JPS6271873A - Emission ct device - Google Patents

Abstract

PURPOSE:To reconstruct an RI distribution image with excellent position resolu tion by detecting the quantity of inflection of a radiation position detector by its own weight and correcting the position signal error of detection data at each angle of rotation by the quantity of inflection. CONSTITUTION:The position where radiation from a source point P plated in the center O of rotation of a body to be inspected shifts from the center of the radiation position detector by the quantity (a) of inflection is detected by the detector 1 at each angle and gravity center positions on an X and a Y axis are calculated by a calculating circuit 10. Then, an arithmetic device 1 performs approximating calculation for finding the gravity center position obtained by the circuit 10 as the function of each angle of rotation and stores the result. Then, when projection data for an actual RI distribution image are collected, said function is utilized to correct the position signal error of the detected data by movement by the reciprocal of the quantity (a) of inflection at the collection angle.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a device used in the field of nuclear medicine, in which a detector is rotated around a subject to whom a radioactive isotope (hereinafter abbreviated as RI) has been administered. The present invention relates to an emission CT device (hereinafter abbreviated as ECT device) that collects R1 images and obtains tomographic images of the distribution of R1 in the body.

[Technical background of the invention and its problems] As is well known, the ECT device injects and inhales a radioactive isotope (hereinafter abbreviated as RI) into the body of a subject (patient). The radiation emitted from this Rr is measured outside the subject's body when it is introduced by a method such as ingestion and accumulates in a specific organ, and this measurement data is subjected to image reconstruction processing to create a tomographic image of the distribution of RI. It is then reconstructed and displayed.

Conventionally, a scintillation camera is used as a device to detect radiation, and the necessary data is collected while avoiding rotation of the scintillation camera, and from this data R1
A so-called scintillation camera rotation type ECT device that reconstructs a distribution image is known. This type of ECT device normally uses a scintillation camera as the radiation position detector 1, as shown in Fig. 2, which is held by an arm 2, which is attached to a rotating frame 3, A driving device 4 is configured to rotate the rotating frame 3 around an axis 0. The patient, who is the object, is laid down so that its body axis coincides with the axis O, and the radiation position detector 1 revolves around this object. This revolution occurs once every unit angle, for example, 5 degrees, rotates 5 degrees and then stops.
At this projected angle, data is collected by radiation position detection +PJi.

However, when collecting data using the detector in an ECT device, the detector bends due to its own weight, so if the detector is bent and rotated 360° around the subject, one point on the subject can be moved to a different slice plane of the detector. The disadvantage is that the positional resolution during reconstruction is degraded due to the fact that the image is viewed in the image. When data movement is corrected by detector deflection, this detector deflection differs from device to device and also changes over time.

[Purpose of the Invention] The present invention was made in view of the above circumstances, and provides R1 tomographic imaging (data collection) using an emission CT device.
At this time, the amount of deflection due to the detector's own weight, which is different from ECTff1 and changes over time, is measured, and the measured value is corrected for the amount of deflection measured against the collected data, and the Rfli layer is An object of the present invention is to provide an emission CT device that does not reduce the positional resolution of images.

The present invention detects radiation emitted by radioactive isotopes distributed within the subject by rotating and scanning a scintillation camera around the subject's body axis, and reproduces a tomographic image of the subject. In the 1st place of the constituent emission CTi,
Radiation from a reference radiation source placed at a predetermined position within the rotational scanning range is detected by rotational scanning of the scintillation camera, and based on the position signal of the obtained detection data of the reference radiation source, the An emission CT apparatus comprising: means S for correcting an error in a position signal of projection data that varies at each rotation angle due to the amount of deflection of the scintillation camera in a direction substantially orthogonal to the rotational scanning surface of the scintillation camera. It is.

1 Examples of the invention] The present invention will be specifically explained below using Examples.

In FIG. 3, reference numeral 1 denotes a scintillation camera equipped with a parallel multi-hole collimator, which is attached to a rotating frame 2. The rotating frame 2 is held by a drive unit (not shown) supported by a support base (not shown), and rotates around the body axis 0 of a subject lying on a bed. It will be done. R accumulated in specific organs within the subject
The ams from the scintillation camera 1 are incident on the scintillator provided on the incident side of the scintillation camera 1 in any direction. The light emitted from the scintillator is guided to a photomultiplier tube via a light guide, and the position measurement circuit 10 calculates the two-dimensional position of the light emission based on the output of the photomultiplier tube, and outputs a position signal X1Y.

The calculation and storage device 11 obtains a one-dimensional count distribution of the number of incident radiation M when the scintillation camera 1 is at a certain angle with respect to the subject, and this is stored for each rotation angle. The data for each can be treated as projection data.

