JPH0556637B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an X-ray device such as a CT (computer tomography X-ray device for medical diagnosis), and particularly relates to an inverter type X-ray device suitable for generating pulsed X-rays. .

[Background of the invention]

In medical diagnostic equipment that uses X-rays, such as CT equipment and cine imaging equipment (X-ray cinematography equipment), the period during which each X-ray is generated is as short as a few milliseconds, and moreover, this is generated over several tens of seconds in one second. The process is repeated from 100 times to over 100 times. Therefore, it is necessary to raise a high voltage of 100 kV to 150 kV within 200 μs as the tube voltage applied to the X-ray tube. This kind of so-called pulsed X
Conventionally, rays have been generated using a switching method using a tetrode connected in series with a diode X-ray tube, or a method using a triode X-ray tube that has an anode current opening/closing mechanism in the X-ray tube itself. was used. However, all of these are made for the purpose of switching current on the secondary side of a high voltage transformer, that is, on the high voltage side. For this reason, the grid voltage control circuits of tetrodes and triode X-ray tubes are often placed in insulating oil due to the need to protect against electric shock and ensure voltage resistance. Conventionally, the tanks that housed these devices were large and heavy, so special consideration was required when installing the device.

In this regard, the applicant of the present invention filed a patent application filed in 1983.
A possible method is to use a DC-AC converter (inverter) made of semiconductor switching elements on the primary side of the high-voltage transformer as shown in No. 123736.

This method will be briefly explained using FIG. The voltage E of the DC voltage source 17 is the switching element Q _a ,
It is converted into alternating current by an inverter consisting of Q _b , Q _c , Q _d and diodes D _a , D _b , D _c , D _d , stepped up by a high voltage transformer 6 , and rectified by a high voltage rectifier 7 Afterwards, it is applied to the X-ray tube 9. FIG. 4 shows the operation of the inverter. 2 of Q _a and Q _d or Q _b and Q _c
A DC-AC conversion operation is performed by driving the two pairs of switching elements alternately. According to this method, since the frequency of the voltage applied to the transformer can be arbitrarily increased, it is possible to reduce the magnetic flux density of the transformer core and reduce its volume. Furthermore, since the X-rays can be switched on and off on the low voltage side, there is no need to consider insulation of the switching elements much. However, in this method, the leakage reactance and stray capacitance of the high-voltage transformer 6, and the capacitance of the high-voltage cable 8 are added as circuit elements, so the X-ray tube voltage waveform X _x becomes oscillatory as shown in Figure 4-c. Therefore, it was necessary to increase the circuit time constant by connecting a resistor to absorb this vibration. For this reason, the rise of the tube voltage waveform is delayed, and the above-mentioned pulsed X-rays cannot be obtained. Therefore, this method requires only a relatively long X-ray generation period, which does not require a very high rise speed.
It was only used for line equipment.

[Purpose of the invention]

An object of the present invention is to generate a small and lightweight pulse X-ray that does not cause vibration in the tube voltage waveform even when the primary side of a high-voltage transformer is switched on and off, and that enables high-speed X-ray generation. An object of the present invention is to provide an X-ray device for generating X-rays.

[Summary of the invention]

The present invention provides a rectifier circuit as a voltage adjustment means and a DC-AC converter (inverter) as a switching means on the primary side of a high-voltage transformer, and adjusts the DC voltage input to the inverter to the tube voltage in advance by feedback control of the rectifier circuit. By setting the voltage to a value corresponding to , and then opening and closing the switching elements of the inverter, it is possible to quickly raise the tube voltage. At this time, the vibrations caused in the tube voltage due to the circuit constants are suppressed by the following method.

FIG. 5 is a circuit diagram showing the principle of vibration suppression.
DC power source 17 with electromotive force E and first switch 18
and a circuit element such as coil 1 with an inductance L corresponding to the leakage reactance of the high voltage transformer.
9 and a load 21 (having a conductance G corresponding to the equivalent resistance of the X-ray tube) connected in parallel with a capacitor 20 having a capacitance C corresponding to the capacitance of the high-voltage cable are connected in series.
A second switch 22 is connected in parallel to a load 21 to which the coil 19 and the capacitor 20 are connected in parallel.
It consists of Note that in FIG. 5, the symbol R represents the resistance of the wiring.

In such a circuit configuration, in order to supply power from the DC power source 17 to the load 21, first, the first switch 18 is closed and turned on at time _t0 , as shown in FIG. 6a. Then, in Figure 5, 17→
Current flows through the circuit 18→19→R→(2021)→17, and power supply to the load 21 is started. At this time, the voltage V applied to the load 21 is
It rises as shown by the solid line 23 in FIG.

