JPS586499A - Ray source for correcting positron ct device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a calibration line that is installed in a positive aycT device and is used to calculate a correction amount during image reconstruction by adjusting the amount of attenuation of gamma rays in a subject to the needle side. Regarding the source.

The Bosito ayCT device is a device that generates a distribution image of a positron-emitting nuclide administered to a subject in the subject from measurement data of positron/extinction gamma rays. 1st
The figure is an overall view of the gamma ray detection section of the positron CT apparatus. The detector 2 is arranged on a ring, and the subject 1 is located near the center of the ring.

- Now, if detectors 2A and 2B detect annihilation gamma rays at the same time, the positron-emitting nuclide is detected by detector 2A.

It can be seen that it existed near the straight line 4 connecting 2B.

Therefore, the coincidence values of the detectors 2A and 2B are proportional to the integral value of the positron emitting nuclide concentration on the straight line 4. However, in reality, attenuation correction for the object must be performed. That is, as shown in the figure, the two annihilation gamma rays generated at point X are transmitted within the subject by lengths X and L -X (where L is the length that a straight line crosses the subject), and during that time, . -μx, o-μ(L-X):, -μL6900010
9. Attenuation of (1)? box office. However, μ is an absorption coefficient. This amount of attenuation is related to the annihilation position of the positron (and is always constant on a straight line. Therefore, if the coincidence value of the detector pair is divided by this amount of attenuation (that is, the amount of attenuation
499(2)), a quantity representing the integral value of the positron-emitting nuclide concentration can be obtained. Note that 3A is a coincidence circuit, and 3B is a data recording device.

A typical method for determining the amount of attenuation described above is to place a positive) O-emitting nuclide between the subject and the detector and to determine the coincidence value. A radiation source that can be used for this purpose is the axis G@-1G&, but since it has a half-life of 280 days, if it is installed in a positron CT apparatus, it will need to be replaced quite frequently. Considering this point, Derenzo of the United States (Der@nzo) proposed in his paper the use of a single gamma ray source. In this case, L is determined using the absorption coefficient μ' of the subject for gamma rays emitted from the radiation source. After that, we further use the absorption coefficient μ of the subject for annihilation gamma rays, and
- Calculate μm. This method of determining the amount of attenuation of a subject using a single gamma ray source simply replaces the X-ray generator of the X-ray CT apparatus with a single gamma ray source, and the basic operating principle is the same. As can be seen from this point, each detector requires 5 counting circuits to record its counted values. Note that although the above is an example of attenuation amount correction, the same applies to detector sensitivity correction.

In the case where a single gamma ray source is used as described above, gamma rays must be incident on one detector from only one direction. Therefore, only point sources can be used. For example, if you want to equivalently form a linearly distributed line source, it is necessary to move the point source linearly (
Ru. Therefore, the time required for measurement becomes longer. This is a major drawback when using a single gamma ray source.

An object of the present invention is to provide a radiation source for calibrating a positron CT apparatus that can utilize a single gamma ray source and shorten measurement time.

The gist of the present invention is to arrange a plurality of gamma ray sources while satisfying the condition that the gamma rays incident on one detector are limited to one direction, and to collect data from only a part of the range with one gamma ray source. This is intended to shorten the measurement time. Hereinafter, the present invention will be explained in detail with reference to the drawings.

6 (In the case of CT equipment, the object to be examined is located in the center of the detector ring, and the size of the object is limited to a range that does not exceed about half the diameter of the detector ring.) .

Therefore, the number of opposing detectors combined with one detector is %-, 1/3 of the number of detectors on the opposite side of the annular array of detectors.
Detectors are limited to: Therefore, in Fig. 2, detectors 2mb to 2ac correspond to the single gamma ray source a in the pot t1, so that when looking at the subject 1 from the position of the source a, The amount of attenuation for the detector versus straight line is determined. Such single gamma ray sources &+b and c are designed to be able to emit gamma rays only to the detectors facing each other.Conversely speaking, the detector group 2a etc. on the back side of radiation source a can emit gamma rays only to the detectors facing each other. In order not to detect gamma rays, the detector group zb for the radiation source does not detect the gamma rays from the line gb, and for the radiation source, the detector group 2c etc. do not detect the gamma rays from the radiation source C.
Each shielding body 7 is provided.

With the above configuration, the radiation sources a, b, and c have their relative positions 7
By moving the eaves until the source is located and calculating the coincidence values, you can obtain the data necessary for attenuation correction. This radiation source arrangement has the advantage of shortening the measurement time to approximately 173 seconds.

The present invention can be applied to a detection device with a multilayer structure.

In order to detect ocitron annihilation gamma rays, a multilayer system is adopted in addition to a single layer system for the arrangement structure of the detector.

FIG. 3 is an example of a four-layer detector device. Four detector groups 2OA, 20B, 20C, and 20D are installed in a ring shape on a frame (not shown). And 4
Detector groups 2OA, 20B, 20C, 20D
are arranged along the tomographic direction of the tomographic plane 10 of the subject 1. Lead collimators 9A are placed on both sides of each detector group.

