JPH03115989A - Positron ct device - Google Patents

Abstract

PURPOSE:To increase the detection sensitivity by making the radial length of a stylus collimator relatively longer at both side parts in the axial direction of a detector body than at the center part. CONSTITUTION:Many detectors 5 are arrayed in a ring shape and those ring- shaped detectors are arrayed in many layers in a fixed direction to form the detector body B. Many stylus collimators 6 are arrayed at specific intervals on the internal surface side of the detector body B. Then the stylus collimators 6 arranged on both side parts in the axial direction of the body are relatively longer in radial length than those arranged at the center part. Consequently, the sensitivity can be increased in the center of a visual field as well as the removal of the stylus collimators 6.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a detector body formed by arranging detectors arranged in a ring in multiple layers in the axial direction of the ring; The present invention relates to a positron CT apparatus having a slice collimator disposed inside.

[Conventional technology]

positron CT
dtowography is a technique in which a drug labeled with a nuclide that emits positrons, ie, positrons, is administered to a patient, and the distribution of the radionuclide in the body is extracted as a cross-sectional tomographic image through external measurement. While X-ray CT depicts the morphological structure of a living body, positron CT has the characteristic of capturing physiological and biochemical changes and metabolic functions within a living body as images. Compared to similar tomographic imaging methods (single photon emission CT) that use gamma-ray emitting nuclides, this method has superior sensitivity, resolution, and quantitative performance.

A positron emitted from a positron-emitting nuclide taken into a living body loses kinetic energy in the vicinity and then combines with the electrons that make up the material and annihilates. At this time, a pair of annihilation photons are sent in opposite directions. released into the These γ-ray pairs are measured by simultaneous counting of a pair of detectors placed opposite each other with the subject in between, and only the positron-emitting core in the cylindrical part connecting the pair of detectors is detected. . In positron CT,
This property is used to measure coincidence in multiple directions along a cross-section of a subject. Then, from these data, a computer calculates the positron-emitting nuclide distribution in the cross section and displays it as an image (“Positron CTJ,
p. 41, published by Igaku Shoin Co., Ltd., September 1983, 1st edition).

FIG. 4 is a sectional view showing an outline of a conventional positron C-child device. This positron C-child device includes a detector 1 that detects gamma rays, and a slice collimator 2 that limits the detection range expected by one detector. By providing the slice collimator, it is possible to reduce the influence of noise N1 due to accidental events and noise N2 due to scattering events.

A large number of detectors 1 are arranged in a ring shape, and these ring-shaped detectors are arranged in multiple layers in a fixed direction to form a cylindrical portion (detector body) of the positron C-child device. The subject 4 is inserted into this cylindrical portion. A large number of slice collimators 2 are arranged at predetermined intervals inside the cylindrical portion. Shield collimators 3 are provided on both sides of the slice collimator to prevent radiation from entering from the outside.

[Problem to be solved by the invention]

However, the conventional positron C-device has the drawback of low detection sensitivity, which is a major problem especially in clinical application.

Therefore, an object of the present invention is to provide a positron C device with high detection sensitivity.

[Means to solve the problem]

In recent years, the sensitivity and S when removing the slice collimator have increased.
Research has been conducted on the influence of /N ratio
D Imaging'' (A 5TUDY OF T
IIIE PO35IBILITV OF US
INCM old, Tl-3LICI PET 5YSTI MS Idol? 3D IMACING), IEEE Transactions on Nuclear Science (IEEE Transactions)
onNuclear 5science), Vol. 3
B, No. 1, February 1989゜pp,
1066-1071, “The Effect on Collimation on Scatter Fraction in Multi-Slice BEET” (THEEPPEC
T OF COLLIMATION ON 5 CATT
ERPRACTION INMULTI-8LICE
PET), IEEE Transactions on Nuclear Science (IEEE Trans
actions on Nuclear 5cienc
e), Vol.

35, No. 1. Pebrary 1988. pp,
59g-602 reference). According to this study, along the body axis, noise increases almost uniformly across the visual field, while true signal increases in the center of the visual field but less at the periphery. It has been reported that as a result, the image quality obtained around the visual field deteriorates.

