JPH11101874A - Emission ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change the size of the opening of a shield mechanism installed to the opening of a gantry. SOLUTION: A PET (positron CT) device provided with a gantry 1 having an opening 2a for inserting an object M to be inspected is also provided with a shield mechanism 5. The mechanism 5 is constituted of two shield plates 20 and 21 which become nearly concentric to the opening 2a of the gantry 1 when the mechanism 5 is mounted on the gantry 1, a carrying truck 10, and a holding frame 11 which holds the plates 20 and 21 erected on the truck 10. One of the shield plates 20 and 21 is fixed to the frame 11 and rotatably supports the other shield plate 21 through a bearing 23. The shield plates 20 and 21, in addition, have an elliptic hole 22 which is smaller than the diameter of the opening 2a of the gantry 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a radioisotope R
An emission CT apparatus that arranges a ring detector around a subject to which I (radio isotope) has been administered, detects γ-rays emitted from the subject, and obtains an RI distribution image as a tomographic image of the subject, particularly The present invention relates to a shield mechanism provided in an opening of a gantry having an opening through which a subject is inserted and having a ring detector disposed around the opening.

[0002]

2. Description of the Related Art A positron CT apparatus (hereinafter referred to as a P-type) is one of emission CT apparatuses (hereinafter referred to as an ECT apparatus).
An example of the configuration of the ET device will be described with reference to FIGS. 6 and 7 are longitudinal sectional views showing the internal structure of a gantry (not shown). The PET apparatus shown as the conventional example is an apparatus capable of collecting two-dimensional data and three-dimensional data. The gantry (not shown) includes a ring detector 3 formed by laminating a plurality (six in this example) of a large number of detectors 4 arranged in a ring between a pair of shields 2 having an opening 2a.
A slice shield S is provided between the ring detectors 3 of each layer, thereby limiting annihilation gamma rays incident on the ring detectors 3 of each layer. The slice shield S is located at a position close to the ring detector 3 (two-dimensional data collection position) as shown in FIG. 6 and at a position where the slice shield S is moved and retracted in the stacking direction of the ring detector 3 as shown in FIG. (Three-dimensional data collection position) and 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 PET 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, the annihilated γ-rays 10H from the radioisotope RI accumulated in the head H portion are incident on the surrounding multilayer ring detector 3 and detected. In the example shown in FIG. 6, the annihilation gamma rays 10H are incident on the second and third detectors 4 from the left among the six ring detectors 3,
What is counted by the coincidence circuit (not shown) is the annihilation γ shown by a solid line that is simultaneously incident on the opposing detector 4.
Only line 10H. In addition, since the radioisotope RI administered to the subject M accumulates not only on the head H, which is the site of interest, but also on the chest B, for example, it disappears from the chest B.
Line 10B occurs. Since the annihilation gamma rays 10B generated from the chest B are blocked by the slice shield S at the two-dimensional data collection position, only the annihilation gamma rays 10H generated from the head H can be made incident on the ring detector 3. , The tomographic image of the head H can be obtained without lowering the S / N ratio.

However, as shown in FIG. 7, the slice shield S is moved to a three-dimensional data collection position separated in the stacking direction of the ring detector 3, and the annihilation gamma rays from the head H (both solid and dotted lines) are removed. When the three-dimensional data collection of the head H is performed by detecting the annihilation γ-ray 10H, since the slice shield S is located at a position away from the ring detector 3, the annihilation γ from the chest B which is an extra area is obtained. When the line 10B is incident on the ring detector 3 and the annihilation gamma rays 10H are counted, the coincidence coincidence counting for counting the extraneous annihilation gamma rays incident on the detector 4 simultaneously with the annihilation gamma rays 10H from the head H, or Compton The trajectory of the annihilation γ-ray changes due to scattering such as scattering, and the simultaneous coincidence of scattering that counts the annihilation γ-ray 10B incident on the detector 4 simultaneously with the annihilation γ-ray 10H occurs, and the S / N ratio of the tomographic image decreases. It was something to do. Such a problem is caused by the head imaging PE.
This phenomenon occurs remarkably in a PET device for whole body imaging in which an opening is larger than that in a T device. 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 a slice shield S.

