JPH04303598A - X-ray high voltage device - Google Patents

Abstract

PURPOSE:To improve the quality of images without eliminating the trailing edge of waveform of X-ray while eliminating disorder in rising-up of high voltage waveform due to remaining accumulated electric charge so as to ensure smooth tube voltage rising-up, in a combination with a triple pole X-ray tube. CONSTITUTION:In a combination with a triple pole X-ray tube 11, tube voltage is detected by means of high voltage detection resistance 9a-9d and adder 13 to thereby carry out automatic judgment with existence of remaining voltage. Based on the result, the rising-up system of tube voltage is changed over to the first/second system. In the first system, through control of an inverter controller 12, the switching frequency is made high constant for rising-up, and thereafter detection tube voltage is fed back to the switching frequency so as to control the voltage of tube after the detection tube voltage reaches the set voltage read out from memories 20, 21. In the second system, feeding-back is performed to the switching frequency from the start to control the tube voltage. With such a constitution, the quality of images is improved without the railing edges of X-ray waveform.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray high voltage device, and more particularly to an improvement in a tube voltage output control system in an inverter type X-ray high voltage device.

0002

[Prior Art] An inverter-type X-ray high-voltage device first rectifies and smoothes an AC power supply, then switches it at high speed to create an AC, boosts this AC with a transformer, rectifies and smoothes it again, and generates a high voltage. It obtains direct current and supplies it to the X-ray tube. The supplied tube voltage is basically controlled by feedback control, which measures the tube voltage, compares the measured value with a set value, and changes the switching frequency so that the error between them is minimized. .

This inverter type X-ray high voltage device and 3
When combined with a polar X-ray tube, conventionally, after setting the cathode to a potential capable of emitting electrons with respect to the grid of the triode X-ray tube, a high voltage Switching of the device is started and high voltage is applied between the cathode and anode for a predetermined period of time to emit X-rays, and when that time is over, switching is stopped and the high voltage is cut off, after which a certain period of time has elapsed. After that, the bias potential of the cathode is changed to a potential that does not allow electron emission.

0004

[Problems to be Solved by the Invention] However, if the bias potential of the cathode is set to a potential at which electrons cannot be emitted after a period of time after the high voltage is cut off, it is difficult to perform low-dose, high-speed pulsed X-rays using an In fluoroscopy, there is a problem in that the X-ray waveform has a wave tail, which deteriorates the quality of the image.

[0005] In this regard, it is conceivable to turn off the bias voltage between the cathode and the grid at the same time as the inverter type X-ray high voltage device is turned on, and to turn on the bias voltage at the same time as the switching is turned off. Then, the charges accumulated in the stray capacitance of the high-voltage cable are no longer discharged through the triode X-ray tube and remain, disturbing the rise of the next high-voltage waveform.

In view of the above, the present invention eliminates disturbances in the rise of the high-voltage waveform due to residual accumulated charges and ensures a smooth rise of the tube voltage when combined with a triode X-ray tube, while improving the X-ray waveform. An object of the present invention is to provide an improved X-ray high-voltage device that eliminates wave tails and improves image quality.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the X-ray high voltage device according to the present invention automatically determines the combination with a triode X-ray tube, and changes the X-ray tube voltage rise method as follows. Switch to either the first or second. In the first method, after quickly starting up the inverter's switching frequency at a constant high value, it is determined that the detected tube voltage has reached the set tube voltage, and then the detected tube voltage is fed back to the switching frequency to increase the tube voltage. Shift to control. In the second method, the latter feedback control is performed from the beginning, that is, the detected tube voltage is fed back to the switching frequency to control the tube voltage. In combination with a triode X-ray tube, the bias between the grid and cathode is turned on at the same time as the inverter is turned off to prevent electron emission, thereby preventing the generation of wave tails in the X-ray waveform and improving image quality. This can be improved, but this prevents the accumulated charge from discharging through the X-ray tube and disrupts the rise of the next high-voltage waveform. This disturbance in the rise of the high voltage waveform can be prevented and smoothed by automatically determining the combination with the triode X-ray tube and controlling the tube voltage by feeding back the detection tube voltage to the switching frequency from the beginning. It is possible to achieve a rise in tube voltage.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In Figure 1, AC power supply 1
The AC output is rectified by a rectifier 2, smoothed by a smoothing capacitor 3, and converted into a DC output. Then, this DC output is switched by the switching elements 4a to 4d (switching elements 4a, 4d and switching elements 4b, 4c are turned on and off alternately) and converted into an alternating current output, which connects the resonant capacitor 5 and the resonant inductance 6. Then, it is sent to the primary side of the high voltage transformer 7. A high-voltage AC output appears on the secondary side of the high-voltage transformer 7, which is rectified by a rectifier 8, smoothed by a smoothing capacitor 10, and converted to high-voltage DC output. is applied between the grids 32.

