JPS6052788A - Scintillation camera - Google Patents

Abstract

PURPOSE:To improve a spatial distortion and a uniformity in the peripheral part of a visual field by adjusting amplification factors of PMTs (photomultipliers) or amplifying systems and making nonlinear pints of amplifying systems related to PMTs in the peripheral part and those related to PMTs in the central part different from each other in accordance with magnitudes of outputs of individual amplifying systems. CONSTITUTION:Amplification factors of PMTs 302 and 303 or preamplifiers 402 and 403 (or amplifying sytems including waveform shaping circuits 502 and 503, etc.) related to PTMs 302 and 303 in the peripheral part are made different from the amplification factor related to a PTM 301 in the central part, and outputs inputted to individual nonlinear amplifiers 6 are different from one another even if the same radiation sources are placed just above individual PTMs 3 to give the same radiation input to them. With respect to nonlinear amplifiers 6, input/ output characteristics different from those of a nonlinear amplifier 601 corresponding to the central part are given to nonlinear amplifiers 602 and 603 corresponding to the peripheral part in accordance with the difference of inputs of nonlinear amplifiers 6.

Description

[Detailed description of the invention] (b) Industrial application fields This invention relates to improvements in scintillation cameras.

(b) Conventional scintillation cameras, as is well known,
Radiation is incident on a scintillator to generate scintillation light, and this light is transferred to a large number of photoelectric converters (usually photomultipliers; PM) arranged on the back side of the scintillator.
(hereinafter referred to as PMT),
By inputting the output of each P\T through an amplification system to a position calculation circuit consisting of an addition circuit for weighting,
An image is obtained by calculating the position where scintillation light is generated.

Conventionally, in order to improve the spatial resolution or improve the spatial distortion in such scintillation cameras, it has been possible to provide nonlinear characteristics to the amplification system connected between each PMT and the position calculation circuit. It has also been proposed to change the nonlinear characteristics in proportion to the energy wind level of the pulse height analyzer or the energy signal for each event (Japanese Patent Publication No. 51-29839,
(Refer to Japanese Patent Publications No. 56-51312, No. 53-84378, No. 55-44998, etc.) However, in the configurations related to these conventional proposals, the spatial shape and non-uniformity peculiar to the peripheral part of the visual field There was a problem of remaining gender.

In other words, in one of the above proposals, the amplification factors of each PMT and the amplification system connected to them are all equal, and in this case, there is no PMT outside the outermost PMT in terms of wood structure. Due to the local asymmetry of the field of view, the disadvantage is that the spatial type and the positional dependence of the energy signal height are significant in the periphery of the field of view.

In another proposal, the weight in the adder circuit is set to the outermost PM.
The configuration is such that the weight is made larger only for T, which is different from the weights of other PMTs. Although this configuration certainly improves the position dependence of the energy signal wave height, the spatial type in one periphery is However, it still has the disadvantage that it is significant.

In yet another proposal, PM only for the outermost PMT
A configuration in which the amplification factor of the T or amplification system is made different (for example, by increasing the amplification factor) is adopted, and this configuration improves the position dependence of the energy signal wave height and also reduces the spatial type of peripheral effect (for example, the peripheral effect). However, the phenomenon of distortion toward the center at the periphery of the P
A disadvantage arises in that a spatial pattern appears in which a hot spot or hot spot is directly above the MT.

(c) Purpose This invention aims to improve the spatial shape and non-uniformity of the peripheral part of the field of view in a scintillation camera in which the amplification factors of each PMT and each corresponding amplification system are nonlinear.

(d) Configuration In the scintillation camera of this invention, PM in the peripheral area
The amplification factors of the PMTs or amplification systems are adjusted so that the output of each amplification system for the same human power is different compared to the central PMT only with respect to T, and the nonlinear point (
The bending point and/or threshold level is also configured to be different for the PMTs in the peripheral area and for the PMTs in the central area, depending on the magnitude of the output of each amplification system.

