JPH07954Y2 - Positron ECT device - Google Patents

Description

[Detailed Description of the Device] A. Field of Industrial Application This device is used for accumulating data for absorption correction of a positron ECT device used to obtain tomographic increase of a subject such as a human body in nuclear medicine diagnosis. Regarding technology.

B. Conventional Technology In the positron ECT device, positrons (positrons) emitted in the body lose energy by ionizing and exciting biological materials, and when they combine with nearby electrons, the positrons and electrons disappear, and It utilizes the phenomenon that two photons are emitted in opposite directions. These photons are called annihilation gamma rays (annihilation radiation).

An outline of an example of the structure of the positron ECT device will be described with reference to FIGS. 8 to 13.

Inside the gantry (not shown), as shown in the sectional view of FIG. 8, BGO (Bi ₄ Ge ₃ O) that converts annihilation γ-ray 1 into visible light is used.
₁₂ ), NaI, BaF ₂ etc. containing a scintillator 2a,
A large number of detectors 2 each consisting of a photomultiplier tube 2b for converting the light into an electron and amplifying the light are equally arranged in a ring shape, and a plurality of detector rings 3a thus constructed are stacked. A multi-layer detector ring 3 is provided.

Radioisotope (RI) administered to subject (human body) m
Causes β ⁺ decay to emit positrons, and when a pair of annihilation γ rays 1 are emitted, they are simultaneously detected by two detectors 2 facing each other. This is the coincidence counting beam indicated by a in FIG. The outputs from the two opposing detectors 2 are input to the coincidence counting circuit 4, and the output pulses are obtained from the coincidence counting circuit 4 only when the two detectors 2 simultaneously detect the annihilation γ-ray 1.

However, annihilation γ-rays from a large number of RIs other than the target slice also enter each detector 2 at the same time as the coincidence counting beam. That is, the coincidence coincidence counting indicated by B and C and the scattering coincidence counting indicated by D in FIG. These random coincidences and scattered coincidences become disturbances and deteriorate the image quality of the reconstruction tomographic image.

Therefore, the coincidence counting is deliberately shifted by using a delay circuit to eliminate the coincidence counting, or the inter-slice shield 5 is provided as shown in FIG. It has been devised to cut off the coincidence counts by blocking.

In this way, the data of the coincidence counting beams obtained from all the pairs of the detectors 2 facing each other are collected by the computer, and the data are rearranged after the measurement is finished, as shown in FIG. 10 (A). The data for each measurement direction is collected to create a count rate distribution curve. This is the projection data D1, and the projection data D1 is subjected to correction of absorption of annihilation γ-rays in the body described later, correction of nonuniformity of the sensitivity of the detector, and other corrections.

The data for detector sensitivity correction is collected as follows. That is, as shown in FIG. 11 (A), the detector array circle 6
The flat plate radiation source 7 is placed inside (see FIG. 8) and rotated to obtain the normalized data N as shown in FIG. Then, 1 is divided by N to obtain sensitivity correction data (1 / N) as shown in FIG.

The data for absorption correction is collected as follows. That is, as shown in FIG. 12 (A), with the ring radiation source 8 placed inside the detector array circle 6 (no subject exists), the blank data B as shown in FIG. obtain.
Further, as shown in FIG.
With the subject m to which RI is not administered placed, the transmission data T as shown in FIG. Then, the blank data B is divided by the transmission data T to obtain absorption correction data (B / T) as shown in FIG.

Next, as shown in FIG. 13 (A), the ring source 8 is removed, and the RI-administered subject m is placed inside the detector array circle 6 as shown in FIG. 13 (B). Obtain emission data E.

The correction is performed by multiplying the emission data E by the sensitivity correction data (1 / N) shown in FIG. 7C and the absorption correction data (B / T) shown in FIG. .
That is, the distribution of true RI is This is the true distribution of radioisotopes (see (E) in the figure).

Finally, after correction by the superposition integration method to obtain final data D2 as shown in FIG. 10 (B), a tomographic image is reconstructed by back projection.

The present invention relates to collection of absorption correction data among the above corrections.

