JPS5946572A - Radiation detector - Google Patents

Abstract

PURPOSE:To facilitate the adjustment of output characteristics of a radiation detector by providing a means of introducing an artificial light. CONSTITUTION:A light shield case 5 of a radiation detector is provided with an optical fiber 8 or the like of a means of introducing an artificial light having an optical fiber connector 9 at one end thereof together with a scintillator 1 and a photomultiplier 2 of a photoelectric conversion element and the like. A certain intensity of light from a light emitting element 10 propagating through the optical fiber 8 is introduced into the photomultiplier tube 2 via the scintillator 1 and a corresponding electric signal is outputted via a connector 4 and a preamplifier 3 and the like. This enables easy and accurate adjustment of output characteristics of the radiation detector.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation detector used in an XICT device or a positron CT device.

Radiation detectors used in X@CT devices or positron CT devices include a phosphor that emits fluorescent light proportional to the amount of incident radiation, and a photoelectron intensifier that receives the fluorescent light and outputs an electrical signal corresponding to it. It has an array of multiple detector elements consisting of doubler tubes. The XWACT device performs t-A-D conversion on analog signals output from these detector elements, and then reconstructs the digital information to assemble an OCT image of the subject. If there are variations in the output characteristics of each detector element, it is difficult to obtain an accurate CT image. For this purpose, it is necessary to adjust the output characteristics of each detector element to be uniform. Conventionally, radiation is incident on each detector from a radiation source with known properties (for example, intensity), and the output at that time is Adjustments are being made to keep it constant. However, among the radiation sources currently in use, there is no radiation source that generates X-rays or gamma rays with good reproducibility and constant intensity, and that can be easily handled.

An object of the present invention is to provide a radiation detector whose output characteristics can be easily adjusted.

Embodiments of the radiation detector of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of the radiation detector of the present invention. In the figure, 1 is a scintillator that emits fluorescence upon receiving radiation, 2 is a photomultiplier tube, 3 is a preamplifier, and 4 is a socket for connecting the photomultiplier tube and the preamplifier.

The scintillator 1 and the photomultiplier tube 2 are housed in a light-shielding case 5, and radiation passes through the light-shielding case 5 and enters the scintillator 1. Fluorescent light generated by the scintillator 1 enters the photomultiplier tube 2 through an optical window 7 provided on the light receiving side of the photomultiplier tube. The inner wall of the light-shielding case 5 is coated with a light-reflecting agent so that a portion of the fluorescent light leaking from the scintillator is reflected by the agent and enters the photomultiplier tube 2. These fluorescent lights are converted into electrical signals proportional to the amount of light in the photomultiplier tube 2, amplified in the preamplifier 3, and outputted from the output end 4'. In the detector of the present invention, in addition to the detector elements as described above, a light introduction path 8 for introducing pseudo light into the photomultiplier tube 2 is provided. The light introducing path 8 is formed of an optical fiber, and one end thereof is optically coupled to the scintillator 1, and the other end is connected to an optical fiber connector 9 disposed outside the light-shielding case 5. Optical connector 9
is connected to the light emitting element 10. The light-emitting element 10 is of a type that blinks when a current is passed through it for a certain period of time, and the light from the light-emitting element 10 enters the inside of the scintillator l via the light introduction path 8, and the light from the light-emitting element 10 enters the scintillator l in proportion to the amount of light. 2
An output signal is output from.

Therefore, in order to adjust the output of the detector, the light emitting element I
0 is turned on and test light is introduced into the scintillator 1 via the optical fiber 8. Then the test light is photomultiplier tube 2
According to the amount of light, the light is converted into an electrical signal by the photomultiplier tube 2 and output.

By measuring this output signal, the detector can be calibrated. In this embodiment, one end of the optical fiber 8 is optically coupled to the scintillator 1 and the simulated light is introduced into the scintillator l, but it is connected to the light receiving part of the photomultiplier tube 2 to directly generate the simulated light. The light is photomultiplier tube 2
It may be configured so that it is introduced in In addition, the light emitting element 9 is arranged outside the light-shielding case containing the scintillator and the photomultiplier tube, and pseudo light is introduced from the outside of the detector element. It is also possible to arrange it close to.

