JPH02208592A - X-ray detector for ct apparatus - Google Patents

Abstract

PURPOSE:To make it possible to prevent the dispersion in characteristics between detecting elements by combining a scintillator material wherein light- shielding applied film layer are formed at both end parts and a silicon photodiode (SPD) having sensitivity only at the central part in contact with the scintillator material. CONSTITUTION:An SPD 2 on a printed wiring board 4 and a scintillator material 1 are bonded 6. The scintillator material is separated with channel grooves 8 and partitioned with partitioning plates 3 which are inserted in the grooves. Light-shielding applied film layers 7 comprising epoxy paint and the like are formed at the end parts of the material 1. Thus the leaking of the light emitted in the scintillator is prevented. An SPDP layer 2c is provided only at the central part where the SPD 2 and the material 1 are in contact optically. A signal current in response to the incident light is obtained. A part outer than the material 1 becomes a dead zone 2g. Even if light is inputted, a signal current is not generated. In this structure, the effect of the light leaked from the end surface of the material 1 on the signal output can be decreased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an X-ray detector for X-ray cTifflliW,
In particular, it relates to reducing characteristic variations between detection elements and realizing an X-ray detector with high measurement accuracy.

[Conventional technology]

An X-ray detector for a CT apparatus is constructed by arranging a predetermined number of multi-channel X-ray detection element arrays in a polygon shape, each of which is a combination of a scintillator and a photoelectric conversion element. The structure of one conventional X-ray detection element array has been changed to a second one.
As shown in the figure. (a) shows the outside, and (b) (Q) shows the cross-sectional structure.

An X-ray detection element is constructed by combining a scintillator material that converts incident X-rays into light according to their intensity and a photoelectric conversion element that receives the light and converts it into an electrical signal.

One element of the X-ray detector is composed of a scintillator material 1 processed to a predetermined size and a photoelectric conversion element combined so that the scintillator material and the light-receiving surface are in contact with each other. The scintillator material is determined by its scintillation efficiency (a value that indicates how much incident X-ray energy can be converted into light energy) and the light transmittance (a value that indicates how much light emitted inside the scintillator can be converted into light energy without being attenuated). It is necessary to make a selection by taking into consideration factors such as (a value indicating whether the light reaches the light receiving surface), afterglow characteristics (a characteristic indicating the time it takes for the emission from the scintillator to disappear after the incident X-ray disappears, and whether the emission has decreased), etc. Generally, materials such as BGO and CaW are used.

The photoelectric conversion element must have high conversion efficiency to convert incident light into a current signal, and must also use a material with high sensitivity near the emission wavelength of the scintillator; silicon photodiodes and the like are commonly used. has been done.

Further, each element is separated into channels by a partition wall plate 3. The partition plate 3 reduces crosstalk caused by secondary fluorescent X-rays generated by X-rays incident on the scintillator of each element and scattered X-rays from the scintillator leaking into adjacent channels, and efficiently converts the light emitted by the scintillator into photoconverters. It is used to guide the light to the light receiving surface of the conversion element.
The surface of a tungsten plate or molybdenum plate, which is a material with a high X-ray absorption coefficient, is polished and aluminum is further vapor-deposited on the surface to increase the light reflectance.

The manufacturing process of this X-ray detection element array is shown in Figures 3(a) to (
Shown in d). First, scintillator material 1 processed into a plate with a predetermined thickness, and scintillator material 1 slightly wider than this scintillator material 1.
Silicon photodiodes 2, each consisting of several channels of elements, are bonded together on a single wafer using a transparent adhesive 6 with high light transmittance so that their centers coincide (Fig. 3(a), (b)”).

Next, grooves 8 are cut in the scintillator plate 1 and silicon photodiode 2 bonded together so that the scintillator is separated into channels (FIG. 3(C)).

This groove processing is performed using the pattern of the signal electrode of the silicon photodiode 2, which is slightly exposed at both ends of the scintillator, as a position reference, and the groove depth is determined so that the scintillator is completely separated. , the depth is set to such an extent that the bottom of the groove reaches the silicon photodiode 2.

Finally, the partition plate 3 is inserted into this groove 8 and fixed with adhesive 5. An opaque adhesive 5 is used to prevent light leakage at both ends. In other words, the adhesive 5 used here has two roles: fixation and light shielding.

[Problem to be solved by the invention]

In the detector structure, if the opaque adhesive 5 fixing both ends is insufficiently filled into the scintillator end face and the exposed portion of the light receiving surface at both ends of the silicon photodiode,
A part of the light emitted inside the scintillator follows a path that exits from the end face and enters the silicon photodiode 2.

The ratio of the amount that enters the silicon photodiode 2 after exiting from the end of the scintillator to the row section varies depending on the filling state of the opaque adhesive 5. This directly leads to variations in X-ray detection characteristics between elements.

If the characteristics of the X-ray detection element vary widely, errors will occur during measurement, and ultimately artifacts will occur on the image, significantly reducing diagnostic performance.

As described above, the conventional structure has a problem in that the detection characteristics of each element vary depending on the filling state of the adhesive fixed at the end of the scintillator material 1.

[Means to solve the problem]

The above problem can be solved by providing a light-shielding layer at the end of the scintillator 7 and by creating a structure in which the exposed portion of the silicon photodiode 2 is not sensitive to light.

