JPH0511059A - Scintillation camera - Google Patents

Abstract

PURPOSE:To improve counting-rate characteristic and position operating accuracy and to make it possible to prevent the deterioration of an image by dividing the period into three or more stages in time for every pulse signal, performing integration, and converting the integrated value for two or more stages for beginning half part into the estimated value. CONSTITUTION:The combination of three or more sets of photoelectric converters, linear amplifiers, A/D converters and digital integrators is provided. The light from a scintillator is converted into the pulse signal. The pulse signal is linearly amplified. The digital position signal is obtained from the amplified pulse signal. In each integrator, an input digital signal Zd undergoes integration operation in an adder 61 and respective registers 62-64 during the respective periods. A plurality of the registers 62-64 are selected during the respective periods, which are divided into three or more stages in time from the rise-up with a multiplexer 65. At the normal time, the integrated values are added in an adder 68, and the integrated output INTZ is outputted. When the pile-up occurs, a value, which is stored in a conversion table memory 66 as an estimated value, is added to the sum of the values in the registers 62 and 63.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear medicine diagnostic device such as an Anger type gamma camera and an ECT device, and more particularly to a scintillation camera.

[0002]

2. Description of the Related Art In a scintillation camera, a pulse signal is obtained by converting light generated in a scintillator by the incidence of radiation into an electric signal by a photomultiplier tube, and the output pulse signal of each photomultiplier tube is respectively supplied by a preamplifier. After amplification, the signal is sent to a position calculation circuit via a non-linear amplifier to obtain a position signal. This position calculation circuit includes an integrator that integrates the respective pulse signals from the non-linear amplifier or the signals after adding them. This is because the above-mentioned non-linear amplifier adjusts the pulse height of the pulse signal depending on the radiation incident position. For example, when the radiation enters the vicinity of the center of the photomultiplier tube, the pulse signal wave height becomes larger than when it enters the periphery of the photomultiplier tube. Therefore, the signal wave height is reduced by providing suppression characteristics. In addition, the threshold circuit may be provided to prevent the subsequent circuits from operating with a signal having a small wave height.

As the above-mentioned integrator, an analog integrator is generally used in a normal gamma camera. Further, in order to improve the counting rate characteristic, a digital integrator may be used (Japanese Patent Laid-Open Nos. 61-3284 and 61-61284).
-39618).

[0004]

However, the use of the analog integrator has a problem in the count rate characteristic, and even when the digital integrator is used, the configuration in which the digital integrator is simply used as in the conventional case is used. However, there is a problem that the accuracy of the position calculation result is poor. That is, because the nonlinear amplifier is used as described above, it may or may not be suppressed for each wave height, so that the amplification factor changes depending on the temporal increase of the wave height even within a single pulse. Therefore, in a general digital integrator, the threshold characteristic becomes weak and the suppression characteristic becomes strong when the integration time is shortened during pile-up. Occurs, and the position calculation result changes considerably.

In view of the above, an object of the present invention is to provide a scintillation camera which has improved count rate characteristics and improved position calculation accuracy to prevent image deterioration.

[0006]

In order to achieve the above object, in the scintillation camera according to the present invention, a digital integrator is included as an integrator included in the position calculation circuit and integrating each nonlinear amplifier output or its addition output. When the digital integrator is used, the digital integrator is divided into three or more steps in time for each pulse signal, and each digital signal is integrated by three or more digital integrator circuits, and at least two stages of integrated values in the first half are piled up. It is characterized in that it is configured to include a converter for converting into a predicted value of. The predicted value is obtained from the integrated value of the first two stages, and the integrated output can be obtained by using this predicted value at the time of pile-up, and the integration time of up to two stages is sufficient. Counting is eliminated and the counting rate characteristic is improved. Also, there is no position calculation error due to pile-up,
Moreover, since the predicted value can be one that also incorporates the effect of the non-linear amplifier, even when this predicted value is used, an integrated output that is almost the same as an integrated output due to a normal long integration time can be obtained. Therefore, at a high count rate, it is possible to improve the accuracy of position calculation and prevent image distortion and uniformity deterioration.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a scintillation camera according to this embodiment. In this figure, a scintillator and a light guide 1 are shown.
, 2n are coupled to a plurality of photomultiplier tubes 21, 22, ..., 3n, and their outputs are preamplifiers 31, 32 ,.
, 4n through the respective non-linear amplifiers 41, 42, ..., 4n. In this example, the non-linear amplifiers 41, 42,
It is assumed that 4n has a suppression characteristic of suppressing the input pulse wave height when it is high.

