JPS63300985A - Ring type ect device - Google Patents

Abstract

PURPOSE:To prevent an area where position arithmetic is impossible from being formed by performing position arithmetic based upon the output of a photoelectron multiplier tube (PMT) which generates a maximum output among PMTs arrayed in a ring shape and outputs of its peripheral PMTs, and adding a signal showing the absolute position of the maximum output PMT to the arithmetic result. CONSTITUTION:Sum outputs of respective groups of PMTs 13 grounded in the circumferential direction are sent to an X-directional position calculating circuit 17 through an A/D converter 16. The outputs of respective 1st-(n)th PMTs 13 in the circumferential direction are sent to a maximum PMT detecting circuit 18, which detects where the PMT which generates the maximum output is. When it is assumed that gamma rays are made incident on the periphery of the 4th PMT and light emission is caused at a point (a), the circuit 18 detects the 4th PMT output is being maximum. Then the circuit 17 varies weighting to perform position calculation based upon the 4th PMT as an origin, and an adding circuit 19 adds a signal showing the absolute value of the 4th PMT to perform circumferential position arithmetic without forming any disabled area of position arithmetic.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an ECT device that obtains a distribution image of RI (radioactive isotope) in the body of a subject, and particularly relates to an ECT device in which a radiation detector is formed in a ring shape.

[Conventional technology]

In a conventional ring-type ECT device, a large number of individual scintillation crystals are arranged in a mosaic shape to form a cylindrical shape, and a large number of photomultiplier tubes are arranged on the outside of the cylindrical shape. The position calculation in the circumferential direction is performed using the so-called M L
E 0110ST LIKELYI(OOD ESTI
(MATION) method, and it is determined which scintillator the radiation has entered.

[Problems to be solved by the invention]

As described above, when determining which scintillator the radiation has entered using the MLE method, there is a problem that the spatial resolution depends on the arrangement density of the scintillators, and the inherent resolution is poor. Furthermore, since the scintillators are arranged in a mosaic pattern, assembly is not easy and the degree of filling tends to be low, which is disadvantageous in terms of count rate characteristics. On the other hand, it has been considered to solve these problems by using one continuous cylindrical scintillator, but in that case, the MLE method cannot be used for position calculation, so it cannot be used with a normal scintillation camera. I have no choice but to use a resistance matrix method like the one shown in the figure below. However, in the case of this resistance matrix method, there are regions where the position cannot be calculated at both ends of the resistance value, which is inconvenient for position calculation in the circumferential direction where no ends exist. An object of the present invention is to provide a ring-type ECT device that eliminates the occurrence of a region in which position calculation is not possible when one continuous cylindrical scintillator is used.

[Means to solve the problem]

The ring-type ECT device according to the present invention includes one continuous cylindrical scintillator, a large number of photomultiplier tubes arranged in a ring shape on the outer surface side of the scintillator, and a maximum photomultiplier among these photomultiplier tubes. a circuit for detecting what has produced an output; a circuit for substantially selecting the output of the maximum value photomultiplier tube and the outputs of a plurality of photomultiplier tubes around it and performing a position calculation based on these outputs; and a circuit that adds a signal representing the absolute position of the maximum value photomultiplier tube to this position calculation result.

[For production]

The one that produces the maximum output out of a large number of photomultiplier tubes is detected, the output of this photomultiplier tube and the outputs of the surrounding photomultiplier tubes are selected, and position calculation is performed between these. There is. That is, this means that the position calculation is performed only between the photomultiplier tubes near the radiation incident position, and the area where the position calculation is performed is dynamically moved according to the incident position. Therefore, even if the correct position calculation cannot be performed at the edge of the area where this position calculation is performed, the area itself moves so that the radiation incident position is near the center of the area, so there is no problem and This solves the problem that an area where position calculation is not possible occurs when performing position calculation.

