JP4127728B2 - Pulse X-ray device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diagnostic X-ray apparatus, and more particularly to a pulse X-ray apparatus that generates pulse X-rays using an X-ray tube having a grid as a control electrode.
[0002]
[Prior art]
As a conventional pulse X-ray apparatus, for example, there is a pulse X-ray apparatus (Japanese Patent Application No. 8-254082) by the present applicant. FIG. 6 is a circuit diagram showing the configuration of this conventional example.
[0003]
In FIG. 6, a pulse X-ray apparatus 101 includes a commercial AC power source 3, a rectifying / smoothing circuit (AC / DC) 5 that rectifies and smoothes the commercial AC power source 3 and outputs a DC voltage, and an inverter circuit that converts the DC voltage into an AC voltage. (DC / AC) 7, a high voltage transformer 9 that converts an alternating voltage into a predetermined high voltage, a high voltage rectifier 11 that rectifies the alternating high voltage, an anode A, a cathode K, and a grid G. 13. Capacitor 15 connected between the grid and cathode of the X-ray tube, series capacitors 17 and 19 connected between the grid and anode of the X-ray tube 13, and the anode between the X-rays on the grid side of the X-ray tube 13 A diode 21 having cathodes connected to the cathode side and bleeder resistors 23, 25, and 27 are provided.
[0004]
The AC voltage generated by the operation of the inverter circuit 7 is boosted by the high voltage transformer 9, rectified to DC by the high voltage rectifier 11, smoothed by the core-to-ground capacitances 17 and 19 of the high voltage cable, and X-rays Applied to the tube 13. At this time, since the diode 21 is forward-biased, the grid voltage of the X-ray tube 13 (voltage of the grid G with respect to the cathode K of the X-ray tube, hereinafter the same) is almost zero, and no current flows through the X-ray tube 13. Flow X-rays are irradiated.
[0005]
Next, when the operation of the inverter circuit 7 is stopped, the secondary voltage of the high voltage transformer 9 becomes zero, so that the charges of the capacitor 17 and the capacitor 19 are discharged through the X-ray tube 13. At this time, since the diode 21 is reverse-biased, the grid voltage of the X-ray tube 13 of the capacitor 15 which is the capacitance between the grid and the cathode of the minus extra high voltage cable becomes negative due to the discharge current of the capacitors 17 and 19. Charged in the direction. When the grid voltage of the X-ray tube 13 reaches the cut-off voltage, no current flows between the anode and the cathode of the X-ray tube, and X-ray irradiation stops.
[0006]
In this way, the grid voltage of the X-ray tube 13 changes between zero and the cut-off voltage simply by starting and stopping the inverter circuit 7, and the current of the X-ray tube 13 can be turned on / off. As a result, a pulse current flows through the X-ray tube 13, and pulse X-rays are emitted from the pulse current.
[0007]
In order for this circuit to function, the capacitor 19 and the capacitor 15 must be connected in series, and the connection point of the two capacitors must be connected to the grid of the X-ray tube 13. When the line capacitance of the high voltage cable is used as the capacitors 19 and 15, the cross section of the high voltage cable used on the negative electrode side of the X-ray tube is one core wire 41C as the cathode electrode wiring as shown in FIG. The coaxial conductor 43 that wraps around the core wire is configured to be a grid electrode wiring. In FIG. 3, the remaining two core wires 41 </ b> S and 41 </ b> L are used for filament wiring (not shown) of the X-ray tube 13.
[0008]
[Problems to be solved by the invention]
By the way, it is desirable that the rise time of the voltage applied to the X-ray tube (the voltage between the anode and the cathode, also called the tube voltage) is as short as possible. This is because harmful soft X-rays are generated by low-energy electrons corresponding to a low tube voltage during the rise of the tube voltage. This soft X-ray has low permeability, is almost absorbed by the human body, and does not contribute to X-ray imaging.
[0009]
However, in the conventional pulse X-ray apparatus, if the rise time of the tube voltage is shortened, an overshoot is likely to occur in the tube voltage. If there is an overshoot in the tube voltage, the diode 21 is temporarily reverse-biased when the overshooted tube voltage recovers to a steady value, and the discharge current of the capacitors 17 and 19 causes the capacitor 15 to pass through the X-ray tube 13. Since the grid voltage is charged in the negative direction, the current flowing through the X-ray tube 13 is reduced, resulting in a lack of pulse X-ray output.
