JPH0526154B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to a scintillation radiation detector using a cicitillator that emits radiation due to radiation such as X-rays and γ-rays, and particularly to an X-ray tomography device (X-ray CT). The present invention relates to a radiation detector suitable for use.

[Conventional technology]

There are various types of X-ray CT devices depending on their scanning methods. An example is shown in FIG. X-ray beam 2 spread out in a fan shape and multiple X-ray beams (30 to 2000) arranged in an arc with the X-ray source 1 at the center
The multi-element radiation detector 4 includes a small radiation detector 3. Generally used as the radiation detector are an ionization box type detector that utilizes the ionization effect of gas, and a scintillation detector that combines a scintillator and a photodetector.

Scintillation detectors include those that use a photomultiplier tube as a photodetector, those that use a microchannel plate, and those that use a semiconductor photodetector (Si
The most common type is one that uses a photodiode (such as a photodiode). In order to realize a high-density multi-element X-ray CT detector, it is effective to use small semiconductor light-receiving elements that can be arranged in high density as photodetectors.

An example of a radiation detector for X-ray CT using such a scintillator and a semiconductor light-receiving element is shown in Japanese Patent Application Laid-Open No. 58484/1984.

[Problem to be solved by the invention]

In X-ray CT detectors, it is known that slight sensitivity differences between arrayed detection elements cause ring-shaped artifacts on the final CT image. Therefore, in a detector using a scintillator and a photodiode as described above, it is necessary to equalize the optical output of each scintillator and the photodetection sensitivity of each photodiode. Furthermore, even if these are sufficiently uniform, if there is light or X-ray leakage between two adjacent detection elements, the apparent sensitivity of those two detection elements will be higher than that of the other detection elements. It becomes high, and a ring-shaped artifact also occurs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a radiation detector that has a simple configuration and can minimize sensitivity differences and crosstalk between detection elements.

[Means to solve the problem]

A feature of the present invention is that a plurality of detection elements are formed by a plurality of photodiodes arranged on a substrate with minute intervals and a scintillator arranged on each of the photodiodes, and A plurality of grooves are formed in accordance with the positions between the detection elements, and a partition plate for radiologically and optically isolating the detection elements is inserted between the gaps and the grooves. It's in the detector.

[Effect]

The photodiode array surface is truly flat,
Further, if the tip of the partition plate is also truly straight, it is possible to make the two parts close together, and light and X-rays will not leak into adjacent elements. However, in reality, the board may have minute irregularities or warps.
Also, the substrate may warp due to changes in ambient temperature. Even in such a case, according to the above configuration, the tip of the partition plate is inserted into the groove of the substrate, so the amount of light and scattered X-rays that leak into the adjacent element through the gap at the tip of the partition plate is reduced. can be made extremely small, resulting in a multi-element radiation detector with less crosstalk and therefore less difference in sensitivity between elements.

〔Example〕

The partitioning method between adjacent detection elements (small radiation detectors) in the high-density multi-element scintillation radiation detector according to the embodiment of the present invention is the second method.
The structure is as shown in the figure.

A thin groove is formed in the light shielding plate 5 and a printed circuit board 8 on which Si photodiodes 7 optically coupled with a scintillator crystal 6 are arranged at a predetermined distance. A partition, ie a partition plate 9, is inserted for providing isolation between the optical and radiological elements.

Since the light shielding plate 5 also serves as an entrance for radiation, it is preferably made of a material that absorbs little radiation, and its thickness is preferably as thin as possible. However, when inserting the partition plate 9 and forming a groove to prevent light leakage between adjacent detection elements as described above, a minimum width of 1 mm is required. In this case, the radiation attenuation is 0.5 to several percent, reducing the dose utilization efficiency for radiation detection.

Next, another embodiment shown in FIG. 3 that also eliminates the above-mentioned decrease in utilization efficiency will be described in more detail.

