JPS60180053A - Ionization chamber type radiation detector - Google Patents

Abstract

PURPOSE:To prevent the variation of the pitch of the joints between electrode blocks owing to the ambient temperature change, by fixing each of the adjacent electrode holding plates of the adjacent electrode blocks together respectively through connecting plates having thermal expansion coefficient nearly equal to that of said holding plates as one body. CONSTITUTION:Signal electrode plates 11 and high voltage electrode plates 12 are holded alternately between the pairs of holding plates 13 of ceramics or the like to form an electrode block 1a each. These electrode blocks are contained air-tightly within a container 22 of aluminum or the like with the intervention of a bottom plate 16 made from 45% Ni-Fe alloy and thus an ionization chamber type radiation detector is formed. In this case, the upper and lower holding plates 13 of the adjacent electrode blocks 1a are fixed respectively by connecting plates 24 of 45% Ni-Fe alloy having thermal expansion coefficient nearly equal to that of the holding plates 13 as one body. Therefore, it is possible to absorb the variation of the pitch of the joints between the electrode blocks owing to the ambient temperature change and to assure accurate performance of the detector.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ionization chamber type radiation detector, and particularly to a multi-channel ionization chamber type radiation detector.

[Background of the invention]

This type of scanner is widely used in a so-called low-motion rotation type OCT scanner in which an X-ray tube and a detector rotate around a subject while maintaining their relative positional relationship. Detectors for such scanners require stability of each detection element over time or external temperature, since slight variations in the characteristics of each detection element arranged in an array can cause large artifacts in the final CT image. Ru. The detector itself consists of cutting a large number of grooves into an insulating material, arranging the insulating material so that one set of the grooves faces each other, and inserting signal electrode plates and high voltage electrode plates alternately between the grooves, and inserting the insulating material The structure is such that an electrode assembly is assembled by fixing the electrode assembly to a container, and this electrode assembly is sealed in a container together with an ionized gas. In general, the electrode assembly is divided into units of several tens or pixels from the viewpoint of material availability, processing accuracy, and response when a defective detection element occurs. A detector assembly of several hundred elements is constructed by arranging several electrode blocks composed of a plurality of elements, and this electrode assembly is fixed in a container.

A problem with such detectors is that when the ambient temperature changes, the electrode plate pitch between the electrode blocks varies, causing artifacts in the final CT image.

In other words, ceramic is generally used as the insulating material, and aluminum is used for the container because it requires low radiation absorption and strength as a pressure vessel, but these materials have significantly different coefficients of thermal expansion. , the electrode plate pitch between the electrode blocks changes due to changes in ambient temperature, and the characteristics of the detection elements between the electrode blocks differ from those of the remaining electrode blocks. In roti-sion/rotation-type OCT scanners, in order to eliminate the effects of non-linearity variations in the detection characteristics of individual detection elements, for example, before measuring the subject, measurements are taken in advance using a water fan dome, and the data is is used to calibrate the data obtained by the sampler, but when a pitch variation occurs, the characteristics of the detection element change and cannot be corrected by the above calibration.

Therefore, a detector was devised whose main parts were constructed as shown in FIG. In FIG. 1, 1a is an electrode block constituting an electrode assembly 1. In FIG. 11 is a signal electrode plate, 12 is a high voltage electrode plate, 13 is an electrode holding plate, 14 is a lower plate, 15 is a container lid, 16 is a bottom plate, and 17 is a screw.

The electrode holding plate 16 is made of an insulating material such as ceramics, and has a coefficient of thermal expansion α of about 6.8×10 2 .

On the other hand, the lower plate 14 and the container lid 15 are made of aluminum, α=? It is 26×10.

The bottom plate 16 includes the electrode holding plate 13 and the lower plate 14. Both plates 13 are used to absorb the difference in thermal expansion coefficient α with the container lid 15.
．． 14 interposed between each other, for example, the electrode holding plate 1
It is made of a 45'% Ni--Fe alloy with a coefficient of thermal expansion α approximately equal to 3.

In the above configuration, the screw 17 is tightened by the plate 13.
, 14, and 16 due to thermal expansion and contraction, etc., there is almost no restraining force because it is within the normal elastic change range. The dimensional change caused by this is absorbed by the sliding of the bottom plate 16 and the lower plate 14. Therefore, distortion between the electrode holding plate 16 and the lower plate 14 is prevented. As a result, the seam pitch variation between the electrode blocks 1a, 1a has decreased from 6.6 μm at 7° C. when the conventional bottom plate 16 is not interposed to approximately 0.6 μm at 7° C.
It was possible to reduce the temperature to below μrrL/°C and '/lo.

However, even in the above-mentioned detector, the improvement effect is insufficient when the ambient temperature changes significantly, for example by 10° C. or more, and the drawback remains that artifacts are produced in the final CT image.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks, and even when the ambient temperature changes are large, it is possible to suppress the variation in the joint pitch between electrode blocks to a much smaller extent, and the final C.
It is an object of the present invention to provide an ionization chamber type radiation detector that can prevent the occurrence of artifacts in T images.

[Summary of the invention]

In the ionization box-type radiation detector of the present invention, the electrode holding plates of adjacent electrode blocks in the container are integrated with each other via a connecting plate made of a material having the same or similar coefficient of thermal expansion as that of the electrode holding plates. By fixing the electrode blocks together, the adjacent electrode blocks are integrated, and fluctuations in the pitch of the joints between the electrode blocks due to changes in ambient temperature are prevented.