The output of the above preamplifier is the addition circuit 5
The signal after the addition is sent to the timing circuit 6 as a signal Ea representing the energy of the incident radiation. In the timing circuit 6, this input signal Ea
A timing signal for determining the timing of each part of the circuit is generated based on

Outputs of the above-mentioned nonlinear amplifiers 41, 42, ..., 4n are sent to weighting addition circuits 7 and 8 to be weighted and added, and signals Xa and Y corresponding to the radiation incident position in the X direction.
A signal Yb corresponding to the direction incident position is obtained from each of the adder circuits 7 and 8. In addition, these nonlinear amplifiers 41,
The outputs 42, ..., 4n are simply added by the adder circuit 9 to obtain a simple addition signal Za (this signal corresponds to the incident radiation energy).

These signals Xa, Ya, Za and Ea are A / D converted by the parallel type A / D converters 10, 11, 12 and 13, respectively. FIG. 3 shows the output signal Za of the adder circuit 9.
Is shown, and the sampling axis of the A / D converter 12 is shown on the horizontal axis. The pulse signal P1, as shown in FIG.
The size of P3 or the like is sequentially sampled and output as a digital signal. Obtained digital signals Xd, Yd,
Zd and Ed are sent to the digital integrators 14, 15, 16 and 17 for integration, and integrated outputs INT X, INT Y, INT Z,
INT E is obtained respectively. The integral output INT X is divided by INT Z in the division circuit 19, and the integral output INT Y is divided by INT Z in the division circuit 20 to obtain the X direction position signal DIV.
X and Y direction position signals DIV Y are respectively obtained. The integrated output INTE is output as an energy signal and is also sent to the wave height analyzer 18, where it is judged whether or not the energy signal wave height is within a predetermined window. If not, the timing circuit 6 outputs the timing signal. The generation is stopped and the processing for this radiation incident event is stopped, and if it is input, the timing signal is generated and the UNBLANK signal is generated.

Adder circuits 7, 8, 9 and A / D converter 10,
A position calculation circuit is formed by 11, 12, the digital integrators 14, 15, 16 and the division circuits 19, 20.

In this embodiment, the four digital integrators 14 to 17 are configured as three-division type digital integrators that temporally divide the input digital signal into three parts and integrate them, and then add them. Since they all have the same configuration, details of the digital integrator 16 are shown in FIG. 2 and only that will be described. In FIG. 2, the input digital signal Zd first passes through the adder 61 and is stored in the register 62. This input digital signal Zd is A
Since the signals have been sampled and A / D converted by the / D converter 12, the pulse signals P1, P3, etc. in FIG. 3 are sequentially sent as digital values representing the magnitude at each sampling time. The digital value stored in the register 62 is selected by the multiplexer 65, sent to the adder 61 again, added to the next digital value, and stored in the register 62 again. , The integrated value is formed in the register 62. The integrated values are obtained in the same manner in the registers 63 and 64, but the multiplexer 65 uses the pulse signal P
1, the register 62 is selected in the period a, the register 63 is selected in the period b, and the register 64 is selected in the period c from the rising edge of P3. Therefore, the integration operation in the period a is performed by the adder 61 and the register 62 in the period b. Is performed by the adder 61 and the register 63.
And the register 64, respectively.

Then, the integrated value obtained at the end of each of these periods is held in each of the registers 62, 63 and 64. The integrated value in the period a and the integrated value in the period b are sent to the conversion table memory 66 to access it, and the value stored therein is read. Registers 62, 63, 64
, And the value from the conversion table memory 66 are sequentially selected by the multiplexer 67, and the adder 68 and the register 6 are sequentially selected.
By repeatedly adding 9 to register 6
The integrated value of the register 64 or the value read from the conversion table memory 66 is added to the sum of the integrated values of 2, 63.

For example, as shown in FIGS. 3A and 3B, c
In the period, the pulse signals P2 and P4 are changed to the pulse signals P1 and P3.
When is piled up, the value added from the conversion table memory 66 is output as the integral output INT Z. In the normal case where such pile-up does not occur,
The integrated values of the respective periods formed in the registers 62, 63 and 64 are added and output as an integrated output INT Z. The control of the multiplexer 65 according to each period is performed by a signal from the timing circuit 6. In addition, pile-up detection is performed separately, but since a normal configuration is sufficient,
The description is omitted here.