[0010]
In view of the above problems, an object of the present invention is to provide a pulse X-ray apparatus capable of obtaining a stable pulse X-ray output without being affected by the grid bias even if there is an overshoot at the rise of the X-ray tube voltage. Is to provide.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an X-ray tube having an anode, a cathode and at least one grid electrode for exposing X-rays, a high-voltage transformer for generating a high voltage, and the high-voltage transformer. An excitation circuit that excites the output voltage, a high-voltage rectifier circuit that rectifies the output voltage of the high-voltage transformer and supplies a DC high voltage between the anode and cathode of the X-ray tube, and a connection between the grid and cathode of the X-ray tube First capacitor, at least one second capacitor connected between the anode and grid of the X-ray tube, the anode as the grid of the X-ray tube, and the cathode as the cathode of the X-ray tube A connected diode, a grid-on circuit for receiving an external signal between a grid and a cathode of the X-ray tube, and an operation timing of the excitation circuit and the grid-on circuit; A timing circuit for instructing the timing, and the timing circuit is configured so that the timing at which the grid-on circuit establishes a conductive state between the grid and the cathode of the X-ray tube is the same as or delayed from the time when the excitation circuit starts operating. And the timing at which the grid-on circuit is in a non-conducting state between the grid and cathode of the X-ray tube is controlled at the same time as or before the circuit that excites the high-voltage transformer stops operating. It is characterized by this.
[0012]
(Function)
According to the present invention having the above configuration, when an overshoot occurs in the X-ray tube voltage, the grid bias voltage is reduced by clamping the negative voltage to be generated in the grid of the X-ray tube by the grid-on circuit. It is possible to stabilize and prevent loss of pulse X-ray output.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block circuit diagram showing the overall configuration of an embodiment of the present invention.
In FIG. 1, a pulse X-ray apparatus 1 includes a commercial AC power source 3, a rectifying / smoothing circuit (AC / DC) 5 that rectifies and smoothes the commercial AC power source 3 and outputs a DC voltage, and an inverter circuit that converts the DC voltage into an AC voltage. (DC / AC) 7, a high voltage transformer 9 that converts an alternating voltage into a predetermined high voltage, a high voltage rectifier 11 that rectifies the alternating high voltage, an anode (A), a cathode (K), and a grid (G). A tripolar X-ray tube 13, a capacitor 15 connected between the grid and cathode of the X-ray tube, series capacitors 17 and 19 connected between the grid and anode of the X-ray tube 13, and the grid side of the X-ray tube 13 A diode 21, a bleeder resistor 25 and 27, a timing circuit 31, and a grid-on circuit 33, each having an anode connected to the cathode side between the X-rays, is provided.
[0014]
First, the basic operation of the present invention will be described with reference to FIG. The basic operation is the same as that of Japanese Patent Application No. 8-254082, which is a known example shown in FIG. 6, and the same constituent elements are given the same reference numerals.
[0015]
The alternating current obtained from the commercial alternating current power supply 3 is converted into direct current by an AC / DC converter (rectifying and smoothing circuit) 5 and supplied to an inverter circuit 7 which is a DC / AC conversion circuit. The alternating current (high frequency) voltage generated by the operation of the inverter circuit 7 is boosted by the high voltage transformer 9, rectified to direct current by the high voltage rectifier 11, and then smoothed by the core-ground capacitances 17 and 19 of the high voltage cable. And applied to the X-ray tube 13. At this time, since the diode 21 is forward-biased, the grid voltage of the X-ray tube 13 (voltage of the grid G with respect to the cathode K of the X-ray tube, hereinafter the same) is almost zero, and no current flows through the X-ray tube 13. Flow X-rays are irradiated.
[0016]
Next, when the operation of the inverter circuit 7 is stopped, the secondary voltage of the high voltage transformer 9 becomes zero, so that the charges of the capacitor 17 and the capacitor 19 are discharged through the X-ray tube 13. At this time, since the diode 21 is reverse-biased, the grid voltage of the X-ray tube 13 of the capacitor 15 which is the capacitance between the grid and the cathode of the minus extra high voltage cable becomes negative due to the discharge current of the capacitors 17 and 19. Charged in the direction. When the grid voltage of the X-ray tube 13 reaches the cut-off voltage, no current flows between the anode and the cathode of the X-ray tube, and X-ray irradiation stops.