In this case, light emission is controlled by external electrical signals.

FIG. 2 is a conceptual diagram when a plurality of radiation detectors of the present invention are arranged and their output characteristics are adjusted. An apparatus for monitoring the characteristics of several dozen detectors, such as an X-ray CT apparatus, is described. In the figure, numeral 11 indicates a detector group, 11a from the left.

11b, . . . 11p, a total of 16 detector elements. The actual X-ray-〇T rack equipment is (
9) Although some detector elements are made up of more than 16 elements, only 16 are shown in the figure. The structure of these detector elements is the same as that explained in FIG. 1, and optical fibers 12a, 12b, . One end is optically coupled and the other end is connected to the optical selection device 14.
It is connected to the. The light selection device 14 selectively routes the light from the light emitting source 16 to each optical fiber 12 a +12 b.
r...12p. In addition, the output portion of each detector 11 has measurement paths 13a, 13b, . . . 1 for extracting detection signals, respectively.
One end of 3p is connected. The other end of each measurement path 13 is connected to a signal measurement device 15 .

Each of these detector elements 11 has a common light source 16.
The same amount of light of the same wavelength is selectively introduced from the optical fiber 12 through the optical fiber 12, and the electrical signal output from each detector is input to the signal measuring device 15 via the measuring path 13 [7, and measured. . Each detector 11a, 11b+...
....

The output characteristics of the lip are adjusted based on the signals input to the signal measuring device 15 so that they are uniform. Each detector 11a prior to this adjustment of output characteristics.

The output characteristics of each detector are made uniform by adjusting each detector, each party fiber, and the light selection device so that the same amount of light enters the photomultiplier tube of 11b, ..., lip. It is necessary to adjust to In the example shown in FIG. 2, the output characteristics of a plurality of detectors can be monitored using one common light emitting source, so that adjustment work can be done efficiently and economically.

FIG. 3 is a schematic explanatory diagram of a method for monitoring the outputs of a pair of detectors arranged facing each other when the radiation detector of the present invention is applied to a positron CIT device. Positron C
In the T device, several hundred detectors are arranged in a ring around the subject, and it is necessary to count only the cases where gamma rays are simultaneously incident on two of the detectors. For this purpose, it is desirable to adjust the output characteristics for all of the two detector pairs that should perform coincidence counting. In the figure,
A pair of detectors 22 and 23 are shown, each of which has an optical fiber 22' at its receiving portion.

One end of 23' is connected. and 22', 23
The other end is connected to a common light pulse emission source 25 so that the light pulses are incident on the detectors 22 and 23. The output parts of the detectors 22 and 23 are connected to a coincidence circuit 24, so that when a light pulse is simultaneously incident on each detector, a corresponding electrical signal is sent from the output part to the coincidence circuit 24. It's orange.

In this case, light pulses are simultaneously introduced into the detectors 22 and 23 from a common light emitting source 25 so that gamma rays are transmitted to the detectors 22 and 23.
It is possible to suspect that the rays are incident on the rays 3 and 3 at the same time.

It is also possible to simulate a case where the timing of incidence of gamma rays is shifted by introducing them from different light emitting sources.

Let me explain in detail. Figure 4 shows the actual position.

The plurality of optical fibers 32 are bundled, for example, in contact with the peripheral edge A of the disc-shaped member, and are arranged with their end faces facing upward (parallel to the plane of the paper).

The end faces of these optical fibers are indicated by reference numeral 33, from which pseudo light is introduced into the respective detectors. FIGS. 5 and 6 schematically show an apparatus for supplying light pulses from a common light source to two specific fiber ends into which simulated light is introduced.

The pseudo light introduction device is indicated by the symbol ``A'', and includes a case 40 having a length slightly larger than its diameter, three reflectors 36 and 37 arranged within the case, and a case 4.
and means for rotating and moving 0.

