JPH0220952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a radiation detector used in a radiation tomography apparatus.

Computerized tomography is one of the radiation tomography devices.
There is a device called tomography (hereinafter abbreviated as CT device). As shown in Fig. 1, this device is a radiation detector consisting of an X-ray source 1 that emits, for example, flat fan beam X-rays FX in a pulsed manner, and a plurality of radiation detection cells that detect the X-rays arranged in parallel. 2 through the subject 3, and these X-ray sources 1
The radiation detectors 2 are rotated around the subject 3 in the same direction and at the same speed to collect X-ray absorption data in various directions of the cross section of the subject 3. After collecting sufficient data, this data is analyzed by a computer, the X-ray absorption rate for each position of the object cross section is calculated, and the object cross section is reconstructed with a gradation level corresponding to the absorption rate. This enables analysis to be performed in as many as 2,000 gradation levels depending on the composition, making it possible to obtain clear tomographic images of tissues ranging from soft to hard.

Incidentally, the radiation detector 2 detects the energy of the X-rays transmitted through the cross section of the subject 3 as an ionizing current, and outputs this as X-ray absorption data.

In other words, when collecting this X-ray absorption data, the energy of the X-rays that have passed through the line connecting each radiation detection cell that makes up the ionization chamber and the X-ray source (this is called an X-ray path) is is detected as an ionization current, this is integrated for a predetermined time, the integrated value is discharged in a discharge circuit with a predetermined time constant, and the discharge time value is used as X-ray absorption data. When the data collection for the X-ray path from one direction is completed, data collection for the X-ray path from the next direction is completed, but during this time, the ionization current and discharge of the integral value due to the previous X-ray pass completely disappear. If the process is not completed, errors will appear in the next data collection. That is, X
The radiation repetition period of the line beam is generally limited by the recovery time of the radiation detector. This is a factor that greatly affects the data collection time (that is, the imaging time) per tomographic plane, and in today's world where there is a demand for shortening the imaging time, this must be shortened as much as possible. Furthermore, the resolution of the reconstructed image is determined by the sensitivity and resolution of the radiation detector, so in order to obtain an excellent CT system, it is necessary to use a radiation detector with a fast recovery time, high sensitivity, and high resolution.

In order to have excellent spatial resolution, it is desirable that the electrode plates constituting each radiation detection cell be disposed close to each other and uniformly over the entire length of the radiation detection cell row. Furthermore, since the radiation detector used in the CT apparatus detects a very weak current as a signal, it is necessary to be careful about leakage current between electrodes.

The present invention has been made in view of the above circumstances, and is achieved by alternately arranging a large number of electrode plates for high voltage and signal detection at predetermined intervals, and obtaining detection signals from each of the electrode plates for signal detection. In a radiation detector with spatial position resolution, an insulating support is used in which a plurality of grooves are formed into which the ends of the electrode plates are inserted, and the electrode plates are inserted and held in the grooves, and the signals are The electrode plate for detection and high voltage application is provided with a bag-shaped conductor at the support side end portion corresponding to the groove and insulated from the signal electrode plate and the high voltage electrode plate, and this conductor is grounded. This structure doubles the effect of leakage current on the detection signal, and the cushioning action of the bag-shaped conductor absorbs the vibration of the electrode plate, reducing microphonic noise, resulting in high sensitivity and high resolution. The purpose of the present invention is to provide a radiation detector that achieves the following.

Hereinafter, one embodiment of the present invention will be described in Figures 2 to 1.
This will be explained with reference to FIG. As described above, the radiation detector is placed facing the X-ray source through the subject. The X-ray source and the radiation detector, which are arranged facing each other, emit an X-ray beam in a pulsed manner while rotating around the subject at an arbitrary time. The X-ray beam passes through the cross section of the object while expanding in a fan shape with a spread angle θ. This X-ray beam then enters the radiation detection cell array and is ionized in accordance with its energy. Thereby, the photon intensity at the leading edge of the X-ray beam is detected by the electrode plate of the incident radiation detection cell in the form of an ionizing current and spatially identified.

As mentioned above, in order to obtain excellent spatial resolution, the electrode plates constituting each radiation detection cell row are brought close to each other to increase the number of X-ray passes.
It is desirable to arrange the X-ray paths at a constant pitch so that the width of the X-ray path is uniform.

In order to obtain this state, in the present invention, micropitch grooves are formed on the insulating material, and along the grooves, a bag-shaped conductive material is pasted on the side of the signal electrode and high voltage electrode plate. By inserting the side end of the hole, pitch accuracy can be easily achieved.

Hereinafter, one embodiment of the present invention will be described in order.

FIG. 2 is a perspective view showing the configuration of this device, in which reference numeral 4 denotes an arcuate box-shaped case that covers the electrode group and others;
Reference numeral 5 denotes a lid that closes the open side of the case 4 and mounts the electrode group and others. These case 4 and lid 5
is bolted to maintain sufficient strength and airtightness against the high pressure gas filled inside. In this radiation detector, the entrance portion 4b of the entrance surface 4a is thinned in accordance with the spread angle θ of the fan beam X-rays FX, so that sufficient X-rays can be incident thereon.

