JPH0564310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a ring-type ECT device (emission-type computerized tomography device), and particularly relates to an improvement of its collimator.

(b) Prior art In a ring-shaped ECT device, a ring-shaped radiation detector is constructed by arranging a large number of small radiation detectors in a ring-shaped arrangement or by making a ring-shaped radiation detector in one piece. A ring-shaped collimator is rotatably arranged inside the collimator. Conventionally, as this ring-type collimator, one in which three or more parallel collimators are connected in a ring-shape is known (although there are other types).
However, this ring-type collimator has a problem in that a large area where no radiation is incident on the detector occurs at the boundary between each parallel collimator.

To explain with reference to the drawing, the conventional ring type
In the ECT device, as shown in FIG. 4, a rotatable ring collimator 2 is arranged inside a ring radiation detector 1. This ring-shaped radiation detector 1 is constructed by arranging a large number of combinations of small NaI scintillators and photoelectric conversion elements such as photomultipliers in a ring shape, or by arranging a large number of photoelectric conversion elements in a ring-shaped integral NAI scintillator. It consists of optically coupled materials. In addition, the ring-type collimator 2 is replaced by a parallel collimator 3 here.
It consists of four pieces connected in a ring shape,
Each parallel collimator 3 is provided with a large number of parallel aperture pieces 31 facing toward the center. This aperture piece 3
1 is made of a plate made of a material with high radiation shielding properties, such as tungsten or lead, and performs collimation in the direction of radiation incidence within a plane perpendicular to the rotation axis (a plane parallel to the plane of the paper). The inside of this ring-shaped collimator 2 is a circular field of view 5. When a subject (the patient's head in this figure) 6 is inserted into this field of view 5 and the ring-shaped collimator 2 rotates 1/4, the radiation From the detector 1, projection data of the radiation emitted from the radioactive drug in the subject 6 is obtained in a 360° direction, and this data creates a concentration distribution image (emission tomography) of the radioactive drug in the subject 6 on a plane parallel to the plane of the paper. image) is reconstructed.

In this case, as can be seen from the figure, since the incident radiation is collimated by the diaphragm piece 31 of the parallel collimator 3, the radiation does not enter the connecting part between the adjacent parallel collimators 3 and the parallel collimator 3 is insensitive. It is inevitable that part 4 will occur. Corresponding to this dead part, a dead part also occurs in the radiation detector 1, and since no radiation enters this dead part and it does not contribute to radiation detection, it becomes a wasted part, and the larger this part is, the more the whole system A problem arises in that the sensitivity of the camera decreases, and the field of view 5 also decreases. In the example shown in the figure, the utilization rate of the radiation detector 1 is only about 67%. The longer the diaphragm piece 31 is made to ensure collimation of the incident radiation, the larger this insensitive portion becomes. Aperture piece 31
By increasing the arrangement density, the length of the aperture piece 31 can be shortened and the size of the insensitive area can be reduced to some extent, but there is a limit to this.

(C) Purpose This invention aims to minimize the insensible part,
The purpose of the present invention is to provide a ring-type ECT device that can improve the sensitivity of the entire system and enlarge the field of view.

(d) Configuration This invention has a ring-shaped radiation detector and a ring-shaped collimator rotatably arranged inside the ring-shaped radiation detector, and this collimator is composed of two or more parts divided in the circumferential direction, In each section, a large number of radiation aperture pieces are arranged in parallel or in parallel so that they face the center.
Rings arranged to converge on a point
In the ECT device, the inside of the radiation aperture piece near the boundary of each adjacent portion of the collimator is removed by a predetermined length to shorten the length, and each adjacent portion with a short length is A wire rod with high radiation shielding properties is arranged so as to be located at the intersection of the extension lines of the radiation aperture pieces and to extend in the direction of the rotation axis of the ring-shaped collimator.