In order to solve such a problem, a shield mechanism is provided in the vicinity of the opening in the front of the gantry so that the site other than the site of interest, for example, as shown in FIGS. In some cases, the annihilation gamma rays 10B generated from the chest B are blocked from entering the detector 4 of the ring detector 3. The shield mechanism 5 provided near the opening 2a of the gantry, as shown in FIG.
It is composed of a disk-shaped shield member 9 made of lead or the like, a carrier 10 movable on the floor, and a holding frame 11 erected on the carrier 10 and holding the shield 9. . As shown in FIG. 9, the shield member 9 is provided with a hole 12 having a diameter smaller than the opening diameter of the opening 2a of the gantry and slightly larger than the diameter of the head of the subject M. The gantry is formed so that the center positions thereof and the opening 2a substantially coincide with each other. The outer diameter of the shield member 9 is formed slightly smaller than the diameter of the gantry opening 2a. When the region of interest is the chest, a hole having a diameter slightly larger than that of the chest and indicated by a dotted line in the figure is provided.

The carriage 10 is a pair of left and right L-shaped bases 1.
An inverted U-shaped frame 15 is provided upright on the vertical support shaft of the L-shaped base 13 which is composed of three and four casters 14 arranged at four locations. Inside the frame 15 is a holding plate 1 having a mounting hole corresponding to a substantially outer diameter of the shield member 9.
A shield member 9 is detachably screwed to an edge protruding slightly rearward of the mounting hole. A screw fixing member 17 for positioning and fixing the gantry and the shield mechanism 5 is provided on the holding plate 16 of the holding frame 11.
It is provided in the place. That is, this screw fixing member 17
Is screwed into a screw hole (not shown) provided on the front surface of the gantry, so that the center of the opening 2a of the gantry and the center of the hole 12 of the shield member 9 are substantially aligned. Note that the width of the pair of bases 13 of the transport carriage 10 is formed to be slightly wider than the lateral width of the bed (not shown), and the height of the lower side of the holding plate 16 of the holding frame 11 is such that the top plate is in a lowered posture. The height is higher than a certain bed, and the shield mechanism 5 is arranged so as to straddle the bed when mounted on the gantry.

[0007] The screw fixing member 17 is screwed into a screw hole on the front surface of the gantry 1 and the shield mechanism 5 is moved to the opening 2 of the gantry.
In the state where the radioactive isotope RI is disposed on the head H, which is a site of interest, as shown in FIG.
The line 10H is incident on the detector 4 of the ring detector 3 stacked therearound and detected. On the other hand, the annihilation gamma rays 10B from the radioisotope RI accumulated in the chest B outside the site of interest of the subject M are transmitted to the shield member 9 of the shield mechanism 5.
As a result, accidental coincidence counting and scattering coincidence counting are suppressed, and the S / N ratio of a tomographic image resulting from these can be improved.

[0008]

However, the prior art having such a configuration has the following problems. That is, the shield member to be mounted on the opening of the gantry is formed in a plate shape with lead or the like, and a plurality of types of shield members having different opening diameters according to the examination site such as for a subject's head and abdomen are used. And it is displayed and stored in the shield storage shelf. Then, before the examination, the operator or the like brings the transport trolley to the storage place, removes the shield member having the hole of the size adapted to the diagnostic site from the shield storage shelf,
The shield member is held by a holding frame erected on a transport carriage, is conveyed to the opening of the gantry, and a shield mechanism for holding the shield member is mounted on the opening of the gantry by, for example, screwing. Conversely, when the shield member attached to the opening of the gantry is replaced with one that is compatible with another diagnostic site or stored in a shield storage shelf, the transport cart is shielded, contrary to the above operation. It is necessary to convey to a storage place where a storage shelf is located, store it, and hold another shield member in a holding frame.

Therefore, the work of holding and removing the shield member from the holding frame provided on the carrier is complicated, and since the shield member is a heavy object, the work of replacing it cannot be performed easily. There is a problem of danger. In addition, since it is necessary to lower the subject from the bed each time the shield member is attached to or detached from the opening of the gantry, it takes time to replace the shield member and attach / detach the shield mechanism, thereby lowering the inspection efficiency. Problem. This problem is particularly remarkable when the same subject (patient) is examined continuously for the head and the torso.

The present invention has been made in view of such circumstances, and has as its object to provide an emission CT apparatus capable of easily changing the size (opening area) of an opening of a shield member.

[0011]

In order to achieve the above object, in the emission CT apparatus of the present invention, the shield mechanism provided at the opening of the gantry has two non-circular holes. The shield members are provided side by side, and at least one of the shield members is configured to be rotatable.

