JP3329133B2 - Positron emission CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a radioisotope RI
Around the subject to which (radioisotope) was administered,
A detector is arranged in a ring shape, and a positron emission CT device (hereinafter, positron EC) that detects a positron (positron) emitted from the subject to obtain a tomographic image of the subject.
In particular, the apparatus has a gantry having an opening for inserting a subject, and a multi-layered detector including a plurality of detectors arranged in a ring around the opening. The present invention relates to a positron emission CT apparatus capable of collecting three-dimensional data.

[0002]

2. Description of the Related Art In a positron ECT apparatus, a positron (positron) emitted in a living body loses energy by ionizing and exciting a biological substance. When the positron is combined with a nearby electron, the positron and the electron disappear. This utilizes the phenomenon in which two photons are emitted in exactly opposite directions.
These photons are called annihilation gamma rays (also called annihilation radiation).

An example of the structure of a conventional positron ECT device of this type will be described with reference to FIGS. 5 and 6 are longitudinal sectional views showing the internal structure of a gantry (not shown). The positron ECT device shown as the conventional example is a device capable of collecting two-dimensional data and three-dimensional data.

A plurality of gantry (not shown) is provided between a pair of shields 2 having an opening 2a (six in this example).
Are provided in a ring shape. The multilayer detector 3 is provided with shield plates (slice shields) 5 arranged between the respective layers and arranged in a direction perpendicular to the laminating direction to limit annihilation γ-rays incident on each layer of the multilayer detector 3. It has become so.

The slice shield 5 moves in a position close to the multilayer detector 3 (two-dimensional data collection position) as shown in FIG. 5 and in a stacking direction of the multilayer detector 3 as shown in FIG. And a position (three-dimensional data collection position) determined according to a tomographic image to be obtained.

A description will be given of an example of taking a tomographic image of the head H of the subject M in the positron ECT apparatus configured as described above. First, a radioisotope RI (radio isotope) is administered to the subject M, and the subject M is inserted into the opening 2a of the gantry. Then, annihilation γ-rays 10H from the radioisotope RI accumulated in the head H are incident on the surrounding multilayer detector 3 and detected. In the example shown in FIG. 5, the annihilation gamma rays 1 are incident on the second and third detectors 4 from the left among the six detectors 4, but are counted by a coincidence circuit (not shown). , Annihilation gamma rays 10 shown by solid lines simultaneously incident on the opposing detector 4
H only. The radioactive isotope RI administered to the subject M is different from the head H which is the site of interest, for example, the chest B
Γ-rays also disappear from this chest B
B occurs. Annihilation gamma rays 10B generated from this chest B
Is shielded by the slice shield 5 (disposed between the layers of the multilayer detector 4) at the two-dimensional data collection position, so that only the annihilation gamma rays 10H generated from the head H are incident on the multilayer detector 3. And a tomographic image of the head H can be obtained without lowering the S / N ratio.

[0007]

However, the prior art having such a structure has the following problems. That is, as shown in FIG. 6, the slice shield 5 is moved to a three-dimensional data collection position separated in the stacking direction of the multilayer detector 3, and an annihilation γ ray 10 H from the head H (both solid and dotted annihilation γ rays) Line) is detected and the slice shield 5 is located away from the multilayer detector 3, so that the annihilation γ-rays 10B from the chest B, which is an extra area, are multi-layered. At the time of counting the annihilation gamma rays 10H incident on the detector 3, the coincidence coincidence counting the [irrelevant] annihilation gamma rays incidentally simultaneously with the detector 4 [with the annihilation gamma rays 10H from the head H] The trajectory of the annihilation gamma ray changes due to the scattering such as Compton scattering, etc. [and the annihilation gamma ray 10H from the head H], and the simultaneous coincidence of the scattering that counts the annihilation gamma ray 10B incident on the detector 4 occurs. S / of image
There is a problem that the N ratio decreases. Such a problem occurs remarkably in a positron ECT apparatus for whole body imaging which has a larger opening than that in a positron ECT apparatus for head imaging. A similar problem occurs not only in a device for collecting two-dimensional and three-dimensional data but also in a device for collecting three-dimensional data without the slice shield 5.

The present invention has been made in view of such circumstances, and suppresses accidental coincidence counting and scattering coincidence counting by reducing annihilation γ-rays from other regions except for a site of interest. It is an object of the present invention to provide a positron emission CT apparatus capable of improving the S / N ratio of a tomographic image.