Then, methods such as convolution and pack projection that reconstruct the original image from multidirectional projection data are used to obtain a two-dimensional distribution image of the radiation incident on the scintillator, that is, an R1 distribution image viewed from the Z direction, and display it. It is displayed on the device a12. Now, by placing a point source on the body axis 0 and detecting the radiation from this point source with the scintillation camera 1,
This is to measure the deflection a of the sinderesis camera 1 due to its own weight. When obtaining a two-dimensional radiation distribution image using a normal ECT device, projection data for each corner is collected by a slice plane of the scintillation camera 1 perpendicular to the target virtual 11i layer plane. However, if the scintillation camera is deflected by the value a due to self-righting as shown in Fig. 3, the point that includes the point source p and is perpendicular to the scintillation camera 1 will be tilted with respect to the virtual plane, and the scintillation camera 1 will be tilted. The intersection position tFjl) is considered to be a position shifted by a from the center blue of the scintillation camera 1. Therefore, C1 Thus, the position (center of gravity) of the projection data of point source p on scintillation camera 1 of point source p
Calculate the RI that resembles it and accumulate it in the actual specific organ.
By calibrating the tIl copper wire data from the detector, the influence of deflection of the scintillation camera can be excluded.

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

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

The center of gravity of the detected projection data in the X and Y axes is calculated in the position calculation four-way 10. This calculation is performed for each rotation angle, and the center of gravity of the projection data of the point source p at each angle is similarly determined. In order to find the position of the obtained center of gravity on the X and Y axes as a function of the rotation angle, an approximate h1 sieve is performed. For example, it is conceivable to Fourier transform the radiation detection data from the point source p and perform the above-mentioned approximate calculation in frequency space. This approximate calculation is carried out in the arithmetic unit 12, and the obtained functions for each rotation angle of the center of gravity of the reference point source p are stored simultaneously.

Thereafter, when collecting projection data for an actual R1 distribution image, the position signal of the detected data is moved by the reciprocal of the deflection amount a at the collecting angle using the previously determined function. In this way, it is stored in the calculation and storage device 12 as new position information.

In this way, from the obtained projection data from multiple directions, the calculation and storage unit 12 reconstructs a two-dimensional distribution image of the radiation incident on the scintillation camera, that is, an RI distribution image viewed from two directions.

As is clear from the configuration and operation above, the scintillation camera bends due to its own weight, making it impossible to detect the virtual surface of the test object at the same detection position on the detection surface of the scintillation camera. This can prevent a decrease in positional resolution.

Furthermore, the deflection of the scintillation camera can be measured simply by rotating the normal scintillation camera around the subject without providing any special means for measuring the deflection of the scintillation camera. It's easy.

Although one embodiment of the present invention has been described above in detail, the present invention is not limited to the above-mentioned 1111 pH, and can be implemented with various modifications within the scope of the gist of the present invention.

1. Effects of the invention] The following effects can be achieved by this invention. That is, the scintillation camera bends due to its own weight, and the virtual tomographic plane of the desired object and the detection plane of the scintillation camera are not in an accurate perpendicular relationship. Rotate and scan while maintaining this relationship, and emit radiation from inside the subject.
When il is detected, the positional information of the detected data is not accurate, and therefore, when reconstructed based on that data, the positional resolution of the final image will be reduced. On the other hand, by determining the amount of deflection described above at each rotation angle during rotational scanning of the scintillation camera and calibrating the position signal of the detected data using the determined deflection m, the position signal of the detected data at each rotation angle is calculated. By reconstructing an image using standardized and calibrated detection data, it is possible to always reconstruct an RI distribution image with excellent positional resolution.

[Brief explanation of drawings]

FIG. 1 is a flowchart for explaining the deflection correction operation in the emission CT apparatus according to the present invention, and FIG.
The figure shows the main configuration of the emission CT device, and Figure 3 shows the main configuration of the emission CT device.
FIG. 2 is a diagram illustrating the principle of deflection compensation in the emission CT apparatus according to the present invention, and a diagram illustrating its correction processing section. 1... Scintillation camera 2... Rotating arm 3... Rotating frame 4... Rotating drive device 10... Position calculation circuit 11... Calculation and storage device

Claims (1)

[Claims] In an emission CT system, a scintillation camera rotates and scans around the subject's body axis to detect radiation emitted by radioactive isotopes distributed within the subject and reconstructs a tomographic image of the subject. Radiation from a reference radiation source disposed at a predetermined position in the scintillation camera is detected by rotational scanning of the scintillation camera, and based on the position signal of the detection data of the obtained reference radiation source, radiation is detected on the rotational scanning surface of the scintillation camera. An emission CT apparatus comprising means for correcting errors in position signals of projection data at each rotation angle due to deflection of a scintillation camera in substantially orthogonal directions.