Therefore, at time _t1 when the voltage V applied to the load 21 becomes equal to a predetermined voltage, for example, the electromotive force E of the DC power source 17, the first switch 18 is opened and turned off as shown in FIG. 6a. , 6th
As shown in Figure b, the second switch 22 is closed and turned on. Also, between the above time t ₀ and t ₁ , the fifth
The current i flowing through the coil 19 in the figure, that is, the inductance L, rises as shown by the solid line 26 in FIG.
It is a larger value than EG. Due to the magnetic energy caused by this current change, the current i now changes from 19→R→(202
It flows through the circuit of 1)→22→19. However, since the first switch 18 is off, the power supply from the DC power supply 17 has stopped, and the load 2
1 is supplied with power only by the magnetic energy possessed by the inductance L, and the current i rapidly decreases as shown by the solid line 27 in FIG. 6d. At this time,
The voltage of the capacitor 20 does not change much because the amount of discharge to the load 21 and the amount of charge of the inductance L due to magnetic energy are approximately equal.

In this state, as shown in Figure 6d, the current i flowing through the inductance L reaches a steady value EG.
At time _t2 , when the second switch 22 becomes equal to , the second switch 22 is opened and turned on as shown in FIG.
8 and turn it on. Then, the current i is the fifth
In the figure again 17 → 18 → 19 → R → (20
21) → Flows through the circuit of 17. At this time, as mentioned above, the voltage across the capacitor 20 does not change much and is approximately equal to E, which is shown by the solid line 25 in FIG. Since the value is EG, the coil 19 with inductance L and capacitance C
Since there is no energy transfer between the capacitor 20 and the capacitor 20, the voltage V applied to the load 21 does not oscillate as shown in FIG. 6c. Therefore, according to the vibration suppression circuit shown in FIG. 5, the time for the voltage V applied to the load 21 to reach the predetermined voltage E at the start of power supply may be delayed, as shown by the solid line 23 in FIG. 6c. At the same time, vibrations in the voltage applied to the load 21 can be suppressed.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The rectifier circuit 1 converts an AC voltage input from a power input terminal 10 into a DC voltage. Rectifier circuit 1
The DC output voltage of reactor 2 and capacitor 3 is
The signal is smoothed by a smoothing circuit formed by , and is input to the inverter 5 . The inverter 5 converts the DC voltage into an AC voltage, and the high voltage transformer 6 boosts the output voltage of the inverter 5 and inputs it to the high voltage rectifier 7. The DC output voltage of the high voltage rectifier 7 is applied to the X-ray tube 9 via the high voltage cable 8.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2. Although a thyristor is used here as a switching element in the rectifier circuit 1, this can be realized by using a reverse blocking type rectifier such as a GTO. Thyristor 1-a, 1-b, 1-c,
1-d, 1-e, and 1-f are synchronized with the power supply by the rectifier drive circuit 12 and set to the phase angle setting voltage.
The preparation signal 14 is controlled to fire when the phase angle according to V〓 is reached, and is generated before X-ray exposure.
Starts operation by. Voltage of capacitor 3
When V _c rises, the difference between the detected voltage V _{c '} of V _c divided by the voltage dividing resistor 4 and the tube voltage setting signal 15 is amplified by the error amplifier 11, and the difference between the setting signal 15 and the detected voltage V _c is amplified by the error amplifier 11. V〓 is controlled so that ′ match. Therefore, the inverter input voltage _Vc can be easily adjusted by simply adjusting the tube voltage setting signal 15.
Even if the input power supply voltage fluctuates, V _c will always remain at the value set at 15 due to these feedback loops. In a pulsed X-ray generator, reproducibility for each pulse is important, and according to the present invention, it is possible to always set a constant value during the rest period of each pulse. The inverter 5 is composed of four transistors Q _a , Q _b , Q _c , Q _d connected in a bridge type, and similarly four diodes D _a , D _b , D _c , D _d . The transistor part is a self-extinguishing element such as a GTO or FET, and any element can be used as long as it has a fast response speed and a large current capacity. Each transistor corresponds to each base signal 13-a, 13-b, 13-c, 1 of the inverter drive circuit 13.
3-d. 13-a and 13-d or 13-b and 13 by the X-ray exposure signal 16
-c are paired, and the inverter drive circuit 13
Since Q _a and Q _d or Q _b and Q _c are paired and alternately conduct, the inverter input DC voltage V _c becomes an AC voltage and is supplied to the high voltage transformer 6 .