Conventionally, in collecting absorption correction data, instead of using the ring radiation source 8 described above, a line source (linear radiation source) that rotates inside the detector array circle 6 with a constant radius is used. Known from. An example of this will be described below with reference to FIG.

An annular fixing plate 9 is arranged at the opening of the detector array circle 6, and a plurality of support rollers 10 are axially supported by the annular fixing plate 9 in an equidistant state. A rotary ring 11 is rotatably supported by these support rollers 10 in a state where the axis of rotation is horizontal and coincides with the center of the field of view, that is, the axis O of the detector array circle 6. A V-shaped peripheral groove 11a is formed on the outer peripheral surface of the rotary ring 11,
A V-belt 14 for transmission is stretched between a V-groove of a pulley 13 attached to the second output shaft and a circumferential groove 11a of the rotary ring 11.

A horizontal through hole is formed in the rotary ring 11, and the end of the line source 15 is inserted into and removed from the through hole. The line source 15 is ⁶⁸ Ge−
It contains a radioisotope (RI) such as ⁶⁸ Ga.

The detector ring array 3, the line source 15, the rotary drive mechanism of the line source, and the like are housed in a gantry (not shown) having an opening for inserting the subject m.

After collecting data for detector sensitivity correction, line source 15
End of the rotary ring 11 is inserted into the through hole of the rotary ring 11 and the motor 12 is driven to rotate the rotary ring 11 a plurality of times via the V-belt 14, and the line source 15 of the detector array circle 6 is accordingly rotated. The blank data B is obtained by rotating at the position just inside.

Next, the line source 15 is rotated in the same manner with the subject m to which RI is not applied being placed, and the transmission data T
To get

The line source 15 is rotated at a position just inside the detector array circle 6 so that the slice position of the subject changes in various ways such as the head, the chest, and the abdomen. is there.

When this rotating line source 15 is used, data collection takes longer than when using the ring radiation source 8 (see FIG. 12), but the extremely expensive RI is extremely small and cost can be reduced. There is an advantage.

C. Problems to be Solved by the Invention In the absorption correction data collection mechanism using the line source, the line source 15 is rotated at a position outside the large subject such as the chest and abdomen. However, since the radius of rotation of the object is always fixed, instead of changing the size of the subject, the following problems occur.

That is, when a small subject such as the head or neck is targeted, the turning radius of the line source 15 is too large compared to the size of the subject, and there are many invalid data from the area other than the target subject. Since the collection time of the absorption correction data becomes long, and there are many errors in the absorption correction data due to the large amount of invalid data and the large proportion of the coincidence coincidence count. ,
As a result, there is a problem that the image quality of the tomographic image is deteriorated.

Specifically, as shown in FIG. 15, when a small subject m ₂ such as a head is targeted, the rotation trajectory L of the line source 15
The radius r _{1 of} is considerably larger than that of the subject m ₂ .

Focusing on one detector 2, the view angle α _{1 at which the} detector 2 collects data from the line source 15 moving on the rotation trajectory L is larger than the view angle α ₂ required for collecting absorption correction data. Quite large. The circular arc S is the detector array circle 6
Is an arc centered on the axis O of the above, and is an arc in contact with a line segment that forms the viewing angle α ₂ necessary for absorption correction data collection.

When the line source 15 moves along the rotation trajectory L, the detector 2 detects and counts the radiation from the large viewing angle α ₁ .

The data collected at the orbit portions L ₁ and L ₂ shown by the thick solid lines located inside the small viewing angle α ₂ required for absorption correction data collection are valid data, but outside the viewing angle α ₂ The collected data in the orbital portions L ₃ and L ₄ indicated by the broken line are invalid data.

If the measurement time is a predetermined fixed time, the total count number in the sinogram shown in FIG. 16 (B) will be almost constant, but since the viewing angle α ₁ is large, the profile shown in FIG. As shown in the figure, the number of counts within a predetermined measurement time decreases, and in addition, the proportion of coincidence coincidence counts increases, so that the S / N ratio deteriorates as a whole.

In order to obtain a predetermined S / N ratio, it is necessary to increase the number of counts in one detector 2, and for that purpose, the measurement time must be extended (the number of rotations of the line source 15 must be increased).

