JPS62203076A - Method for regulating pmt gain - Google Patents

Abstract

PURPOSE:To make it possible to regulate the gain of PMT simply and accurately, by a method wherein a plurality of PMT outputs are added and the number of times of entering a predetermined window are counted to control the gain of a regulating circuit. CONSTITUTION:An ECT apparatus is equipped with a ring-shaped scintillator 1 and a large number of PMTSs 3 arranged through a cylindrical light guide 2 and the outputs of PMTs 3 are added by an adder circuit 9. At the time of the regulation of a gain, radioactive rays from a radiation source 6 are incident on the scintillator 1 through apertures 5. For example, the gains of all of gain regulating circuits 7 other than the gain regulating circuit 7 con nected to the first PMT3 are controlled to zero and the output of the adder circuit 9 corresponds to that of the first PMT3. The energy signal alpha of said adder circuit 9 is sent to a single channel analyzer to detect whether there is the peak of a wave form in a window and, when there is said peak in the window, the circuit 7 is regulated so that the counting thereof becomes max. Similar regulation is performed with respect to other circuits 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for adjusting the gain of a PMT (photomultiplier tube), and in particular to a method for adjusting the gain of a PMT (photomultiplier tube), and in particular to a method for adjusting the gain of a PMT (photomultiplier tube). The present invention relates to a method for adjusting the gain of a PMT.

In a ring-type ECT device that uses the conventional Anger method positioning method, one or more integrated scintillators are formed into a ring shape, and a plurality of PMTs are arranged for each scintillator on the outside of the ring-shaped scintillator. The radiation incident position within one scintillator is set in the Angular method, that is, each PM
The weighting of T outputs is determined by adding them according to their positions.The problems that the invention aims to solveIn this Anger type ring type ECT device,
If the gains of a large number of PMTs are not the same, the accuracy of positioning will deteriorate, resulting in a problem that large distortions will occur in the reconstructed image. but.

In reality, the gains of many PMTs vary even when the same high voltage is applied, and moreover, they change over time.

An object of the present invention is to provide a PMT gain adjustment method that can easily and accurately adjust the gain of a PMT.

Means for Solving the Problems In the PMT gain adjustment method of the present invention, first, a ring-shaped radiation shielding plate is inserted inside a ring-shaped scintillator, in which a radiation-transmitting hole is provided corresponding to the center position of each PMT. A radiation source is placed inside this ring-shaped radiation shielding plate. Then, after setting the gain adjustment circuit provided for each PMT to zero by removing only one gain adjustment circuit, a signal obtained by adding the outputs of a plurality of PMTs arranged for one scintillator is led to, for example, a single channel analyzer, and a predetermined signal is output. Count the number of times you enter the window. Then, the gain of the gain adjustment circuit whose gain is not set to zero is adjusted so that the count number becomes maximum. This operation is repeated for each of all gain adjustment circuits.

Effect If a gain adjustment circuit is connected to each of a large number of PMTs, and the gain is set to zero except for the north 1fi, the signal obtained by adding the outputs of multiple PMTs in one scintillator will be sent to that one gain adjustment circuit. It corresponds to only the output of one connected PMT.

Inside the scintillator, a radiation shielding plate is arranged with a radiation transmitting hole corresponding to the center position of each PMT. This means that the output corresponds to

Therefore, the above-mentioned PMT output addition signal is led to, for example, a single channel analyzer, and the number of times it falls within a predetermined window is counted.
By adjusting the gain of one gain adjustment circuit whose gain is not set to zero, the window described above corresponds to the photoelectric peak of the radiation emitted from the source placed inside the ring-shaped radiation shielding plate. As long as it is adjusted to
This means that the gain can be adjusted.

If you repeat this operation for all gain adjustment circuits,
The gains of all of the large number of PMTs are the same, the positioning accuracy of the angler method is increased, and distortion of the reconstructed image can be removed.

Embodiment In FIG. 1, a ring-type ECT device that performs position calculation using the Anger method includes a scintillator L integrally formed in a ring shape, and a large number of PMTs 3 arranged on the outside of the scintillator L via a cylindrical light guide 2. It has The scintillator 1 is made of NaI crystal, for example.

As shown in FIG. 2, the output of each PMT3 is sent to the Anger-type position calculation circuit via a gain adjustment circuit 7 and an amplifier 8, and is also sent to an adder circuit 9, where the outputs of all PMT3 are added together. and an energy signal α is obtained. This energy signal α is used to determine the energy of the incident radiation, so that position calculation and counting are performed only for radiation of a specific energy.