In the multi-element detector shown in FIG. 3 as well, adjacent detector elements are partitioned by partition plates 9 which serve as partition walls, and each detector is independent. The partition plate 9 is made of a material with high radiation absorption, such as W, Mo, Ta, etc. from 0.05 to
A metal plate with a thickness of 0.2 mm is used. The partition plate 9 is inserted and fixed into a grooved portion of a grooved wiring board 8 in which grooves are provided at regular intervals (1 mm to 6 mm). The grooved wiring board 8 is a special printed wiring board that has the above-mentioned grooves on one side and an electrical signal wiring pattern on the opposite side. A semiconductor photodetector 7 is inserted into the grooved wiring board 8 between the grooves, and the signal line is connected to the electrical signal wiring pattern on the back surface with solder to be fixed electrically and mechanically. This semiconductor photodetector 7
The photocathode is made of a material with a relatively high refractive index, such as Si.
Using grease or epoxy resin, single crystal scintillator 6 such as CsI, CdWO ₄ ,
Optically bond _ZnWO4 . scintillator 6
A light reflecting plate 11 is provided on the radiation incident direction side for reflecting the light emitted from the scintillator 6 and effectively guiding it to the photocathode of the semiconductor photodetector 7. The light reflecting plate 11 is a thin Al plate with a thickness of 20 to 50 μm and has a mirror surface, or a polymer resin sheet (10
A thin plate with a high reflectance (~50 μm thick) is coated with Al evaporation to give it a mirror surface. The light plate reflection plate 11 is formed from the opposite side of the scintillator 6 through a cushion material 10 such as a polymer foamed steel roll or sponge containing a large amount of air, and a light shielding plate/pressing plate 12 (aluminum plate with a thickness of 0.2 to 0.5 mm). It has a structure in which it is pressed against the partition plate 9 and the scintillator 6. in this case,
The partition plate 9 has a structure that protrudes from the surface of the scintillator 6 by about 0.5 to 1 mm.

The radiation incident on the detector first enters the light shielding plate/suppressing plate 12 made of Al material that allows the radiation to easily pass through and is hardly absorbed.After passing through, most of the radiation is air and the radiation is not absorbed. The light reaches a small cushion material 10, passes through this, further passes through a light reflecting plate 11, and reaches a scintillator.
The loss due to radiation absorption up to this point is less than that of conventional products, and is 1 to 3% or less. Here, since the light reflecting plate 11 is a thin plate, its shape is deformed to match the unevenness of the scintillator 6 and the partition plate 9, and is further pressed by the cushion material 10 and the light shielding plate/pressing plate 12, thereby separating the scintillator 6 and the partition plate. Closely attached to the board. This allows light to be reflected and adjacent detectors to be optically isolated. Therefore, there is no need for a groove into which a partition plate for isolation is inserted, as in the light shielding plate 5 of the embodiment shown in FIG. 2, and slicing can be omitted. The radiation reaching the scintillator is converted into light within the scintillator, and the light is detected by the semiconductor photodetector 7 and extracted as an electrical signal. Therefore, the electrical signal extracted is proportional to the amount of incident radiation.

The common structure of these embodiments is that the partition plate is not simply pressed against the surface of the substrate, but its tip is inserted into a groove provided in the substrate, which prevents warping of the substrate. Light or scattering from the gap at the tip of the partition plate caused by
It is possible to effectively prevent a phenomenon in which a line leaks into an adjacent detection element, and the actual sensitivity of the detection element where the leakage occurs increases, resulting in a difference in sensitivity between array elements.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to extremely reduce the occurrence of differences in sensitivity between elements due to leakage of light or radiation at the tip of the partition plate between the detection elements, and it is particularly suitable for use in X-ray CT. A radiation detector can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram schematically showing an example of an X-ray CT device;
2 and 3 are perspective views showing the structure of a scintillation radiation detector according to an embodiment of the present invention, respectively. 2...X-ray beam, 6...scintillator, 7...
...Semiconductor photodetector, 8...Grooved wiring board, 9...
Partition plate, 10...Cushion material, 11...Light reflecting plate, 12...Shading plate and holding plate.

Claims (1)

[Claims] 1 A plurality of photodiodes arranged at minute intervals on a second surface opposite to the first surface of a substrate having an electrical signal wiring pattern on the first surface, and a plurality of photodiodes arranged on each of the photodiodes. A plurality of detection elements are formed by the disposed scintillators, and a plurality of grooves are formed on the second surface of the substrate in alignment with the positions between the detection elements, and an optical path is formed between the detection elements. A radiation detector characterized in that a partition plate is inserted between the space and the groove to isolate the target and radiation, and radiation is incident from the second surface side of the substrate.