JPS59180477A - Emission ct apparatus - Google Patents

Abstract

PURPOSE:To improve the quantitative measurement accuracy by a method wherein a radiation source and a collimator are rotated integrally about an object and a data on the absorption of a radiation passing through the object is detected with a radiation detector to correct the data concerning the concentration distribution of a radioactive isotope. CONSTITUTION:A lead shield 4 and a collimator 5 rotate integrally being held with a frame 6. A radiation emitted from a radiation source 7 passes through an object 3 and enters a radiation detector 1 via the collimator 5. As an output is obtained from the radiation detector 1 according to the attenuation of the radiation depending on the object 3, a data is detected from the radiation detector 1 concerning the absorption of the radiation in the object 3. Data can be collected in any direction by rotating the frame 6 to obtain a distribution image of a radiation absorption coefficient. The lead shield 4 and the collimator 5 are removed together with the frame 6 and instead, a normal collimator is mounted to collect data. The data is corrected by said data of radiation absorption coefficient distribution to remove the effect thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to improvement of an emission CT apparatus (emission type computed tomography apparatus).

(b) As is well known, in the prior art emission CT device, a radiation detector is positioned around the subject on one tomographic plane of the subject, and radiation is emitted from radioactive isotopes contained in the subject. The radiation is incident on the radiation detector through a collimator to obtain data on the number of incident radiation, and this data is processed by a computer to reconstruct the radioisotope concentration distribution image in the tomographic plane of the object as a tomographic image. It is something to do.

A so-called ring type emission CT apparatus is constructed as shown in FIGS. 1 and 2. In FIG. 1, a large number of radiation detectors l are arranged and fixed in a ring shape, and a rotating ring-shaped collimator 2 is placed inside the detector.
A subject 3 is placed inside this collimator 2. Second
As shown in the figure, a large number of sets of radiation detectors 1 and ring-shaped collimators 2 are arranged in three layers in a direction perpendicular to the tomographic plane of the subject 3. Each of these ring-shaped collimators 2 is arranged so that the direction of collimation faces different tomographic planes in the plane perpendicular to the tomographic plane (parallel to the plane of the paper in Fig. 2). For example, as shown in FIG. 1, the directions of the radiation transmitting holes are determined so that the directions differ slightly within the plane (parallel to the plane). When the direction of the radiation transmission hole is determined as shown in FIG. 1, if the ring-shaped collimator 2 is rotated 180 degrees,
When looking at each of the many radiation detectors l, the direction of the incident radiation swings so as to cover the entire subject 3 within one tomographic plane.

This ring-shaped collimator 2 is rotationally driven by an appropriate rotational drive mechanism (not shown). Necessary data is collected by rotating the ring collimator 2 by 180 degrees, and since there are three layers in this case, tomographic images in three different tomographic planes are reconstructed.

Other types are constructed as shown in FIG. When viewed from the side, it looks the same as in Figure 2. A parallel plate-like collimator 2 and a radiation detector l are arranged in a straight line on each side of a square surrounding the subject 3, so that the collimator 2 and the radiation detector l rotate around the subject 3 as a unit. The necessary data can be collected by rotating each layer four times.

In addition, instead of using a ring-shaped collimator 2 that is integrated into a ring-shaped structure and rotates as a whole as shown in Fig. 1, the entire ring-shaped collimator 2 is fixed so that the direction of each radiation transmitting hole can swing. There is also a type that uses a collimator configured to swing each of a number of radiation shielding thin plates.

By the way, in these emission CT devices, the data collected is related to radiation emitted from radioactive elements inside the subject 3, transmitted through the internal tissues of the subject 3, reaching the body surface, and exiting the body. It is affected by absorption of radiation by body tissues before it reaches the body surface. Therefore, there is a drawback that quantitative evaluation of the obtained tomographic image is difficult.

(c) Purpose This invention provides an improved emission CT device that can improve the accuracy of quantitative measurement of data regarding the concentration distribution of radioactive isotopes by correcting the effects of radiation absorption within the body. purpose.

(D) Configuration This invention provides an emission CT apparatus in which a collimator other than the collimator for obtaining a radioisotope concentration distribution image in a tomographic plane of the object is replaced with a collimator,
A radiation source is placed opposite this collimator with the subject in between, and the radiation source and collimator are rotated together around the subject, and data regarding the absorption of emitted Q4 rays emitted from this radiation source and transmitted through the subject are collected from the radiation source. It is characterized in that it is detected by a detector and the data regarding the concentration distribution of the radioactive isotope is corrected using this data.