【Example】

In one embodiment of the invention shown in FIGS. 1 and 2,
The scintillator 11 is a continuous scintillation crystal formed into a cylindrical shape, and a large number of photomultiplier tubes (PMT) 13 are arranged on the outer peripheral surface of the scintillator via a light guide 12 in the circumferential direction (X direction). Slice thickness direction (Y direction)
are also arranged. All the outputs of the large number of photomultiplier tubes 13 are sent to the energy calculation circuit 14 and added without weighting to obtain an energy signal, which is determined by pulse height analysis to be within a predetermined energy window. The Z signal and the unrank signal are output only when the
Figure 1). The output of the photomultiplier tube 13 is weighted according to the Y-direction position and sent to the Y-direction position calculation circuit 15 . That is, the outputs of the photomultiplier tubes 13 arranged in the circumferential direction at the same position in the Y direction are added, and then the positions A, B, and C in the Y direction are calculated. For example, +3°+2.
+1. Each weight of O, -1, -2, -3 is given. A Y-direction position signal is obtained by dividing the result of such weighted resistance matrix addition by the energy signal. To calculate the position in the X direction, the summed output of each group of photomultiplier tubes 13 grouped in the circumferential direction is sent to the A/D converter 16 as shown in FIG. That is,
Here, assuming that they are arranged from No. 1 to No. 1 in the circumferential direction, No. 1, No. 9, No. 17, etc.
Group, No. 2, No. 10, No. 18, etc.
Group,..., No. 8, No. 16, No. 24, etc.
・is divided into 8 groups, such as 8th group. The reason why the photomultiplier tubes 13 are divided every eight in this manner is that light from one radiation incident does not simultaneously enter two photomultiplier tubes 13 that are eight apart. The distance is not limited to every eight as long as the distance does not affect each other. The output of each group is converted into a digital signal by the A/D converter 16, and then sent to the X-direction position calculation circuit 17. On the other hand, each output from No. 1 to No. 1 in the circumferential direction is sent to the maximum value photomultiplier tube detection circuit 18, and it is detected which number is the maximum. Now, suppose that γ-rays are incident near No. 4 and light emission occurs at point a, as shown in FIG. At this time, the detection circuit 18 detects that the output of the No. 4 photomultiplier tube 13 is the maximum, so for example, the weight of the fourth group to which this No. 4 photomultiplier tube 13 belongs is 0, the weight of the third group to which number 3 belongs is +
1. The weight of the second group to which the second photomultiplier tube 13 belongs is +2, the weight of the first group to which the first photomultiplier tube 13 belongs is +3, and the weight of the fifth photomultiplier tube is +3. Double tube 1
The weight of the 5th group to which No. 3 belongs is -1, and the weight of the 6th group to which No. 6 photomultiplier tube 13 belongs is -2.
, the weight in the X-direction position calculation circuit 17 is changed so that the weight of the seventh group to which the No. 7 photomultiplier tube 13 belongs is -3. As a result, the fourth point closest to point a
Position calculation will be performed using the position of the photomultiplier tube 13 of the number as the origin. This calculation result is normalized by being divided by the energy signal, and then added to the signal representing the absolute position of the fourth photomultiplier tube 13 in an adder circuit 19. In this way, a relative position signal with the origin at the No. 4 position obtained from the output of the photomultiplier tube 13 near No. 4 is converted into an absolute position signal. FIG. 3 shows a second embodiment. In this embodiment, instead of selecting the output near the light emitting point by grouping, the analog multiplexer circuit 20 directly selects the output. That is, the maximum value photomultiplier tube detection circuit 18 detects the fourth photomultiplier tube 13.
When the maximum output is detected, the outputs of the surrounding photomultiplier tubes 13 are transferred to the analog multiplexer circuit 2
0 is selected, and each weighting of the X-direction position calculation circuit 17 is sent to the input terminal. In this way, relative position calculation is performed with the position of the fourth photomultiplier tube 13 as the origin, and the adding circuit 1
9, it is added to the signal representing the absolute position of the fourth photomultiplier tube 13 from the maximum value photomultiplier tube detection circuit 18.

【Effect of the invention】

According to the ring-type ECT device of the present invention, since one continuous cylindrical scintillator is used to perform position calculation in the circumferential direction without creating a region where position calculation is not possible, the inherent resolution can be improved. Furthermore, since the degree of filling is high, the count rate characteristics are good. Furthermore, since the scintillator is integrated, it is easy to assemble.

[Brief explanation of the drawing]

1 and 2 are block diagrams of an embodiment of the present invention,
FIG. 3 is a block diagram of another embodiment. 11...Scintillator, 12...Light guide, 1
3... Photomultiplier tube, 14... Energy calculation circuit, 15... Y direction position calculation circuit, 16... A/D converter, 17... X direction position calculation circuit, 18...・Maximum value photomultiplier tube detection circuit, 1...Addition circuit, 20・
...Analog multiplexer circuit.

Claims (1)

[Claims] (1) One continuous cylindrical scintillator, a large number of photomultiplier tubes arranged in a ring shape on the outer surface of the scintillator, and the one that produced the maximum output among these photomultiplier tubes. A detection circuit, a circuit that essentially selects the output of the maximum value photomultiplier tube and the outputs of multiple photomultiplier tubes around it and performs position calculation based on these outputs, and a circuit that performs position calculation based on these outputs, and A ring-type ECT device consisting of a circuit that adds a signal representing the absolute position of a value photomultiplier tube.