JP4498779B2 - X-ray ion chamber detector and X-ray detector - Google Patents

Description

  The present invention relates to an X-ray multi-ion chamber detector used for an X-ray detector for general X-ray diagnosis or CT scan in the medical field, and more particularly to an X-ray multi-ion chamber for detecting low energy X-rays. It relates to a detector.

The X-ray ion chamber detector is a metal container in which an inert gas such as xenon gas having a large X-ray absorption coefficient is enclosed, and a high voltage electrode and a signal electrode are placed opposite to each other. Since current flows between the high voltage electrode and the signal electrode, X-rays can be detected.
The X-ray multi-channel ion chamber detector has a large number of pairs of high voltage electrodes and signal electrodes arranged adjacent to each other, and the position where the X-rays are incident can be known from the current detected by the signal electrodes.
The X-ray multi-ion chamber detector is used as a normal X-ray diagnostic detector, a CT (computer tomography) X-ray detector, or the like as an X-ray detector for medical diagnosis.

For example, in Patent Document 1 and Patent Document 2, there are detectors used in X-ray CT apparatuses, computer radiography, etc., which are multichannel ionization chamber types in which a plurality of electrode plates are mounted on a pair of insulating plates arranged in parallel. A radiation detector is described.
In the multi-channel ion chamber detector described in this document, although the pitch between the electrodes is as narrow as 0.5 mm to 1.5 mm, the length of the detection unit reaches about 800 mm. Therefore, in the invention described in this document, when a long detector is formed by combining a plurality of ceramic short insulating plates equipped with a large number of electrode plate pairs, the processing accuracy differs slightly for each insulating plate. Therefore, a highly accurate detector cannot be obtained, so that the accuracy is improved by machining a groove into which the electrode plate is fitted after the insulating plate block is integrated. An electrode block having a rectangular cross section formed in this way is inserted into a sheath having a rectangular internal cross section formed of a light metal such as aluminum having a low X-ray absorption rate, and filled with Xe gas.
In Patent Document 2, a groove is formed to make the wall of the portion where X-rays are incident thin, and the deformation of the container is suppressed by applying a fiber reinforced plastic having a high tensile strength across the groove. It is.

Non-Patent Document 1 discloses an X-ray apparatus that moves an X-ray source and an X-ray detector in synchronization to acquire an X-ray image of a patient standing between the source and the detector. . As shown in the figure, the X-ray ion chamber detector used in this X-ray apparatus is filled with 10 atm of xenon gas by arranging the high-voltage electrode plate and the linear signal electrode formed on the printed circuit board facing each other. It is a thing. The chamber container is a square box made of aluminum having a sufficient thickness to prevent X-rays from entering from the outside. However, a groove is formed in the X-ray incident part to capture X-rays between the electrodes. And thinned.
If a high voltage of 2 kV is applied between the high-voltage electrode plate and the linear signal electrode, the charge generated by the ionization of the xenon gas by the invading X-ray is captured by the signal electrode at the X-ray intrusion position. The X-ray incident position can be detected by sequentially reading out the accumulated charges of each signal electrode with a multiplexer installed in the chamber container.
Each of the linear signal electrodes has a width of 0.4 mm and a length of 800 mm, and 1024 lines are developed on the radiation centering on the X-ray source position on a linear printed board arranged perpendicular to the X-ray incident direction. Since the printed circuit board manufacturing technique is utilized, it can be formed relatively easily and with high accuracy.
Japanese Patent Publication No. 6-90289 JP-A-6-111758 EA Babichev et al. "Photon counting and integrating analog gaseous detectors for digital scanning radiography" Nuclear Instruments and Methods in Physics Research A 419 (1998) pp.290-294

In conventional ion chamber detectors, the container is made of a light metal such as aluminum so that the X-ray incident from a direction other than the measurement purpose is sufficiently blocked and the target X-ray is sufficiently transmitted, and the X-ray is used as a counter electrode. It has a structure that improves the detection efficiency by partially reducing the wall thickness of the container wall at the loading position. However, since a high-pressure rare gas is sealed in the ion chamber detector, there is a limit to reducing the wall thickness, and the X-ray on the low energy side is hardly transmitted even by a light metal, and the detection efficiency is remarkably lowered.
Therefore, when it is desired to observe an X-ray image at a low energy of 40 keV or less, a conventional detector is not sufficient.

