JP2540863B2 - Ring type ECT device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

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 to an ECT device in which a radiation detector is formed in a ring shape.

[Prior art]

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 outside thereof. Then, the position calculation in the circumferential direction is performed by the so-called MLE (MOS
T LIKELYHOOD ESTIMATION) method to determine which scintillator the radiation enters.

[Problems to be Solved by the Invention]

As described above, in determining which scintillator the radiation is incident on by the MLE method, there is a problem that the spatial resolution depends on the scintillator array density and the intrinsic resolution is poor. Further, since the scintillators are arranged in a mosaic pattern, the assembling is not easy, and the filling degree is low, which is also disadvantageous in terms of counting rate characteristics. On the other hand, it is also considered to solve these problems by using one continuous scintillator having a cylindrical shape, but in that case, since the MLE method cannot be used for position calculation, it is used in a normal scintillation camera. There is no choice but to use the resistance matrix method as described above. However, in the case of this resistance matrix method, regions where the position cannot be calculated occur at both ends of the resistance value, which is inconvenient for position calculation in the circumferential direction where there is no end. It is an object of the present invention to provide a ring-type ECT device that eliminates the occurrence of a position calculation inability region when one continuous cylindrical scintillator is used.

[Means for solving problems]

The ring-type ECT device according to the present invention comprises one continuous cylindrical scintillator, a large number of photomultiplier tubes arranged in a ring shape on the outer surface side of the scintillator, and the maximum value among these photomultiplier tubes. A circuit for detecting what has generated an output, a circuit for substantially selecting the output of the maximum value photomultiplier tube and the outputs of a plurality of photomultiplier tubes in the vicinity thereof and performing position calculation by these outputs, A circuit for adding a signal representing the absolute position of the maximum value photomultiplier to the position calculation result.

[Action]

Detecting the one that generated the maximum value output among many photomultiplier tubes, select the output of this photomultiplier tube and the output of the photomultiplier tubes around it, and perform position calculation between them. There is. That is, this means that the position calculation is performed only between the photomultiplier tubes near the radiation incident position, and the region 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 end of the region where this position calculation is performed, the region itself moves so that the radiation incident position is near the center of the region, so there is no problem and there is no end in the circumferential direction. It is solved that the position calculation impossible area is generated when the position calculation is performed.

【Example】

In the embodiment of the present invention shown in FIGS. 1 and 2, the scintillator 11 is formed by forming one continuous scintillation crystal into a cylindrical shape, and a plurality of photoelectron boosters are provided on the outer peripheral surface of the scintillation crystal via a ride guide 12. Double tubes (PMT) 13 are arranged in the circumferential direction (X direction) and the slice thickness direction (Y direction). All the outputs of these many photomultiplier tubes 13 are sent to an energy calculation circuit 14 to be added without weighting to obtain an energy signal, and the wave height analysis thereof determines that they are within a predetermined energy window. Z signal and unblank signal are output only when
X-direction and Y-direction position calculations described below are performed (first
Figure). 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 respective positions A, B, C, D, E, F, and G in the Y direction are added. For example, + 3, + 2, +
Weights of 1,0, -1, -2, -3 are assigned. A Y-direction position signal is obtained by dividing the result of addition by such weighted resistance matrix addition by the energy signal. For position calculation in the X direction, photomultiplier tubes grouped in the circumferential direction in the A / D converter 16 as shown in FIG.
The sum output of each of the 13 groups is sent. That is, here, it is assumed that Nos. 1 to n are arranged in the circumferential direction, and No. 1, No. 9, No. 17, ...
The second, the tenth, the eighteenth, ... are the second group, the eighth,
No. 16, No. 16, No. 24, etc. are called 8th group
Divided into groups. The reason why the light is divided into every eight pieces is that the two photomultiplier tubes 13 which are separated by eight pieces do not simultaneously receive the light by one radiation incidence. The distance is not limited to every eight, as long as the distances do 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, the outputs from the first to the nth in the circumferential direction are sent to the maximum value photomultiplier tube detection circuit 18 and the number which is the maximum is detected. Now, it is assumed that γ-rays are incident on the vicinity of No. 4 as shown in FIG. 2 and issuance occurs at point a. At this time, the detection circuit 18 detects that the output of the fourth photomultiplier tube 13 is maximum.
The fourth group to which the # 3 photomultiplier tube 13 belongs has a weight of 0, the third group to which the # 3 group belongs has a weight of +1 and the 2nd group to which the # 2 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 group to which the fifth photomultiplier tube 13 belongs is -1, 6th No. photomultiplier tube 13
The weight in the X-direction position calculation circuit 17 is changed so that the weight of the sixth group to which is belonged to is −2, and the weight of the seventh group to which the seventh photomultiplier tube 13 is to be −3. To be As a result, the fourth photomultiplier tube closest to point a
Position calculation will be performed with the position of 13 as the origin.
The result of this calculation is normalized by being divided by the energy signal, and then added by the adder circuit 19 with a signal representing the absolute position of the fourth photomultiplier tube 13. In this way, the relative position signal having the origin at the fourth position obtained by the output of the photomultiplier tube 13 near the fourth position is converted into an absolute position signal. Although FIG. 3 shows the 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, when the maximum value photomultiplier tube detection circuit 18 detects that the output of the fourth photomultiplier tube 13 is the maximum, the analog multiplexer circuit 20 outputs the outputs of the photomultiplier tubes 13 around it. It is selected and sent to each weighted input terminal of the X-direction position calculation circuit 17. In this way, relative position calculation is performed with the position of the fourth photomultiplier tube 13 as the origin, and in the adder circuit 19, the fourth photomultiplier tube 13 from the maximum value photomultiplier tube detection circuit 18 is calculated. Is added to the signal representing the absolute position of.

【The invention's effect】

According to the ring-type ECT device of the present invention, since one continuous cylindrical scintillator is used and the position calculation in the circumferential direction can be performed without generating the position calculation impossible region, the inherent resolution can be improved. Moreover, since the filling degree is high, the count rate characteristic is good. Furthermore, since the scintillator is an integral type, it is easy to assemble.

[Brief description of drawings]

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, 13 …… 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, 19 ... addition circuit, 20 ... analog multiplexer circuit.

Claims (1)

(57) [Claims] 1. A continuous cylindrical scintillator, a large number of photomultiplier tubes arranged in a ring shape on the outer surface side of the scintillator, and maximum output of these photomultiplier tubes. A circuit that detects objects, a circuit that substantially selects the output of the maximum value photomultiplier tube and the outputs of a plurality of photomultiplier tubes around it, and performs position calculation by these outputs, and the position calculation result. A ring type ECT device comprising a circuit for adding a signal representing the absolute position of the maximum value photomultiplier tube.