By combining a scintillator plate 1 with a coating film or the like formed on the side surface of the scintillator plate 1 in advance and a silicon photodiode 2 that is sensitive only in the central part in contact with the scintillator material 1, the role of the adhesive 5 at the end can be reduced. It is only for fixing the partition plate 3 and does not need to serve as a light shielding function.
The filling state does not affect the detection characteristics.

[Effect]

In this way, by reducing the variation in detection characteristics between each element, measurement accuracy can be further improved.
It becomes possible to provide an X-ray detector that can obtain images with high diagnostic ability.

〔Example〕

An embodiment of the invention is shown in FIG. FIG. 1(a) shows the external appearance of the X-ray detection element array, and FIGS. 1(b) and 1(c) show the cross section.

A silicon photodiode array 2 is placed on a printed wiring board 4, and a scintillator material 1 is placed on top of the silicon photodiode array 2 using a transparent adhesive 6.
are pasted together. Each channel has a groove 8 of a predetermined width.
The grooves 8 are made of a material with low X-ray transmittance, such as molybdenum or tungsten.
They are separated by partition plates 3 whose surfaces are plated or aluminum vapor-deposited to increase the light reflectance. At the end of the scintillator material 1, there is a light-shielding coating FI7 made of opaque epoxy paint or the like that shields light, and prevents light emitted from inside the scintillator from leaking to the outside.

The partition plate 3 is attached to the scintillator material 1 with an opaque adhesive 5.
and is fixed to the photodiode array 2. The following describes how the xi detector having the structure of this embodiment detects incident X-rays.

When the X-rays entering from above in FIG. 1(a) enter the scintillator, they emit visible light corresponding to the intensity of xi. Most of the light emitted inside the scintillator passes through the scintillator and directly enters the light-receiving surface of the silicon photodiode 2, but the negative part goes outside from the side of the scintillator, is reflected by the surface of the partition plate, and returns to the inside of the scintillator. and enters the light receiving surface of the silicon photodiode 2.

The silicon photodiode 2 is called a PIN photodiode because of its structure. Substrate of N (
A high-resistivity layer 2d is provided on the base layer 2e, and on top of that, there are two layers 2c separated for each channel,
The signal electrode 2a is connected to these two layers 2c, and the common electrode 2f is connected to the N layer 2.
electrically connected to e. A surface protective film 2b covers the two layers 2c. The light incident on the silicon photodiode 2 passes through the 2nd layer 2c and passes through the 1st layer 2 in the middle.
When it jumps into d, it generates electron-hole pairs, which are carriers. These electrons and holes diffuse into the second layer 2c and the N layer 2e, respectively, and reach each electrode to become a signal current.

In this way, an X-ray detector is configured that outputs a signal current corresponding to the intensity of incident X-rays.

In this embodiment, a light-shielding coating layer 7 is provided to prevent light emitted from inside the scintillator from leaking to the outside. In addition, the internal structure of the silicon photodiode 2 also includes P only in the portion that is in optical contact with the scintillator material 1.
WJ2c is provided, and outside of that, 2 layers 2c are not provided and 1
Leave layer 2d as is.

As a result, only the part of the silicon photodiode light-receiving surface that is in contact with the scintillator material 1 (the part with PI2c) becomes a sensitive part and a signal current corresponding to the incident light can be obtained, but the part outside the scintillator material 1 2g
The portion (where the second layer 2c is not present) becomes an insensitive portion and does not generate a signal current even if light is incident thereon.

〔Effect of the invention〕

With such a structure, the contribution of light leaking from the end face of the scintillator material to the signal output can be significantly reduced. For this reason, the X-ray detection characteristics between each element can be made uniform without variation regardless of the filling state of the edge adhesive.

In addition, since the adhesive at the end only fixes the partition plate, it is not necessary to make it evenly filled, which has the effect of improving the workability of bonding.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, in which (,) shows the external appearance, (b) shows a cross section along line A-A, and (c) shows a cross section along line B-B. Figure 2 shows a conventional example; (,) indicates the external appearance;
(b) shows a cross section along CC, and (Q) shows a cross section along D-D. FIG. 3 is a diagram showing the manufacturing process of the X-ray detection element array. DESCRIPTION OF SYMBOLS 1...Scintillator material, 2...Silicon photodiode, 2a...Silicon photodiode signal electrode, 2b...Silicon photodiode surface protective film, 2
c...Silicon photodiode 2-layer region, 2d-Silicon photodiode 1-layer region, 2e...Silicon photodiode N-layer region, 2f...Silicon photodiode common electrode, 2g...Silicon photodiode insensitive region , 3... partition board, 4... printed wiring board,
5... Opaque adhesive, 6... Transparent adhesive, 7...
Light-shielding coating layer, 8...grooves. prisoner

Claims (1)

[Claims] 1. An X-ray tube and a multi-element detector are placed facing each other with the subject at the center, and as they rotate, they measure X-ray transmission data from each direction of the subject, and from that data the cross-sectional area of the subject is determined. A CT device that reconstructs an X-ray transmittance distribution image includes a scintillator material that emits visible light according to the intensity of incident X-rays, and a scintillator that converts the visible light incident on the light receiving surface into a current signal. Multi-element PIN with a light-receiving surface wider than the material
In an X-ray detector combining a silicon photodiode array with a mold structure, a light-shielding coating layer is provided on both ends of the scintillator material to prevent light emitted from inside the scintillator from leaking to the outside, and the silicon photodiode An X-ray detector for a CT apparatus, characterized in that the X-ray detector for a CT apparatus has a structure in which the portion other than the portion in contact with the scintillator material has no sensitivity to light.