JP2508853B2 - Scintillation camera - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

 The present invention relates to scintillation cameras.

[Prior art]

When detecting radiation such as gamma rays with a scintillation camera, it is necessary to detect only radiation from a specified radiation source, so a specified window is set for the energy spectrum of the radiation, and only signals that enter the window are set. Is adopted. That is, if the radiation energy spectrum is as shown in FIG. 3, for example, a range A of ± 10% with respect to the peak value a.
Is set as the window, and only the signals whose energy signal wave height falls within them are adopted, and signals outside the range are ignored.

However, it is undeniable that the handling of signals is rough only by performing energy discrimination based on whether or not a predetermined energy window is entered in this way, and the reliability of the obtained information is high. Is difficult to raise. That is, even if the energy signal enters the window, if it enters the lower side, it is highly likely that the energy signal is caused by the radiation that is incident in a state where the energy is absorbed and scattered and the energy is reduced. The radiation that has been absorbed or scattered in this way is not directly incident on the detector from the radiation source, but is incident on a complicated path (non-linear path) due to absorption or scattering. The obtained position information will lack reliability. The present invention provides a scintillation camera improved so as to increase the reliability of information by not only performing energy discrimination based on whether or not a window has been entered but also giving different weights among those entered into a window. The purpose is to

[Means for Solving the Problems]

To achieve the above object, in a scintillation camera according to the present invention, a scintillator, a plurality of photoelectric converters coupled to the scintillator, and respective outputs of the photoelectric converter are input, and radiation incident on the scintillator is incident. A position calculation circuit that calculates a position and generates a position signal that represents the position, an addition circuit that adds all the photoelectric converter outputs to generate an energy signal, and a predetermined window related to the energy signal wave height is subdivided into a plurality of sub-windows. Each of the above-mentioned individual sub-windows, each of which has a plurality of wave height discriminating circuits which generate a signal by discriminating that the wave height of the above energy signal enters into each window, and is weighted according to the output of each wave height discriminating circuit. A circuit that produces a bait signal,
A display device for displaying a point corresponding to the weighted event signal is provided at the position represented by the position signal.

[Action]