  Furthermore, in the conventional ion chamber detector, it is not easy to adjust the position of the electrode unit and the signal processing unit during assembly and to perform the mounting work in a state where it cannot be visually checked. In addition, since the electrode plate is moved three-dimensionally to adjust the orientation, assembly is not easy. For this reason, there has been a demand for measures that can be easily adjusted and worked.

Therefore, the problem to be solved by the present invention is to provide an X-ray multi-channel ion chamber detector and an X-ray detection device with high detection efficiency of low energy X-rays, and an ion chamber that can be easily assembled and adjusted. It is to provide a detector and an X-ray detection device .

  In order to solve the above-mentioned problems, an X-ray ion chamber detector of the present invention comprises a sealable outer container and a core that can be taken in and out of the outer container, and a pair of electrodes arranged opposite to the core. The board and signal readout circuit are fixed, and the outer container is molded from fiber reinforced plastic that is easy to transmit low energy X-rays. After inserting the core, it is sealed and sealed with a sensitive gas. A high voltage is applied to X-rays entering a space sandwiched between electrode plates.

In the X-ray ion chamber detector of the present invention, since the outer container is formed of fiber reinforced plastic, it can sufficiently withstand the pressure of a sensitive gas such as xenon gas filled under pressure, and the components are mainly carbon and hydrogen. In addition, since it does not contain an element having a large atomic number, the transmittance of low energy X-rays is high.
In particular, when the outer container is made of carbon fiber reinforced plastic, the low energy X-ray attenuation per unit thickness is small because it is mainly carbon, and the strength of the housing is high, so the wall of the container can be made thin. This is preferable because the overall low-energy X-ray detection efficiency is remarkably improved.

  In addition, the core of the X-ray ion chamber detector of the present invention has a metal carrier on which an electrode plate and a signal readout circuit are mounted, and the carrier has an X in a space sandwiched between a pair of electrode plates. It is preferable to have an opening in the part that takes in the line. Further, the outer casing container may be formed in a cylindrical shape, and the outer side of the core may be formed in a columnar shape so that the core can be rotated in the outer casing container.

By providing the core carrier with an opening serving as an X-ray passage, the attenuation amount of the X-ray can be further suppressed. In addition, the strength of the detector can be sufficiently provided by an outer container made of fiber reinforced plastic. In addition, when an X-ray passage is provided by providing an opening in the core, it is not necessary to consider the X-ray transmittance in the core material. Therefore, not only a light metal but also an appropriate metal or other material can be used. it can.
Furthermore, when the core is configured to rotate, the direction of the space sandwiched between the electrode plates can be easily adjusted to the X-ray incident direction. Furthermore, if the position of the electrode plate is determined with respect to the opening position of the core, it is possible to easily position the electrode plate by inserting the core into a plastic outer container and depending on the opening position.

Note that one of the pair of electrode plates mounted on the core may be one high-voltage electrode plate and the other may be a signal electrode plate formed by arranging a plurality of linear signal electrodes in the axial direction.
The signal electrode plates are disposed at a dimensional interval of a 0.1 mm level. For example, accurate dimensional accuracy can be easily obtained by using a printed circuit board manufacturing technique.
The signal readout circuit includes a switch connected to the signal electrode, and switches each signal electrode by the switch to sequentially read out the electric charge accumulated in the signal electrode, thereby giving a one-dimensional image of X-rays.
The signal readout circuit must be connected to each of the signal electrodes, but since it is mounted together on the core, there is no need to connect a large number of signal lines between the detector and the external circuit device. There may be a signal line that supplies a signal converted and integrated by the readout circuit to the external circuit.

The X-ray detection apparatus of the present invention uses the X-ray ion chamber detector of each aspect described above, and has an advantage that detection efficiency is high even for low energy X-rays and the position of an electrode plate can be easily adjusted. There is.

  Hereinafter, the X-ray ion chamber detector of the present invention will be described in detail using examples.

  The X-ray ion chamber (ionization chamber) detector of the present embodiment is a so-called multi-channel type that has a large number of signal electrodes and can sequentially read out to detect the incident position and measure the energy. An X-ray transmission image is measured. Therefore, a detector for creating a two-dimensional X-ray image by continuously moving the part to be formed, or a CT (computer tomography) for obtaining a stereoscopic image by processing images irradiated with X-rays from various directions ) Can be used as a detector.