[0017]
In this way, the grid voltage of the X-ray tube 13 changes between zero and the cut-off voltage simply by starting and stopping the inverter circuit 7, and the current of the X-ray tube 13 can be turned on / off. As a result, a pulse current flows through the X-ray tube 13, and pulse X-rays are emitted from the pulse current.
[0018]
In the present invention, in order to solve the problems of the conventional circuit, a grid-on circuit 33 that receives an external signal between the grid and the cathode of the X-ray tube 13 and makes it conductive, and an inverter circuit 7 that excites the high-voltage transformer 9. And a timing circuit 31 for instructing the operation timing of the grid-on circuit 33. FIG. 2 is a detailed circuit diagram illustrating a configuration example of the grid-on circuit.
[0019]
In FIG. 2, a grid-on circuit 33 includes a DC power supply 131, a rectangular wave generating circuit 132 such as an astable multivibrator, a transistor 136, an insulating pulse transformer 139 having a withstand voltage equal to or higher than 1/2 of the X-ray tube voltage, Diodes 140 and 141, a choke coil 142, a high breakdown voltage transistor 144, a Zener diode 145, resistors 134, 135, 138, 143, and 146, and a capacitor 137 are provided.
[0020]
Hereinafter, the operation of the grid-on circuit of FIG. 2 will be described. The DC power supply 131 supplies power to the driving transistor 136 of the pulse transformer 139. The output of the rectangular wave oscillator 132 is connected to one input of the AND gate 133. The grid on signal b from the timing circuit 31 is connected to the other input of the AND gate 133.
[0021]
When the grid on signal b becomes “H”, the transistor 136 is repeatedly turned on / off at the output frequency of the rectangular wave oscillator 132, and an intermittent current flows through the primary winding of the pulse transformer 139. The AC voltage generated in the secondary winding of the pulse transformer by exciting the pulse transformer 139 is rectified by the diodes 140 and 141 to turn on the transistor 144. As a result, the grid-on circuit dc becomes conductive.
[0022]
Note that a snubber circuit including a capacitor 137 and a resistor 138 arranged in parallel between the collector and emitter of the transistor 136 suppresses the whisker voltage during reverse recovery of the transistor 136, and between the collector and emitter of the transistor 144. The zener diode 145 connected to the capacitor protects the transistor 144 from an excessive collector voltage.
[0023]
Next, the overall operation of the first embodiment will be described with reference to the time charts of FIGS.
Time t1: The inverter operation signal a for operating the inverter circuit 7 is output from the timing circuit 31, and the inverter circuit 7 starts its operation. The high voltage transformer 9 is excited by the alternating current generated by the inverter circuit 7, and the high voltage generated on the secondary side thereof is rectified by the high voltage rectifier 11 to charge the capacitors 17 and 19. When the capacitors 17 and 19 are charged, the voltage of the X-ray tube 13 rises, so that the diode 21 is forward biased and X-ray irradiation is started.
[0024]
Time t2: When the X-ray tube voltage rises, the timing circuit 31 outputs a grid-on signal b for operating the grid-on circuit 33. As a result, the grid-on circuit dc becomes conductive. When the X-ray tube voltage recovers from the overshoot to the steady state, the charges of the capacitors 17 and 19 are discharged through the X-ray tube 13, so that the diode 21 is temporarily reverse-biased. Since the gap is in a conductive state, the discharge current of the capacitors 17 and 19 flows between dc of the grid-on circuit 33 and does not charge the capacitor 15. Therefore, the grid voltage of the X-ray tube 13 is kept almost zero, the current of the X-ray tube 13 does not decrease, and a stable X-ray output can be obtained.
[0025]
Time t3: Prior to stopping the X-ray output, the grid on signal b output from the timing circuit 31 to the grid on circuit 33 is turned off. As a result, the grid-on circuit 33d-c becomes non-conductive.
[0026]
Time t4: In order to stop the X-ray output, the inverter operation signal a of the inverter circuit 7 output from the timing circuit 31 is turned off. As a result, the electric charges of the capacitor 17 and the capacitor 19 are discharged through the X-ray tube 13. At this time, the non-conducting state between dc of the grid-on circuit 33 and the reverse bias of the diode 21 cause the discharge current of the capacitor to charge the capacitor 15 and negatively affect the grid of the X-ray tube 13. Is applied. When the grid voltage reaches the cut-off voltage, the discharge of the capacitors 17 and 19 is stopped and the X-ray output is also stopped.