The abscissa R in the sinogram represents one detector 2
Indicates the direction perpendicular to the line segment connecting the detector 2 and the center O of the field of view. Further, θ represents the positions of many detectors 2 on the detector array circle 6.

The present invention has been made in view of such circumstances, and a run source is used to collect absorption correction data, and the radius of rotation of the line source within the detector array circle of this line source is set to the size of the subject. According to the present invention, the time required to collect the absorption correction data can be shortened, the image quality of the tomographic image can be improved, and the configuration of the mechanism for switching the radius of gyration of the line source is simple, and An object of the present invention is to provide a positron ECT device in which a detector ring, a line source, and a rotation drive mechanism thereof are accommodated, and particularly, a length of the gantry in the axial direction is shortened to reduce the size of the gantry.

D. Means for Solving Problems The present invention has the following configuration in order to achieve such an object.

That is, in the positron ECT device of the present invention, a rotary ring is arranged coaxially with the detector array circle, and a line source holder can be attached to and detached from the rotary ring and protruded in the radial direction inside the rotary ring when the device was installed. The line source holder is rotatably supported at a first position and a second rotation position tilted in the radial direction, and is substantially aligned with the axis of the detector array circle on the protruding end side of the line source holder. The line source is attached in a parallel posture, and a locking mechanism for positioning and locking the line source holder on the rotary ring at the first and second rotational positions is provided on the rotary ring.

E. Action The action of the configuration of this invention is as follows.

When the subject is relatively small, such as the head or neck of the human body, the locking mechanism positions and locks it at the first rotation position, and the radius of rotation of the line source is adjusted to a size corresponding to the small subject. Reduce. In this case, the radius of rotation of the line source is such that the line source does not contact the subject, and
It is desirable that the radius be such that the position near the subject is rotated.

Focusing on one detector, the radiation data captured by that detector comes from a region of the same size as the region required to collect absorption correction data, or a region slightly larger than that. . Therefore, in the radiation data captured by the detector, the components effective as absorption correction data greatly increase, and the ineffective components significantly decrease.

Then, the number of counts per unit time by the detector increases as compared with the case of the conventional example. Further, since the radius of gyration is small, the proportion of coincidence coincidence counts decreases, and the S / N ratio improves.

When the subject is large, such as the chest or abdomen of the human body, the locking mechanism positions and locks the second rotation position.

Further, since the line source holder to which the line source is attached by using the rotating ring can be detached from the rotating ring, the opening for inserting the subject into the gantry can be formed as a through opening, so that the length of the gantry in the axial direction can be shortened. it can.

F. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

1 to 3 relate to an embodiment of the present invention. (A) of FIG. 1 is an enlarged front view of a main part, (B) is a partially broken side view, and FIG. 2 is a part thereof. FIG. 3 is a cross-sectional view showing the overall schematic configuration, which is a broken perspective view.

As shown in FIG. 3, similarly to the conventional example, a large number of detectors 2 each including a scintillator and a photomultiplier tube are equally arranged in a ring shape, and a plurality of detector rings 3a thus configured are arranged. A multi-layer detector ring 3 constructed by stacking layers is provided.

An annular fixing plate 9 is arranged at the opening of the detector array circle 6, and a plurality of support rollers 10 are axially supported by the annular fixing plate 9 in an equidistant state. A rotary ring 11 is rotatably supported by these support rollers 10 in a state where the rotation axis O is horizontal and coincides with the center of the visual field.

A V-shaped peripheral groove 11a is formed on the outer peripheral surface of the rotating ring 11, and a transmission V belt 14 is provided between the V groove of the pulley 13 attached to the output shaft of the motor 12 and the peripheral groove 11a of the rotating ring 11. It is hanging. It should be noted that these mechanisms are housed in a gantry (not shown) having an opening penetrating in the rotation axis O direction for inserting the subject m.

The above configuration is similar to the conventional example.

This embodiment differs from the conventional example in the following points.

As shown in FIGS. 1 and 2, a pin 17 is integrally fixed and protruded on a strip plate-shaped line source holder 16 in a posture perpendicular to the plate surface. It is inserted in a state in which it can be freely inserted into and removed from the horizontal through hole 11b formed in. The pin 17 is rotatable while being inserted into the through hole 11b.