FIG. 3 is a plan view of this radiation detector, FIG. 4 is a front view thereof, and FIG. 5 is a sectional view taken along the line AA in FIG. As can be seen from the figure, the inside of the main body 4 is hollow, and the X-ray incident part 4b has a thin wall thickness.

FIG. 6 is a diagram showing how the electrode plates 6 and 7 are arranged in the case 4, and a pair of opposing electrode plates 6 and 7 constitute one radiation detection cell. In reality, the electrode group is attached to the lid that closes the case 4.

Figure 7 shows the raw plate 6a of the signal and high voltage electrode plates 6 and 7.
A protrusion 6b is formed in a part of a rectangular extremely thin conductive plate (tungsten plate or molybdenum plate). The terminal 6 of this blank plate 6a
In the vicinity of the opposing sides where b is not formed (groove insertion part), a thin strip-shaped insulator (for example, a flexible material such as polyimide or polyamide) as shown in Figure 8a is placed parallel to each side. A film) 8 is attached to the front and back sides of the electrode plate 6. That is, as shown in FIGS. 9 and 10, the end portion of the blank plate 6a is wrapped in a bag-like shape with this strip-shaped insulator 8, and is attached in parallel. and,
Furthermore, on the upper surface of this bag-shaped insulator 8, a thin bag-shaped conductor (copper foil, etc.) 9 with a small hole 9a bored at the end as shown in FIG. 8b is placed. Paste it like that. The conductor 9 is narrower in width than the bag-shaped insulator 8, and by making it longer, it is completely insulated from the base plate 6a via the bag-shaped insulator 8. Furthermore, the end portion of the bag-shaped conductor 9 having the small hole 9a protrudes from the base plate 6a as shown in FIG. 9, and by using the small hole, the bag-shaped conductor 9 can be used by grounding. become. As described above, the electrode plate shown in FIG. 9 is used as the signal electrode plate 6.

FIG. 10 shows a high voltage electrode plate 7 to which high voltage is applied.
This figure basically has exactly the same structure as the signal electrode plate, and the signal electrode plate 6 can be used as is. However, in order to avoid complication of the signal extraction line, the direction of the electrode terminal 6b is changed from the signal electrode plate 6 (the ninth
Insert it into the groove of the insulating support 10, which will be described later, in the opposite direction to that shown in Figure b).

The electrode plates 6 and 7 having such a configuration are alternately inserted and disposed on the insulating support attached to the lid 5. That is, as shown in FIG.
The electrode plate 6,
Strictly speaking, the electrode plates 7 are inserted and held between the electrode plate insertion grooves 10a so as to be arranged alternately along the X-ray transmission direction, and then the lid 5 is covered with the case 4. In this case, the terminals 6b of the electrode plates 6 and 7 should be placed on the opposite side of the X-ray entrance window 4b, and the terminals 6b should be placed on the signal electrode plate 6 and the high voltage electrode plate 7 so that their positions do not overlap, as shown in FIG. Alternate as shown. The high-voltage electrode plate 7 is connected to a high-voltage power source by connecting each terminal 6b with a lead wire 11, and the conductor 9 of each of the signal electrode plate 6 and high-voltage electrode plate 7 protrudes from the electrode plates 6 and 7. Connect with the lead wire 12 and ground using the end. The connection by this lead wire 12 is made through a small hole 9a provided at the end of the bag-shaped conductor 9.
This is done through this small hole 9a.

After the electrode plates 6 and 7 are attached, an insulating adhesive 13 such as thermosetting epoxy resin is poured into the side portion of the electrode plates 6 and 7 that is in contact with the insulating support 10. To suppress leakage current and securely fix electrode plates 6 and 7 to an insulating support 10. At this time, the insulating adhesive 13 is poured so as to come into contact with the conductor 9 on the electrode plate 6 so that a portion of the conductor 9 is covered with the adhesive. Also, the bag-shaped insulator 8 and the conductor 9, which have relatively low rigidity, are inserted into the groove 10a of the insulating support 10, and are integrated with the adhesive 13 to form the electrode plate 9,
It also contributes to the vibration absorption of No.7. That is, the harmonic noise of the electrode plates 6 and 7 is reduced.

Further, the detection signal is taken out in a direction perpendicular to the X-ray incident direction, that is, from the lid 5. That is, a plurality of electrodes 14 whose outer skins are insulated are attached to the lid 5 by penetrating them at regular intervals, and the terminals 6b of the electrode plates 6 facing each other are connected to each of the electrodes 14 to output a detection signal to the outside. There is.

This device with such a configuration has a cover 5 that connects the case 4.
It is used with the opening side closed airtight. Since the radiation detection cell constitutes an ionization tank, ionization occurs when radiation enters the gas (for example, xenon gas) between the high-voltage electrode plate 7 and the signal detection electrode plate 6. The ionized charges generated by this ionization phenomenon are attracted to the electrode plates 6 and 7 and extracted from the electrode plate 6 as a weak ionization current.