(E) Embodiment In FIG. 1, a rotatable ring collimator 2 is arranged inside a ring radiation detector 1. This ring-type radiation detector 1 is a small
It consists of a combination of a NaI scintillator and a photomultiplier or other photoelectric conversion element arranged in a ring shape, or a ring-shaped integral NaI scintillator with a large number of photoelectric conversion elements optically coupled. In addition, ring type collimator 2
In this embodiment, the parallel collimator 3 is made up of four parallel collimators 3 connected in a ring shape, and each parallel collimator 3 is provided with a large number of parallel aperture pieces 31 facing toward the center. A diaphragm piece 32 perpendicular to this diaphragm piece 31 is also provided as shown in FIG. This aperture piece 32 is ring-shaped. These aperture pieces 31 and 32 are made of plates made of a material with high radiation shielding properties, such as tungsten or lead, and the aperture pieces 31 prevent radiation in a plane perpendicular to the rotation axis (a plane parallel to the plane of the paper in FIG. 1). Collimation is performed in the incident direction, and the aperture piece 32 performs collimation in the incident direction of the radiation within a plane parallel to the rotation axis (a plane perpendicular to the plane of the paper in FIG. 1). Then, in the inner approximately triangular part 33 near the boundary where the four parallel collimators 3 are adjacent to each other and connected, the aperture piece 3
1 has been cut off and made shorter. Note that it is of course possible to use a shorter length from the beginning instead of making it shorter. In this portion 33, a wire 34 located at the intersection of the extension lines of the shortened aperture pieces 31 belonging to each of the adjacent parallel collimators 3, 3 extends in a direction parallel to the rotation axis, as shown in FIG. It is arranged like this. The wire 34 is made of a material with high radiation shielding properties, such as tungsten.

The inside of this ring-shaped collimator 2 is a circular field of view 5. When a subject (the patient's head in this figure) 6 is inserted into this field of view 5 and the ring-shaped collimator 2 rotates 1/4, the radiation From detector 1,
Projection data of the radiation emitted from the radioactive drug in the subject 6 is obtained in a 360° direction, and this data reconstructs a concentration distribution image (emission tomogram) of the radioactive drug in the subject 6 on a plane parallel to the plane of the paper. This is similar to a normal ring-type ECT device.

In the ring-shaped collimator 2 having the above configuration, since the aperture piece 31 is shortened at the end of each parallel collimator 3, the dead area 4 that occurs near the boundary where the parallel collimators 3 are adjacent to each other is reduced, and as a result, the system The overall sensitivity can be improved, and as can be seen from FIG. 1, the field of view 5 can be enlarged if the inner diameter of the ring-shaped radiation detector 1 is the same. Since the aperture piece 31 is shortened at the end of the parallel collimator 3, the collimation effect worsens in that area, but since the collimation effect is supplemented by the wire 34, the collimation effect as a whole is improved even at this end. will not deteriorate. That is, as shown in FIG. 3, the wire 34 can block the radiation A and B in the directions that would otherwise enter the diaphragm piece 31 because the diaphragm piece 31 is short when the wire 34 is not present. It is possible to supplement the collimation effect. Furthermore, if the field of view 5 is kept the same size as the conventional one, the diameter of the ring-shaped collimator 2 can be made smaller, and as a result, the inner diameter of the ring-shaped radiation detector 1 can be made smaller, thereby making it possible to detect radiation from radioactive drugs in the subject 6. The distance to the device 1 can be shortened and sensitivity can be improved.

In addition, although the above describes a ring-type collimator in which four parallel collimators are connected in the circumferential direction, it is not limited to four, but it is also possible to connect three, five, six, etc. parallel collimators in the circumferential direction. The present invention can be similarly applied to a ring type collimator or a focusing type collimator in two or more directions.

(f) Effects According to this invention, the dead area can be made smaller without deteriorating the collimation effect of incident radiation, and the sensitivity of the entire system can be improved, and the field of view can be enlarged to expand the scope of inspection. It becomes possible to do so. Furthermore, if the field of view is the same size, the diameters of the ring collimator and the ring radiation detector can be made smaller, which allows the detector to be closer to the radiation source and improve sensitivity.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a schematic partially enlarged perspective view of a ring-shaped collimator 2 of the same embodiment, and FIG. 3 is a schematic diagram for explaining the collimation effect. FIG. 4 is a schematic diagram of a conventional example. 1...Ring type radiation detector, 2...Ring type collimator, 3...Parallel collimator, 31, 32
...Aperture piece, 34...Radiation shielding wire, 4...
Blind area, 5... field of view, 6... subject.

Claims (1)

[Claims] 1 has a ring-shaped radiation detector and a ring-shaped collimator rotatably arranged inside the ring-shaped radiation detector,
This collimator is composed of two or more parts divided in the circumferential direction, and in each part, a large number of radiation aperture pieces are arranged in parallel so as to face the center or so as to focus on one point. By removing a predetermined length of the inner side of the radiation aperture pieces near the boundaries of the adjacent parts of the collimator described above, the length is shortened, and the radiation aperture pieces of each adjacent part with shorter lengths are A ring-shaped ECT device characterized in that a wire rod with high radiation shielding properties is arranged to extend in the direction of the rotation axis of a ring-shaped collimator so as to be located at the intersection of the extension lines.