JPH0616093B2 - Emission CT device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to those used in the field of nuclear medicine, in which a detector is rotated around a subject administered with a radioisotope (hereinafter abbreviated as RI). The present invention relates to an emission CT device (hereinafter, abbreviated as ECT device) that collects RI image images and obtains a tomographic image of the distribution in the RI.

[Technical Background of the Invention and Problems Thereof] As is well known, the ECT device is a subject (patient).
A drug of radioisotope (hereinafter abbreviated as RI) is introduced into the body of the subject by a method such as injection, inhalation, and ingestion, and the radiation emitted from the RI when accumulated in a specific organ is measured outside the subject's body. By subjecting this measurement data to image reconstruction processing, the RI distribution image is reconstructed and displayed as a tomographic image.

Conventionally, a scintillation camera is used as a device for detecting radiation, the scintillation camera is rotated to collect necessary data, and RI is extracted from this data.
A so-called scintillation camera rotation type ECT device of the type for reconstructing a distribution image is known. This type of ECT device generally uses a scintillation camera as a radiation position detector 1 as shown in FIG. 2, which is held by an arm 2 and which is attached to a rotating frame 3 to form a rotation base. The drive device 4 is configured to rotate the rotating frame 3 around the axis 0. Then, the patient as a subject is laid so that the body axis thereof coincides with the axis 0, and the radiation position detector 1 revolves around the subject. This revolution is performed every unit angle, for example, every 5 degrees, and after rotating 5 degrees, it stops and the radiation position detector 1 collects data at this stopped angle.

However, when data is collected by the detector in the ECT device, the detector bends due to its own weight. Therefore, if the detector is rotated 360 ° around the subject, one point of the subject is different from the slice plane of the detector. However, there is a drawback in that the position resolution is degraded during reconstruction. When the amount of data movement is corrected by the deflection of the detector, the deflection amount of the detector varies from device to device and changes with time.

[Object of the Invention] The present invention has been made in view of the above circumstances, and a detector that changes for each ECT and changes with time when capturing an RI tomographic image (data collection) by an emission CT apparatus is also provided. An object of the present invention is to provide an emission CT device that measures the amount of deflection due to its own weight and corrects the measured amount of deflection with respect to the collected data based on the measured value, without deteriorating the positional resolution of the RI tomographic image. .

SUMMARY OF THE INVENTION The present invention detects the radiation emitted by a radioisotope distributed in a subject by rotating a scintillation camera around the body axis of the subject to reconstruct a tomographic image of the subject. In the emission CT device to do, the radiation from the reference line source arranged at a predetermined position within the rotation scanning range is detected by the rotation scanning of the scintillation camera, and based on the position signal of the detection data of the obtained reference line source, The emission CT apparatus is provided with means for correcting an error in a position signal of projection data at each rotation angle due to a deflection amount of the scintillation camera in a direction substantially orthogonal to the rotary scanning plane of the scintillation camera.

[Examples of the Invention] The present invention will be specifically described with reference to the following examples.

In FIG. 3, reference numeral 1 is a scintillation camera having a parallel porous collimator, which is attached to a rotating frame 2. The rotating frame 2 is held by a driving unit (not shown) supported by a support (not shown) and is rotated about the body axis 0 of the subject lying on the bed as a central axis. . Radiation from RI accumulated in a specific organ in the subject enters the scintillator provided on the incident side of the scintillation camera 1 in any direction. Light emission from the scintillator is guided to a photomultiplier tube through a light guide, and the position calculation circuit 10 calculates a two-dimensional position of light emission by the output of the photomultiplier tube and outputs position signals X and Y. The calculation and storage device 11 obtains a one-dimensional count distribution of the number of incident radiation when the scintillation camera 1 makes an angle with the subject,
This is stored for each rotation angle. The data for each angle can be treated as projection data. Then, methods such as convolution and back projection for reconstructing an original image from multidirectional projection data are used to obtain a two-dimensional distribution image of radiation incident on the scintillator, that is, an RI distribution image viewed from the Z direction, and displayed. It is displayed on the device 12. Now, a point source is placed on the body axis 0, and radiation from this point source is detected by the scintillation camera 1 to measure the deflection amount a due to the weight of the scintillation camera 1. When a two-dimensional distribution image of radiation is normally obtained by an ECT apparatus, projection data for each angle is collected by the slice plane of the scintillation camera 1 perpendicular to the virtual tomographic plane of interest. However, if the scintillation camera bends by a value due to its own weight as shown in FIG. The position (straight line) is considered to be a position deviated from the center position of the scintillation camera 1 by a. Therefore, in this way, the position (center of gravity) of the projection data of the point source p on the scintillation camera 1 of the point source p is calculated, and the radiation data from the RI accumulated in the actual specific organ is similarly calibrated. This makes it possible to exclude the projection caused by the deflection of the detector and the scintillation camera.

