JPH0537267Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention relates to gamma cameras, and in particular,
ECT imaging (emission computer tomography)
The present invention relates to a correction device that corrects magnetism in a rotating type gamma camera that is capable of rotating.

BACKGROUND TECHNOLOGY A gamma camera, which is known as a type of nuclear medicine diagnostic equipment, has a plurality of photomultiplier tubes (hereinafter abbreviated as PMT) arranged on the back side of a single scintillator.
The light emitting position on the scintillator is determined from these output signals, and a distribution image of the radioisotope drug administered to the subject viewed from one direction is reconstructed (normal spot photography). By rotating this gamma camera around the subject and processing the data collected by a computer to reconstruct the image, a tomographic image (so-called ECT image) in a cross section perpendicular to the axis of rotation can be obtained.

However, the amplification factor of the PMT used for this tends to fluctuate due to the influence of external magnetism. Therefore, due to changes in the geomagnetic field or other causes,
As the magnetic field applied to the PMT varies, the output from the PMT changes and the reconstructed image deteriorates. In particular, when rotating the gamma camera to take ECT images or performing spot imaging from various angles, it is inevitable that the influence of geomagnetism will change depending on the angle, which can cause problems. It is.

Therefore, in the past, magnetic shielding material was wrapped around each PMT, and the gain of the PMT was corrected at regular intervals using a light emitting diode built into the PMT.

Problems that the invention aims to solve However, it is difficult to achieve complete shielding by wrapping magnetic shielding material around each PMT, and in the case of using a light emitting diode, the temperature characteristics of the light emitting diode are poor, and the temperature characteristics between the light emitting diode and PMT are difficult to achieve. There are problems such as the optical coupling being different from the optical coupling between the scintillator and the PMT.

This idea does not have the disadvantages of using magnetic shields or light emitting diodes, and can be used for geomagnetism and other magnetic fields.
It is an object of the present invention to provide a gamma camera that can accurately correct the influence on PMT that fluctuates as the gamma camera rotates.

Means for Solving the Problems According to this invention, in a gamma camera in which a head section having a scintillator and a photomultiplier tube is held by a rotating stand, a rotation detector and a rotation detector for detecting the rotational position of this head section are provided. , and a correction circuit. The correction circuit stores correction coefficients for each angle, determined in advance using a certain radiation source, for correcting the influence of surrounding magnetism, and when collecting data from the actual subject. The correction coefficient is then read out based on the detection signal of the rotation detector, and the output of each photomultiplier tube is corrected based on this correction coefficient, thereby eliminating the influence of surrounding magnetism.

Effects Ambient magnetism caused by geomagnetism and other causes is mostly stationary and does not vary significantly with time. Therefore, once a gamma camera is installed at a certain location, the magnetism applied to each PMT of the gamma camera can be considered to be constant. just,
If the gamma camera rotates, the magnetism applied to each PMT will change depending on its rotational position, so this variation needs to be corrected.

Therefore, in this invention, if the head of the gamma camera is of the type that can be rotated, a correction coefficient for correcting the influence of surrounding magnetism is calculated in advance for each rotation angle, and this is stored. Ok,
When the head section assumes a certain angular position, the angular position is detected, the corresponding correction coefficient is read out, and each PMT output is corrected based on this.
This removes the influence of magnetism that varies depending on the angular position, ensuring a constant output from each PMT.

Example In the gamma camera shown in the figure, the radiation from the radioactive drug administered to the subject 1 is transmitted to the collimator 2.
The light enters one scintillator 3 through the filter. Light generated within the scintillator 3 due to the incidence of radiation is guided via the light guide 4 to a plurality of PMTs 5 arranged on the back surface thereof. The output of each PMT 5 is sent to a processor 7 through a preamplifier 6 to obtain a position signal and an energy signal, and by accumulating the position signals within a certain energy range, the radioactive drug being administered to the subject 1 Of, 1
A distribution image (spot image) viewed from the direction is reconstructed.

This head section consisting of the collimator 2, scintillator 3, light guide 4, and PMT 5 is held by a rotating stand 8 and driven to rotate around the subject 1 by a motor 9. This rotation angle is detected by the rotary encoder 10. The detected rotation angle signal is sent to the correction circuit 11, and the high voltage control circuit 12 controls the high voltage applied to each PMT 5 according to the angle.

First, prior to photographing the subject 1, a certain radiation source (not shown) is placed at the center of rotation instead of the subject 1, and the motor 9 is driven to rotate the head section.
Then, a rotary encoder 10 is installed for each rotation angle.
The angle signal obtained in , and the position signal and energy signal obtained from the processor 7 are led to a correction circuit 11 to calculate correction coefficients for correcting the output of each PMT 5 which fluctuates due to the influence of magnetism. Remember this. The operation of calculating and storing the correction coefficient is performed for each angle, and the correction coefficient is stored in association with each angle.

When actually photographing the subject 1, a correction coefficient corresponding to the angle detected by the rotary encoder 10 is read out, and the high voltage control circuit 12 adjusts the high voltage applied to each PMT 5 based on this correction coefficient. . Therefore, no matter what the angle, it is possible to obtain an output that does not fluctuate due to magnetism.

In addition, in the case of ECT imaging, the head section is simply rotated around the body axis of the subject 1 as described above, so it is sufficient to calculate the correction coefficient for each angle of rotation. In the case of photography, in addition to rotation around the body axis, the head may also be rotated in a plane parallel to the body axis (a plane parallel to the plane of the drawing); It is necessary to find and store the correction coefficients for each angle.

In addition, in the above, the PMT output is corrected by controlling the high voltage applied to the PMT 5, but it is also possible to adjust the gain of the preamplifier 6, or the gain of the processor 7. Control for this correction may be performed in an energy correction circuit or a linearity correction circuit (not shown) connected at a subsequent stage.

Effects of the invention According to this invention, it is possible to accurately correct, with a simple configuration, the fact that when the head of a gamma camera is rotated, the influence of magnetism such as earth's magnetism inevitably differs as the head portion of the gamma camera rotates. Therefore, it is possible to avoid data unevenness due to angular position, reconstruct an ECT image without artifacts, and obtain an image with excellent uniformity even when spot photography is performed from any angle. I can do it.

[Brief explanation of drawings]

The figure is a block diagram of one embodiment of this invention. 1... Subject, 2... Collimator, 3... Scintillator, 4... Light guide, 5... PMT,
6... Preamplifier, 7... Processor, 8... Rotating stand, 9... Motor, 10... Rotary encoder, 11... Correction circuit, 12... High voltage control circuit.

Claims (1)

[Scope of utility model registration request] In a gamma camera, a head section including a scintillator and a photomultiplier tube is held by a rotating stand. A correction coefficient for each angle is stored in order to correct the influence of magnetism, and when data is collected from the actual subject, the correction coefficient is read out using the detection signal of the rotation detector, and this correction coefficient is used. A gamma camera comprising a correction circuit that removes the influence of surrounding magnetism by correcting the output of each photomultiplier tube based on.