(E) Embodiment FIGS. 4 and 5 show an embodiment in which the present invention is applied to the emission CT apparatus shown in FIGS. 1 and 2. In FIGS. 4 and 5, a collimator 5, which is made separately, is used instead of the collimator 2 (see FIGS. 1 and 2) for obtaining a concentration distribution image of radioactive isotopes within the subject 3. A lead shield 4 containing a radiation source 7 is placed inside the ring of the radiation detector 1. The lead shield 4 and collimator 5 are held by a frame 6 so as to rotate together. The lead shield 4 is used to prevent radiation from the radiation source 7 from traveling in directions other than the collimator 5. Radiation emitted from the radiation source q passes through the subject 3, passes through the collimator 5, and enters the radiation detector 1.

Since the radiation detector l provides an output corresponding to the amount of attenuation of radiation by the subject 3, data regarding radiation absorption in the subject 3 is detected from the radiation detector l. By rotating the frame 6, data from all directions is collected, and by image reconstruction processing of this data by a computer, a distribution image of radiation absorption coefficients can be obtained, similar to the third generation CT apparatus. This distribution image is the same as the tomographic plane from which the radioisotope concentration distribution image is to be obtained.
are obtained for three tomographic planes.

After collecting data for absorption correction in this way,
The lead shield 4 containing the radiation 1IA7 and the collimator 5 are removed along with the frame 6, and a normal collimator 2 is installed in their place as shown in FIGS. 1 and 2. The collimator 2 is then rotated to collect data. Since this data is influenced by radiation absorption within the body of the subject 3 as described above, it is corrected using the radiation absorption coefficient distribution data described above to remove that influence. In this way, it is possible to obtain a tomographic image of the radioisotope concentration distribution with high precision in a fixed manner, in which the influence of radiation absorption within the body of the subject 3 is removed.

In this case, the tomographic plane from which data was collected to reconstruct the tomographic image of the concentration distribution of radioactive isotopes and the tomographic plane from which the radiation absorption distribution data for supplementary IF were collected are from the same subject 3.
It should be noted that since the images are the same tomographic plane, correction data related to the object to be corrected can be obtained, and correction can be performed with extremely high precision in accordance with the actual object 3.

FIG. 6 shows an embodiment applied to the emission CT apparatus shown in FIG. The lead shield 4 and collimator 5 are arranged. In this case, the lead shield 4 housing the radiation source 7 and the collimator 5 are integrated together with the radiation detector 1.
By this rotation, data regarding the distribution of the radiation absorption coefficient of the subject 3 is obtained, and data regarding the concentration distribution image of radioactive isotopes within the subject 3 is corrected using this data. In this case as well, since the tomographic planes from which both data are collected are the same tomographic plane of the same subject 3, as in the embodiment described in section 2 above, accurate correction can be performed.

In addition, when applying to other types of emission CTl1, as in the above embodiment, the collimator is replaced and the radiation source is placed to obtain data regarding the distribution of radiation absorption coefficient of the subject, and this data is used for correction. It should be used for.

(f) Effects The emission CT device according to the present invention can extremely accurately eliminate the influence of radiation absorption within the body of the subject, and improve the accuracy of measuring the tomogram of the concentration distribution of radioactive isotopes within the subject. can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a conventional example seen from the front, Fig. 2 is a schematic sectional view of the same conventional example seen from the side, Fig. 3 is a schematic diagram of another conventional example seen from the front, and Fig. 4 is a schematic diagram of the conventional example seen from the front. The figure is a schematic diagram of one embodiment of this invention seen from the front, FIG. 5 is a schematic sectional view of the same embodiment seen from the side, and FIG. 6 is a schematic diagram of another embodiment seen from the front. be. 1...Radiation detector 2.5...Collimator 3...Subject 4...Lead shield...Frame 7...Radiation source Patent applicant Shimadzu Corporation Note 1 item 1) 2 Note 3 area happiness qfu 5 ministers

Claims (1)

[Claims] (1) A radiation detector is positioned around the subject at a predetermined tomographic plane of the subject, and radiation emitted from radioactive isotopes contained in the subject is made incident on the radiation detector through a collimator. In an emission CT device that obtains data on the number of radiation particles and processes this data with a computer to reconstruct the radioisotope concentration distribution image in the tomographic plane of the object as a tomogram, the collimator is removed and A radiation source is placed inside the radiation detector, and the radiation from this radiation source is placed inside the radiation detector at a position facing the radiation source across the subject. Another collimator is arranged to make the radiation incident on the detector, and this collimator and the radiation source described in 1 are rotated together around the object to obtain distribution data of the radiation absorption coefficient on the tomographic plane of the object. An emission CT apparatus characterized in that data is subjected to absorption correction for reconstructing the tomographic image.