JPH09236664A - Single photon emission CT device - Google Patents

Abstract

(57) Abstract: Data for a reconstructed image is collected at a small rotation angle of a gamma camera. SOLUTION: Three gamma cameras 11, 12, 13 are arranged at intervals of 120 ° in the circumferential direction, a subject 10 is placed at the center thereof, and the gamma cameras 11, 12, 13 are integrated into one unit.
The data acquisition memory 16 is rotated 0 ° to 0 ° to 6 °.
The data of 0 °, 120 ° to 180 °, 240 ° to 300 ° are collected, and the image reconstructing device 17 makes 240 ° to 300 °.
Data is converted into data of 60 ° to 120 ° and image reconstruction processing is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear medicine inspection apparatus, and more particularly to a single photon emission CT apparatus of a type that rotates a gamma camera.

[0002]

2. Description of the Related Art A single photon emission CT apparatus uses a radioisotope (RI) of a single photon-emitting radionuclide and detects gamma rays emitted from the radioisotope (RI) to capture a distribution image of the nuclide. For example, when a drug labeled with a single photon-emitting radionuclide is administered to the human body, it accumulates in a specific organ. At that time, gamma rays emitted to the outside of the human body are detected by a detector arranged outside the human body. Projection data can be collected by detecting the incident position while controlling the direction of the gamma rays incident on the detector with a collimator and counting the radiation events for each position. By obtaining such projection data from multiple directions, it is possible to reconstruct the RI concentration distribution image in the human body using an algorithm such as the back projection method.

A gamma camera rotating type single photon emission CT apparatus uses a gamma camera as a detector for detecting gamma rays outside the subject and rotates the gamma camera around the subject. In this type of single photon emission CT apparatus, instead of administering RI to the inside of the subject, an RI radiation source is arranged at a position facing the gamma camera, and the subject is placed between this radiation source and the gamma camera. Then, the radiation source and the gamma camera can be integrally rotated, and gamma ray transmission data (transmission data) can be collected for each rotation angle. In this case, the image reconstruction device will reconstruct the absorption distribution image of the subject from the collected transmission data.

As this gamma camera rotating type single photon emission CT apparatus, conventionally, three gamma cameras are used, and these are arranged at 120 ° intervals in the circumferential direction so as to rotate integrally. It has been known. In this case, three gamma cameras are integrated into 120
If the rotation is performed by 360 °, the data of 360 ° around the subject can be collected, so that the data collection time can be shortened by decreasing the rotation angle.

[0005]

However, even in a conventional gamma camera rotating single photon emission CT apparatus of the type in which three gamma cameras are arranged at 120 ° intervals and integrally rotated, it is not possible to shorten the data acquisition time. There is a problem that the subject (patient) is restrained for a long time.

In view of the above, the present invention makes it possible to obtain a reconstructed image with a smaller rotation angle, thereby reducing the constraint time of the subject (patient) and reducing the burden on the subject. It is an object of the present invention to provide a single photon emission CT apparatus which is improved so as to improve the safety of the subject and reduce the data collection failure.

[0007]

To achieve the above object, a single photon emission CT according to the present invention is provided.
In the apparatus, there are provided first, second and third radiation camera detection means arranged at intervals of 120 degrees in the circumferential direction, and means for rotating these three radiation camera detection means integrally by substantially 60 degrees. A rotation angle detecting means for detecting a rotation angle, and an address determined by the position signal obtained from the first, second and third radiation camera detecting means and the rotation angle signal obtained from the rotation angle detecting means. Data collecting means for counting radiation events and collecting data, first group data collected by the first radiation camera detecting means and having a rotation angle of 0 ° to 60 °, and second data collecting means Rotation angle 12 by radiation camera detection means
By using the data of the second group of 0 ° to 180 ° and the data of the third group of the rotation angle of 240 ° to 300 ° by the third radiation camera detection means, inverting the data of the third group by 180 ° It is characterized in that an image reconstructing means for performing an image reconstructing process as data of 0 ° to 180 ° as a whole is provided.

The first, second and third radiation camera detecting means are arranged at intervals of 120 ° in the circumferential direction, and since they are integrally rotated by 60 °, the first radiation camera detecting means. The data of the first group having a rotation angle of 0 ° to 60 ° is output from the second radiation camera detection means from the rotation angle of 120 °.
The data of the second group of 180 ° to 180 ° and the data of the third group of 240 ° to 300 ° of rotation angle can be collected from the third radiation camera detecting means, respectively. The data for this third group is 2
Since it is the data of the rotation angle of 40 ° to 300 °, 18
By reversing 0 ° (for example, minus 180 ° in the rotation angle), it is possible to handle the data as 60 ° to 120 °. Therefore, by performing such an operation, it is possible to assume that the data of the rotation angle of 0 ° to 180 ° can be obtained for all the data of the first group, the second group, and the third group. By performing the image reconstruction process, a reconstructed image can be obtained. Only 60 ° of rotation is needed to collect the data to obtain the image,
It is possible to reduce the burden on the subject by reducing the restraint time of the subject (patient). Also, because the rotation angle is small,
There is less mechanical movement, less risk to the subject and greater safety. Further, since the data collection angle (time) is small, the failure of data collection can be reduced. Since a small rotation angle is required, it is possible to suppress wear of the device such as bending of the cable being reduced.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In the single photon emission CT apparatus shown in FIG. 1, three gamma cameras 11, 12, 13 are arranged at 120 ° intervals in the circumferential direction, and the subject 10 is placed at the center thereof.

