JP2631477B2 - Scintillation camera - Google Patents

Description

The present invention relates to a method for administering a substance labeled with a radioisotope to a subject, detecting radiation such as γ-ray emitted from the radioisotope, For scintillation cameras that perform medical diagnoses by determining the distribution of radioisotopes in the interior, in particular, it is possible to automatically correct variations in the amplification degree of a plurality of photomultiplier tubes that convert the light emission of the scintillator into electrical signals. Related to a scintillation camera that can be used.

[Prior Art] As shown in FIG. 1, a conventional scintillation camera is a collimator that passes only γ-rays incident on a detector surface in a direction perpendicular to the detector surface among γ-rays emitted from a radioisotope in a subject. 1 and γ incident through this collimator 1
A scintillator 2 that emits light by a line, a light guide 3 that transmits an optical signal of the scintillator 2, and is optically coupled to the scintillator 2 via the light guide 3 to convert the light into an electric signal and amplify the light. Photomultiplier tube (hereinafter abbreviated as "PMT") 4 and this PMT
A preamplifier circuit 5 for amplifying an output signal from the A / D converter 4, an A / D conversion circuit 6 for integrating the output signal of the PMT 4 amplified by the preamplifier circuit 5 and converting the PMT 4 into a digital signal;
A position calculating circuit 7 for obtaining the position of the γ-ray incident on the scintillator 2 based on the signal strength of the digital signal from the A / D conversion circuit 6 and data of the position of the γ-ray obtained by the position calculating circuit 7 are inputted. At the same time, the addition circuit 8 reads out the contents of the memory corresponding to the incident position of the γ-rays from the memory circuit 9 storing the γ-ray image as a scintigram, adds “1” and writes the same again in the same memory of the memory circuit 9.
A memory circuit 9 for storing the γ-ray image generated by the adding circuit 8 as a scintigram, and reading the scintigram stored in the memory circuit 9 to display the incident position of the γ-ray obtained by the position calculation circuit 7 And a display device 10.

In such a conventional scintillation camera,
In order to determine the position of the γ-ray incident on the scintillator 2, a signal proportional to the magnitude of the optical signal incident on the PMT 4 must be input to the position calculation circuit 7. Where
Since PMT4 has a large amplification degree (for example, about 10,000 times),
Since the amplification degree among the plurality of PTMs 4, 4,... Is slightly different and varies, the signal input to the position calculation circuit 7 when the same magnitude optical signal is incident on the PMT 4 is the same magnitude. It is necessary to adjust in the middle so that it becomes. The adjustment is performed by the A / D conversion circuit 6. This A
As shown in FIG. 4, the / D conversion circuit 6 separates the potentiometer 11 for adjusting the output signal of the preamplifier circuit 5, that is, the output signal of the PMT 4, and the potentiometer 11 and the subsequent integrator 13 from each other to match the circuit. It comprises a buffer amplifier 12 for preventing electrical interference, an integrator 13 for integrating an output signal from the buffer amplifier 12, and an A / D converter 14 for converting an output signal from the integrator 13 into a digital signal. The optical signals having the same magnitude are input to the respective PMTs 4, 4,... Shown in FIG. 1, and the output signal of the buffer amplifier 12 or the integrator 13 is changed by operating the potentiometer 11. , 4, ... were adjusted to be the same size.

[Problems to be solved by the invention]

However, in such a conventional scintillation camera, the operator must manually adjust the knob of the potentiometer 11 of the A / D conversion circuit 6 while observing the output of the buffer amplifier 12 or the integrator 13. Without
It takes a lot of time and effort to set the desired state. Further, the adjustment by the potentiometer 11 requires skill, and the administrator or user of the apparatus cannot easily perform the adjustment on a daily basis. Therefore, the operability of the entire scintillation camera is reduced.

Therefore, an object of the present invention is to provide a scintillation camera that can solve such a problem.

[Means for solving the problem]

Means of the present invention for solving the above problems include a scintillator emitting light by incident radiation, a photomultiplier tube optically coupled to the scintillator and converting the light into an electric signal, and a photomultiplier tube. An A / D conversion circuit that integrates an output signal from the amplifying circuit and converts the signal into a digital signal; and a digital signal from the A / D conversion circuit converts a radiation incident on the scintillator into a digital signal. In a scintillation camera having a position calculation circuit for obtaining a position and a display device for displaying an incident position of radiation obtained by the position calculation circuit,
An A / D converter that performs A / D conversion a plurality of times for one radiation input, and a latch that sets a predetermined value to be corrected for the difference in amplification degree of the photomultiplier tube. And the above A /
A multiplier for inputting and multiplying an output signal from the D converter and a predetermined value signal from the latch to correct a difference in the amplification degree of the photomultiplier tube; and an output signal from the A / D converter or the multiplier. Is input to and accumulated by a scintillation camera.