A plurality of wave height discriminating circuits discriminate that the energy signal wave height has entered in each window and generate a signal,
The individual windows are each a plurality of predetermined windows related to the energy signal wave height. For this reason, the wave height discriminating circuit having each subdivision window is used for both detection of entry into the entire window and detection of entry into each subwindow, so that the configuration is simplified. Then, since an event signal weighted according to the output of each wave height discrimination circuit is generated, the event signal not only indicates that the energy signal wave height has entered the entire window, but also the energy in the window. It also represents the magnitude of the signal wave height. In other words, an event signal with a large weight is generated for a signal whose energy signal wave height is high in the entire window and is of high importance, and the energy signal wave height is low in the entire window and of high importance. For a low signal, an event signal with a small weight is generated.
Then, on the display device, a point corresponding to the weight of the event signal is displayed at a position defined by the position signal, and a radiographic image (scintigraphy) is formed by the large number of points.
Is configured. In general, radiation has a very sharp energy spectrum when it is captured immediately after it is emitted from a radiation source, but when it passes through an object, the energy decreases due to absorption and scattering, so the energy spectrum after passing through the object is gentle. It will be That is, the spectrum spreads to the low energy side from the original sharp energy peak. Therefore, it is considered that the signal on the low energy side in the window is due to the radiation after absorption and scattering, and the information such as the incident position of the radiation is unreliable. On the other hand, the signal on the high energy side in the window is considered to be due to the radiation that has entered without absorption or scattering, so the reliability of the information such as the position of incidence of the radiation is high. Even for signals that enter the same window in this way, their importance varies depending on the magnitude of the energy signal wave height in that window. By weighting the event signal as described above, the importance of the event signal can be reflected in the points forming the image, and by attaching a small weight to the event signal with low reliability, deterioration of the data can be prevented and The reliability can be improved.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a scintillation camera to which the present invention is applied.
A large number of photomultiplier tubes 2 are coupled to the scintillator 1, and the output thereof is guided to the position calculation circuit 3 and the addition circuit 4. The position calculation circuit 3 calculates the incident position of the gamma ray incident on the scintillator 1 from each output of the photomultiplier tube 2 and outputs a position signal indicating the position to the CRT device 8.
The addition circuit 4 adds the outputs of the all-photomultiplier tube 2 to obtain an energy signal having a wave height corresponding to the energy of the gamma rays incident on the scintillator 1. This energy signal is sent to three analyzers 51, 52, 53 in this example. This analyzer 51, 52,
53 is for detecting that the energy signal wave height is within a predetermined window. Here, the energy spectrum of the gamma rays to be detected is shown in Fig. 2 (a).
Assuming that the whole window is A, the detection windows of the analyzers 51, 52 and 53 are in the window A.
It is defined as B, C, D. And each analyzer 51, 5
The outputs of 2 and 53 are input to the one-shot multivibrators 61, 62 and 63, respectively. These one-shot multivibrators 61, 62, 63 are adapted to generate one pulse having different lengths, and their lengths are 1 μsec, 0.8 μsec, and 0.4 μsec here. The outputs of these one-shot multivibrators 61, 62, 63 are sent to the CRT device 8 as unblank signals via the OR circuit 7. Therefore, when the energy signal wave height is in the window B on the larger side of the window A, an output is generated from the analyzer 51 and an unblank signal having a length of 1 μsec is generated, and when it is in the window C, the analyzer 52 is generated. From the output, an unblanked signal with a length of 0.8 μsec occurs,
When in the window D, an output is generated from the analyzer 53 and an unblank signal having a length of 0.4 μsec is generated. As a result, weighting close to a polygonal line (solid line in the figure) that approximates ideal non-linear weighting is realized.
Therefore, on the screen of the CRT device 8, when the energy signal wave height is on the large side of the window A, a dot having a brighter brightness is displayed, and when it is on a smaller side, a dot having a darker brightness is displayed. It becomes possible to perform weighted display as shown by the dotted line in FIG. 2B according to the magnitude of the energy signal wave height. That is, weighted display can be performed according to the reliability of the position signal, and the reliability of the displayed information can be improved. In this embodiment, three analyzers 51, 52, 53 are provided without providing an analyzer for discriminating only that the wave height of the energy signal has entered within the entire window A, and the wave height of the energy signal is within the entire window A. Since the detection of the entry and the entry of each of the subdivision windows B, C, and D therein are also used, the configuration is simplified. Although the event signals are weighted in an analog manner in the above description, they may be weighted in a digital manner. As digital weighting, analyzers 51 and 5 are used.
2 and 53 are each provided with a pulse generation circuit having a different number of pulses, and the number of pulses generated when one output is generated from each of the analyzers 51, 52 and 53 is, for example, 5
It is conceivable that the number of pieces is set to four, one piece, and these pieces are counted for each position by a memory or the like and then divided by 5.

【The invention's effect】

According to the scintillation camera of the present invention, not only is radiation of a predetermined energy range incident, but also higher energy or lower energy within that range can be detected, and weighting is performed according to the corresponding importance level. Since the above event signal is obtained and reflected on the display image, a more reliable image can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are graphs showing the relationship between the detection window and the weight with respect to the energy spectrum in the above embodiment, and FIG. 3 is a conventional example. 3 is a graph showing the relationship of the detection window with respect to the energy spectrum in FIG. 1 ... Scintillator, 2 ... Photomultiplier tube, 3 ... Position calculation circuit, 4 ... Addition circuit, 51, 52, 53 ... Analyzer, 61, 62, 63 ... One-shot multivibrator,
7 ... OR circuit, 8 ... CRT device.

Claims (1)

(57) [Claims] A scintillator, a plurality of photoelectric converters coupled to the scintillator, and respective outputs of the photoelectric converter are input, and a position indicating the position by calculating the incident position of the radiation incident on the scintillator. A position calculation circuit that generates a signal, an adding circuit that generates an energy signal by adding all the photoelectric converter outputs described above, and an individual subdivision window in which a predetermined window regarding the energy signal wave height is subdivided into a plurality, respectively. A plurality of wave height discriminating circuits for discriminating that the wave height of the energy signal has entered into each window and generating a signal, a circuit for generating an event signal weighted according to the output of each wave height discriminating circuit, and the position described above. A display device for displaying a point according to the weighted event signal at a position represented by a signal. Configuration camera.