[0009]

The present invention has the following configuration to achieve the above object. That is, the positron emission CT apparatus according to claim 1 has an opening for inserting a subject, and a multi-layered detector including a pair of shields and a plurality of detectors is provided on the ring around the opening. A gantry disposed at a position where the slice shields erected in a direction perpendicular to the stacking direction of the plurality of detectors are located close to the multilayer detector and separated from the slice detector in the stacking direction of the multilayer detector. And a positron emission CT apparatus for whole body imaging capable of collecting two-dimensional data and three-dimensional data,
A shield mechanism having a shield member formed at the center with an opening having an opening area equivalent to the opening of the gantry, and a movable shield member movable along the center direction of the opening of the shield member. In the gantry, the movable shield member is moved at the time of three-dimensional data collection so that the opening of the shield member is made smaller than the opening of the gantry.

A positron emission CT apparatus according to a second aspect of the present invention has an opening for inserting a subject, and a multi-layer detector comprising a plurality of detectors together with a pair of shields around the opening. In a positron emission CT apparatus for full-body imaging capable of collecting only three-dimensional data, provided with a gantry disposed on a ring, an opening having an opening area equivalent to the opening of the gantry was formed at the center. The gantry is provided with a shield mechanism having a shield member and a movable shield member movable along a center direction of the opening of the shield member, and the movable shield member is moved so that the opening of the shield member is moved. It is characterized in that it is smaller than the opening of the gantry.

[0011]

The operation of the present invention is as follows. Claim 1
The operation of the invention described in (1) is as follows. That is, at the time of collecting three-dimensional data, the slice shield is moved to a position separated in the stacking direction of a plurality of multilayer detectors, so that, for example, only annihilation gamma rays from the head (site of interest) are collected. In this case, unnecessary annihilation γ-rays other than the head (other regions), for example, from the chest tend to enter the multilayer detector. However, by moving the movable shield member of the shield mechanism,
By making the opening of the shield member smaller than the opening of the gantry, it is blocked, so that unnecessary annihilation γ-rays can be prevented from being incident on the multilayer detector.
Therefore, accidental coincidence counting and scattering coincidence counting can be suppressed.

The operation of the invention described in claim 2 is as follows. Even with a positron emission CT apparatus capable of collecting only three-dimensional data, the same operation as the above-described claim 1 is produced.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an external perspective view showing a gantry of the positron ECT apparatus according to the embodiment, and FIG. 2 is a longitudinal sectional view showing an internal structure of the gantry. This device is a device for whole body imaging, and is configured to be able to collect two-dimensional data and three-dimensional data. The present invention is also applicable to a device that can collect only three-dimensional data.

In FIG. 1, reference numeral 1 denotes a gantry having a ring-shaped multilayer detector for detecting annihilation gamma rays. As shown in FIG. 2, the gantry 1 has a plurality of (in this example, six) detectors 4 between a pair of shields 2 having an opening 2a.
Is provided in a ring shape. The detector 4 converts BGO (Bi4Ge) that converts annihilation gamma rays into visible light.
It comprises a scintillator 4a containing crystals of 3 O12), NaI, BaF2, etc., and a photomultiplier tube 4b for converting the light into electrons and amplifying them.

The multi-layer detector 3 is incident on each layer of the multi-layer detector 3 by a slice shield 5 erected in a direction perpendicular to the laminating direction provided between the respective layers [from a portion other than a desired site of interest]. ] Is configured to limit annihilation gamma rays. In FIG. 2, unlike the position where the slice shield 5 is close to the multilayer detector 3 (as shown in FIG. 1) (the two-dimensional data collection position), the position (3 (Dimensional data collection position).

A shield mechanism 20 is removably mounted near the opening 2a of the gantry 1. The shield mechanism 20 is erected on a base 20a and includes a shield member 20b made of lead or the like, and a base 20a.
and a drive unit 20c, such as a wheel, for supporting the movable member a in the longitudinal direction. Shield member 2
0b is an opening 20d having an opening diameter smaller than the opening diameter of the opening 2a of the gantry 1.
It is formed such that the center position of “a” and the center position substantially coincide with each other. The opening diameter of the shield member 20b is formed smaller than the opening 2a of the gantry 1 and slightly larger than the head diameter of the subject M. This shield mechanism 20 is not used at the time of two-dimensional data collection, is placed around the gantry 1, and performs data collection while moving the slice shield 5 to a position away from the detector 4. At the time of collection, the photographer moves from a position placed around the gantry 1 to the front of the opening 2a of the gantry 1. Note that a rail may be provided on the floor surface, and the drive unit 20c of the shield mechanism 20 may be driven by a motor or the like to move the shield mechanism 20.