(Operation)

The scintillation camera configured in this way is
A predetermined value to be corrected for a difference in the amplification degree of the photomultiplier tube set in the latch by the A / D conversion circuit including the D converter, the latch, the multiplier, and the accumulator is determined by the multiplier. Is determined by feedback control, and the variation is automatically corrected for the difference in the amplification degree of each photomultiplier tube.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a scintillation camera according to the present invention. This scintillation camera performs medical diagnosis by administering a substance labeled with a radioisotope to a subject, detecting radiation such as γ-rays emitted from the radioisotope, and determining the distribution of the radioisotope in the subject. 1, a collimator 1, a scintillator 2, a light guide 3, a photomultiplier tube (PMT) 4, and a preamplifier circuit 5, as shown in FIG.
, An A / D conversion circuit 6, a position calculation circuit 7, and an addition circuit 8
, A memory circuit 9, and a display device 10.

The collimator 1 passes only the γ-rays, which are incident on the lower surface of the scintillator 2 at right angles, out of the γ-rays emitted from the radioisotope in the subject. A scintillator 2 is provided on the upper surface of the collimator 1. The scintillator 2 emits light by gamma rays incident through the collimator 1 and is formed in a circular or rectangular flat plate shape. A light guide 3 is provided on a back surface of the scintillator 2. The light guide 3 transmits an optical signal emitted from the scintillator 2 to the PMT 4, and is formed in a circular or rectangular flat plate shape like the scintillator 2. On the rear surface of the light guide 3, a plurality of PMTs 4, 4,... The PMT 4 is optically coupled to the scintillator 2 via the light guide 3, and the scintillator 2
Is detected, converted into an electric signal proportional to the magnitude of the light signal, amplified, and output. the above
The output signal from PMT 4 is input to preamplifier circuit 5.
The preamplifier circuit 5 serves as an amplifier circuit for amplifying the output signal from the PMT4.

An output signal from the preamplifier circuit 5 is input to an A / D conversion circuit 6. The A / D conversion circuit 6 integrates the output signal of the PMT 4 amplified by the preamplifier circuit 5 in order to reduce statistical noise when the scintillator 2 receives gamma rays and emits light, and integrates the integrated signal. Is converted into a digital signal. The output signal from the A / D conversion circuit 6 is input to a position calculation circuit 7. The position calculation circuit 7 determines a light emitting point on the scintillator 2 based on the signal intensity of the digital signal from the A / D conversion circuit 6, and determines a position of the γ-ray incident on the scintillator 2. An output signal from the position calculation circuit 7 is added to an addition circuit 8
Enter The addition circuit 8 receives the data of the position of the γ-rays obtained by the position calculation circuit 7 and corresponds to the incident position of the γ-rays from a memory circuit 9 described later which stores the γ-ray image as a scintigram. The contents of the memory are read out, "1" is added, and the contents are written into the same memory of the memory circuit 9 again. The output signal from the adding circuit 8 is input to the memory circuit 9. This memory circuit 9
Stores the γ-ray image generated by the addition circuit 8 as a scintigram. Then, the data read from the memory circuit 9 is input to the display device 10. The display device 10 reads the scintigram stored in the memory circuit 9 and displays the incident position of the γ-ray obtained by the position calculation circuit 7, and is composed of, for example, a CRT monitor.

Here, in the present invention, the A / D conversion circuit 6
As shown in FIG. 2, an A / D converter 14 ', a latch 15,
It comprises a multiplier 16 and an accumulator 18. A / D converter 1
4 'is an output signal of the preamplifier circuit 5, that is, PMT4.
Input signal, and multiple times for one radiation input
A / D conversion is performed to convert the digital signal. The latch 15 is used to set a predetermined value for correcting the variation of the amplification degree of each PMT 4 described above. The multiplier 16 receives and multiplies the digital signal from the A / D converter 14 'and the predetermined value signal from the latch 15, and corrects the difference in the amplification degree of the PMT 4. Further, the accumulator 18 inputs and accumulates the output signal from the multiplier 16. In FIG. 2, reference numeral 17 denotes an output signal of the accumulator 18 which is
A microprocessor (MPU) that compares the amplification of T4 with a target value set in advance as a value to be adjusted and changes the predetermined value of the latch 15; 6, ... are provided in common.

Next, the operation of the A / D conversion circuit 6 configured as described above will be described. First, the preamplifier circuit 5 shown in FIG.
Is input to an A / D converter 14 ', and is converted into a digital signal by performing A / D conversion a plurality of times for one radiation input. At this time, the output of the A / D converter 14 'has not been subjected to any correction, and the difference in the amplification degree of each PMT 4 causes a variation in the magnitude of the output signal. Then, the digital signals S ₁ uncorrected from the A / D converter 14 'is input to one input of the multiplier 16. At the same time, the other input of the multiplier 16 has a latch
Predetermined value the signal S ₂ is inputted from the 15. Then, the The uncorrected digital signals S ₁ and the predetermined value signal S ₂ of the multiplier 16
Is multiplied by At this time, since the predetermined value signal S ₂ of the latch 15 is set to a predetermined value for correcting the variation with respect to the difference in the amplification degree of each PMT 4, the output signal S ₃ of the multiplier 16 is , And a digital signal in which the difference in the amplification degree of the PMT 4 is corrected.

