JPH03584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scintillation camera.

A scintillation camera detects radiation such as gamma rays emitted from the accumulated nuclide outside the body when a drug containing a specific radioactive nuclide is injected into a subject and the drug accumulates in a predetermined organ. Images showing the state of distribution of the drug are obtained and used to diagnose the above-mentioned organs. This scintillation camera has a scintillator that generates scintillation upon incidence of radiation such as gamma rays, and a large number of photomultiplier tubes arranged on the back of the scintillator that convert the scintillation light into electrical signals. Sometimes, the signals output from each photomultiplier tube are weighted by a matrix circuit of resistors (or capacitors or delay lines) according to the X- and Y-direction positions of the photomultiplier tubes that output the signals, and then added. Obtain an X position signal and a Y position signal. In addition, an energy signal is created by summing the outputs of all photomultiplier tubes, and by discriminating the level of this energy signal, it is possible to discriminate whether or not the energy of the incident radiation is within a specified range. When it is determined that the scintillation position is within the range, the X position signal and Y position signal are divided by the energy signal to output a signal representing the scintillation position. Then, this signal is converted into shading or brightness depending on the count value for each position.
Displayed on a CRT device, etc.

By the way, with conventional scintillation cameras with a wide field of view, when observing a narrow region of interest,
Even though data outside the region of interest is unnecessary, it is configured to count data in the same way as data inside the region of interest, resulting in a decrease in the counting rate as a scintillation camera and a deterioration in efficiency.

In view of the above, the present invention provides a scintillation camera that improves efficiency by removing data outside the region of interest at an early stage of the signal processing system and eliminating unnecessary data counting. The purpose is to provide.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a large number of photomultiplier tubes 2, 2, etc. are arranged on the back of a scintillator 1, and the output of each photomultiplier tube is input to a resistance matrix circuit 3, and the output of each photomultiplier tube is inputted to a resistance matrix circuit 3. The outputs of each photomultiplier tube are weighted according to the position in the X direction and then added to create an X position signal, and similarly, the outputs of the photomultiplier tubes are weighted and added according to the position in the Y direction to create a Y position signal. The energy signal (Z signal) is obtained by summing the outputs of all the photomultiplier tubes.

When radiation such as gamma rays enters the scintillator 1 and scintillation occurs, the light is detected by the photomultiplier tube 2, and the closer the photomultiplier tube 2 is to the scintillation, the higher the output will be. By performing weighted addition according to the values, an X position signal and a Y position signal that temporarily represent the scintillation position can be obtained. However, the amount of light incident on each photomultiplier tube 2 differs depending on the energy of the incident radiation, and the magnitude of the output differs.
It is necessary to correct the X position signal and Y position signal according to the energy. Therefore, each of the X, Y, and Z signals is guided through an amplifier 4, an analog switch 5, and an integrating circuit 6 to obtain respective integral signals.
The integrated signal of Y is further sampled by the sample hold circuit 7, and the integrated signal of X,
The integral value of Y is divided by the integral value of Z and becomes X÷Z, Y
÷Z is calculated and difX is used as a signal that expresses the scintillation position regardless of energy.
Get the difY signal. Here, the integral signal of Z is further sent to the energy discrimination circuit 9, and it is determined whether the energy of the incident radiation is within the energy range represented by the signal output from the energy setting device 13. Ru. In the energy estimator 13, assuming that the energy spectrum of the radiation from the used nuclide is as shown in FIG. 3, the center value and width of the energy peak are set in accordance with the spectrum. A signal (wind signal) output from the energy setting device 13 and representing the energy at both ends of the width is sent to the energy discrimination circuit 9, and it is determined whether the integral signal of the energy signal Z is within the set range. . Energy signal Z
If the integral signal of is within the set range, the above calculation is performed, and if it is outside the specified range, the integral circuit 6 is immediately discharged through the timing circuit 10, so that no output is generated from the integral circuit 6, and the signals difX,
Prevent difY output from occurring. Integrating circuit 6
are an operational amplifier 61 and a capacitor 62, respectively.
and an analog switch 63 that shortens and discharges the capacitor 62. When a signal is sent from the timing circuit 10, the analog switch 63 is turned on and discharge is performed.

These configurations are similar to ordinary scintillation cameras. According to the invention, a comparison circuit 11, a threshold designation circuit 12, and an aperture setter 14 are further provided. The aperture setter 14 is used to arbitrarily set a narrow visual field 22 by limiting the original visual field (maximum visual field) 21, as shown in FIG. The signal and the Y-direction position signal are sent to the threshold designation circuit 12.

The threshold designation circuit 12 multiplies the boundary X and Y direction position signals by a coefficient corresponding to the energy peak of the radiation of the nuclide used to generate a reference voltage and sends it to the comparison circuit 11. In other words, the larger the energy peak of the radiation of the nuclide used, the larger the X and Y direction position signals output from the integrating circuit 6, so the X and Y direction position signals on the reference side must also be increased accordingly. It is from. Therefore, the above coefficient corresponds to a signal representing the center value of the set energy output from the energy setter 13. In the comparator circuit 11, the integrated value of the X position signal and this reference voltage are connected to comparators 111,1.
12 and when the X position signal is outside the field of view 22
An output is generated from the OR circuit 113, and the integrated value of the Y position signal and the reference voltage are compared by comparators 114 and 115, and when the Y position signal is outside the visual field range 22, the OR circuit 1
An output is generated from 16, and from OR circuit 117,
An output is generated when the sensor deviates from the viewing range 22 in either or both Y directions and when the output of the energy discrimination circuit 9 is generated.