1 is a cross-sectional view of an X-ray multi-channel ion chamber detector according to one embodiment of the present invention, FIG. 2 is an exploded view thereof, and FIG. 3 is the thickness and X-ray transmittance of aluminum material and carbon fiber reinforced plastics material. It is a diagram which shows the relationship of these.
The X-ray multi-channel ion chamber detector of the present embodiment is a columnar detector having a long detection region in the axial direction, as can be seen from the exploded view of FIG. Is inserted into a cylindrical outer casing 2 and sealed with a lid 3, and a rare gas such as xenon gas is injected under pressure.

The core 1 is mounted with a high voltage electrode plate 11, a signal electrode 12 formed in a large number of lines, and a multiplexer circuit 13 for sequentially reading out charges accumulated in the signal electrode.
The high voltage electrode plate 11 is a metal plate having a length corresponding to the core, and the signal electrodes 12 are linear electrode pieces formed in large numbers on a printed board. The signal electrode 12 is disposed opposite to the high voltage electrode plate 11 with a narrow space interposed therebetween.
X-rays entering from the outside collide with xenon atoms and dissociate into electrons and ions. The dissociated electrons are collected and accumulated at a nearby signal electrode before being recombined by the action of the applied high voltage. For example, the charges collected by 1024 signal electrodes 12 arranged in parallel are scanned and read by the multiplexer 13 and sequentially transmitted to an external signal processing device. An external signal processing apparatus (not shown) generates a one-dimensional X-ray image from the input detection signal, and further develops it in two dimensions to form a two-dimensional X-ray transmission image, or perform advanced processing for CT. Go and get tomography.

  The size and interval of the electrode pieces differ depending on the required accuracy of the measurement object. For example, in the case of an X-ray diagnostic imaging apparatus, 1024 electrode pieces 0.5 mm wide and 80 mm long are arranged in parallel at 800 mm. It is done. Such a very precise structure can be manufactured relatively easily by applying the printed circuit board manufacturing technique.

The multiplexer circuit 13 is constituted by an integrated circuit, and in order to read out the stored charge of the signal electrode 12, a signal line must be connected to each electrode. Therefore, the signal line arranged and connected immediately behind the signal electrode 12 Are arranged in a short way.
The core 1 may include a base frame 14 that supports the signal electrode 12 and the multiplexer circuit 13. The high voltage electrode plate 11 is supported at a predetermined distance from the signal electrode 12. The high voltage electrode plate 11 is connected to an electric wire 15 suspended from the ceiling, and a high voltage of several kV is applied via the electric wire 15. The electric wire 15 may be a metal rod.
The core 1 is provided with an opening 16 in the wall, and X-rays entering from the opening 16 are guided to the space between the electrodes, and the amount of electric signals ionized according to the position and X-ray energy is integrated. Will be measured.
The core 1 configured in this manner is inserted into a hole provided in the outer casing container 2 and the position is fixed, then the lid 3 is tightened to seal the container, and after vacuuming, a rare pressure of several hundred kPa to several MPa Fill with gas.

  The outer welder 2 is made of fiber reinforced plastic. Since fiber reinforced plastic has carbon as a main component, it has a higher X-ray transmittance than light metals such as aluminum. In particular, since the difference is remarkable when the transmittance of low energy X-rays is compared, it is suitable for forming an X-ray transmission portion. Moreover, since the strength of the material such as tensile strength is larger than that of light metal, it can be used as a container for an X-ray ion chamber detector that encloses a high-pressure gas.

  The strength of the fiber reinforced plastic can be calculated from the mixing ratio of the reinforcing fiber and the matrix by a composite rule, but in the case of carbon fiber reinforced plastic (CFRP) using carbon fiber as the reinforcing fiber and epoxy resin as the matrix resin The tensile strength of 2000 MPa or more, which is 10 times that of aluminum having a tensile strength of about 200 MPa, can be provided. Therefore, an outer container made of CFRP can sufficiently withstand high-pressure gas even with a wall thickness thinner than that of an aluminum container.

  In addition, since CFRP contains carbon as a main component and does not contain metal atoms such as sodium and potassium, X-ray absorption is small and X-ray transmittance is high compared to aluminum and the like. FIG. 3 is a graph in which the transmittance of 20 keV X-rays is plotted against the thickness of material for aluminum and CFRP. From this, the transmittance of aluminum decreases to about 0.6 even when the thickness is 0.5 mm, whereas the thickness of CFRP decreases only to about 0.8 even with a thickness of about 4 mm. Therefore, by using a CFRP outer casing, it is possible to configure a detector that can sufficiently detect X-rays without thinning the X-ray inlet.

