JPH0452427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in scintillation cameras.

A scintillation camera calculates the position each time radiation enters the scintillator, obtains a position signal corresponding to the incident position, and displays a bright spot on the screen at the position indicated by this position signal.
This is stored on the screen. In this case, it is necessary to detect only the radiation from the RI (radioisotrope) administered to the human body, which is the measurement target, and therefore an energy window must be set that corresponds to the energy range of the radiation generated by the administered RI. Then, it is analyzed whether the wave height of the energy signal falls within this window.

On the other hand, apart from this wave height analysis, it is necessary to detect the incidence of radiation and start position calculation, so conventionally the energy signal is compared with a certain trigger level as shown in Figure 1. An activation signal is generated when the energy signal exceeds this trigger level.

This trigger level is used to prevent the position calculation circuit from malfunctioning due to noise, rather than to distinguish energy signals from noise, etc., and is usually set to the minimum level that will not cause malfunction. .

However, in reality, a considerable amount of scattered radiation is incident, and although the energy signal due to this scattered radiation has a lower wave height than the energy signal of radiation directly incident from the RI, it still exceeds the trigger level, which is the minimum level mentioned above. There are many things to overcome. Therefore, since an operation start signal is also issued by this scattered ray, position calculation regarding this scattered ray is started, and a position signal regarding this scattered ray is obtained. Since the position signal related to the scattered radiation is ultimately eliminated by the pulse height analysis of the energy signal related to the scattered radiation, the position calculation is performed for a useless signal. In other words, from the viewpoint of the position calculation circuit, since the operation is started even for unnecessary incident radiation, the position calculation operation for necessary incident radiation cannot be performed during that time. If such unnecessary position calculation time increases, there is a problem that the dead time for the necessary incident radiation becomes longer, the opportunity to calculate the necessary incident radiation is lost, and the counting rate decreases. .

In view of the above, an object of the present invention is to provide a scintillation camera which is improved so that unnecessary position calculations are not performed due to scattered radiation, etc., and which improves the count rate characteristics.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 2, RI is administered to the subject (patient body) 11,
Radiation emitted from the RI distributed there passes through the collimator 12 and enters the scintillator 13. A large number of photomultiplier tubes 15 are arranged on the back surface of the scintillator 13 via a light guide 14, and these photomultiplier tubes 15 are optically coupled to the scintillator 13 via the light guide 14. scintillator 13
In this case, scintillation light emission occurs every time radiation is incident, and the light is guided to a large number of photomultiplier tubes 15 by a light guide 14. From each photomultiplier tube 15, a pulse signal corresponding to the light incident on each of them is obtained. That is, these photomultiplier tubes 15 function as photoelectric converters that convert incident light into pulse signals having wave heights corresponding to the incident light.

The output of each photomultiplier tube 15 is sent to a weighting addition circuit 17 and an addition circuit 21 through a preamplifier 16, respectively. A position calculation circuit is constituted by the weight addition circuit 17, the integration circuit 18, and the division circuit 19. The division circuit 19 divides the output signal of the integration circuit 18 by the energy signal. Position signals X and Y obtained from this position calculation circuit are sent to the display device 20.

On the other hand, an energy signal is obtained from the addition circuit 21 as the addition result. This energy signal is integrated by an integrating circuit 22 and then sent to a pulse height analyzer 23. The wave height analyzer 23 analyzes whether the wave height of the energy signal is within the window set by the window setter 24. When the wave height of the energy signal is within the window, an output is generated from the wave height analyzer 23, and an unblank signal is generated from the timing circuit 26,
This is sent to the display device 20.

The display device 20 displays a bright spot at the position on the screen indicated by the position signals X and Y at the timing of this unbundling signal.

The window setter 24 is for setting the energy level window width (expressed as a percentage, such as 20% of the energy level) according to the RI administered to the subject 11. Therefore, when the wave height analyzer 23 analyzes that the wave height of the energy signal is within the window, it is determined that it is radiation from the RI administered to the subject 11, and only that incident radiation is transmitted to the incident position. Accordingly, it will be displayed on the display device 20 as a bright spot.

Such display of bright spots due to incident radiation is performed on the display device 20 every time the radiation is incident, and a distribution image of RI in the subject 11 appears on the screen.

The energy signal from the adder circuit 21 is also sent to the comparator 25, where it is compared with the trigger level from the trigger level generation circuit 27, and as shown in FIG. 3, the energy signal exceeds the trigger level. An operation start signal is issued when the

The trigger level generation circuit 27 calculates a lower limit value of the window based on the energy level and the signal representing the window width sent from the window setter 24, and outputs a signal at a level slightly lower than this value as a trigger level.