(E) Example In this example, 61 PMTs 3 are arranged in a hexagonal dense arrangement as shown in FIG. 1, and in this way, as shown in FIG. installed. Each of the 61 PMTs 3 is numbered 1 to 61 as shown in Figure 1, and these are classified into three types: No. 2 to No. 4, No. 6, No. IT, No. 12, and No. 18. No. 19, No. 26, No. 36, No. 43, No. 44, No. 50, No. 51, No. 56, No. 58-
PMT3 numbered 60 is called PMT302 at the outermost periphery,
No. 1, No. 5, No. 17, No. 35, No. 57, No. 6
The first PMT3 is called the outermost apex PMT303,
The other PMTs 3 will be referred to as the central PMT 301. When radiation is incident on the scintillator 1, scintillation light is generated within the scintillator 1, and this light is guided to each of the PMTs 3 via the light guide 2.

In this way, an output is generated from each of the PMTs 3, and each of these outputs is connected to a corresponding preamplifier 4 and a waveform.

The signals are inputted to a position calculation circuit 7 via a shaping circuit 5 and a nonlinear amplifier 6, and the position calculation circuit 7 adds weights and performs division (normalization) regarding energy to obtain position signals X and Y. It will be done.

These preamplifier 4, waveform shaping circuit 5, nonlinear amplifier 6
is also classified into three types according to PMT301, 302, 303, and the corresponding numbers 401 to 403, 50 respectively.
1-503.601-603 are attached. The output of each of the waveform shaping circuits 5 is also input to an adder circuit 8 to obtain an energy signal Z. This energy signal Z is sent to a pulse height analyzer 9, which converts the energy signal It is determined whether or not Z is within a certain energy window, and if so, an unblank signal is generated from this pulse height analyzer 9. The energy signal Z is also input to the nonlinear point control voltage generation circuit IO, which generates a nonlinear point control voltage so that the nonlinear point of the nonlinear amplifier 6 changes according to the energy for each event of radiation incidence, and converts the nonlinear point control voltage to the nonlinear amplifier 6. Send to each of 6. The input/output characteristics of the nonlinear amplifier 601 corresponding to the central PMT 301 are, for example, so-called suppressed nonlinear characteristics with a small amplification factor for high input signals, as shown by the solid line in FIG. The higher one is LNLI and the higher one is HNLl), and these are controlled by nonlinear point control voltages Ll and Hl, respectively. PMT302 at the outermost edge and apex
．． The same goes for the nonlinear amplifiers 602 and 603 corresponding to 303, the former having two bending points LNL2, HNL2 and LNL3 and HNL3, and each of these bending points has a nonlinear point control voltage L2.
, H2 and L3, H3. By providing suppressed nonlinear characteristics to the input/output characteristics in this way,
Since the spatial pattern (and the resulting non-uniformity) of hot spots directly above each of the PMTs 3 can be improved, and as a result it becomes possible to make the light guide 2 and the scintillator l thinner, This indirectly has the effect of improving spatial resolution.

Here, according to the present invention, PMT302.3 in the peripheral part
For 03, PMT302.303 or preamplifier 402,403 (or waveform shaping circuit 502,503
Regarding the amplification system including
301, so that even when the same radiation source is placed directly above each PMT 3 and the same radiation input is applied, the outputs input to each of the nonlinear amplifiers 6 will be different. ing. In addition, in accordance with the difference in the input of the nonlinear amplifier 6, the nonlinear amplifiers 602 and 603 corresponding to one peripheral part of the nonlinear amplifier 6 are made to have different input/output characteristics from the nonlinear amplifier 601 corresponding to the central part. There is.

Specifically, for example, the amplification factor for the PMT 302 on the outermost side is about 1.5 times that of the PMT 301 in the center,
P so that the amplification factor for the PMT 303 at the apex of the outermost circumference is about 0.7 to 0.8 times that of the PMT 301 at the center.
Adjust the amplification factor of the MT3 or preamplifier 4 (or the amplification system including the waveform shaping circuit 5), and adjust the amplification factor of the nonlinear amplifier 6.
The input/output characteristics of each of ゜l, 602, and 603 are as shown by the solid line in FIG.
The edge of the outermost periphery, that is, the nonlinear amplifier 602, is indicated by a dashed line in the figure, and the vertex of the outermost periphery, that is, the nonlinear amplifier 6
03 is adjusted as shown by the dotted line.