The present invention has focused on this fact, and in order to achieve the above object, a detector body formed by arranging detectors arranged in a ring shape in multiple layers in the axial direction of the ring; A positron C-child device having a slice collimator placed inside the body, the slice collimator having a radial length that is relatively longer at both side portions than at a central portion in the axial direction of the detector body. It is characterized by the presence of

[Effect]

Since the present invention is configured as described above, the sensitivity in the central part of the visual field is increased, while the noise in the peripheral part of the visual field is reduced. Therefore, the sensitivity of the positron C-child device is improved overall.

[Embodiment] Hereinafter, a positron C device according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the description, the same elements are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a sectional view showing a positron C-child device according to one embodiment. This positron C device is expected to have a detector 5 that detects gamma rays and one detector.

A slice collimator 6 is provided to limit the detection range. As the detector 5, for example, a scintillation detector using an inorganic crystal as a scintillator is used. A scintillation detector includes a scintillator that converts gamma rays into visible light, and a photoelectric conversion element such as a photomultiplier tube that converts visible light into an electrical signal. A large number of detectors 5 are arranged in a ring shape, and a detector body B is formed by arranging these ring-shaped detectors in multiple layers in a fixed direction.

A large number of slice collimators 6 are arranged on the inner surface of the detector body B at predetermined intervals. The important thing here is that
The point is that the length in the radial direction of the slice collimator 6 arranged at both sides is relatively longer than the length in the radial direction of the slice collimator 6 arranged at the center in the body axis direction.

Thereby, the sensitivity can be increased at the center of the field of view in the same way as when the slice collimator 6 is removed. Also,
By suppressing scattering events and accidental events in the periphery of the visual field, where no increase in sensitivity can be expected, it is possible to reduce noise in the same manner as in the prior art. Therefore, the sensitivity at the center of the visual field can be improved without reducing the S/N over the entire visual field in the body axis direction. In this case, the amount of change in the radial length of the slice collimator 6 in the body axis direction is preferably set in consideration of the amount of change in sensitivity in the body axis direction. Note that shield collimators 7 are provided on both sides of the slice collimator 6 to prevent radiation from entering from the outside.

FIG. 2 is a partial sectional view showing a positron CT apparatus according to another embodiment of the present invention. The positron CT apparatus shown in FIG. 1A differs from the slice collimator shown in FIG. 1 in that the length of the slice collimator in the radial direction changes stepwise in two steps. The positron CT apparatus shown in FIG. 1B differs from the slice collimator shown in FIG. 1 in that the plurality of slice collimators located at the center have equal lengths in the radial direction. Furthermore, the positron CT apparatus shown in FIG. 2(C) is obtained by removing the slice collimator located at the center of the positron CT apparatus shown in FIG. 4(b).

FIG. 3 is a process diagram showing an example of a method for manufacturing a positron CT apparatus according to the present invention. According to this manufacturing method, a shape is formed in which the positron CT device is divided into two parts along a plane perpendicular to the body axis direction (see figure (a)), and then these two parts are divided into two parts.
The two shapes are combined ((b) in the same figure). This method is effective in manufacturing a positron CT device whose shape is bilaterally symmetrical with respect to a central plane perpendicular to the body axis.

Note that this invention is not limited to the above embodiments. For example, an appropriate rate of change in the length of the slice collimator in the radial direction from the periphery toward the center in the body axis direction is selected depending on the subject, measurement conditions, device shape, and the like. Therefore, the shape of the slice collimator does not need to be symmetrical with respect to the central plane perpendicular to the body axis.

Further, the detector array type is not limited to the circular array type. For example, it may be a polygonal array type. What is important is that the length of the slice collimator in the radial direction is relatively longer at both sides than at the center in the axial direction of the detector body.

〔Effect of the invention〕

Since this invention is configured as explained above,
While the sensitivity in the central part is increased, noise in the peripheral part of the visual field is reduced, and the detection sensitivity of the positron CT apparatus can be increased.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an outline of a positron CT apparatus according to an embodiment of the present invention, FIG. 2 is a partial cross-sectional view showing a positron CT apparatus according to another embodiment of the present invention, and FIG. FIG. 4 is a process diagram showing an example of a method for manufacturing a positron CT device according to the prior art, and FIG. 4 is a sectional view showing an outline of a positron CT device according to the prior art.

Claims (1)

[Claims] A positron CT comprising a detector body formed by arranging detectors arranged in a ring in multiple layers in the axial direction of the ring, and a slice collimator disposed inside the detector body. A positron CT apparatus, wherein the length of the slice collimator in the radial direction is relatively longer at both side portions than at the center portion in the axial direction of the detector body.