Then, the output signal S ₃ of the multiplier 16 is input to the accumulator 18. The output signal S ₃ from the multiplier 16 is stored in the accumulator 18.
Is accumulated. In this case, since the A / D converter 14 'performs A / D conversion a plurality of times for one gamma ray input, the output of the accumulator 18 is analogized by the integrator 13 shown in FIG. Is equivalent to the integration of That is, after performing the multiplication in the multiplier 16 and then performing the accumulation in the accumulator 18, the PM
Variations in the degree of amplification of T4 can be corrected.

Here, a predetermined value for correcting the variation in the amplification degree of each PMT 4 in the latch 15 is set as follows. First, a target value is set in advance in the MPU 17 provided commonly to each of the A / D conversion circuits 6, 6,... As a value to which the amplification degree of the PMT 4 should be adjusted. Next, each PMT4,
With a constant optical signal incident on 4,.
Read in MPU17 as a signal accumulated in the accumulator 18 output signal S ₃ after correction is outputted from the output signal S ₃
Is compared with the preset target value. And
If the output signal S ₃ from the multiplier 16 as compared with the target value large, the set predetermined value in the latch 15 reset to "1" value less than the above MPU 17. In addition, the multiplier compared to the target value
If the output signal S ₃ from 16 small, the predetermined value set in the latch 15 reset to "1" value greater than the MPU 17. Then, MPU 1 as a signal which is accumulated in the accumulator 18 output signal S ₃ after correction is outputted from the multiplier 16 again
Read at 7 and compares the output signal S ₃ and the preset target value. Then, the multiplier 16 is compared with the target value.
Depending on whether the output signal S or ₃ is large or small from, reset appropriately set predetermined value in the latch 15 in the MPU 17. By repeating such an operation, the multiplier 16
The output signal S ₃ from the relative set target value to the MPU 17, for example, go falls within the allowable error range of ± 2%. Thus, the predetermined value of the latch 15 to be paying an output signal S ₃ of the multiplier 16 for example within the permissible error range of ± 2% is, PM
This is a value for correcting the variation in the difference in the amplification degree of T4. And such operation is performed for all PMT4,4,4
, The variation in the amplification degree of the plurality of PMTs 4, 4,... Can be automatically corrected.

FIG. 3 is a block diagram showing a modification of the embodiment shown in FIG. In this modification, the accumulator 18 is provided between the A / D converter 14 'and the multiplier 16. In this case, prior to performing the multiplication in the multiplier 16, the output signals S ₁ from the A / D converter 14 'accumulated in the accumulator 18, the multiplier and the cumulative results
By inputting to one of the 16 input sections, the same result as in FIG. 2 can be obtained.

〔The invention's effect〕

Since the present invention is configured as described above, the predetermined value to be corrected for the difference in the amplification degree of the PMT 4 set in the latch 15 inside the A / D conversion circuit 6 is the output signal S ₃ of the multiplier 16. Each PMT4,4,4,4
.. Can be automatically corrected for the difference in amplification degree. Therefore, the operator operates the knob of the potentiometer 11 by hand as in the prior art, and
The work of adjusting each of the PMTs 4, 4,... One by one can be eliminated, and the variation of the amplification degree of each of the PMTs 4, 4,. In addition, the above adjustment does not require any skill, and the administrator or the user of the apparatus can easily perform the adjustment on a daily basis. Thus, the operability of the entire scintillation camera can be improved.

Further, since an analog integrator is not used unlike the conventional apparatus, space can be saved and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention and a conventional scintillation camera, and FIG. 2 is an A / D according to the present invention.
3 is a block diagram showing a modification of the embodiment shown in FIG. 2, and FIG. 4 is a block diagram showing an internal configuration of an A / D conversion circuit according to a conventional example. . 2 ... Scintillator, 4 ... Photomultiplier tube (PMT), 6
... A / D conversion circuit, 7 ... Position calculation circuit, 10 ... Display device, 13 ... Integrator, 14,14 '... A / D converter, 15 ... Latch, 16 ... Multiplier, 17 ... Microprocessor (MP
U), 18 ... accumulator.

Claims (1)

(57) [Claims] 1. A scintillator for emitting light by incident radiation, a photomultiplier tube optically coupled to the scintillator and converting the light into an electric signal, and an amplifier circuit for amplifying a signal from the photomultiplier tube. An A / D conversion circuit that integrates an output signal from the amplification circuit and converts the signal into a digital signal, a position calculation circuit that obtains the position of radiation incident on the scintillator based on the digital signal from the A / D conversion circuit, In the scintillation camera having a display device for displaying the incident position of the radiation determined by the position calculation circuit, the A / D conversion circuit performs a plurality of A / D conversions for one radiation input. A / D converter, a latch for setting a predetermined value to be corrected for a difference in amplification degree of the photomultiplier tube, and an output signal from the A / D converter and a predetermined value signal from the latch. A multiplier that corrects the difference in the amplification degree of the photomultiplier tube by multiplying and accumulator that receives and accumulates an output signal from the A / D converter or the multiplier. Scintillation camera.