In the line source holder 16, the plate surface of the outer portion 16a is in contact with the plate surface of the rotating ring 11 with the pin 17 as a boundary, while the inner portion 16b projects inside the rotating ring 11 and its protruding end. The part has a cylindrical boss 16c. This boss 16c
A through hole is formed in the horizontal direction, and the small diameter portion 15a at the end of the line source 15 is detachably attached to the through hole. The line source 15 is in a posture substantially parallel to the rotation axis O of the rotation ring 11 (the axis of the detector array circle 6).

When an external force around pin 17 is applied to line source holder 16, line source holder 16 rotates with pin 17
The line source 15 is rotated with respect to 11, and the line source 15 is also rotated accordingly, and the distance between the rotary ring 11 and the rotation axis O, that is, the radius of rotation of the line source 15 is changed.

When the subject is relatively small, such as the head or neck, it is indicated by a solid line in FIG. 1 (A), and as shown in FIG. 2, the posture of the line source holder 16 is set in the direction toward the rotation axis O. To do. This posture is referred to as a first rotation position P1. The turning radius of the line source 15 at this time is small.

When the subject is relatively large, such as the chest and abdomen, the posture of the line source holder 16 is set substantially along the inner circular arc of the rotary ring 11 as shown by the alternate long and short dash line in FIG. . This posture is referred to as a second rotation position P2. The turning radius of the line source 15 at this time is large.

In order to stabilize the postures of the line source holder 16 at the first rotation position P1 and the second rotation position P2 and prevent unexpected rotation, the rotation ring 11 has the following locking mechanism. 18 are provided.

A cover 19 covering the outer portion 16a of the line source holder 16 is attached to the rotating ring 11. This cover 19
Top plate 19a parallel to the plate surface of the rotating ring 11 and two side plates 19b, 1
9c, an arc-shaped outer plate 19d, a flange 19e bent from one side plate 19d, a flange 19f bent from the other side plate 19c, and a flange 19g bent from the outer plate 19d.
have.

An opening 1 for inserting and removing the outer portion 16a of the line source holder 16 with respect to the cover 19 is provided in the central portion of the top plate 19a.
9h is formed. A state in which the holder outer portion 16a is positioned at the opening 19h is shown by a chain double-dashed line in FIG. 1 (A). This state is referred to as a third rotation position P3. Third
The rotation position P3 of the first rotation position P1 and the second rotation position P2 are
Equivalent to the middle of.

The inner surface of the top plate 19a is in contact with the plate surface of the holder outer portion 16a. The flanges 19e, 19f, 19g are in contact with the plate surface of the rotating ring 11 and are fixed with screws 20.

At both sides covered by the cover 19, the rotating ring 11
A recess is formed in each of the recesses, and the first and second spring plungers 21 and 22 are fitted into each recess. Line source holder 1
When 6 is in the first rotation position P1, the holder outer portion 16a
Is sandwiched between the first spring plunger 21 protruding from the plate surface of the rotating ring 11 and the one side plate 19b of the cover 19 and positioned and locked, so that unexpected rotation thereof is prevented.

When the line source holder 16 is in the second rotation position P2, the holder outer portion 16a has a second spring plunger 22 protruding from the plate surface of the rotating ring 11 and the other side plate 19c of the cover 19. It is sandwiched by and locked for positioning, and its unexpected rotation is prevented.

When the line source holder 16 is rotated by applying an external force, the holder outer portion 16a retracts the first spring plunger 21 or the second spring plunger 22 against its elasticity, so that the spring plungers 21, 22 You can get over and rotate.

In this embodiment, the cover 19 and the first and second spring plungers 21 and 22 form a locking mechanism 23.

As shown in FIG. 3, inside the detector array circle 6,
The cylindrical blind cover 24 can be put in and taken out at a position corresponding to the inside of the rotation path of the line source 15 at the first rotation position P1 and the outside of the small subject m ₂ .

Next, the operation of this embodiment will be described.