A light emitting diode is disposed at one end of the case 40, and a first reflecting mirror section is disposed at a position where light from the light emitting diode section is directly incident. Second and third reflector 3
7 and the wings are arranged to receive the light reflected by the reflecting mirror part, and are spaced apart from each other by a distance equal to the distance between two specific light introduction ends on the circle A, and the inclination is equal to the distance between the two specific light introduction ends on the circle A. The same light beam is arranged at the introduction end 33. In this way, reflector 3
A case 40 that includes 6, 37, and 2 is provided with a rotation center 41, and a drive device (not shown) for rotating the case 40 around the center 41 is disposed. The rotation center 41 is disposed approximately at the midpoint between the reflecting mirrors 37 and 38, so that when the case 40 rotates around the center 41, the light reflected by the reflecting mirrors 37 and 38 is directed to a specific point on the circle A. The light is supplied to the two light introducing ends 33 one after another.

Also provided is a means (not shown) for horizontally moving the case 40 in the direction of the arrow shown in FIG. It is also possible to move.

This makes it possible to introduce pseudo light to all required detector pairs.

Further, the output ends of each pair of detectors are respectively connected to a coincidence circuit (not shown). Therefore, when the radiation detector of the present invention is used as a detector of a positron CT apparatus as described above, the rotation drive device of the case 40 is used to introduce test light into each pair of detectors. As a result, the same amount of light is simultaneously introduced into the light receiving sections of the photomultiplier tubes of a specific pair of detectors, and it is possible to simulate simultaneous incidence of gamma rays on the detectors. By performing such an operation for different pairs of detectors, test light can be introduced to all required pairs of detectors. Further, by driving the rotating device and the horizontal moving device to change the moving path of the case 40, it is possible to obtain the detector output in various patterns. By utilizing this function, the same input data can always be obtained in the portion of the positron CT apparatus that processes the detector output signal, and this can also be used to find faults in the signal processing circuit.

As explained above, the radiation detector of the present invention includes a scintillator that emits fluorescent light upon receiving radiation, a photoelectric conversion element that receives the light emitted from the scintillator and generates an electric signal corresponding to the scintillator, and the scintillator and the photoelectric conversion element. and a light-shielding case that houses the photoelectric conversion element, and includes a means for introducing simulated light into the photoelectric conversion element, so that it is possible to easily simulate the detector input signal and to obtain highly accurate detector output with less effort. Can be adjusted.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the radiation detector of the present invention, Fig. 2 is a schematic explanatory diagram showing a method of adjusting the output characteristics of a plurality of detectors, and Fig. 3 is a schematic diagram showing an embodiment of the radiation detector of the present invention. Positron C
4 is a schematic diagram showing the relationship between the annularly arranged detector of the positron CT device and the optical fiber for introducing light, and FIG. A schematic explanatory diagram showing a method of introducing light into the light introduction end of an optical fiber, and FIGS. 6A and 6B are schematic diagrams of a light introduction device. 1...Scintillator, 2...Photomultiplier tube, 3...
- Preamplifier, 4... Socket, 5... Light shielding case, 8... Optical fiber, 9... Optical fiber connector, 10... Light emitting element, 11... Detector group, 12・・・
- Optical fiber, 13... Measurement path, 14... Light selection device, 15... Signal measurement device, 16..., 13 Light emitting source, 22, 23... Detector pair, 22', 23
'... Optical fiber, 24... Output detection device, 25.
...Light emission source, 31...Detector, 32...Optical fiber, 33...Light introduction end, Ah...Light introduction device, Song...
Light emitting diode, 36, 37, 38...reflector,
4o...Case, 41...Rotation center. Patent applicant Makoto Ishiita, Director of the Agency of Industrial Science and Technology - Figure 3 Figure 4 Figure 1 Figure 5 Figure 6 (a) (b)

Claims (1)

[Scope of Claims] 1. A scintillator that emits fluorescence upon receiving radiation, a photoelectric conversion element that receives light emission from the scintillator and generates an electric signal corresponding to the scintillator, and a light-shielding case that houses the scintillator and the photoelectric conversion element. A radiation detector comprising means for introducing pseudo light into the photoelectric conversion element. 2. A patent characterized in that the means for introducing the pseudo light is an optical fiber having one end optically connected to the light receiving part of the photoelectric conversion element and the other end disposed outside the light shielding case. A radiation detector according to claim 1.