[0027]
Time t5: In order to irradiate the second pulse of X-rays, the timing circuit 31 outputs an inverter operation signal a for operating the inverter circuit 7.
[0028]
Thereafter, by repeating the same operation, a high voltage continues to be applied between the anode and the cathode of the X-ray tube 13, but a pulse current synchronized with the inverter operation signal a flows through the anode of the X-ray tube 13, Pulsed X-rays are emitted from the tube 13. The purpose of turning on the grid on signal b later than the inverter operation signal a is to reduce the load on the grid on circuit 33 after the output of the second pulse.
[0029]
In the second and subsequent pulses, the capacitor 15 is charged up to the cut-off voltage of the X-ray tube 13 before X-ray irradiation. Therefore, in order to irradiate the X-ray with the X-ray tube turned on, the capacitor 15 is charged. Must be discharged. However, by operating the inverter circuit 7, the output current of the high-voltage rectifier 11 can charge the capacitors 17 and 19, and the capacitor 15 can be discharged. Since the grid-on circuit 33 is turned on after the voltage of the capacitor 15 is lowered, the transistor 144 in the grid-on circuit 33 may have a small rating. Moreover, since the electric charge accumulated in the capacitor 15 is regenerated to charge the capacitors 17 and 19, energy waste can be saved.
[0030]
The purpose of turning off the grid-on signal b prior to the inverter operation signal a is for the following two reasons. First, when the X-ray tube 13 is cut off, the charges of the capacitors 17 and 19 are discharged through the X-ray tube 13. At this time, if the grid-on circuit 33 is in a conductive state between dc, the capacitor 15 is not charged and the X-ray tube 13 cannot be cut off.
[0031]
The second reason is that since the tube current of the X-ray tube 13 flows in the grid-on circuit 33, the burden on the transistor 144 increases. Such a problem can be avoided if the operation of the inverter circuit 7 is stopped after the dc of the grid-on circuit 33 is made non-conductive. The signal output timing of the timing circuit 31 takes into account the delay time from when the grid-on signal b is turned off to when the grid-on circuit 33 becomes non-conductive between dc and c. Turn off prior to a.
[0032]
FIG. 5 is a detailed circuit diagram for explaining a modification of the grid-on circuit 33. In the grid-on circuit 33 shown in FIG. 2, the pulse transformer 139 bears the withstand voltage between the timing circuit 31 and the X-ray tube circuit, but it is not easy to create a pulse transformer having a withstand voltage of several tens of kV. The circuit also becomes larger.
[0033]
Therefore, in this modification, the withstand voltage can be easily ensured by transmitting the grid-on signal, which is a control signal from the timing circuit to the grid-on circuit, via the photocoupler. In FIG. 5, a light-emitting diode that is an element on the light source side of a photocoupler is included in the grid-on circuit for convenience. However, the light source-side element is arranged in the timing circuit so that the timing circuit and the grid are arranged. It is obvious that the on-circuit may be connected by an optical transmission medium such as an optical fiber.
[0034]
FIG. 5A is a first modification using a photocoupler. The grid-on circuit 33a receives light from the light-emitting diode 151 and the light-emitting diode 151 that receive a grid-on signal b from a timing circuit 31 (not shown). Insulating gate that is turned on / off depending on the presence / absence of an electromotive force in a light transmission medium 152 such as an optical fiber that transmits light, a light transmission rod 152, a solar cell 153 154 that receives light from the light transmission medium 152, and a solar cell 153 154 A bipolar transistor (IGBT) 155, a Zener diode 145 for protecting the IGBT 155, and a resistor 146 are provided.
[0035]
The operation of the grid-on circuit 33a is as follows. When the grid on signal b is input from the timing circuit 31 (not shown), the light emitting diode 151 emits light, and this light enters the solar cells 153 and 154 through the light transmission medium 152. The solar cells 153 and 154 receive the light from the light transmission medium 152 and generate a photovoltage, and the photovoltages of the solar cells 153 and 154 connected in series cause the IGBT 155 to conduct.