At this time, an appropriate stop period is given to 13-c or 13-d. In other words, Δt ₁ after turning on
After the time, turn off the signal for a time of Δt ₂ , and then turn it off again.
Turn on and return to normal operation. Here, if the step-up ratio of the high-voltage transformer is n, Δt ₁ is the tube voltage V _x after the switches Q _a and Q _d (or Q _b and Q _c ) are turned on
Δt ₂ is the time it takes for the inverter output current I _p to decrease and become n times the tube current I _x after Q _{d (} or Q _c ) turns OFF. This is the time it takes to become

When such an operation is performed, the circuit shown in FIG. 1 has the same effect as the vibration suppression method in the vibration suppression circuit shown in FIG. 5 described above. That is, in the circuit elements shown in FIGS. 1 and 5, the leakage reactance of the high voltage transformer 6 in FIG. 1 is the reactance 19 in FIG. 6 winding resistance etc. is resistance R
In addition, the X-ray tube 9 corresponds to the conductance G, the voltage V _c can be replaced with E, and the voltage V _x can be replaced with V.
Also, when Q _a and Q _d are ON, the current I _p is 3
→Q _a →6→Q _d →3, and Q _a and Q _d are the fifth
It plays the role of the first switch 18 in the figure. Here, if Q _d is turned OFF, I _p becomes 6 → D _b → Q _a →
6, D _b and Q _a are connected to the second switch 22
Work as. Similarly, the polarity is reversed and Q _b and Q _c are turned on.
Even if Q _b and Q _c are the first switch 18
Also, Q _b and D _a function as the second switch 22. In this way, by setting Δt ₁ and Δt ₂ in advance, or by detecting V _x and I _p and switching when they reach their respective optimum values, I _p and V _x will generate vibrations due to transient phenomena. It is possible to transition to a steady state without any problems. In other words, the tube voltage waveform V _x rises rapidly as shown in Figure 2,
And it can be made vibration-free. On the other hand, if the method of this embodiment is not used, V _x will have an oscillating waveform as shown by the dotted line in FIG. Furthermore, if a braking resistor is inserted into the circuit, the rise time to reach a predetermined tube voltage becomes longer as shown by the dashed line in FIG. 2, and neither of these can be used as the tube voltage waveform of pulsed X-rays.

〔Effect of the invention〕

According to the present invention, it is possible to generate pulsed X-rays used in applications such as X-ray CT equipment by simply opening and closing the primary side of a high-voltage transformer.
It has a remarkable effect on weight reduction.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 is a circuit diagram of an embodiment of the present invention.
The figure is a time chart of the embodiment, Fig. 3 is a circuit diagram of a conventional example, Fig. 4 is a time chart of Fig. 3, and Fig. 5 is a time chart of the embodiment.
The figure is a circuit diagram explaining the principle of the present invention, and FIG. 6 is a time chart of FIG. 5. 1... Rectifier circuit, 5... Inverter, 6... High voltage transformer, 9... X-ray tube, 11... Error amplifier,
12... Rectifier drive circuit, 13... Inverter drive circuit.

Claims (1)

[Scope of Claims] 1. A pulse that consists of a power conversion means, a high voltage transformer, a high voltage rectifier, and an X-ray tube, and has an X-ray generation period of several ms and a repetition period of several ms to several tens of ms. In an X-ray apparatus for generating X-rays, the power conversion means includes a rectifier circuit that converts alternating current into direct current and has an output voltage adjustment function, a smoothing circuit that smoothes the output voltage of the rectifier circuit, and a smoothing circuit that smoothes the output voltage of the rectifier circuit. a feedback circuit that detects the output voltage and controls the rectifier circuit so that it becomes the tube voltage setting value converted to the primary side of the high-voltage transformer; and a feedback circuit that converts the output voltage of the smoothing circuit into alternating current and simultaneously generates the X-rays. The output voltage of the smoothing circuit is set to a predetermined voltage immediately before the generation of X-rays, and then the inverter is driven. An X-ray device characterized by opening and closing. 2 The inverter includes a first switch for energizing the output voltage of the smoothing circuit connected to the input thereof to the high voltage transformer connected to the output thereof, and a first switch for energizing the high voltage transformer connected to the output thereof, and a first switch for energizing the high voltage transformer connected to the output of the inverter. and a second switch for circulating the current energy generated in the high voltage transformer, and when the first switch is closed, the voltage generated on the secondary side of the high voltage transformer is transferred to the primary side of the high voltage transformer. When the applied predetermined voltage becomes equal to the converted value on the secondary side, the first switch is opened and the second switch is closed at the same time, so that the current flowing through the primary side of the high voltage transformer increases. Claim 1, wherein the first switch is closed at the same time as the second switch is opened when the current becomes equal to the primary side converted value of a predetermined current to be passed through the secondary side. The X-ray device described.