The triode X-ray tube 11 includes an anode 31 and a grid 3.
2. It has a cathode (filament) 33, and the cathode 33 is heated by being supplied with current from a heating circuit 34. A bias voltage control circuit 41 is connected between the grid 32 and the cathode 33. This bias voltage control circuit 41 includes a resistor 42 and a bias potential applied to the cathode 33 through this resistor 42.
It is composed of a bias power supply 43 for applying the bias potential, and a switch S5 for turning on/off the application of the bias potential.

The switching operations of the switching elements 4a to 4d are controlled by an inverter control device 12. That is, the high voltage DC voltage applied to the triode X-ray tube 11 is detected by the high voltage detection resistors 9a to 9d and the adder 13, and this is fed back to the switching frequency via the inverter control device 12. The detected tube voltage (output voltage of adder 13) is sent to comparator 14 and also to comparator 27 via switch S4.

[0011] Here, explanation will be given while also referring to the timing chart of FIG. First, the imaging conditions, which are imaging time, tube current, and tube voltage, are set by the imaging time setting device 22, tube current setting device 23, and tube voltage setting device 24, respectively. Then, Vs and Vn are read out from the memories 20 and 21 according to the set tube current value and set tube voltage value.

Next, the X-ray exposure button (not shown) is pressed at time p.
When pressed, the shooting time setting device 2 is pressed as shown in Figure 2A.
2, an X-ray exposure signal that remains High for a set time is generated, and this signal is applied to the V/F converter 18 and the latch circuit 25. As a result, the V/F converter 18 loses its reset input and is brought into operation, and the latch circuit 25 also loses its reset input. Furthermore, this X-ray exposure signal is transmitted to the bias voltage control circuit 41.
When the switch S5 is closed, current flows through the closed loop formed by the bias power supply 43, the resistor 42, and the switch S5, and the cathode 33 is brought to a potential capable of emitting electrons with respect to the grid 32.

When this X-ray exposure signal becomes High, the switch S4 is closed for a short time at time p, and the detection tube voltage at that time is sent to the comparator 27. This comparator 27 has
Tube voltage setter 2 multiplied by 0.75 by multiplier 26
The set tube voltage from 4 is added, and this is compared with the detected tube voltage described above. At this point p, the actual tube voltage is zero, so the comparator 27 produces no output. Also, in the comparator 14, a comparison is made between the detected tube voltage and the set tube voltage from the tube voltage setting device 24.
Similarly, since the actual tube voltage is zero at this point p,
No output is produced from comparator 14. Therefore, OR circuit 2
8 is Low, the switch S1 is on, and the latch circuit 25 remains reset and is not set, so the Q output of the latch circuit 25 remains Low.

When the V/F converter 18 becomes operational, it starts oscillating at a frequency corresponding to the input voltage Vin (see FIGS. 2B and 2C). The output Fo of this V/F converter 18 is sent to a drive circuit 19, and this drive circuit 19 drives the switch element 4 at a frequency corresponding to the output Fo.
A to 4d are driven by switching. Then, a current I1 as shown in FIG. 2D begins to flow through the primary side of the high voltage transformer 7, and the tube voltage gradually rises as shown in FIG. 2E.

In the process of rising the tube voltage, the adder 1
Since the tube voltage obtained from No. 3 is lower than the set tube voltage sent from the tube voltage setting device 24, the output of the comparator 14 remains Low. Therefore, switch S
1 is on, the OP amplifier and resistor R
1 and capacitor C1 remains in an off state. Furthermore, the Q output of the latch circuit 25 remains Low, and in that state, the switch S
2 is off and S3 is on. At this time, the output ΔV of the integrator 16 is zero, and the other input of the adder 17 is Vs read from the memory 21. Therefore, the output of the adder 17, that is, the input voltage Vin of the V/F converter 18, becomes a constant value corresponding to Vs (see FIG. 2B), and the output Fo of the V/F converter 18 is a constant frequency pulse corresponding to Vs. (See FIG. 2C), and the switching of the switching elements 4a to 4d is repeated at a constant frequency.