Of course, the above values should be determined depending on the thickness of the scintillator 1 and light guide 2, the diameter and spacing of PMT 3, etc. Depending on these factors, it may be 1.5 times the above value,
A value of 0.7 to 0.8 times is not optimal.

Since the amplification factor and nonlinear characteristics are changed between the periphery and the center in this way, the position dependence and spatial pattern of the energy signal wave height in the periphery are improved, and as a result, the effective field of view is relatively Can be expanded.

In the above embodiment, the input/output characteristic of the nonlinear amplifier 6 was explained as a suppressed nonlinear characteristic having two bending points as shown in FIG.
For example, when the curve is smooth, when the curve is smooth, when the curve has continuous nonlinear characteristics, when there is a threshold characteristic in addition to the suppression type characteristic as shown in Fig. 4, when there is only a threshold characteristic as shown in Fig. 885. etc. - The same applies to other nonlinear characteristics.

Furthermore, in the above embodiment, the input/output characteristics of the nonlinear amplifier 6 are configured to change according to the energy signal Z for each event of radiation incidence, but instead of this, the input/output characteristics of the nonlinear amplifier 6 are changed according to the energy wind level of the pulse height analyzer 9. It can also be configured.

Furthermore, in the above, a large number of PMTs 3 were classified into three types according to their positions, but it is also possible to classify them into two or four or more types, and the 61 PMTs shown in the first factor It is similarly applicable to configurations other than the hexagonal densely arranged configuration.

Alternatively, a configuration in which the position calculation method is slightly different from that in Fig. 2 (for example, a configuration in which the preamplifier 4 is a non-integrating type, does not have the waveform shaping circuit 5, and performs peak detection, or performs integration during position calculation) may be used. The present invention is applicable even if this is adopted.

In addition, the weight of the position calculation circuit 7 is not necessarily proportional to the position of each PMT 3, and the weight of the signal related to the energy on the denominator side of the division circuit for normalizing energy is not necessarily equal for all PMTs 3. It is also applicable to configurations where there is no

(f) Effects According to the present invention, the spatial front type inherent to the peripheral part of the visual field and the non-uniformity caused by it are improved, and the position dependence of the wave height of the energy signal unique to the peripheral part and the non-uniformity caused by it are improved. sex is improved. Furthermore, the effective field of view of the synnarration camera is relatively expanded.

[Brief explanation of drawings]

Figures 1 and 2 relate to one embodiment of the present invention; Figure 1 is a plan view showing the arrangement of PMTs, Figure 2 is a block diagram, and Figure 3 shows the input/output characteristics of this embodiment. The graphs in FIGS. 4 and 5 are graphs showing the input/output characteristics of modified examples of i, respectively. l...Scintillator 2...Light guide 3...
PMT 4...Preamplifier 5...Waveform shaping circuit 6...Nonlinear amplifier 7...
Position calculation circuit 8... Addition circuit 9... Wave height analyzer 10... Nonlinear point control voltage generation circuit

Claims (1)

[Claims] (1) A scintillator, a large number of photoelectric converters arranged on the back side of the scintillator, an amplification system with nonlinear characteristics that amplifies the output of each photoelectric converter, and each photoelectric converter that passes through each of these amplification systems. In a scintillation camera having a position calculation circuit into which the output of the converter is input,
The amplification factors of the photoelectric converters or the amplification systems are adjusted so that only the photoelectric converters in the periphery have different outputs from the amplification systems for the same human power compared to the photoelectric converters in the center, and The synnarration camera is characterized in that the nonlinear points in the peripheral photoelectric converter and the center photoelectric converter are configured to be different depending on the magnitude of each amplification system output. .