According to such a configuration, by rotating one of the shield members, the weight of the peripheral portion of the non-circular hole formed in the two shield members changes, and the one shield member is formed by the two shield members. The size (opening area) of the hole to be formed can be changed. For example, the shape of the non-circular hole is as shown in FIG.
When the long side is slightly larger than the width of the torso of the subject and the short side is slightly larger than the diameter of the head as shown by the oblique lines in the oblique lines, the two shield members are formed. If the long side and the short side of the elliptical hole overlap each other as shown in FIG. 4, a hole (opening) of a size suitable for the examination of the torso (chest) is obtained, and one shield member is rotated by 90 °. When the long side of the elliptical hole of one shield member and the long side of the elliptical hole of the other shield member are orthogonal to each other as shown in FIG. ), And the shield member shields the region of interest (chest or head) and the region other than the region of interest (head or chest), and cuts off extra noise from regions other than the region of interest. Lines can be prevented from entering the ring detector.

Since the size of the opening formed by the two shield members can be changed by rotating one of the shield members,
Variable operation can be performed easily and easily. In addition, since it is not necessary to replace and hold a shield member having a different hole diameter on a holding frame erected on a transport trolley as in the related art, inspection efficiency is improved, and inspection of different sites of interest such as a head and a chest is continuously performed. Can be done. Further, the size of the opening can be changed by rotating one of the shield members, and the shield mechanism can be incorporated in the gantry since the shield member does not need to be replaced as in the related art.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. This embodiment will be described by taking a PET apparatus as an example similarly to the conventional example. FIG. 1 shows a positron C equipped with a shield mechanism according to an embodiment showing a state in which the head of a subject placed on a bed is inserted into a gantry.
FIG. 2 is a schematic view showing a side cross section of the T device, and FIG. 2 is a cross section showing the configuration of the shield mechanism. Although this apparatus is used for whole-body imaging and capable of collecting two-dimensional data and three-dimensional data, the present invention can be applied to an apparatus capable of collecting only three-dimensional data. In the drawings, the same components as those in FIGS. 6 and 8 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 1, the PET apparatus includes a gantry 1 having an opening 2a into which a subject M is inserted,
The bed 6 is provided in front of the bed. The couch 6 is configured such that a top 7 on which the subject M is placed is vertically movable and horizontally movable, and a headrest 8 on which the head H of the subject M is placed is attached to an end on the gantry 1 side. ing. The opening 2a on the front surface of the gantry 1 is provided with a shield mechanism 5, which is a main part of the present embodiment. As shown in FIG. 2, the shield mechanism 5 includes two disk-shaped shield members (shield plates) 20, 21 made of lead or the like.
, A transport vehicle 10 comprising a base 13 and casters 14 provided thereunder, and a holding frame 11 comprising a frame 15 and a holding plate 16 erected on the transport vehicle 10 and holding the shield plates 20 and 21. It is composed of

The two shield plates 20 and 21 include:
As shown in FIG. 3, an elliptical hole 22 whose long side is slightly larger than the width of the torso of the subject M and whose short side is slightly larger than the head diameter.
Are formed so that the center positions of the elliptical hole 22 and the opening 2a of the gantry substantially coincide with each other in the mounted state. The holding plate 16 of the holding frame 11 is formed with an opening 16 'which is equal to or slightly larger than the opening diameter of the opening 2a of the gantry 1. In this embodiment, a projecting ring 20' is provided at the periphery in the embodiment. An integrally formed shield plate 20 is fixed, and the shield plate 21 is rotatably held in the protruding ring 20 ′ via a bearing 23.

Further, the shield plate 20 is formed with a 90 ° arc groove 24 indicated by a dotted line in the figure, and an operation rod 25 fixed to the shield plate 21 penetrates the groove 24 and protrudes from the holding plate 16. ing. Therefore, by rotating the operation rod 25 along the arc groove 24, the shield plate 21 is rotated.
Rotates with respect to the shield plate 20.

The arc groove 24 is formed on both shield plates 20, 2
It has the effect of regulating the position where the long sides of the elliptical holes 22 formed in the part 1 overlap with each other and the position where the long sides of each other are orthogonal. The operation of the shield mechanism configured as described above will be described. First, the shield mechanism 5 is disposed on the front surface of the opening 2a of the gantry 1 as shown in FIG. In this state, the shield plates 20 and 21 have entered the opening 2a. Next, when the region of interest is the chest, the shield plate 21 is rotated so that the long sides of the elliptical holes 22 formed in the shield plates 20 and 21 overlap (coincide) with each other. As shown, openings of elliptical holes 22 formed in both shield plates 20 and 21 into which the chest can be inserted are formed,
Data of the tomographic image of the chest is obtained by the ring detector 3. In this case, annihilation γ-rays from the radioisotope RI accumulated at the lower (foot) side site of interest are blocked by the shield plates 20 and 21.