When the tube voltage reaches the set value, the output of the comparator 14 becomes High, and the output of the OR circuit 28 becomes High. Then, the switch S1 is turned off, the latch circuit 25 is set and its Q output becomes High, the switch S2 is turned on, and the switch S3 is turned off. Therefore, one input of the adder 17 is switched from Vs to Vn, and the other input is given the output ΔV of the integrator 16, which has started operating when the switch S1 is turned off. This Vn and ΔV are added by an adder 17 and become the input Vin of the V/F converter 18.

The output ΔV of the integrator 16 is determined by the error amplifier 15
The output is the integral of the error between the tube voltage from the adder 13 and the set tube voltage value from the tube voltage setter 24, and the difference between the two is zero immediately after the tube voltage reaches the set value. Therefore, the output of the error amplifier 15 is also zero, and the output of the integrator 16 is also zero, so Vin becomes Vn (see FIG. 2B). Therefore, as long as the power supply voltage is constant,
Switching is performed at a frequency determined by the value of Vn, and the tube voltage is supposed to be kept at the set value. However, in reality,
Since the power supply voltage drops due to the impedance of the power supply circuit and wiring, the tube voltage tends to decrease, causing an error between it and the set value. As a result, the output ΔV of the integrator 16 gradually increases, and this ΔV is added to Vn by the adder 17, increasing the switching frequency and increasing the tube voltage. When the tube voltage reaches the set value, the output of the error amplifier 15 becomes zero, and the input of the integrator 16 becomes zero, so that the integration operation is stopped. In this way, feedback control is performed so that the tube voltage becomes equal to the set value.

The memories 20 and 21 store in advance the values of Vs and Vn according to the tube voltage and tube current, as shown in FIGS. 3 and 4. The value of Vn corresponds to the switching frequency necessary to obtain the set tube voltage and tube current, and is uniquely determined by the combination of the tube voltage and tube current. FIG. 4 shows an example of the value of Vn depending on the combination of tube voltage and tube current.

On the other hand, the value of Vs is determined to be larger than the above-mentioned Vn, as shown in FIG. This is because if the value of Vs, which determines the switching frequency, is set to be the same as Vn when the tube voltage has not yet reached the set value during the rise process, not only will the rise to reach the set value be slow, but the set load This is because the time required for the tube voltage to reach the set value may be different depending on the conditions (tube voltage, tube current), which is an inconvenience. For example, when the set value of the tube voltage is the same and the tube current is changed, the rising waveform of the tube voltage becomes as shown in FIG. Therefore, instead of setting the switching frequency at the rise of the tube voltage as Vn, it is set as, for example, Vs as shown in FIG. 3, which has a higher frequency as the tube current decreases. As a result, the lower the tube current, the higher the frequency until the tube voltage reaches the set value at rise, making the rise faster, and the time it takes for the tube voltage to reach the set value even under different load conditions. They can be made almost the same as shown in FIG. In other words, the value of Vs is determined in advance and stored in the memory 20 so that the time required to reach the set value of the tube voltage is the same under each load condition.

These Vn and Vs data are obtained by measuring data at several points using the tube current or tube voltage as a parameter in an actual device, and other data are obtained by interpolation or the like.

[0021] In this way, the two memories 20 and 21
In addition to storing predetermined data in the controller and reading it out using the set values for tube voltage and tube current,
Only a few points of measurement data and a calculation program are stored, and when the tube voltage and tube current are set, a microcomputer is used to calculate the set values for the tube voltage and tube current using the calculation program from the several points of data. It is also possible to adopt a configuration in which Vn and Vs are calculated accordingly.

In this way, X-ray exposure is carried out while feedback control is performed so that the actual tube voltage becomes equal to the set value, and as shown in A in FIG. 2, the set time is reached at time q, and the imaging time ends. The X-ray exposure signal from the setting device 22 is low
Suppose that it becomes Then, the V/F converter 18 and latch circuit 25 are reset, and the oscillation of the V/F converter 18 is stopped. Then, switching of the switching elements 4a to 4d is stopped, so that the rectifier 8 and the smoothing capacitor 10
The AC output that was being supplied to the At this time, the switch S5 of the bias voltage control circuit 41 is turned off at the same time, so that the potential of the cathode 33 is set to a potential at which electrons cannot be emitted with respect to the grid 32. Therefore, by turning on the bias voltage, the triode X-ray tube 11 immediately enters the cut-off state, and the X-ray radiation is immediately cut off.
Wave tails no longer occur in the line waveform, improving image quality.

On the other hand, since the triode X-ray tube 11 immediately enters the cut-off state, the charges accumulated in the stray capacitance of the high voltage cable remain without being discharged through the triode X-ray tube 11. In other words, the tube voltage is E in FIG.
As shown in , it will not fall immediately.