After collecting the data for detector sensitivity correction, with the outer portion 16a of the line source holder 16 positioned in the opening 19h in the central portion of the cover 19, the pin 17 protruding from the line source holder 16 is attached. Insert into the through hole 11b of the rotating ring 11. This is the third rotation position P3 shown by the chain double-dashed line in FIG. 1 (A).

As shown in FIG. 4 (A), when the diagnosis target is a large subject m ₁ such as the chest or abdomen, the line source holder 16
It rotates in the counterclockwise direction around the pin 17 with the inner portion 16b of the. Then, the holder outer portion 16a gets over the second spring plunger 22 and contacts the side plate 19c of the cover 19. The second spring plunger 22 elastically returns to the original projecting posture to prevent the holder outer portion 16a from coming off.

In this state, the line source holder 16 is in the second rotation position.
At P2, the line source 15 comes to a position having a turning radius r ₁ corresponding to a large subject m ₁ . In addition, the retainer outer portion 16
Since a is sandwiched between the side plate 19c of the cover 19 and the second spring plunger 22 and positioned and locked, unexpected rotation of the line source holder 16 is restricted, and the line source holder is prevented.
16 will maintain its second pivot position P2.

Further, as shown in FIG. 4 (B), when the diagnosis target is a small subject m ₂ such as a head or a neck, the inner portion 16b of the line source holder 16 is rotated clockwise around the pin 17. Move. Then, the holder outer portion 16a rides over the first spring plunger 21 and contacts the side plate 19b of the cover 19. The first spring plunger 21 elastically returns to the original projecting posture to prevent the retainer outer portion 16a from coming off.

In this state, the line source holder 16 is in the first rotation position.
P1 is reached, and the line source 15 comes to a position having a turning radius r ₂ corresponding to a small subject m ₂ . In addition, the retainer outer portion 16
Since a is sandwiched between the side plate 19b of the cover 19 and the first spring plunger 21 and positioned and locked, unexpected rotation of the line source holder 16 is restricted, and the line source holder is prevented.
16 will maintain its first pivot position P1.

The line source holder 16 is rotated by a large amount to move from the first rotation position P1 to the second rotation position P2, and vice versa, from the second rotation position P2 to the first rotation position P2. It goes without saying that it is possible to switch to the moving position P1.

Before placing the small subject m ₂ inside the detector array circle 6, the blind cover 24 is set inside the detector array circle 6.

After the position of the line source 15 is determined, the motor 12 is driven to rotate the line source 15 integrally with the rotating ring 11 through the V-belt 14 multiple times to obtain the blank data B. Next, the line source 15 is similarly rotated with the subject to which RI is not applied being placed, and transmission data T is obtained.

If the subject to be diagnosed is a large subject m ₁ such as the chest or abdomen,
The line source 15 is rotated at the second rotation position P2 (see the dashed line in FIG. 1 and FIG. 4A), but the line source 15 is located near the inside of the rotary ring 11. As compared with the conventional example in which the line source 15 is inserted into the through hole of the rotary ring 11, the absorption correction data collection time is shortened, although it is a little.

When the diagnosis target is a small subject m ₂ such as the head or neck, the first rotation position P1 (solid line in FIG. 1, FIG. 4B)
(See), the line source 15 is rotated, and the radius of rotation r ₂ of the line source 15 in that case is a small radius corresponding to the small object m ₂ , so the absorption correction data collection time is It can be greatly shortened compared to the example.

Specifically, as shown in FIG. 5, when a small subject m ₂ such as a head or a neck is targeted, the radius r ₂ of the rotation trajectory L of the line source 15 is small corresponding to the subject m _2. , The line source 15 is the viewing angle α ₂ required for collecting absorption correction data.
Rotate only inside. Therefore, when focusing on one detector 2, the radiation data captured by the detector 2 is data from an area that coincides with the area necessary for collecting absorption correction data, and the radiation taken by the detector 2 is taken. In the data, effective components as absorption correction data are significantly increased, and ineffective components are significantly decreased.

Then, the detector 2 detects and counts only the radiation from the viewing angle α ₂ necessary for collecting the absorption correction data.

If the radiation concentration of the line source 15 and the measurement time are the same as in the case of the conventional example, the total count number in the sinogram shown in FIG. 6 (B) is the same as that of the conventional example, but the viewing angle α ₂ is Because it is small, it is not counted on both sides of the sinogram, and the counts are concentrated on the center side.

