JPH1199148A - Transmission ct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To semipermanently use a radiation source by providing a scatterer scattering the radiation from the radiation source, providing a scattered light generator covering the radiation source with the radiation shield body to discharge only the scattered light to the outside, and collecting the transmitted data by the scattered light to generate an absorption map. SOLUTION: A scattered light generator 10 radiating backward scattered light 11 to a testee 20 radiates only the radiation discharged from a line-like radiation source 12 and scattered by a scatterer 13 to the testee 20 side, and the radiation sent directly to the testee 20 side is shielded by a radiation shield body 14. The scattered light generator 10 is arranged at the focal position of a fan beam collimator 31, and the scattered light transmitting the testee 20 is fed to a detector 30 through the fan beam collimator 31. The detection section 30 is the detection section of a γ-camera, and it outputs the position signal indicating its position and the energy signal corresponding to the energy of the incident radiation when radiation is fed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nuclear medicine diagnostic apparatus, and more particularly to a transmission CT apparatus.

[0002]

2. Description of the Related Art A transmission CT apparatus transmits radiation from a radiation source disposed outside a subject, collects transmission data of the radiation, and obtains a distribution image (absorption map) of a radiation absorption coefficient in the subject. ) Is reconstructed. The absorption map thus obtained is used for absorption correction in the emission CT apparatus. The transmission CT device and the emission CT device merely differ in whether or not a radiation source is placed outside, and therefore are often used as the configuration of the device.

Conventionally, as a radiation source in a transmission CT apparatus, Tc-99m (144 keV) or I-123 (1
Co-57 (122 ke) whose energy is relatively low because it is close to the energy of a nuclide such as 59 keV).
V) and Gd-153 (100 keV).

[0004]

However, conventionally used radiation sources are 272 for Co-57.
The half-life of Gd-153 is relatively short, 240 days, and there is a problem that running costs are too high for clinical use.

[0005] In view of the above, the present invention, in view of cost,
It is an object of the present invention to provide a transmission CT apparatus in which a radiation source is improved to be used semipermanently.

[0006]

In order to achieve the above object, in a transmission CT apparatus according to the present invention, only a radiation source, a scatterer that scatters radiation from the radiation source, and only the scattered radiation are externally provided. A scattered radiation generator comprising a radiation shield covering the radiation source so that emitted direct rays are not emitted is provided, and the scattered radiation generator is arranged to face the radiation detector with the subject interposed therebetween, and It is characterized in that transmission data based on scattered radiation transmitted through the subject is collected from a signal obtained from a radiation detector and an arithmetic unit creates an absorption map.

[0007] The subject is not irradiated with direct rays from the radiation source, but is irradiated with only scattered rays, and data based on the scattered rays transmitted through the subject is collected. When the radiation is scattered, it becomes a spectrum having a component whose energy is lower than that of a direct ray. Therefore, for example, Cs-
137 etc. can be used. That is, this Cs-137 has a high emission energy peak of 662 keV,
Scattered radiation having a low energy of about 50 keV to 300 keV can be obtained. Therefore, by utilizing this scattered radiation, it becomes possible to use an appropriate radiation source having a high emission energy but a long half-life, and the same radiation source can be used semi-permanently. Costs can be reduced.

[0008]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, a scattered ray generator 10 irradiates a subject 20 with backscattered rays 11. The scattered radiation transmitted through the subject 20 enters the detector 30 through the fan beam collimator 31. The scattered radiation generator 10 is arranged at the focal position of the fan beam collimator 31. The detector 30 is a detection unit of a gamma camera, and outputs a position signal indicating the position and an energy signal corresponding to the energy of the incident radiation when the radiation enters.