[Embodiments of the invention]

The present invention will be described in detail below with reference to FIGS. 2 to 4. FIG. 2 is a partially cutaway perspective view showing an embodiment of the ionization chamber type radiation detector according to the present invention, and in the figure, reference numeral 1 denotes an electrode assembly consisting of a plurality of electrode blocks 1a.

Each electrode block 1a has a signal electrode plate 11 and a high voltage electrode plate 12 between a pair of electrode holding plates 13 and 13 arranged oppositely.
and are arranged and held alternately at predetermined intervals.

In this case, among the pair of electrode holding plates 13, 13,
At least the one on the lower plate side, which will be described later, has a step formed on the outer surface side of its end as shown in FIG.
．． A recess 21 is formed between the holes 13.

η is a pressure vessel (detector) in which the electrode assembly 1 is sealed together with ionized gas;
．． Lower plate 14. The main component is a container lid 15 and a signal extraction plate (not shown), and airtightness is maintained.

Each electrode block 1a is fixed in the pressure vessel n by screw tightening, and in this case, between each electrode block 1a and the lower plate 14, for example, 45% Ni-Fe
A bottom plate 16 made of alloy is interposed therebetween.

24 is an adjacent electrode block 1a in the container 22.
The electrode holding plates 15 and 13 of , 1a are connection plates that integrally fix the adjacent electrode blocks 1a.

1a are integrated to form an electrode assembly 1. In this case, the connecting plate 24 is made of a material having the same or similar coefficient of thermal expansion α as the electrode holding plate 13, for example, the electrode holding plate 16 is made of alumina ceramic (α÷6.8×1O−6).
, the coefficient of thermal expansion α is approximately equal to 45%
Made of Ni-Fe alloy. Moreover, this connecting plate 24 is
On the lower plate 14 side, it is arranged in the recess 21 formed between the adjacent electrode holding plates 13, 13, and on the bottom side of the container body 23, it is simply straddled over the outer surfaces of the ends of the adjacent electrode holding plates 13, 13. will be placed. The reason why the connecting plate 24 is provided not only on the lower plate 14 side but also on the bottom side of the container body 23 is to reduce vibration noise as well as reduce joint pitch fluctuation between the electrode blocks ia.

The connecting plate 24 and each electrode holding plate 13 are bonded together with an adhesive 25 as shown in FIG. As the adhesive 25, an epoxy resin having a large adhesive force is used here, but if decomposition during repair is taken into consideration, a thermoplastic resin that can be removed by heating after adhesion is preferable.

In the above-mentioned detector, the electrode block 1a formed by the bottom plate 16
, 1a is the same as in the case of FIG. 1.

In the detector of the present invention, when the ambient temperature changes significantly, for example increases, the electrode holding plate 13. The lower plate 14 and the bottom plate 16 undergo thermal expansion, but as mentioned above, the lower plate 14 made of aluminum has the largest coefficient of thermal expansion, so the electrode holding plates 13.1 of the adjacent electrode blocks 1a and 1a in FIG.
The opposite ends of 5 tend to extend away from each other.

However, at this time, since the connecting plate 24, which has a coefficient of thermal expansion approximately equal to that of the electrode holding plate 13, is fixed between the electrode blocks with the adhesive 25, acts in the direction in which they approach, thus changing the distance between the opposing ends, i.e. the electrode block 1a
, ia will be absorbed. Thereafter, when the ambient temperature drops, the electrode plate 13
, 13 and the connecting plate 24 undergo an action opposite to that described above, so that the above seam pitch variation is similarly absorbed.

〔Effect of the invention〕

As described above, the present invention enables the electrode holding plates of adjacent electrode blocks in a container to be integrally fixed to each other via a connecting plate made of a material having the same or similar coefficient of thermal expansion as that of the electrode holding plates. By integrating the adjacent electrode blocks, even if the ambient temperature changes, variations in the seam pitch between the electrode blocks can be absorbed and reduced, thereby preventing the occurrence of artifacts in the final CT image. It can be prevented.

In particular, as in the above-mentioned embodiment, by also using a means to interpose a bottom plate between the electrode block and the lower plate, the seam pitch fluctuation can be reduced to 0.111 m 1°C or less, when only the bottom plate is used. A remarkable effect is obtained in that the resistance can be further reduced to less than b.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the main parts of an improved ionization chamber-type radiation detector, FIG. 2 is a partially cutaway perspective view of an embodiment of the ionization chamber-type radiation detector according to the present invention, and FIG. The figure is a perspective view of the lower electrode holding plate of the detector taken out, and FIG. 4 is a sectional view taken out of the fixed portion between adjacent electrode blocks of the detector. DESCRIPTION OF SYMBOLS 1... Electrode assembly, 1a... Electrode block, 11... Signal electrode plate, 12... High voltage electrode plate, 16
... Electrode holding plate, η... Pressure vessel, 24... Connection plate, 25... Adhesive. Patent Applicant Hitachi Medical Co., Ltd. Agent Patent Attorney Tadashi Akimoto Figure 1! ! ? Figure 2 Figure 3 Figure 4 Figure 4 17, 27

Claims (1)

[Claims] The electrode assembly includes an electrode assembly in which signal electrode plates and high voltage electrode plates arranged alternately are held by an electrode holding plate, and a container in which the electrode assembly is sealed together with an ionized gas. In an ionization box-type radiation detector which is not made up of a plurality of electrode blocks, and which is fixed in the container, and in which the electrode holding plate and the container are made of materials having different coefficients of thermal expansion, the adjacent cells in the container are The adjacent electrode blocks are integrated by integrally fixing the electrode holding plates of matching electrode blocks to each other via a connecting plate made of a material having the same or similar coefficient of thermal expansion as that of the electrode holding plates. An ionization chamber type radiation detector characterized by: