JPH0756837B2 - X-ray generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an X-ray generator, and particularly to an abnormality in which X-ray emission does not stop even when the X-ray emission time limit signal is cut off. An X-ray generation device equipped with an abnormality detection circuit that is suitable for detecting and erroneously emitting X-rays and resulting X-ray exposure of a subject, and secondary damage to the device due to overload of the X-ray tube. It is about.

[Conventional technology]

According to FIG. 2, a circuit for detecting an abnormal condition such that the X-ray emission does not stop even if the X-ray timer has expired and forcibly stopping the X-ray emission. An X-ray generator equipped with will be described.

The X-ray generator is an X-ray tube 7, a high-voltage transformer 4 that generates a high voltage, and a rectifier that rectifies the output of the high-voltage transformer 4.
5a, 5b and the output of the high-voltage transformer 4, that is, the three-phase slide auto-transformer 1 for setting the high voltage and the input voltage of the transformer 4 so that the tube voltage of the X-ray tube 7 becomes a desired value.
And a switch 2 that opens and closes the output of the three-phase slide auto transformer 1 at the stage of preparing for X-ray radiation, and contacts 2a, 2b,
Controls the X-ray preparation circuit 23 that controls the switch 2c and the switch 2, the thyristor switch 3 that conducts during X-ray radiation and inputs the output of the three-phase slide autotransformer 1 to the high-voltage transformer 4, and the thyristor switch 3. The X-ray timer circuit 24, the current at the secondary side neutral point of the high-voltage transformer 4, that is, the current detector 6 that detects the actual tube current of the X-ray tube 7 as a voltage value, and the current detector 6
Comparator 8 for comparing a constant threshold value (voltage value) made by resistors 9 and 10 and a diode for making a comparison between the output of comparator 8 and the signal made by X-ray timer 24. 11, 12, a thyristor 16 that operates as a result of the matching, and a relay 15 that is driven by the thyristor 16.

Next, the operation of this device will be described.

First, in the preparation stage for X-ray radiation, the switch 2 is operated by the X-ray preparation circuit 23, the contacts 2a, 2b, 2c of the switch are closed, and the output of the three-phase slide auto transformer 1 is supplied to the thyristor 16 switch 3. To be done. Next, when an X-ray emission signal is output from the X-ray timer circuit 24, the thyristor switch 3 is turned on, the output of the three-phase slide auto transformer 1 is supplied to the high voltage transformer 4, and a high voltage is applied to the X-ray tube 7. When applied, a current is generated on the secondary side of the high voltage transformer 4. This current is detected by the current detector 6 and input to the comparator 8. The reference value to be compared by the comparator 8 is the voltage between Vcc and GND divided by the resistors 9 and 10. This is when a high voltage is generated on the secondary side of the high voltage transformer 4. Since some dark current is generated even when no current is flowing through the X-ray tube 7, this is for eliminating the effect of the dark current. Therefore, when the signal from the current detector 6 is larger than the reference value, that is, when the current actually flows in the X-ray tube 7, the output of the comparator 8 becomes H level. On the other hand, the X-ray emission signal from the X-ray timer circuit 24 is also input to the inverting amplifier 18, and as a result, the output level of the inverting amplifier 17 becomes L level. That is, the X-ray timer circuit 24
When the X-ray radiation signal of is ON, that is, when the output of the inverting amplifier 17 is at the L level and a current flows through the X-ray tube 7 and the output of the comparator 8 becomes the H level, the resistor 13 is removed from the Vcc power supply. The current supplied via the diode 12 flows into the inverting amplifier 17. However, when the X-ray emission signal of the X-ray timer circuit 24 is off, that is, when the output of the inverting amplifier 17 is at the H level, the output of the comparator 8 also becomes the H level when the current flows through the X-ray tube 7. The thyristor 16 is triggered by the current supplied from the Vcc power supply through the resistor 13 through the resistor 14 and becomes conductive, and the relay 15 is turned on. Contact 15a of relay 15
Is connected in series between the switch 2 and the X-ray preparation circuit 23. When the relay 15 is turned on, the contact 15a is opened, the switch 2 is turned off, and the output of the three-phase autotransformer 1 is forcibly cut off. The X-ray emission stops.

FIG. 3 shows the above operation timing chart.

In FIG. 3, (a) is a preparation signal for the X-ray preparation circuit 23 (turns on at L level), (b) is an X-ray emission signal from the X-ray timer circuit 24 (turns on at L level), (c) ) Is the input of the inverting amplifier 17, (d) is the output of the inverting amplifier 17,
(E) is the current of the X-ray tube 7, (f) is the output of the comparator 8,
(G) is the gate input of the thyristor 16.

[Problems to be solved by the invention]

Next, problems of this circuit will be described. The actual current flowing in the X-ray tube 7 is as shown in FIG. 3- (E), and there is a wave tail due to the electric charge due to the stray capacitance of the high-voltage cable even after the X-ray radiation signal is turned off ( (A part in the figure). Here, when the X-ray tube is regarded as a constant current load, the wave tail time T is Here, it is known that V: X-ray tube voltage I _P : X-ray tube current C _S : stray current of high-voltage cable.

If V = 150KV _P , I _P = 10mA, the stray capacitance of the high voltage cable is 260pF / m and the cable length is 20m in the formula (1). And the wave tail time is T = 39 mS.

Therefore, for example, the maximum tube voltage 15
0 kV _P, the minimum tube current 10 mA, if the maximum pressure cable length was set to 20 m, malfunction the abnormality detection circuit during rated, for that is not clear switch 2 to the normal X-ray at a radiation exit, the X-ray radiation signal After turning off, a non-detection period of about (39 + α) mS must be provided (section B in FIG. 3). Moreover, as is clear from the equation (1), when the X-ray tube current is large, that is, when the internal impedance of the X-ray tube is small, the wave tail is short, and when the X-ray tube current is small, the internal impedance is high, The tail becomes longer. Therefore, the non-detection period of the abnormality detection circuit must be provided in consideration of the corresponding increase.

Therefore, if an abnormality occurs in which X-ray emission is not stopped even though the X-ray emission signal is actually turned off, X
After the radiation signal is turned off, X-rays are radiated only during the non-detection period of the detection circuit, that is, (39 + α) mS in the above example (C in FIG. 3). This causes extra radiation to the subject, and also damages the X-ray tube when the X-ray tube is used at the allowable rating limit. Further, when the X-ray emission is repeatedly performed several tens of times per second like the high-speed cine pulse imaging, the next X-ray emission signal may be input during this non-detection period, so that it is substantially effective. This circuit is completely useless.

It is an object of the invention that X
In an abnormal situation where the radiation does not stop, X is forced immediately.
It is an object of the present invention to provide an X-ray generator including a detection circuit capable of blocking a ray.

[Means for solving problems]

The above-mentioned problem is that in an X-ray generator that inputs a voltage supplied from a power source to a switch, boosts it with a high-voltage transformer, rectifies the voltage and applies it to the X-ray tube through a high-voltage cable. The means for detecting the current, the means for limiting the X-ray emission time, the means for limiting the X-ray emission time, and the means for detecting the X-ray tube current from the time when the X-ray emission end signal is output from the time-limiting means. Means for integrating the X-ray tube current signal to be output and means for generating a reference signal determined by the stray capacitance of the high voltage cable and the X-ray tube voltage are provided, and the output of the integrating means and the reference signal are compared. An X-ray generator configured to open the switch when the output of the integrating means exceeds a reference signal.

Will be solved by.

[Action]

When the tube voltage and the high voltage cable length are made the same and the tube current is changed, a tube current waveform as shown in FIG. 4 is obtained. When the X-ray emission signal (C ') is turned off, the tube current decreases as shown in the figure. The tube current after the X-ray radiation signal is turned off is due to the charge Q accumulated in the stray capacitance C _S of the high voltage cable as described above. This charge Q is obtained by the product of the high-voltage cable length and the tube voltage, and if the high-voltage cable length and the tube voltage V are constant, then Q = C _S × V = constant (2).

The fact that the charge Q is constant means that the areas of the tube current wave tail (the tube current integrated with respect to time) after the X-ray emission signal in FIG. That is,
The area of the wave tail (A) + (B) = (B) + (C). The point where the wave tail becomes zero changes depending on the tube current value. Therefore, the value of Q determined by the rated values of the maximum tube voltage of the X-ray device and the longest high-voltage cable length, in other words,
By using the mAS value as a reference value and comparing it with the mAS of the tube current wave tail after turning off the X-ray emission signal, when the wave tail mAS value exceeds the reference mAS value, the X-ray generation main circuit is forcibly cut off. Therefore, the problems of the conventional device can be solved.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. The device configuration is a three-phase slide auto transformer 1, a switch 2 and its contacts 2a, 2b, 2c, a thyristor switch 3, a high-voltage transformer 4, high-voltage rectifiers 5a, 5b, a current detector 6,
The X-ray tube 7, the high-voltage cables 25a and 25b, the relay 15, its contact 15a, the thyristor 16, the X-ray preparation circuit 23, the X-ray timer circuit 24, and the inverting amplifier 18 are those shown in FIG. It has the same function as the above. In this embodiment, the integrator 30 for integrating the current value flowing from the current detector 6 through the X-ray tube 7, the analog switch 31 for resetting the output of the integrator 30, and the output of the integrator 30 are compared. There are provided resistors 32 and 33 for producing a reference value for the operation, and a comparator 36 for comparing the reference value with the output of the integrator 30.

Next, the operation of this device will be described.