As shown in FIGS. 2 and 3, the scattered radiation generator 10 includes a linear sealed radiation source 12, a scatterer 13 for scattering radiation from the radiation source, and a direct radiation from the radiation source 12. And a radiation shield 14 that shields the radiation so as not to be emitted in the direction of 20. This radiation source 12 is made of, for example, Cs-137. The radiation shield 14 is made of a radiation shielding material such as lead in a rectangular parallelepiped shape. In this case, the radiation shield 14 has a function as a shield and a function of holding the linear sealed radiation source 12.
That is, the linear sealed radiation source 12 is fixed to one surface of the rectangular radiation shield 14.

The scatterer 13 is formed of a material having a low atomic number, such as iron or aluminum, having a property of scattering radiation, and is formed in a rectangular parallelepiped box shape. This box-shaped scatterer 1
The radiation shield 14 is attached to the opening side of the third.

The radiation emitted from the radiation source 12 is scattered by the scatterer 13 only.
The radiation is directed to the zero side, and the radiation directed directly toward the subject 20 is blocked by the radiation shield 14. That is, the radiation applied to the subject 20 is only backscattered radiation.

When Cs-137 is used as the radiation source 12, the emission gamma ray has a peak energy of 662 ke.
V is scattered, and the energy spectrum is as shown in FIG. That is, the scattered radiation is close to the energy of the nuclide used in the emission CT imaging.
It has a low energy component of about 0 keV to 300 keV.

The output of the detector 30 when the object 20 is irradiated with such backscattered radiation is guided to an energy analyzer 32, and only those whose incident energy is within a predetermined energy window are taken out, and a correction circuit is provided. After performing various corrections in 33, the data is stored in the collection memory 34 and collected. The scattered radiation generator 10 and the detector 30 are
This data collection is performed by rotating it around the When the data of each direction and position is prepared, the arithmetic unit 35 performs processing by an algorithm such as back projection to create a distribution map of the absorption coefficient inside the subject 20.

At the time of emission CT imaging, the subject 20
A drug labeled with a radionuclide is administered therein, radiation emitted from the nuclide inside the nuclide is detected by the detector 30, the detector 30 is rotated in the same manner as described above, data is collected, and the nuclide An image representing the density distribution is reconstructed. At this time, absorption correction and the like are performed using the above absorption map.

As described above, by utilizing scattered radiation having low energy, Cs-137 having a long half-life of 30 years can be used as the radiation source 12, and the radiation source 12 can be used semipermanently. Therefore, it is very effective in reducing running costs.

Since low energy scattered radiation is used by scattering by the scatterer 13, other suitable nuclides which have a long half-life even with a high emission energy and are easily available are used. You can also. Further, the shape and material of the scatterer 13 and the radiation shield 14 may be different. Fan beam collimator 3
It is also possible to use a parallel collimator instead of 1, but in that case, a mechanism for moving the scattered radiation generator 10 is provided to scan the entire surface of the subject 20. In addition, various changes can be made without departing from the spirit of the present invention.

[0017]

As described above, according to the transmission CT apparatus of the present invention, since scattered radiation having low energy is used, a radiation source having high emission energy but a long half-life can be used. become. That is, since the radiation source can be used semi-permanently, it is very effective in terms of running cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a scattered radiation generator.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a graph showing an energy spectrum of scattered radiation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 scattered ray generator 11 backscattered rays 12 line-shaped radiation source 13 box-shaped scatterer 14 radiation shield 20 subject 30 detector 31 fan beam collimator 32 energy analyzer 33 correction circuit 34 collection memory 35 arithmetic unit

Claims (1)

[Claims] 1. A scatter comprising a radiation source, a scatterer for scattering radiation from the radiation source, and a radiation shield covering the radiation source so that only the scattered radiation is emitted to the outside and no direct radiation is emitted. A radiation generator is provided, and the scattered radiation generator is disposed to face the radiation detector with the subject interposed therebetween, and transmission data by the scattered radiation transmitted through the subject is collected and calculated from a signal obtained from the radiation detector. Transmission CT characterized in that an absorption map is created by an apparatus
apparatus.