JPS5849835B2 - scintillation camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scintillation camera equipped with a peak value analyzer having a function of removing a superimposed signal by ANDing a peak value discrimination signal and an input detection signal.

Wave height analyzer in conventional scintillation camera (
Pulse Height Analyzer
) is generally called PHA and is widely used in radiation measurement.

The PHA has the function of selecting only those pulse signals whose peak values are within a certain range (within a window) from among a large number of pulse signals, and outputting a rectangular wave only at that time.

FIG. 1 shows a waveform diagram when the PHA is operating normally.

When the input pulse interval is long as shown in this figure, the PHA
operates accurately, but if the input pulse interval becomes narrow and the next pulse signal is superimposed on the pulse signal, the output pulse signal of the PHA will not be output at the correct timing.

FIG. 2 shows a waveform diagram when this malfunction occurs.

In this figure, when there is an input pulse signal 101 having a constant peak value, an output pulse signal 108 is generated at a zero crossing point a of this human pulse signal 101.

Pulse signals 102 and 103 are input pulses obtained by superimposing a subsequent pulse signal 105 or 107 on a previous pulse signal 104 or 106, respectively.

Since the peak value of the pulse signal 102 is within the window, an output pulse signal 109 is generated.

However, the time from the rise of the input pulse signal to the zero crossing point, that is, the rise of the output, should be t1, but is
The pulse signal 102 extends to t2 for combining the two pulse signals.

Original pulse signals 106 and 10 of composite pulse signal 103
7 is similar to the original pulse signals 104 and 105 of the composite pulse signal 102, but indicates that such a pulse signal is generated depending on the timing of the preceding and succeeding pulse signals.

Since the pulse signal 103 does not reach the window level, there is no output thereof.

The scintillation camera calculates the position of incidence of gamma rays on the scintillator by dividing the signals into three signals: X, Y, and Z.

The input pulse signal of the PHA is the Z signal, and the PHA generates an output when the peak value of the Z signal is within a certain range, starts calculating the coordinate position X, Y, and displays the calculated position on the X, Y oscilloscope. Displayed as a bright spot at the top.

The PHA only judges whether the peak value of the human pulse signal is within a certain range, so even if a pulse signal with a different shape than the original is input, as shown by the pulse signal 102 in FIG. If this condition is met, there will be an output.

At this time, the X and Y signals for position calculation are similarly superimposed, resulting in a pulse signal with an approximate shape different from the original one.

This causes an error in position calculation, and a bright spot appears at an inaccurate position.

This lowers the S/N ratio and deteriorates the resolution and uniformity that are most required of a scintillation camera.

The present invention eliminates the drawbacks of the prior art as described above, and provides a scintillation camera that can draw scintigrams with good resolution and uniformity even at high counting rates.

Hereinafter, the present invention will be specifically explained in detail with reference to Examples.

FIG. 3 is a diagram showing the principle of a scintillation camera.

In this figure, gamma rays 100 emitted from radioisotopes distributed within the body 21 pass through a collimator 22 and enter a scintillator 23 .

The incident gamma rays are absorbed by the scintillator and emit a flash of light.

This flash of light passes through a light pipe 24 and is converted into pulse signals x, y, and 2 by a preamplifier 26 of a photomultiplier tube 25.

These pulse signals X and y are input to the waveform analyzer 30 as X and Y position signals, respectively, and the pulse signal Z is input to the Z summing circuit 27 as a Z signal used for brightness modulation.
(a circuit that synthesizes the output from the photomultiplier tube).

Z summing signal 3 which is the output of this Z summing circuit 27
2 is input to the waveform shaping circuit 28 and PHA 29.

Therefore, the waveform-shaped signal 33 and the Z summing signal 32 are input to the PHA 29.

Then, only when there is an output 34 from the PHA 29, a bright spot is displayed on the X, Y oscilloscope 31 at the coordinate position calculated by the waveform analysis circuit 30.

FIG. 4 shows an embodiment of a PHA according to the present invention having a function of removing superimposed signals, and FIG. 5 is a timing chart of the PHA.

In FIG. 4, a low level discriminator 1 and a high level discriminator 2 determine the peak value of the waveform shaped signal 33, and the low level discriminator 1
is inverted, and when the high level discriminator 2 is not inverted, take the timing with the monostable multivibrator 4,
The AND circuit 5 outputs a peak value discrimination signal 37.

When the Z summing signal 32 is input to the input detector 3, the input detector 3 is always inverted, and at that time, the monostable multi-bi break 6 is triggered and the output pulse signal 36 is output.

Then, this output pulse signal 36 and peak value discrimination signal 37 are ANDed by an AND circuit 7, and an output pulse signal 34 of the PHA is output.

Since the low level discriminator 1 adopts a method in which the comparison voltage changes before and after being triggered by the waveform shaping signal 33, when the peak value of the input signal is within the window,
The pulse signal 38 generated by the monostable multivibrator 4 passes through the AND circuit 5 and appears as a peak value discrimination signal 37 at the zero crossing point of the waveform shaping signal 33.

Therefore, A of the pulse signal 36 and the peak value discrimination signal 37 is
If the period from the rising edge of the waveform shaping signal 33 to the zero crossing point becomes longer than specified by the pulse width of the output pulse signal 36 of the monostable multivibrator 6 by taking ND, in FIG. Output pulse signal 3
As shown in 4, even if there is a peak value discrimination signal 37, the PHA
is not output.

Setting the time of this period and the degree of overlap allowed can be easily done by adjusting the pulse width of the output pulse signal 36 of the monostable multivibrator 6.

That is, the narrower the pulse width of the pulse signal 36 and ANDL with the peak value discrimination signal 37 and the output pulse signal, the more severe the operation will be in preventing the superposition of the pulse signals.

As can be seen from the above description, modifications can be made without changing the circuit structure of the peak value analyzer of this embodiment or the gist of the present invention.

According to the present invention, it is possible to avoid counting pulse signals that deviate from the original pulse waveform due to the superimposition of pulse signals that occur at high counting rates in radiation measurement, and the degree of superimposition of pulse signals to be excluded can also be reduced by monostable multipliers. This can be easily done by varying the pulse width of the vibrator's output pulse, which minimizes the decline in resolution and uniformity that degrades at high count rates, resulting in scintigrams with high diagnostic efficiency. .

[Brief explanation of drawings]

Figure 1 is a waveform diagram when the peak value analyzer PHA is operating normally, Figure 2 is a waveform diagram when PHA malfunctions due to superimposition of pulse signals, Figure 3 is a diagram of the principle of the scintillation camera, FIG. 4 is a configuration diagram of an embodiment of a PHA that excludes a superimposed pulse signal according to the present invention, and FIG. 5 is a timing chart of a PHA that excludes a superimposed pulse signal according to the present invention. 1 is a low level discriminator, 2 is a high level discriminator, 3 is an input detector, 4 and 6 are monostable multivib breakers, 5 and 7 are AND circuits, and 29 is a peak value analyzer.

Claims (1)

[Claims] 1. In a scintillation camera equipped with a peak value analyzer for determining whether the peak value of a human input signal is within a certain range, detecting the time from the rise of the input signal of the peak value analyzer to the zero crossing point. 1. A scintillation camera characterized by comprising means for outputting an output only when the detection time is within a predetermined range and the peak value of the input signal is within a predetermined range.