In addition to the epoxy resin, various synthetic resins such as a polyester resin, a phenol resin, a polyimide resin, a polyether ether ketone (PEEK) resin, a polyphenylene sulfide (PPS) resin can be used for the matrix of the fiber reinforced plastic. Further, even when high-strength synthetic fibers such as aramid fibers are used as reinforcing fibers, the low-energy X-ray transmittance is high, and the same effect can be obtained.
In the X-ray ion chamber detector of the present embodiment, the inner pressure is supported by the outer container, and the core cylinder has an X-ray entrance opening so that X-rays can freely pass therethrough. Therefore, the material of the core is not limited and may be a metal.

The X-ray ion chamber detector of the present embodiment is configured by mounting an electrode and a signal extraction circuit on a core and inserting the core into an outer container. In the X-ray ion chamber detector, the X-ray incident position and the electrode plate position adjustment are important factors that affect the detection efficiency.
In the case of the detector of the prior art, advanced technology is required to adjust the position of the electrode plate in the aluminum container in an invisible state. However, in the X-ray ion chamber detector of this embodiment, Since the electrode plate and the like are fixed to the core before the core is inserted into the cylindrical outer container, the position adjustment operation can be performed while confirming the position of the electrode plate from the opening of the core. Furthermore, the core with the electrode plate or the like fixed at a predetermined position with respect to the opening was inserted into the outer container and rotated slightly to the left and right, and the mark and the core marked on the surface of the outer container were marked By aligning the mark, it can be easily put in place.
In this way of assembling, even if it is not an expert, accurate alignment can be performed easily. In addition, it can be easily stored in the correct position even during reassembly during maintenance.
In addition, although the case where the cross-sectional shape was circular was demonstrated about the outer casing container or the core above, it cannot be overemphasized that other shapes may be sufficient if it can mutually fit.

1 is a cross-sectional view of an X-ray ion chamber detector according to one embodiment of the present invention. It is an assembly exploded view of the X-ray ion chamber detector of a present Example. It is a graph showing the X-ray transmittance of the fiber reinforced plastic and aluminum used for a present Example. It is the elevational sectional view and plane sectional view of the conventional X-ray ion chamber detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 2 Outer casing 3 Lid 11 High voltage electrode plate 12 Signal electrode 13 Multiplexer circuit 14 Base mount 15 Electric wire 16 Opening

Claims (6)

An X-ray ion chamber detector comprising a cylindrical outer casing capable of sealing and a core provided with a cylindrical metal carrier coaxial with the outer casing , wherein the carrier is an inner wall of the outer casing. A pair of electrode plates and a signal readout circuit are fixed to each other having an outer wall side surface that can be fitted into the side surface and can be inserted and removed in the axial direction and rotated around the shaft , and an X between the pair of electrode plates is fixed. The outer casing is formed of a fiber reinforced plastic that easily transmits low-energy X-rays, is sealed after inserting the core, and encloses a sensitive gas. An X-ray ion chamber detector, wherein an X-ray entering a space between the electrode plates is detected by applying a high voltage between the electrodes.   The pair of electrode plates is characterized in that one of the pair of electrode plates is one high voltage electrode plate and the other is a signal electrode plate formed by arranging a plurality of linear signal electrodes in the axial direction. The X-ray ion chamber detector according to claim 1. The X-ray ion chamber detector according to claim 1 or 2 , wherein the outer casing is made of carbon fiber reinforced plastic. 2. The core according to claim 1, wherein the electrode plate and the signal readout circuit are mounted on a metal carrier, and the carrier has an opening in a portion for guiding X-rays between the pair of electrode plates. X-ray ion chamber detector according to any one of 3. The signal readout circuit includes a switching unit connected to the signal electrode, and switches each signal electrode by the switching unit to sequentially switch and read out charges accumulated in the signal electrode, thereby giving a one-dimensional image of X-rays. X-ray ion chamber detector according to claim 1, any one of 4, characterized in that. X-ray detector utilizing the X-ray ion chamber detector according to any one of claims 1 to 5.

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