in a desired shape by laminating thin collimator plates processed with fine holes.   The radiation collimator according to claim 1, wherein thin collimator plates made of different materials are laminated alternately or in an arbitrary arrangement.   The radiation collimator according to claim 1, wherein the radiation collimator is shaped to have an opening perpendicular to the radiation detector or an opening that faces a radiation source or a virtual focus.   The radiation collimator according to claim 1, wherein the thin collimator is joined or adhered every several sheets.   5. The radiation collimator according to claim 4, wherein the radiation collimator has a tab for each unit bonded or bonded.

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