The operation start signal is then sent to the timing circuit 26, and each operation timing is determined by this operation start signal. That is, the timing circuit 26
Based on this operation start signal, determines the start timing of the integration operation of the integration circuit 18 constituting the position calculation circuit, determines the operation timing of the division circuit 19 in the position calculation circuit, and further determines the operation timing of the division circuit 19 in the position calculation circuit. The start timing of the integration operation of the integration circuit 22, which integrates the energy signal input to the circuit 22, is determined.

Therefore, as mentioned above, the operation start signal is output when the energy signal exceeds the trigger level, which is slightly lower than the lower limit of the window. In other words, in cases where scattered radiation is incident, this operation start signal is not output. As a result, in the case of such scattered radiation,
Integration and division operations of the position calculation circuit are not started, and integration for analyzing whether the wave height of the energy signal falls within the window is also not started. Therefore, the proportion of time spent on position calculations for unnecessary radiation events, and the proportion of time used for wave height analysis to determine whether the energy signal wave height is within the window, can be significantly reduced. can do. Therefore, the count rate characteristics are improved.

Since the window settings in the window setting device 24 are made according to the RI to be used,
The trigger level for obtaining the operation start signal also changes according to the RI, and it is possible to reduce the time required for unnecessary signal processing and improve the counting rate characteristics in accordance with the RI used.

Note that if the rise of the output of the preamplifier 16 is sufficiently fast, the operation start signal shown in FIG. 3 will not be delayed much compared to the operation start signal shown in FIG. 1 (conventional).
If the rise is slow, the first part of the output of the weighted addition circuit 17 and the first part of the output of the addition circuit 21 cannot be taken into the integration circuits 18 and 22 due to the delay. In such a case, such inconvenience can be avoided by providing a delay circuit before or after the weight addition circuit 17 and the addition circuit 21 and changing the amount of delay according to the trigger level from the trigger level generation circuit 27. Possible and preferable. Alternatively, it is also effective to provide a differentiator before the comparator 25 to speed up the rise of the input to the comparator 25.

As described above with respect to the embodiments, the scintillation camera according to the present invention includes a scintillator into which radiation is incident, and a scintillator arranged on the back side of this scintillator, and the emitted light of the scintillator is guided to each of the scintillators, and each of the guided lights a large number of photoelectric converters that output pulse signals corresponding to an adding circuit that obtains an energy signal with a wave height corresponding to the energy of incident radiation by adding pulse signals; a window setting device that sets an energy range to be detected among the incident radiation; A wave height analyzer that analyzes whether the wave is within a set window and generates an output signal if it is within the window, and a wave height analyzer that is slightly lower than the lower limit of the window that changes in response to the set window. A trigger level generation circuit that generates a trigger level, and an operation that compares the energy signal with the trigger level and starts the operation of the position calculation circuit and the wave height analyzer at the timing when the energy signal exceeds the trigger level. It is characterized by a comparator that generates a start signal, and when the energy signal exceeds a trigger level that is slightly lower than the lower limit of the window, an operation start signal is output and the position calculation circuit and wave height are Since the analyzer operations are started, these operations are not started in the case of incident scattered radiation, which greatly reduces the proportion of time spent on position calculations and wave height analysis on unnecessary radiation events. The rate characteristics can be improved.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram for explaining the conventional example, Figure 2 is a waveform diagram for explaining the conventional example.
The figure is a block diagram of one embodiment of the present invention, and FIG. 3 is a waveform diagram for explaining the operation of FIG. 2. 11...Subject, 12...Collimator, 13...
...Scintillator, 14...Light guide, 15...
...Photomultiplier tube, 16...Preamplifier, 17...
Weighted addition circuit, 18, 22...Integrator circuit, 19
...Division circuit, 20... Display device, 21... Addition circuit, 23... Wave height analyzer, 24... Window setter, 25... Comparator, 26... Timing circuit, 25... Comparator 26...timing circuit,
27...Trigger level generation circuit.

Claims (1)

[Claims] 1. A scintillator on which radiation is incident, and a large number of photoelectric converters arranged on the back side of this scintillator, each of which is guided by the scintillator's light emission, and which outputs a pulse signal corresponding to each guided light.
A position calculation circuit that obtains a position signal representing the position of the incident radiation from the pulse signals from a large number of photoelectric converters, and a position calculation circuit that calculates the pulse signal from each of the above photoelectric converters to correspond to the energy of the incident radiation. an adder circuit that obtains an energy signal with a wave height of a given wave height; a window setting device that sets an energy range to be detected among the incident radiation; and a window setter that analyzes whether the wave height of the energy signal falls within a set window. a pulse height analyzer that generates an output signal when the input signal is input, a trigger level generation circuit that generates a trigger level that is slightly lower than the lower limit of the window that changes in accordance with the set window, and the energy signal that is generated as described above. and a comparator that compares the energy signal with the trigger level and generates an operation start signal for starting the operation of the position calculation circuit and the pulse height analyzer at the timing when the energy signal exceeds the trigger level. Scintillation camera.