Next, at time r, the photographing time setting device 22 is activated again.
When the X-ray exposure signal from the detector becomes High, the switch S4 is turned on for a short time at this time point r, and the detection tube voltage at this time is taken into the comparator 27. Since the tube voltage at this time point r is still high as shown in E in FIG. 2, it is higher than 75% of the set tube voltage output from the tube voltage setting device 24. As a result, the output of the comparator 27 becomes High and passes through the OR circuit 28 to the switch S1.
is turned off, and the latch circuit 25 is set. At this time, the detected tube voltage is lower than the set tube voltage, so the output of the comparator 14 is Low, but the OR circuit 28
Since the output of the comparator 14 becomes High, the same feedback control as described above is performed when the detected tube voltage reaches the set tube voltage and the output of the comparator 14 becomes High.

That is, one input of the adder 17 is Vn
The output ΔV of the integrator 16, which started operating when the switch S1 was turned off, is given to the other input, and this Vn and ΔV are added by the adder 17, and the V/F converter 18 This is the input Vin. Integrator 1
The output ΔV of 6 is the output of the error amplifier 15, that is, the integral of the error between the detected tube voltage from the adder 13 and the set tube voltage value from the tube voltage setter 24, so this error becomes zero. Feedback control of the switching frequency is performed so that the tube voltage is equal to the set tube voltage.

Therefore, in the second and subsequent X-ray exposures, the residual tube voltage is used to avoid starting up from zero, so the error amplifier 15 and the integrator 1 are
6, and feedback control is performed using the switching frequency Vn, and the tube voltage rises smoothly as shown by E in FIG.

In the above embodiment, the tube voltage at the time when the X-ray exposure signal becomes High is detected, and it is determined whether the tube is combined with the triode X-ray tube 11 or not depending on whether there is residual voltage or not. However, this is automatically determined based on the settings of the switches, etc., and the switch S1 is turned off by the second and subsequent X-ray exposure signals, and the latch circuit 25 is turned off.
It is also possible to set the switch S2 to turn on the switch S3, turn off the switch S3, and perform feedback control using the error amplifier 15, the integrator 16, and the switching frequency Vn.

[0028]

[Effects of the Invention] As described above with respect to the embodiments,
According to the X-ray high voltage device of the present invention, when used in combination with a triode X-ray tube, the X-ray waveform is Image quality can be improved by eliminating wave tails.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a timing chart for explaining operation.

FIG. 3 is a diagram showing an example of how Vs is stored in a memory.

FIG. 4 is a diagram showing an example of how Vn is stored in a memory.

FIG. 5 is a waveform diagram showing an example of the rise of tube voltage.

FIG. 6 is a waveform diagram showing another example of the rise of tube voltage.

[Explanation of symbols]

1 AC power supply 2, 8 Rectifier 3, 10 Smoothing capacitor 4a to 4d Switch element 5 Resonance capacitor 6
Resonant inductance 7
High voltage transformers 9a to 9d High voltage detection resistor 11 Triode X-ray tube 12 Inverter control device 13, 1
7 Adder 14, 27 Comparator 15 Error amplifier 16 Integrator 18 V/F converter 19
Drive circuits 20, 21 Memory 22 Shooting time setter 23
Tube current setter 24 Tube voltage setter 25 Latch circuit 26 Multiplier 28 OR circuit 31 Anode 32 Grid 33 Cathode 34 Heating circuit 41 Bias voltage control circuit 42
resistance

Claims (1)

[Claims] 1. A first rectifying means for converting an AC output from an AC power supply into a DC output, a switching means for switching the DC output and converting it into an AC output of a predetermined frequency, and a step-up voltage of the AC output. a means for converting the boosted AC output into a DC output and outputting it as a tube voltage; a means for detecting the tube voltage; and a value of the detected tube voltage and the set tube voltage. a comparison means for comparing the combination with the triode X-ray tube; and a means for determining the combination with the triode X-ray tube; and a means for determining the combination with the triode When it is determined that the tube voltage has reached the set value, the tube voltage is increased by switching at a predetermined frequency according to each value of the set tube voltage and tube current, and the above-mentioned detection is performed from when it is determined that the tube voltage has reached the set value. Feedback control is performed to change the switching frequency so that the error between the detected tube voltage and the set tube voltage is minimized, and when it is determined that the combination with a triode 1. An X-ray high voltage apparatus comprising: control means for performing feedback control such that an error with a tube voltage is minimized.