First, in the standard stage of X-ray radiation, the switch 2 is operated by the X-ray preparation circuit 23, the contacts 2a, 2b, 2c of the switch are closed, and the output of the three-phase slide autotransformer 1 is output to the thyristor switch 3. Supplied. Next, when the X-ray radiation signal is output from the X-ray timer circuit 24, the thyristor switch 3 is turned on, the output of the three-phase slide auto transformer 1 is supplied to the high voltage transformer 4, and the high voltage is supplied to the X-ray tube 7. Is applied to generate a current on the secondary side of the high voltage transformer 4. This current is detected by the current detector 6 and input to the integrator 30. That is, the current (mA) flowing through the X-ray tube 7 is measured by the integrator 30 for a time (S).
Is integrated by (mA) x (S) = mAS value is created. However, while the X-ray emission signal from the X-ray timer circuit 24 is being output, the analog switch 31 is closed, the integrating capacitor 34 is discharged through the resistor 35, and the integrator 30 is in the reset state. The value produced by the resistors 32 and 33 is a value corresponding to the reference mAS value corresponding to the wave tail portion of the X-ray tube current. Therefore, X
When the X-ray device is normal, when the X-ray emission signal from the X-ray timer circuit 24 is cut off, the thyristor switch 3 is cut off, and then the current detector 6 has only the wave tail portion of the X-ray tube current. It flows. At the same time, when the X-ray emission signal is cut off, the analog switch 31 is opened and the integrator 30 starts integration. As a result, the integrator 30 integrates only the wave tail portion of the X-ray tube current, and as a result, the comparator 36
The output of the comparator 36 is always at the L level because it does not exceed the reference value created by the resistors 32 and 33 of FIG. Here, if the current continues to flow in the X-ray tube 7 despite the X-ray emission signal being cut off, the integrator 30 starts integrating the current value from the time when the X-ray emission signal is cut off. , MAS of wave tail of X-ray tube current
When the value is exceeded, that is, when the reference value made by the resistors 32 and 33 is exceeded, the output of the comparator 36 becomes the H level and the thyristor 16 is triggered to activate the relay 15 and the relay 15
The X-ray emission is forcibly stopped by opening the switch 2 by means of the contact 15a of the above, thereby cutting off the input of the high voltage transformer 4.

FIG. 5 shows an operation timing chart.

In FIG. 5, (a ') is the reference signal of the X-ray preparation circuit 20 (ON at L level), (b') is the X-ray emission signal from the X-ray timer circuit 21, and (e ') is the X-ray. Current of tube 7, (h)
Is the output of the integrator 30, and (i) is the output of the comparator 36. A
The part indicates the wave tail of the X-ray tube current. B is the reference value of the comparator 36,
C indicates a time delay until detection. Although the output of the integrator 11 is negatively integrated in this embodiment, this is a problem only for the convenience of the circuit, and positive integration is completely acceptable.

〔The invention's effect〕

According to the present invention, it is not necessary to provide a non-detection period in the detection circuit in consideration of a state where the X-ray tube current is small as in the conventional case, and when an abnormal state occurs, regardless of the amount of the X-ray tube current, X-ray emission can be stopped with a delay only for the mAS value of the wave tail. By the way, if the conventional circuit is provided with a non-detection period of 40 mS in consideration of the X-ray tube current of 10 mA, this device emits an extra X-ray of 1000 mA × 0.04 S = 40 mAS at 1000 mA. According to the method, it is possible to stop at the mAS value of the wave tail, that is, the X-ray emission of at most a few mAS, regardless of the X-ray tube current. Moreover, since there is no detection period, it is also effective during high-speed cine pulse imaging.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an X-ray generator according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional device, FIG. 3 is an operation timing diagram for explaining problems of the device shown in FIG. FIG. 4 is a tube current waveform diagram for explaining the principle of the present invention, and FIG. 5 is an operation timing diagram of the constituent device of FIG. 2 ... Switch, 4 ... High voltage transformer, 5a, 5b ... Rectifier, 6 ... Current detector, 7 ... X-ray tube, 24 ... X-ray timer circuit, 30 ... Integrator, 32,33 ... resistor, 36 ... comparator.

Claims (1)

[Claims] 1. An X-ray generator for inputting a voltage supplied from a power source to a high-voltage transformer through a switch to boost the voltage, rectifying the voltage and applying the voltage to an X-ray tube through a high-voltage cable. Means for detecting the tube current, means for delaying the X-ray emission time, and X output by the X-ray tube current detecting means from the time when the X-ray emission end signal is output from the time delay means.
A means for integrating the tube signal and a means for generating a reference signal determined by the stray capacitance of the high voltage cable and the X-ray tube voltage are provided, and the output of the integrating means and the reference signal are compared to each other. An X-ray generator characterized in that the switch is opened when the output exceeds a reference signal.