9B, 9C, 9D, and 9K are provided to prevent the incidence of gamma rays from outside the field of view for detecting positron annihilation gamma rays, thereby improving accuracy. With this configuration, a tomographic image of the tomographic plane 10 can have seven layers.

An embodiment of such a detection device having a multilayer structure is shown in FIG. Figure 4 is a sectional view q'9t in the direction of A and A' in Figure 3.
1. It is placed. Each radiation source d, . is naturally provided with a shield 7 as shown in FIG. 2 (not shown).

The radiation source d is arranged inside the rotation center side of the detector group 2OA, and the radiation source d is arranged inside the rotation center side of the detector group 2DC, and both are located at 180° different positions when viewed in the direction of the central axis. It is located in The sources d,. are mounted inside a cylinder for a single gamma ray source, for example. Therefore, the source d,
・rotates synchronously.

Measurement is performed by rotating the cylindrical body once and capturing the count values obtained during the rotation.

After one rotation and one measurement, the single radiation source d, is moved to the positions P and Q of the next detector group 20B and 20D.

After the movement is completed, the cylindrical body is rotated again and the count values obtained during that time are captured. By these two rotations, the four-layer detector group 2OA, 20B, 20C, 20D (7
) The acquisition of measured values for all items is completed. The measured values thus obtained should be used as correction data. In addition, in the figure,
Line 4 [i) 8 indicates the radiation direction of gamma rays.

Naturally, the cylindrical body is -1 more transparent than the material that allows gamma rays to pass through. Become.

FIG. 5 is a diagram showing an embodiment of a detection device in which a single gamma ray source is attached to a cylindrical body. (A) is a sectional view corresponding to FIG. 4, (B) is a cross-sectional view of the cylindrical body 10, and (C) is a detailed configuration diagram of a single gamma ray source section. The cylindrical body 10 is inserted into a gap provided in a part of the collimators 9A to 9E, and is mounted so as to be movable in the direction of the arrow. Cylindrical body 1
A single gamma ray source unit 31 is attached and fixed to a part of 0. The radiation source section I is located in the gap of the detector group 2OA, and the radiation source section 31 is located in the gap of the detector group 20C. The cylindrical body 10 is configured to be able to move in the right direction as much as one detector group and collimator. Thereby, the radiation source section I can be used for the detector groups 2OA and 20B, and the radiation source section 31 can be used for the detector groups 20C and 20D. Incidentally, the radiation source part (material) and 31 are in a positional relationship with an angle of 180°. Radiation source department (capital) and 31 (c)
It is configured as shown in the figure. That is, the radiation source parts 30 and 31 are attached to the radiation source housing part of the cylindrical body 10.
, 31, the shield 10 ζl is naturally supported and driven by a support mechanism that supports the cylinder, a rotation mechanism that rotates it, and a mechanism that moves it in the direction of the arrow. Furthermore, after collecting the correction data, the cylinder lO is removed from the collimator cavity.

This removal to the outside from the cavity is achieved by moving the cylinder to the right in the figure using a moving mechanism and housing it in the housing. Furthermore, FIG. 3(C) is for illustration purposes only, and it goes without saying that in reality, the radiation source section and the cylindrical section require a fixing structure to each other. A similar effect can be obtained by installing a drive rod instead of the cylindrical body, fixing a single radiation source to the tip of the drive rod, and driving the drive rod.

According to the above embodiment, the measurement time is 1/2 compared to the conventional method.
It was possible to shorten it to Note that the present invention can naturally be applied to cases other than the four-layer detection groups.

According to the present invention, the measurement time can be made faster.

[Brief explanation of the drawing]

Fig. 1 is a diagram of a conventional example, Fig. 2 is a diagram of an embodiment of the present invention, 11
Figures 5(A), 5(B), and 5(B) are diagrams of other embodiments of the present invention. & T b Hc Hd He...single gamma ray source,
7... Shielding body, 2, 2a + 2b, 2ab
, 2ac--Detector, 9A. 9B, 9C, 9D, 9K...Collimator. Patent applicant: Makoto Nagaishi, Agency of Industrial Science and Technology. Japanese Unexamined Patent Application Publication No. 1999-8-6499 (4) Fig. 1 Fig. 2 Fig. 3 Fig. 5 (b) (/\) de)

Claims (1)

[Claims] 1. In a positron detector group equipped with a single gamma ray source as a radiation source for calibration, a positron detector group provided on a frame around a subject and the subject a single gamma ray source provided in a space between the and a shielding body provided on the opposite side of the single gamma ray source, and the single gun 1 radiation source is integrated with the shielding body to rotate in the space with the rotation center point being the tube center. A radiation source for calibrating a positron φCT device having a configuration in which: 3. The positron detector group has a plurality of tomographic planes. 4. A radiation source for calibrating a positron CT device according to claim 1, which has a multi-layer structure in order to obtain a radiation source. One calibration cylinder is configured to be insertable, the single gamma ray source and the shield are mounted on the cylinder at a position corresponding to at least one positron detector group, and the cylinder is moved so that each positron detector group can be inserted. A radiation source for calibrating a positron CT apparatus according to claim 3, wherein calibration data is obtained for each detector group.