JPH0532785Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field In this invention, radiation detectors are arranged in a ring shape around a subject to whom RI (radioisotope) has been administered. Regarding ring-type ECT (emission computer tomography equipment).

Conventional technology In a conventional ring-type ECT device, a large number of detectors each consisting of a combination of a scintillator and a photomultiplier tube (hereinafter abbreviated as PMT) are arranged in a ring shape within one plane, and the arrangement plane is a tomographic plane. This is the slice position where the image is obtained.

In a multi-slice type ring-shaped ECT device, such a ring-shaped array of detectors is arranged in multiple layers, and the array plane of each layer is used as a slice position for obtaining a tomographic plane in each layer.

Problems that the invention attempts to solve Therefore, with the conventional ring-type ECT device,
Including multi-slice types, the slice positions of tomographic images that can be taken are only at fixed positions, and tomographic images cannot be obtained at arbitrary intermediate slice positions.

The purpose of this invention is to provide a ring-type ECT device that can obtain tomographic images at any slice plane, regardless of the plane in which the detectors are linked in a linked arrangement.

Means for Solving the Problems The ring-type ECT device according to this invention has a cylindrical scintillator whose width is widened in the axial direction, and a large number of scintillators arranged on the outer circumferential surface of the cylindrical scintillator both in the circumferential direction and in the axial direction. A region identification circuit that identifies in which region of the plurality of regions divided in the circumferential direction of the cylindrical scintillator light emission has occurred by comparing the output of each PMT, and Accordingly, using only a circuit that generates a weighting coefficient for each PMT in that region and a region adjacent to that region, and the output of each PMT in the above region and a region adjacent to that region, the above-mentioned weighting coefficient is applied to these. and a positioning calculation circuit that calculates the light emitting position.

A large number of PMTs are arranged on the outer surface of the cylindrical scintillator in both the circumferential and axial directions.
The output of the area discrimination circuit is compared to identify which of the multiple areas divided in the circumferential direction of the cylindrical scintillator the light emission occurred in. Then, weighting coefficients are generated for each PMT in the area discriminated as having light emission and in the area adjacent to that area, and the light emission position is calculated by applying the weighting coefficients to only the PMT outputs in this area and the adjacent areas. In other words, the PMT outputs used to calculate the light emission position are those in the area discriminated as having light emission and its adjacent areas,
Moreover, the weighting coefficients acting on the PMT output within that region are given for each emission, and only those necessary for that calculation are given. As a result, PMT outputs other than the region identified as having an emission and its adjacent regions are not used for position calculation, so signals with low contribution to the position calculation are removed and are not affected by the noise contained in them, allowing the positioning of the emission in the circumferential and axial directions to be performed with a fairly high degree of accuracy, and a tomographic image in a slice at any position (axial position) can be obtained. Moreover, since the region division is in the circumferential direction of the cylindrical scintillator, there is a central symmetry relationship, and the same weighting coefficients can be used regardless of which region is identified as having an emission, simplifying the configuration.

Embodiment In FIG. 1, a scintillator 1 made of NaI or the like is formed into a cylindrical shape, and PMTs 3 are arranged around it via a light guide 2. As shown in Fig. 2, the scintillator 1 has a predetermined width in the axial direction, and the PMT 3 also has a predetermined width in the circumferential direction.
A large number of them are also arranged in the axial direction. In this embodiment, the scintillator 1 is divided into eight blocks A to H in the circumferential direction, and the cylindrical scintillator 1 is formed by connecting these eight blocks A to H in the circumferential direction. .