FIG. 1 shows a flowchart for measuring the deflection amount of the scintillation camera 1 according to the present invention and correcting the position signal of the projection data at each rotation angle based on the measured values.

First, the projection data of the point source p placed at the center of rotation 0 is detected by the scintillation camera 1 at each rotation angle.

The position calculation circuit 10 calculates the center of gravity of the detected projection data on the X and Y axes. This calculation is performed for each rotation angle, and similarly the center of gravity of the projection data of the point source p at each angle is obtained. An approximate calculation is performed in order to obtain the center of gravity position of the obtained center of gravity on the X and Y axes as a function of the rotation angle. For example, it is conceivable to perform Fourier transform on the radiation detection data from the point source p and perform the above-mentioned approximate calculation in the frequency space. This approximation calculation is performed in the arithmetic unit 12, and the obtained function for each rotation angle of the center of gravity of the reference point source p is simultaneously stored.

After that, when the projection data for the actual RI distribution image is collected, the position signal of the detected data is moved by the reciprocal of the deflection amount a at the collection angle by using the previously obtained function. In this way, the new position information is stored in the calculation and storage device 12.

In this way, the two-dimensional distribution image of the radiation incident on the scintillation camera, that is, the RI distribution image seen from the Z direction, is reconstructed in the calculation and storage unit 12 from the obtained projection data from multiple directions.

As is clear from the above configuration and operation, the positional resolution of the RI distribution image resulting from the phenomenon that the scintillation camera bends due to its own weight and the virtual tomographic plane of the subject cannot be detected at the same detection position on the detection surface of the scintillation camera. Can be prevented.

Moreover, it is possible to measure the amount of deflection of the scintillation camera simply by making a rotational movement around the subject of the ordinary scintillation camera without providing any special means for measuring the amount of deflection of the scintillation camera. is there.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and can be variously modified and implemented within the scope of the gist of the present invention.

[Effects of the Invention] The following effects of the present invention can be achieved. That is, the scintillation camera bends due to its own weight, and the desired virtual tomographic plane of the subject and the detection surface of the scintillation camera do not have a correct vertical relationship. When rotational scanning is performed while maintaining this relationship and the radiation from the inside of the subject is detected, the position information of the detected data is not accurate, so if reconstructed based on these data, the position resolution of the final image will decrease. Will result. On the other hand, the deflection amount at each rotation angle in the rotation scanning of the scintillation camera is obtained, and the position signal of the detection data at each rotation angle is standardized by calibrating the position signal of the detection data according to the obtained deflection amount. However, the calibrated detection data is reconstructed in a similar manner, and it is possible to reconstruct an RI distribution image with excellent positional resolution at all times.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining a deflection correction operation in an emission CT device according to the present invention, FIG.
The figure shows the main configuration of the emission CT device, and Fig. 3 shows
It is a figure which shows the principle of the deflection correction in the emission CT apparatus by this invention, and the correction processing part. 1 ... Scintillation camera 2 ... Rotating arm 3 ... Rotating frame 4 ... Rotation drive device 10 ... Position calculation circuit 11 ... Calculation and storage device

Claims (1)

[Claims] 1. An emission CT apparatus for reconstructing a tomographic image of a subject by detecting radiation emitted by a radioisotope distributed in the subject by rotating and scanning a scintillation camera around the body axis of the subject. At
Radiation from a reference line source disposed at a predetermined position within a rotary scanning range is detected by the rotational scan of the scintillation camera, and the rotation of the scintillation camera is detected based on the position signal of the detection data of the obtained reference line source. An emission CT apparatus comprising means for correcting an error in a position signal of projection data at each rotation angle due to a deflection amount of a scintillation camera in a direction substantially orthogonal to a scanning plane.