In the positron ECT apparatus configured as described above, first, a radioisotope RI is administered to the subject M, and the subject M placed on the top of a medical bed apparatus (not shown) is moved horizontally. It is inserted into the opening 2a of the gantry 1 by moving. At this time, the head H of the subject M is inserted into the opening 2a of the gantry 1 through the opening 20d of the shield mechanism 20, so that the head H, which is the site of interest, is within the field of view of the multilayer detector 3. Moving. Then head H
Annihilation gamma rays 10 from the radioactive isotope RI accumulated in the part
H enters the surrounding multilayer detector 3 and is detected. On the other hand, the annihilation gamma rays 10B from the radioisotope RI accumulated in the chest M of the subject M are blocked by the shield member 20b of the shield mechanism 20, so that data collection without the shield mechanism 20 is performed. (FIG. 6 of a conventional example)
), Random coincidence counting and scattering coincidence counting can be suppressed. Therefore, due to these,
A decrease in the S / N ratio of the tomographic image can be prevented. In other words, the S / N ratio of the tomographic image can be improved as compared with the conventional example.

The above-described shield mechanism 20 includes a driving unit 20
Although the floor is movable by c, the present invention can be modified as shown in the external perspective view of FIG.

That is, the shield mechanism 21 includes a flat shield member 21a made of lead or the like and a mounting screw 21b.
And is constituted by. An opening 21c having an opening diameter smaller than the opening diameter of the opening 20a of the gantry 1 is provided substantially at the center of the shielding member 21a, similarly to the shield member 20a of the shield mechanism 20 described above.
Is formed so that the center position of the opening 2a substantially coincides with the center position. Further, the opening diameter of the opening 21c is smaller than the opening 2a of the gantry 1 and the head diameter of the subject M. It is formed slightly larger than. The shield mechanism 21 is not used at the time of collecting two-dimensional data, but is placed around the gantry 1. At the time of collecting three-dimensional data, the opening 2 a of the gantry 1 extends from the periphery of the gantry 1.
It can be attached to the front by the photographer.

The above-mentioned shield mechanism 20 (21)
Of the shield member 20b (21a)
Although (21c) has a circular shape, an opening may be formed in an elliptical shape or a rectangular shape. In addition, although their opening diameters are formed slightly larger than the head H of the subject M, for example, for imaging the chest M, the openings 20d (21c) of the shield member 20b (21a) are formed. The opening diameter may be formed slightly larger than the waist section of the subject M.

The above-mentioned shield mechanism 20 (21)
Is attached to the gantry 1 at the time of three-dimensional data collection. However, as shown in the front view of FIG. Good.

This shield mechanism 22 is made of lead or the like and is formed in a flat plate shape. The shield member 2 has an opening 22a having an opening area substantially equal to that of the opening 2a of the gantry 1 formed at the center.
2b, an attachment screw 22c for attaching the shield member 22b to the gantry 1, four movable shield members 22d inserted into the shield member 22b, and a shield member 22b toward the center of the opening 22a of the shield member 22b. And a grip portion 22 attached to the movable shield member 22d through the long groove 22e.
f. Each movable shield member 22
d can be moved along the direction of the center of the opening 22a by the photographer grasping and moving each of the grasping portions 22f.

The shield mechanism 22 allows the photographer to grip the holding portion 22f attached to each movable shield member 22d and move it toward the center of the opening 22a to change the shape of the opening 22a. It can be adjusted to square or rectangular. For example, a normal state (a state where the opening area is substantially the same as the opening 2a of the gantry 1)
Accordingly, as shown by a two-dot chain line in the figure, the opening 22a 'can be formed to have an opening diameter (opening area) smaller than the opening diameter (opening area) of the opening 2a of the gantry 1.