The output of each PMT3 is A/
After being digitized by the D converter 4, the multiplier 5
The weight coefficients f and g for each PMT 3 are multiplied and sent to the positioning calculation circuit 6. An adder 7 is provided for adding the outputs of the PMT 3 for each block A to H, and a sum signal ΣA to each block is provided.
ΣH is obtained, and these are sent to the area identification circuit 8, which identifies in which block the light emission has occurred by comparing the sizes.The signal P that activates the A/D converter 4 is then sent to the area identification circuit 8, which identifies that the light emission has occurred. A signal Q representing the blocked block is output. For example, when it is determined that light emission has occurred in block B, a P signal is sent to the A/D converter 4 belonging to block B and blocks A and C adjacent to block B.
Only these A/D converters 4 are made active.
Furthermore, a signal Q representing the block B identified as having emitted light is sent to the ROM 9 and belongs to the two blocks A and C adjacent to that block B.
The weighting coefficient for each PMT3 is sent to each multiplier 5, and the weighting coefficient for the i-th PMT3 is set as fi in the circumferential direction (referred to as the X direction) and gi in the axial direction (referred to as the Y direction). , the position of the light emitting point (X, Y) when the output signal Pi of the A/D converter 4 is
is given by: X=Σfi·Pi/(ΣA+ΣB+ΣC) Y=Σgi·Pi/(ΣA+ΣB+ΣC) This calculation is performed by the positioning calculation circuit 6. In this case, only the sum signal for block B and the two blocks A and C adjacent thereto are used for the sum signal of each block.

The weighting coefficients that need to be stored in ROM9 are only for PMT3 belonging to three blocks: the block containing the light emitting point and the blocks on both sides of it.
Since the scintillator 1 has a cylindrical shape and is the same at any part in the circumferential direction, the weighting coefficient can be used no matter which block it is identified that light emission has occurred. This weighting factor is the scintillator 1
This is determined by taking into consideration that optical discontinuities occur between adjacent blocks due to their joint surfaces.

By selecting the A/D converter 4 to be active in this way, the output of the PMT 3 that participates in positioning calculations is limited, and position calculations are performed only in the area of the block containing the light emitting point and the blocks on both sides thereof. Therefore, signals having little relevance to position calculation are removed, noise is removed, and accuracy can be improved.

Further, this is the same even when the scintillator 1 is not divided as described above but is integrally cylindrical, and there is no optical discontinuity at the bonding surface. That is, even in the case of an integrated scintillator, the same effect can be obtained by limiting the area and performing positioning calculations.

In this way, positioning is performed in both the circumferential direction and the axial direction, so if image reconstruction processing is performed using only data at the same axial position, a tomographic image at a slice at any axial position can be obtained. become.

Effects of the invention According to this invention, position calculations are performed by excluding PMT outputs in areas that have a low contribution to position calculations and eliminating the influence of noise contained in them.
The light emitting position in the circumferential direction and the axial direction can be determined with high precision, and a tomographic image in a slice at an arbitrary position (axial position) can be obtained. Moreover, since the region division is performed in the circumferential direction of the cylindrical scintillator, the same weighting coefficient can be used no matter which region it is identified that light emission has occurred, which simplifies the configuration.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view of one embodiment of this invention, FIG. 2 is a schematic side view, and FIG. 3 is a block diagram showing the circuit configuration. 1...Scintillator, 2...Light guide, 3
...PMT, 4...A/D converter, 5...multiplier,
6...Positioning calculation circuit, 7...Adder, 8...
Area identification circuit, 9...ROM.

Claims (1)

[Scope of utility model registration request] A cylindrical scintillator whose width is widened in the axial direction, and a large number of photomultiplier tubes arranged both in the circumferential direction and in the axial direction on the outer peripheral surface of the cylindrical scintillator.
A region identification circuit that identifies which region of the plurality of regions divided in the circumferential direction of the cylindrical scintillator has generated light emission by comparing the outputs of each photomultiplier tube, and , using only a circuit that generates a weighting factor for each photomultiplier tube in that region and the region adjacent to that region, and the output of each photomultiplier tube in the region and the region adjacent to that region. A ring-type ECT device comprising a positioning calculation circuit that calculates a light emission position by applying the weighting coefficient.