The gamma cameras 11, 12, and 13 are, for example, a planar scintillator, a large number of photomultipliers (photomultiplier tubes) optically coupled to the back surface of the scintillator via a light guide, a position calculation circuit, and energy. It consists of an analysis circuit. When gamma rays are incident on the planar scintillator and emit light, the light is incident on some photomultipliers near the light emitting point. A large amount of light is incident on a nearby photomultiplier and a large output is produced. Therefore, the output of each photomultiplier is guided to the position calculation circuit, the radiation incident position on the planar scintillator is calculated from the size thereof, and the position signal representing the position is output.
On the other hand, the energy analysis circuit analyzes whether or not the added value of the outputs of all the photomultipliers is within a predetermined energy range, and if it is, an unblank signal is generated.

The incident planes of these gamma cameras 11, 12 and 13 face the subject 10, and the position signals generated from these are the position signals of the incident planes on which the gamma rays are incident, that is, the direction parallel to the plane of the drawing. It represents a two-dimensional incident position in a direction perpendicular to.

The incident surfaces of the gamma cameras 11, 12 and 13 are provided with collimators 21 and 2 for controlling the incident direction of gamma rays.
2 and 23 are attached respectively. Then, here, the gamma cameras 11, 12, and 1 are sandwiched across the subject 10.
R of single photon emission at a position facing each of 3
The radiation sources 31, 32, 33 made of I are arranged. Source 3
Gamma rays emitted from each of 1, 32, and 33 are transmitted through the subject 10 and are incident on the incident surfaces of the gamma cameras 11, 12, and 13. The collimators 21, 22, 23 are the radiation source 3
In order to make only the gamma rays from each of 1, 32 and 33 incident on each of the gamma cameras 11, 12 and 13, the radiation sources 31 and 3 are arranged.
This is a fan beam collimator having fan-beam-shaped transmission holes facing the respective directions of 2 and 33.

The gamma cameras 11, 12, 13 and the radiation sources 31, 32, 33 are held by an appropriate arm (not shown), and are united (that is, maintaining the above-mentioned positional relationship) by the rotary drive device 14. It can be rotated 60 °. Within the rotation angle of 60 °, the rotation angle is stepwise and stationary, and the rotation angle when the rotation is stationary is detected by a rotation angle detection device (for example, a potentiometer attached to the rotation shaft) 15. , The rotation angle signal is output.

A position signal and an unblank signal from each of the gamma cameras 11, 12, and 13 and a rotation angle signal from the rotation angle detection device 15 are input to the data collection memory 16 at a certain rotation angle. When a position signal and an unblank signal are generated from a certain gamma camera during a stationary period, by adding "1" to the address designated by the signal indicating the gamma camera, the position signal, and the rotation angle signal. Count unblank signals.

In this way, the three gamma cameras 11, 12 are used for data collection as described above while stationary at each minute rotation angle.
When the data acquisition memory 16 is rotated by 60 ° while simultaneously performing the steps of 13, the first data of the rotation angle of 0 ° to 60 ° is stored in the data collection memory 16.
The data of the group, the data of the second group having a rotation angle of 120 ° to 180 °, and the data of the third group having a rotation angle of 240 ° to 300 ° will be collected, respectively.

After the data collection for such 60 ° rotation is completed, the image reconstructing device 17 causes the data collection memory 16
The data is read from and the image reconstruction processing is performed. In the data collection memory 16, the gamma cameras 11, 12, 13
Since the count is made at each of the two-dimensional positions on the incident surface of, only the data in the cross section (slice plane parallel to the paper at a predetermined position perpendicular to the paper) to be image-reconstructed In order to take out, the address corresponding to the slice plane is designated and read.

At this time, the data of the third group is changed from 60 ° to 120 °.
Treated as ° data. That is, for example, by decreasing the rotation angle by 180 °, 240 ° -300
The data of the rotation angle of ° is converted into the data of the rotation angle of 60 to 120 °. As a result, the data of the rotation angles of 0 ° to 180 ° on the desired slice plane are gathered. That is, since the projection data of 0 ° to 180 ° are prepared, the image can be reconstructed by the back projection algorithm or the like. In this case, since the collected data is transmission data and represents absorption of gamma rays, the subject 10
An absorption distribution image in the desired slice plane of is obtained. This image is displayed on the display device 18 or recorded in the recording device 19.