As can be seen here, the value from the conversion table memory 66 substitutes the integrated value of the pulse signals P1 and P3 during the period c during pile-up. These pulse signals P1 and P3 should have the same energy and have the same waveform,
Since the incident positions are different, the sizes are different, and as a result, the suppression effects received by the nonlinear amplifiers 41, 42, ..., 4n are also different. In this example, the pulse signal P
No. 3 is caused by the radiation incident near the center of the photomultiplier tube. Although the wave height should be large as shown by the dotted line, the higher part is suppressed by the non-linear amplification, so the wave height is increased in period b. Is as low as the solid line.

Since the non-linearity is different in each of the periods a, b, and c as described above, the sum of the integrated values in the periods a and b is simply multiplied by a constant magnification to obtain the integrated value in the period c. The approximate method only gives inaccurate predictions. Therefore, it becomes necessary to accurately predict the integrated value in the period c by comparing the integrated values in the periods a and b. In this example,
The predicted value of the integrated value of the period c corresponding to the integrated value of each period of a and b is obtained in advance and stored in the conversion table memory 66, and it is accessed by the integrated value of each period of a and b. I am trying to read it. Therefore, an accurate predicted value of the integrated value in the period c can be obtained at the time of pile-up, and as a result, an accurate integrated output can be obtained at the time of pile-up.
Position accuracy and energy accuracy are improved.

Therefore, when pile-up is likely to occur at a high count rate, the integration time becomes the sum of the periods a and b and becomes short, and counting down is reduced and the count rate characteristic is improved. Further, by shortening the integration time in such a manner, it is possible to eliminate mixing of the second pulse information with the first pulse information, and thus it is possible to prevent an error in position calculation due to pile-up. Since the predicted value of the integrated value can be obtained in consideration of the non-linear effect, it is possible to obtain almost the same integrated output during pile-up as in the case of a long integration time during non-pile-up, and image distortion and uniformity. Does not deteriorate.

The present invention can be variously modified without departing from the gist thereof. For example, although the digital integrator is configured as a three-division type in which the digital integrator is temporally divided into three and integrated, a configuration of four or more divisions is also possible.
In addition, in the above, the addition circuits 7, 8 and 9 (and the addition circuit 5)
Of the pre-amplifiers 31 and 3 are configured to be A / D converted and integrated by a multi-division digital integrator.
3n and non-linear amplifiers 41, 42, ..., 4n for each photomultiplier tube 21, 22, ..., 2n are A / D converted and integrated by a multi-division digital integrator. ,
After that, it is possible to adopt a configuration in which the circuit is passed through an adder circuit and a divider circuit. Furthermore, in the above description, the predicted value in the period c is read from the conversion table memory 66 and the integrated value in the periods a and b is added, but the predicted values a and b stored in the conversion table memory 66 are stored. , C for the entire period, and the integrated value for the periods a, b can be accessed and output as it is as an integrated output for the entire period.

[0019]

As explained in the above embodiments, according to the scintillation camera of the present invention, the counting rate characteristic is improved by reducing the counting down at the high counting rate, and the position calculation accuracy at the high counting rate is improved. It is possible to improve image quality and eliminate image distortion and deterioration of uniformity.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a part of the embodiment in detail.

FIG. 3 is a time chart showing a signal waveform in the example.

[Explanation of symbols]

 1 Scintillator and light guide 21, 22, ... 2n Photomultiplier tube 31, 32, ... 3n Preamplifier 41, 42, ... 4n Non-linear amplifier 5, 7, 8, 9 Adder circuit 6 Timing circuit 10, 11, 12, 13 A / D converter 14, 15, 16, 17 Digital integrator 18 Wave height analyzer 19, 20 Dividing circuit 61, 68 Adder 62, 63, 64, 69 Register 65, 67 Multiplexer 66 Conversion table memory

Claims (1)

Claim: What is claimed is: 1. A scintillator, a photoelectric converter for converting light from the scintillator into an electric pulse signal, a non-linear amplifier for non-linearly amplifying the pulse signal, an A / D converter and a digital device. In a scintillation camera having a position calculating circuit which obtains a digital position signal from an output pulse signal of the non-linear amplifier, including three or more combinations with an integrator, the digital integrator has three time steps for each pulse signal. It is characterized in that it includes three or more digital integrator circuits which are divided into respective parts and each integrate a digital signal, and a converter which converts at least two stages of integrated values in the first half into predicted values at pile-up. Scintillation camera.