Therefore, as shown in the profile of FIG. 6 (A), the number of counts in the detector 2 within a predetermined measurement time increases, and in addition, since the radius of gyration r ₂ is small, the proportion of coincidence coincidence also decreases. , The overall S / N ratio is improved,
The quality of the tomographic image is improved. From another angle, the measurement time required to obtain a predetermined S / N ratio can be shortened as compared with the conventional example.

Since other configurations are the same as those of the first embodiment, corresponding or corresponding portions will be denoted by the same reference numerals and description thereof will be omitted.

This invention also includes the following configurations as examples.

Although the number of the line sources 15 is one in each of the above embodiments,
It is not necessary to limit this to multiple line source holders.
The 16 may be configured to be attached to the same rotating ring 11. In this case, the measurement time can be further shortened.

G. Effect of the Invention According to this invention, the following effects are exhibited.

When a relatively small subject such as the head or neck is targeted, the radius switching mechanism can reduce the radius of gyration of the line source to a size corresponding to the small subject. The ineffective component can be remarkably reduced, and the component effective as the absorption correction data can be remarkably increased.

Therefore, the number of counts per unit time by the detector can be increased as compared with the case of the conventional example, and the time required for collecting the absorption correction data can be shortened.

In addition, since the radius of gyration is small, the ratio of coincidence coincidence counts is reduced and the S / N ratio is improved. As a result, the image quality of the tomographic image can be improved.

Further, since the line source holder using the rotating ring and to which the line source is attached can be removed from the rotating ring, the opening for inserting the subject of the gantry can be formed in the through opening, so that the axial length of the gantry can be shortened. it can.

Therefore, the chest and abdomen can be inspected without giving a feeling of pressure to the subject.

[Brief description of drawings]

1 to 6 relate to an embodiment of the present invention. (A) of FIG. 1 is an enlarged front view of a main part, (B) is a partially cutaway side view, and FIG. 2 is a part thereof. FIG. 3 is a perspective view of a fracture, FIG. 3 is a cross-sectional view showing an overall schematic configuration, FIG. 4 is a front view for explaining the operation, FIG. 5 is a front view showing a trajectory of a line source, and FIG. Is a profile of a measurement image, and (B) is a sinogram. 7 to 12 relate to the outline of a general positron ECT device, FIG. 7 is a schematic sectional view, FIG. 8 is an outline explanatory view of coincidence counting, and FIG. 9A is projection data. Illustration of
(B) is a diagram of backprojection data, FIG. 10 is a diagram showing how to obtain sensitivity correction data, FIG. 11 is a diagram showing how to obtain absorption correction data, and FIG. 12 is emission data and true RI. It is a figure which shows how to obtain | require distribution. 13 to 15 relate to a conventional example, FIG. 13 is a sectional view showing the overall schematic configuration, FIG. 14 is a front view showing the trajectory of a line source, and FIG. 15 (A) is a measurement image. Profile, (B) is a sinogram. 6 …… Detector array circle 11 …… Rotating ring 15 …… Line source 16 …… Rotating type line source holder 18 …… Locking mechanism 26 …… Telescopic line source holder P1 …… First state P2 …… Second state

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kaji Hirose, 1st Kuwabara-cho, Nishinokyo, Nakagyo-ku, Kyoto City, Kyoto Prefecture (56) Reference: Japanese Patent Laid-Open No. 58-108481 (JP, A)

Claims (1)

[Scope of utility model registration request] 1. A rotating ring arranged coaxially with a detector array circle, a first rotating position which is attachable to and detachable from the rotating ring, and which protrudes in a radial direction inside the rotating ring when the rotating ring is attached. A line source holder that is rotatably supported at a second rotation position that is tilted with respect to the radial direction, and is substantially parallel to the axis of the detector array circle on the protruding end side of the line source holder. A line source that is attached in a different posture, and a locking mechanism that positions and locks the line source holder at the first and second rotational positions with respect to the rotating ring,
A positron ECT device characterized in that the locking mechanism is provided on the rotary ring.