Here, the collected data is the transmission data of the subject 10, and is the same even when transmitted from the opposite direction of 180 °. Therefore, even if the data of the rotation angle of 240 ° to 300 ° is reversed by 180 ° and treated as the data of the rotation angle of 60 ° to 120 ° and the image is reconstructed as described above, the rotation angle of 60 ° to 120 ° from the beginning. The same image can be obtained as when the data is collected and image reconstruction is performed.

In the above description, point sources are used as the radiation sources 31, 32, 33 placed outside the subject 10, and fan beam collimators are used as the collimators 21, 22, 23, but they are plate-shaped. It is also possible to use a surface radiation source, in which case a parallel porous collimator is used as the collimator 21, 22, 23.

Further, the present invention can be similarly applied to the case of reconstructing an emission image (RI concentration distribution image) by collecting emission data instead of transmission data. That is, in that case, the subject 1 can be used without using the external radiation sources 31, 32, and 33.
Emission data is collected by administering RI labeled drug to 0. This emission data is a count value of gamma rays emitted from the RI inside the human body and emitted to the outside through the human body, so there is some difference depending on the direction of emission. That is, the gamma rays emitted in the direction in which there are many absorbers such as bone are absorbed more than the gamma rays emitted in the direction in which there are few absorbers, and the count value becomes small.

Therefore, when the data of the rotation angle of 240 ° to 300 ° is treated as the data of the rotation angle of 60 ° to 120 ° and the image is reconstructed, the rotation angle of 60 ° to 1 is originally set.
Not exactly the same image is obtained as when image reconstruction is performed using the data collected at 20 °. However, 2
If an angle range of 40 ° to 300 ° is selected as an angle range having a small number of absorbers, an image with better image quality can be obtained as compared with the case where the image is reconstructed using the data actually collected at the rotation angle of 60 ° to 120 °. Sometimes. Moreover, even if an image of inferior quality is obtained as compared with the case where the image is reconstructed using the data actually collected at the rotation angle of 60 ° to 120 °,
There are many uses that are acceptable. In such a case, the effect of shortening the data collection time obtained by the rotation of 60 ° is greater.

Further, when it is desired to reconstruct an image using data (transmission data or emission data) for 360 °, three gamma cameras 11, 12, 1 are used.
3 will be rotated together by 120 °, but in that case, due to some cause (for example, an abnormality in the mechanical system or the signal system or an abnormality such as movement of the subject 10), 120 ° worth of data is obtained in each case. Although it may not be possible to obtain all data, in such a case, if data is obtained for each 60 °, use them and invert a part by 180 ° as described above to obtain a total of 180 °. The image can be reconstructed by aligning the projection data as the data. That is, it is effective as a backup means against an abnormal situation that an image can be obtained for the time being even if some abnormality occurs.

[0023]

As described above, according to the single photon emission CT apparatus of the present invention, data for image reconstruction can be collected by rotation of 60 °, and the subject (patient) can be restrained. The time can be reduced and the burden on the subject can be reduced. Moreover, since the rotation angle is small, mechanical movement is reduced, the risk to the subject is reduced, and the safety is improved. In addition, data collection angle (time)
Because of the small, data collection failures can be reduced. Since a small rotation angle is required, it is possible to suppress wear of the device such as bending of the cable being reduced.

[Brief description of drawings]

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

[Explanation of symbols]

 11-13 Gamma camera 21-23 Collimator 31-33 RI source 14 Rotation drive device 15 Rotation angle detection device 16 Data acquisition memory 17 Image reconstruction device 18 Display device 19 Recording device

Claims (1)

[Claims] 1. A first, a second, and a third radiation camera detecting means arranged at intervals of 120 ° in the circumferential direction, and these three means.
A unit for rotating one of the radiation camera detection units substantially by 60 °, a rotation angle detection unit for detecting the rotation angle, and position signals obtained from the first, second, and third radiation camera detection units. Data collection means for counting radiation events for each address determined by the rotation angle signal obtained from the rotation angle detection means and collecting data, and rotation by the first radiation camera detection means collected by the data collection means The data of the first group having an angle of 0 ° to 60 ° and the rotation angle 12 by the second radiation camera detecting means
By using the data of the second group of 0 ° to 180 ° and the data of the third group of the rotation angle of 240 ° to 300 ° by the third radiation camera detection means, inverting the data of the third group by 180 ° A single photon emission CT apparatus comprising: an image reconstructing means for performing an image reconstructing process as data of 0 ° to 180 ° as a whole.