When the site of interest is the head, when the shield plate 21 is rotated 90 ° with respect to the shield plate 20 by the operation rod 25, the shield plate 20 and the two shield plates 20 and 21 as shown in FIG. An opening indicated by oblique lines in the figure is formed in a size large enough to allow a head to be inserted therein, and tomographic image data of the head can be obtained by a ring detector. In this case, the annihilation γ generated from the radioisotope RI accumulated in the chest B as described with reference to FIG.
The wire 10B is interrupted by the shield plates 20 and 21. According to the shield mechanism 5, a hole (opening) having a size suitable for the inspection of the head and the chest can be formed only by rotating one of the shield plates by 90 °, so that the inspection is performed on the holding frame as in the related art. There is no need to replace the shield member with a hole having a size suitable for the site of interest, and it is possible to easily and quickly change to a hole having a size suitable for the size of the site of interest. As a result, the examination efficiency can be improved, which is particularly advantageous when successively examining different sites of interest of the same subject, for example, the head and chest.

The present invention can be modified as follows. (1) In the above embodiment, an example in which the shield mechanism 5 is provided in a PET device is taken as an example, but the present invention is not limited to this, and can be applied to, for example, a single photon ECT device. (2) In the above embodiment, the carrier 10 of the shield mechanism 5
Is constituted by an L-shaped base 13, but the base 13 may be formed in a shape along the side surface of the bed 6 so as not to be further obstructive at the time of inspection, and other configurations are possible. You may. The same applies to the holding frame 11 and the like, and the shield mechanism 5 is not limited to the configuration of the above embodiment, but may have another configuration.

(3) In the above embodiment, the transport carriage 10 of the shield mechanism 5 is configured to be moved on the floor by a photographer, for example. The shield mechanism 5 may be moved by driving the motor 10 by a motor or the like. (4) In the above embodiment, the shield mechanism 5 is attached to the opening 2a of the gantry 1 on the insertion side of the subject M, but is also attached to the opening on the side opposite to the insertion side of the subject M. It may be. In this case, for example, when capturing a tomographic image of the abdomen, since the head and lower abdomen protrude from the gantry 1, it is possible to prevent extra annihilation γ-rays from entering the detector 4 from those portions. can do. Therefore, tomographic images of not only the head but also the chest and abdomen can be S / S
Images can be taken with a good N ratio.

(5) In the above embodiment, one of the shield members is supported by the other shield member via a bearing so as to rotate. However, another rotation support mechanism such as supporting the shield member by a roller is used. There may be. (6) In the above-described embodiment, the gantry-side shield member is rotated. However, the bed-side shield member or both shield members may be rotated. Or the like. (7) In the above embodiment, the shield mechanism is configured to be attached to and detached from the gantry, but may be incorporated in the gantry. (8) In the above embodiment, the holes formed in the two shield members are elliptical holes. However, the size of the holes (openings) formed by the two shield plates by rotation of one of the shield plates, such as a rectangle. May be any shape as long as it changes, that is, a non-circular hole.

[0023]

According to the emission CT apparatus of the present invention, only the rotation operation of at least one of the shield members is performed.
The opening can be changed to a size suitable for the region of interest to be inspected, such as the head and chest of the subject, and the change can be performed easily and in a short time, so that the inspection efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a side cross section of an embodiment applied to a PET apparatus.

FIG. 2 is a cross-sectional view illustrating a configuration of a shield mechanism.

FIG. 3 is a plan view showing a configuration of a shield mechanism.

FIG. 4 is a diagram for explaining the operation of the shield mechanism.

FIG. 5 is a diagram for explaining the operation of the shield mechanism.

FIG. 6 is a longitudinal sectional view showing the internal structure of a conventional gantry.

FIG. 7 is a longitudinal sectional view showing the internal structure of a conventional gantry.

FIG. 8 is a perspective view showing a configuration of a conventional shield mechanism.

FIG. 9 is a plan view showing a configuration of a conventional shield member.

FIG. 10 is a longitudinal sectional view showing the internal structure of a conventional gantry equipped with a shield mechanism.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gantry 2a ... Opening 3 ... Ring detector 5 ... Shield mechanism 10 ... Carriage truck (13: Base,
14: caster) 11: holding frame (15: frame, 16: holding plate) 20, 21: shield plate (shield member) 22 ...
Oval hole 23 ... Bearing

Claims (2)

[Claims] 1. A positron CT apparatus having an opening through which a subject is inserted, a gantry having a ring detector stacked around the opening, and a shield mechanism arranged in the opening. Wherein the shield mechanism has two shield members arranged side by side, each having a non-circular hole smaller than the opening of the gantry, and at least one of the shield members being rotationally displaced. An emission CT apparatus characterized in that: 2. An emission CT apparatus according to claim 1, wherein said shield mechanism is held by holding means provided with wheels, and is detachable from an opening of said gantry. apparatus.