Therefore, in the same way as when the energy is outside the specified energy range, when the field of view is outside the set field of view, the timing circuit 10 outputs an output and the integrating circuit 6 is discharged, so that no output is generated from the integrating circuit 6. ,
The difX and difY signals are not generated.
Therefore, unnecessary calculations and data processing are avoided,
In addition, since the signals difX and difY are not counted, the counting rate of the scintillation camera itself is improved and efficiency is increased.

It should be noted that this determination of inside and outside of the visual field range 22 is sufficient for practical use if viewed simply as a means to avoid unnecessary calculations and processing, but it must be noted that it is not strict. be. That is, the energy spectrum of incident radiation for a certain nuclide is as shown in Figure 3, for example,
Its energy peak has a certain range. Therefore, the center and width are set by the energy setter 13, and the X and Y direction position signals are outputted from the integrating circuit 6 only for energy signals Z within the width. X,
This means that variations in the Y-direction position signal can be suppressed within this range. In fact, for example, when using Tc-99m as the nuclide, the energy peak is
140keV, and a 20% width around it is set as the energy range, so the energy signal Z
X and Y direction position signals before being normalized by
The error is kept within ±10%. Furthermore, in reality, there are variations in the outputs of the individual photomultiplier tubes 2, and these variations result in errors in the X and Y direction position signals, which are added to the errors due to variations in energy within the above-mentioned width. However, the field of view 2 that is performed using X and Y direction position signals that include such errors
The accuracy of determining whether or not it falls within 2 is ±10%.
This results in an error that does not exceed significantly. Therefore, it can be said that it is sufficient to simply view it as a means to avoid unnecessary calculations and processing. On the other hand, the fact that the determination of whether or not the object is within the viewing range 22 itself includes a certain error due to such errors in the X and Y direction position signals poses a problem from a different perspective than the above. In other words, X, Y
Field of view 2 where the direction position signal corresponds to scintillator 1
Since it is obtained as a coordinate system with the center of scintillator 1 as the origin, it appears as an error in the position in the far and near direction from the origin, that is, in the radial direction from the center of scintillator 1, and the set visual field range 2
This means that the peripheral data within 2 will be eliminated. Therefore, in fact, taking this into consideration, the fourth
As shown in the figure, it is necessary to set the visual field range 22 to be slightly larger than the region of interest 23. When scanning the whole body of the subject 51 as shown in FIG.
Since the visual field range 22 is a perfect rectangle and the same location must not be counted twice, simply setting a large visual field range as described above is insufficient. Therefore, in such a case, it is necessary to send the signals difX and difY to a circuit for determining whether or not the field of view is within the field of view again to remove peripheral signals due to variations.

As described above with respect to the embodiments, according to the present invention, it is possible to achieve effects such as improving the counting rate, shortening the examination time, and reducing the patient's radiation exposure.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure is a schematic diagram to explain the field of view setting, Figure 3 is an energy spectrum diagram, Figure 4 is a schematic diagram to explain the relationship between the region of interest and the field of view range to be set, and Figure 5 is a diagram of the whole body scan. It is a schematic diagram for explanation. 1...Scintillator, 2...Photomultiplier tube, 3
...Resistance matrix circuit, 4...Amplifier, 5...
Analog switch, 6... Integration circuit, 7... Sample hold circuit, 8... Divider, 9... Energy discrimination circuit, 10... Timing circuit, 11...
Comparison circuit, 12...Threshold specification circuit, 1
3...Energy setting device, 14...Aperture setting device.

Claims (1)

[Claims] 1. A scintillator, a large number of photoelectric converters arranged on the back of this scintillator, and the X of each photoelectric converter.
a matrix circuit that obtains an X-direction position signal and a Y-direction position signal by weighting the outputs of each photoelectric converter according to the array position in the direction and the Y-direction and adding the weighted outputs;
A circuit that generates an energy signal by summing the outputs of all the photoelectric converters, an energy setting device that makes settings related to energy according to the nuclide used, and a circuit that sets the level of the energy signal using the output of the energy setting device. and an energy discrimination circuit that divides the X direction position signal and the Y direction position signal by the energy signal when the energy discrimination circuit discriminates that the energy signal is within a preset energy range. A scintillation camera comprising a divider that outputs a signal representing the scintillation position in the scintillator,
A visual field setter that sets the visual field range, and a signal representing the X-direction boundary and Y-direction boundary of the visual field range outputted from the visual field setter are modified according to the output of the energy setter to generate an X-direction reference signal and a Y-direction reference signal. A threshold designation circuit that generates a direction reference signal, a comparison between this X direction reference signal and the X direction position signal, and a Y direction reference signal.
The direction reference signal and the Y-direction position signal are compared, and it is determined whether or not these X-direction position signals and Y-direction position signals are within the set viewing range. If not, the X-direction position signal is A scintillation camera comprising: a comparison circuit that prevents a direction position signal and a Y direction position signal from being input to the divider.