On the other hand, since a high voltage is applied to the electrode plate 7 for high voltage, in the case of a combination of only the insulating support 10 and the electrode plates 6 and 7, the high voltage causes volume leakage or surface leakage through the insulating support 10. A current flows into the electrode plate 6 and is mixed into the detection signal.

However, in this device, the inter-detection cell leakage current first flows into the conductor 9 which is adhered to the high-voltage electrode plate in the form of a bag. Since the conductor 9 is kept insulated from the electrode plate 6a by the bag-shaped insulator 8 and is grounded via the lead wire 11, leakage current flowing into the conductor 9 flows directly to the ground. , does not affect the electrode plate 6. Even if there is a leakage current that attempts to pass through the conductor 9 of this high voltage electrode plate 7 and flow into the signal electrode plate 6, this leakage current will be absorbed by this signal electrode plate as well as the high voltage electrode plate 7. Conductor 9 provided in 6
As a result, the signal is completely cut off, and no leakage current flows into the signal electrode plate 6. That is, the bag-shaped insulator 8 and the conductor 9 attached thereon serve as a protective electrode for protecting the signal electrode plate 6 from leakage current. A major feature of the present invention is that leakage current can be doubly blocked by attaching the protective electrode to both the signal and high voltage electrode plates.

Furthermore, the insulating adhesive 13 is poured into the insulating support 10 and the electrode plates 6 and 7 so that about half of the conductor 9 on the electrode plate 6 is covered with the insulating adhesive 13 in the width direction. , leakage current can be eliminated and the electrode plates 6 and 7 can be supported more reliably. Therefore, only the ionizing current can be detected with high sensitivity.

In addition, this device uses an insulating support 10 in which fitting grooves 10a, 10a' are formed at predetermined intervals to hold the electrode plates 6, 7.
The fitting grooves 10a, 10a' can be machined in advance with high precision using a numerically controlled machine tool, etc. Therefore, after installing the insulating support 10 on the case 4, the fitting grooves 10a, 10a of this support 10 can be machined with high precision using a numerically controlled machine tool or the like. 'If you insert the electrode plates 6 and 7 between them, the electrode plates 6 and 7 will be inserted at regular intervals.
7 can be arranged alternately, and the arrangement interval of the electrode plates can also be made small. Moreover, these insulating supports 10 and electrode plates 6, 7 are bonded with insulating adhesive 1.
Since it is fixed at 3, mechanical accuracy is maintained, and therefore a high-resolution radiation detector can be obtained.

In this way, radiation detection with spatial positional resolution is achieved by alternately arranging a plurality of electrode plates for high voltage and signal detection at predetermined intervals, and obtaining detection signals from each of the electrode plates for signal detection. In the device, a support having a plurality of grooves for holding the ends of the electrode plate is used, and the electrode plate is inserted and held in the grooves, and each of the electrode plates for signal detection and high voltage has the A bag-shaped conductor is provided near the end of the support side to correspond to the groove and insulated from the electrode plate, and a bag-shaped conductor is provided on the side of the conductor portion at the portion between each electrode plate and the support. Since an insulating adhesive is applied to cover the edges and the conductor is grounded, leakage current flowing into the signal detection electrode plate is blocked by the conductor, so only the ionizing current can be detected with high sensitivity. In addition, by using the support, the grooves can be formed in advance with high precision, so the spacing between the electrode plates can be made with high precision.Furthermore, since the electrode plates and the support are fixed with an insulating adhesive, It is possible to provide a radiation detector with excellent features such as dimensional accuracy can be maintained and resolution can also be improved.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the CT device, Figure 2
3 is a front view thereof, FIG. 4 is a side view thereof, and FIG. 5 is a perspective view of the device according to the present invention.
- A sectional view, Figure 6 is a diagram showing the positional relationship between the electrode plate and case 4, Figure 7 is a diagram showing the raw plate of the electrode plate for signal detection and high voltage application, Figure 8 a and b are strip-shaped insulation Figures 9a and 9b are side views and front views showing the detection electrode plate used in the device of the present invention, and Figures 10a and 10b are side views and front views showing the high voltage electrode plate. The front view, FIG. 11 is a diagram showing the configuration of the electrode plate insertion part of the device according to the present invention, and FIG. 12 is the B
13 is a perspective view thereof. 4... Case, 6... Electrode plate for signal detection, 7... Electrode plate for high voltage, 8... Band-shaped insulator, 9... Conductor, 1
0...Insulating support, 10a...Groove, 13...Insulating adhesive.

Claims (1)

[Claims] 1. In a radiation detector in which a plurality of electrode plates for high voltage and signal electrode plates are arranged alternately at predetermined intervals and detection signals are obtained from each of the signal detection electrode plates, the ends of the electrode plates are An insulating support having a plurality of insertion grooves is used to insert and hold the electrode plate into the grooves, and the signal detection electrode plate and the high voltage electrode plate each correspond to the grooves at the end of the support side. The part is wrapped with a band-shaped conductor through an insulating layer, these conductors are grounded, and at least a part of the conductor and at least a part of the insulating support are fixed with an insulating adhesive. Characteristic radiation detector.