According to the shield mechanism 22 having such a configuration, the shape and size of the opening 22a can be adjusted, so that not only the head but also, for example, a tomographic image of the chest or abdomen of the subject is photographed. In doing so, it is possible to prevent unnecessary annihilation γ-rays from the abdomen and lower abdomen (particularly, the bladder where radioisotopes RI tend to accumulate) from entering the detector 4. That is, it is possible to support imaging of each part of the subject M.

Each movable shield member 22d of the shield mechanism 22 may be configured to be moved via a drive mechanism such as a motor.

As the shield mechanism, a spiral opening / closing mechanism used for a shutter of a camera or the like, specifically, a tongue-shaped shield member is spirally stacked, and each of the spiral shield members is provided. The structure may be such that the opening diameter of the central opening formed by the tongue-shaped shield member can be adjusted by adjusting the degree of overlap.

The shield mechanisms 20, 21, 22 are as follows:
Although the gantry 1 is attached to the opening of the subject M, the gantry 1 may be attached to the side opposite to the side where the subject M is inserted. In this case, for example, when a tomographic image of the abdomen is taken, the head and lower abdomen protrude from the gantry 1, and extra annihilation γ-rays enter the detector 3 from those parts. Can be prevented.
Therefore, tomographic images of not only the head but also the chest and abdomen are S / N
An image can be taken with good efficiency.

[0028]

As is apparent from the above description, according to the first aspect of the present invention, when collecting only an annihilation gamma ray from a site of interest, the movable shield member of the shield mechanism is moved. By making the opening of the shield member smaller than the opening of the gantry, unnecessary disappearance γ from other areas is obtained.
Lines can be prevented from entering the multilayer detector. Therefore, even when collecting three-dimensional data in which the slice shield is located at a position separated in the stacking direction of a plurality of multilayer detectors, it is possible to suppress coincidence coincidence and scattering coincidence. As a result, the S / N ratio of the obtained tomographic image can be improved as compared with the conventional example. Furthermore, by adopting a configuration in which the movable shield member is moved, the shape and size of the opening of the shield member can be adjusted, so that imaging of each part of the subject can be performed.

Further, according to the second aspect of the present invention, 3
Even a positron emission CT apparatus configured to collect only dimensional data has the same effect as the first aspect.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing a gantry and an added shield mechanism of a positron ECT apparatus according to an embodiment.

FIG. 2 is a longitudinal sectional view showing an internal structure of the gantry.

FIG. 3 is an external perspective view showing a modified example of the shield mechanism.

FIG. 4 is a front view showing a modified example of the shield mechanism.

FIG. 5 is a longitudinal sectional view showing the internal structure of a conventional gantry.

FIG. 6 is a diagram for explaining three-dimensional data collection by a conventional gantry.

[Description of Signs] 1 gantry 2 Shield 3 Multi-layer detector 4 Detector 5 Slice shield 20, 21, 22 Shield mechanism 20a Base 20b Shield member 20c Drive unit 20d Opening 22b Shield member 22c Mounting screw 22d Movable shield member 22e Long groove 22f Grip

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 1/161 A61B 6/03 321

Claims (2)

(57) [Claims] An opening for inserting a subject,
Around this opening, there is provided a gantry in which a multilayer detector including a plurality of detectors is arranged on a ring together with a pair of shields, and the gantry is erected in a direction perpendicular to the stacking direction of the plurality of detectors. The slice shield can be moved to a position close to the multilayer detector and a position distant in the stacking direction of the multilayer detector, and can collect two-dimensional data and three-dimensional data. A shield mechanism comprising: a shield member formed at the center with an opening having an opening area equivalent to the opening of the gantry; and a movable shield member movable along the center of the opening of the shield member. In preparation for the gantry,
A positron emission CT apparatus, wherein the movable shield member is moved so that an opening of the shield member is made smaller than an opening of the gantry when collecting three-dimensional data. 2. It has an opening for inserting a subject,
A gantry in which a multi-layer detector composed of a plurality of detectors is disposed on a ring together with a pair of shields around the opening, and a positron emission CT apparatus for whole body imaging capable of collecting only three-dimensional data. A shield mechanism comprising: a shield member formed at the center with an opening having an opening area equivalent to the opening of the gantry; and a movable shield member movable along the center of the opening of the shield member. A positron emission CT apparatus provided in the gantry, wherein the movable shield member is moved to make an opening of the shield member smaller than an opening of the gantry.