[0036]
When the grid-on signal b disappears, the light-emitting diode 151 is turned off, the electromotive forces of the solar cells 153 and 154 are eliminated, and the IGBT 155 is disabled. In this way, the grid-on circuit 33a of FIG. 5A can exert the same action on the grid of the X-ray tube as the grid-on circuit 33 shown in FIG.
[0037]
Two solar cells 153 and 154 are connected in series. However, if one IGBT can sufficiently turn on the IGBT 155, only one solar cell 153 and 154 may be connected as long as necessary. Good.
[0038]
FIG. 5B shows a second modification using a photocoupler. The grid-on circuit 33 b receives light from the light-emitting diode 151 and the light-emitting diode 151 that receive a grid-on signal b from a timing circuit 31 (not shown). Light transmission medium 152 such as an optical fiber for transmitting light, a light transmission rod, etc., a solar cell 153, 154 that receives light from the light transmission medium 152, and a MOS transistor that is turned on / off depending on the presence or absence of an electromotive force of the solar cells 153, 154 156, a Zener diode 145 for protecting the MOS transistor 156, and a resistor 146.
[0039]
The configuration and operation of the grid-on circuit 33b are the same as those of the grid-on circuit 33a described with reference to FIG. 5A except that a MOS transistor 156 is used instead of the IGBT 155 as a main switching element.
[0040]
【The invention's effect】
As described above, according to the present invention, even if an overshoot occurs in the X-ray tube voltage, the grid voltage of the X-ray tube can be maintained in a conductive state by the grid-on circuit, so that the tube voltage is overshot. Even when the voltage returns to a steady state, stable pulse X-rays can be output without missing pulses.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram illustrating an embodiment of a pulse X-ray apparatus according to the present invention.
FIG. 2 is a detailed circuit diagram of a grid-on circuit 33 used in the embodiment.
FIG. 3 is a cross-sectional view showing the structure of a minus extra high voltage cable used in the present invention.
FIG. 4 is a timing chart for explaining the operation of the embodiment.
FIG. 5 is a detailed circuit diagram illustrating a modification of the grid-on circuit.
FIG. 6 is a block circuit diagram showing a configuration example of a conventional pulse X-ray apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Pulse X-ray apparatus, 3 ... Commercial alternating current power supply, 5 ... Rectification smoothing circuit, 7 ... Inverter circuit, 9 ... High voltage transformer, 11 ... High voltage rectifier, 13 ... Tripolar X-ray tube, 15 ... Negative pole high voltage cable Capacitance between the cathode and the grid, 17 ... Capacitance between the pin and the ground of the plus extra high voltage cable, 19 ... Capacitance between the pin and the earth of the minus extra high voltage cable, 21 ... Diode, 31 ... Timing circuit, 33 ... Grid-on circuit, 131 ... DC power supply, 132 ... Rectangular wave oscillator, 133 ... AND gate, 134, 135 ... Resistor, 136 ... Transistor, 137, 138 ... Snubber circuit, 139 ... Pulse transformer, 140, 141 ... Diode , 142, coil, 143, resistor, 144, transistor, 145, Zener diode, 146, resistor.

Claims (1)

An X-ray tube comprising an anode, a cathode and at least one grid electrode for exposing X-rays;
A high voltage transformer for generating a high voltage;
An excitation circuit for exciting the high voltage transformer;
A high-voltage rectifier circuit that rectifies the output voltage of the high-voltage transformer and supplies a DC high voltage between the anode and cathode of the X-ray tube;
A first capacitor connected between the grid and cathode of the x-ray tube;
At least one second capacitor connected between the anode and grid of the x-ray tube;
A diode having an anode connected to the grid of the X-ray tube and a cathode connected to the cathode of the X-ray tube;
A grid-on circuit that receives an external signal between the grid and the cathode of the X-ray tube and is in a conductive state;
A timing circuit for instructing the operation timing of the excitation circuit and the grid-on circuit;
The timing circuit controls the timing at which the grid-on circuit establishes a conduction state between the grid and the cathode of the X-ray tube at the same time as or after the excitation circuit starts to operate, and the grid-on circuit A pulse X-ray apparatus characterized in that the timing of non-conduction between the grid and cathode of the X-ray tube is controlled at the same time as or before the circuit that excites the high-voltage transformer stops operating.

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