This energy signal α is also sent to the position calculation circuit and used for normalizing the position signal. - When adjusting the gain, insert a ring-shaped radiation shielding plate 4 made of lead or the like and having a radiation-transmitting hole 5 inside the ring-shaped scintillator l, and further insert a reference radiation source 6 therein. This ring-shaped radiation shielding plate 4 is provided with a radiation transmitting hole 5 corresponding to the center position of each PMT 3, and the radiation emitted from the radiation source 6 passes through this hole 5 and enters the scintillator 1. incident, producing a photoelectric effect. The radiation transmitting hole 5 has a small diameter so that the light generated within the scintillator 1 does not enter the adjacent PMT 3.

Then, first of all, if the gain is adjusted for the first PMT 3, other gain adjustment tM@
The gains of all paths 7 are controlled to zero. Then, since only the output of the first PMT 3 is output from the adder circuit 9, the energy signal α corresponds to the output of the first PMT 3. However, as described above, since radiation is only incident on the position corresponding to the center of the PMT 3, which is shielded by the shielding plate 4, the output of the PMT 3 corresponds extremely well to the energy of the incident radiation. Therefore, the energy signal α is sent to a single channel analyzer to detect whether the peak of the waveform is between the upper level UL and lower level LL of the window as shown in Figure 3. Count the number of times. The upper level UL and lower level LL of this window are set corresponding to the energy of the photoelectric peak due to the radiation emitted from the radiation source 6, and the above-mentioned first level When the gain adjustment circuit 7 is adjusted, the gain adjustment to exactly capture the photoelectric peak is completed.

When the gain 7JJ section for the first PMT3 is completed in this way, perform the gain adjustment for the second PMT3 using the same operation, and then perform the gain adjustment operation for the next PMT3 and so on sequentially for each PMT3. When the process is completed for all PMT3, the gain has been adjusted to the same value for all PMT3.

After the gain adjustment is completed, when clinical measurements are to be performed on an actual subject, the radiation shielding plate 4 and the radiation source 6 are removed and a collimator is attached inside the scintillator 1 instead, and the radioactive isotope is administered. Insert a subject. In measuring this object, since the gain of each PMT 3 has been adjusted, a reconstructed image with good uniformity and linearity can be obtained.

In the above description, the scintillator l is composed of one piece that is integrally formed in a ring shape, but it may be divided into several parts and joined together to form a ring shape as a whole. In this case, it is particularly important that the gain be the same within the group of PMTs that are optically coupled to the scintillator in each part, since this will affect the positioning accuracy within the scintillator. The above gain adjustment may be performed only within a group.

In addition, in the above ring-type ECT device, a large number of PM
I mentioned adjusting the gain of T, but this PM
The T gain adjustment method can be used to adjust the gain of the PMT of all other radiation position detection devices that perform positioning calculations using the Anger method.

Effects of the Invention According to the PMT gain adjustment method of the present invention, it is possible to accurately align the gains for all of a large number of PMTs with a simple operation, and as a result, the positioning accuracy of the Anger method is increased and distortion of reconstructed images is removed. can.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of the embodiment, and FIG. 3 is a waveform diagram of an energy signal. l...Scintillator 2...Light guide 3.
...PMT 4...Radiation shielding plate 5...
...Radiation transmission hole 6...Radiation source 7...Gain adjustment circuit 8...Amplifier 9...Addition circuit) Principle 2 U, Book 3 (branch) Time gate

Claims (1)

[Claims] (1) One or more integrated scintillators are formed in a ring shape, and a plurality of PMTs are arranged for each scintillator on the outside of the ring-shaped scintillator, so that the radiation inside one scintillator is In a ring-type ECT device in which the incident position is determined by the Anger method, a ring-shaped radiation shielding plate in which a radiation-transmitting hole is provided corresponding to the center position of each PMT is inserted inside the ring-type scintillator, and this ring A signal obtained by adding the outputs of multiple PMTs in one scintillator after setting the gain adjustment circuit provided for each PMT to zero with the radiation source placed inside the type radiation shielding plate. The operation of counting the number of times that the number falls within a predetermined window and adjusting the gain of the gain adjustment circuit whose gain has not been set to zero so that the counted number becomes the maximum is repeated for each of all gain adjustment circuits. Features: PMT gain adjustment method.