JPS6216518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray generator for use in computerized tomography equipment and the like to obtain pulsed X-rays.

Recently, a computer has been used to measure the
Computed tomography, which analyzes data related to lines and forms a tomographic image of the subject on a television monitor.
A diagnostic X-ray device called CT is in practical use.

CT is an X-ray tube that rotates around the subject's body axis, and an X-ray detector that faces and rotates integrally with the X-ray tube. This is an X-ray diagnostic device that analyzes radiation absorption data using a computer and forms a tomographic image of the subject on a television monitor.

In this CT, since it is sufficient to acquire data at each predetermined angle, it is not necessarily necessary to irradiate X-rays continuously, and if we consider reducing the exposure dose of the subject, data acquisition is possible. An effective means is to use pulsed X-rays that do not emit X-rays except during certain times.

Therefore, in this type of X-ray generator, the first
A power supply circuit as shown in the figure is known. That is, the neutral point of the Y-connected primary winding _L1 of the high voltage transformer HT connected to the three-phase AC power supply AC is closed via the switching circuit SW by a control signal from the switching control circuit SC. high voltage transformer
A high voltage is generated at the output terminals of the Y-connected and △-connected secondary windings L ₂₁ and L ₂₂ of the HT, and a pair of high-voltage capacitors HC ₁ and HC ₂ are charged via the high-voltage rectifiers HD ₁ and HD ₂ . Start. The charging pressure is the bleeder resistance R ₁₁ , R ₁₂
The voltage is detected by charging voltage detection resistors R ₂₁ and R ₂₂ connected in series with each other, and each is introduced into a comparator CM for comparison with a reference voltage (not shown). When a predetermined voltage is reached, the switching control circuit SC switches the voltage. The neutral point of the primary winding _L1 is opened via the circuit SW to stop charging the high voltage capacitors _HC1 and _HC2 . Thereafter, when the series-connected output voltage of the high-voltage capacitors HC ₁ , HC ₂ is applied to the X-ray tube XT via a high-voltage switching element, for example, a tetrode tube TT ₁ , TT ₂ , the high-voltage capacitors HC ₁ , HC ₂ are charged. The charges are discharged until the tetrode tubes TT ₁ and TT ₂ open.

Note that the grid voltage of the tetrotubes TT ₁ and TT ₂ is controlled by a control circuit (not shown) to open and close them.

At the timing when the discharge of the high-voltage capacitors HC ₁ and HC ₂ ends, that is, when the X-ray exposure ends, the switching control circuit SC closes the switching circuit SW again and starts charging the high-voltage capacitors HC ₁ and HC ₂ . By repeating the above operations, the X-ray tube XT
Pulsed X-rays will be emitted from the

However, in the power supply device with the above configuration,
There is a predetermined delay in the opening operation of the switching circuit SW, and the charging voltage (high voltage rectifier
The charging voltage varies depending on the ripple phase of the output voltage of HD ₁ and HD ₂ , and the X
The above-mentioned CT for determining the radiation absorption rate has the disadvantage that highly reliable X-ray absorption data cannot be obtained.

That is, the high-voltage capacitors HC ₁ and HC ₂ are charged with a charging voltage including ripples as shown in FIG. 2A, and X-rays are irradiated, that is, the tetrode tube is
When TT ₁ and TT ₂ are opened and closed, the switching control circuit SC sends information to the switching circuit SW from immediately after the time t ₁ from immediately after the end of X-ray exposure until the predetermined charging pressure is reached, as shown in Figure 2C. A release signal is sent. However, since the switching circuit SW that receives the opening signal has a predetermined delay time t ₂ (constant) in the opening operation, the delay time t is added to the pulse width t ₁ of the closing signal as shown in FIG. 2D. It will open and close for the time t ₁ + t ₂ , which is the sum of ₂ . Therefore, the high-voltage capacitors HC ₁ and HC ₂ are charged with an extra charge for the delay time t ₂ , and the time band of the delay time t ₂ is determined by the corresponding ripple phase of the charging voltage. Therefore, as shown in FIG. 2E, the integral amount of charged charge is different, causing variations in charging pressure.

The present invention has been made in view of the above circumstances, and includes an X-ray generator for generating pulsed X-rays by charging and discharging a high-voltage capacitor, in which the voltage charged to the high-voltage capacitor is
It is an object of the present invention to provide an X-ray generator for obtaining pulsed X-rays that is configured so as not to cause variations due to the delayed operation of a charging control switching element when charging is stopped.

An embodiment of the structure of the present invention will be described below with reference to the drawings. Note that the same parts as in FIG. 1 are given the same reference numerals and the explanation will be simplified.

In Fig. 3, PC is a ripple phase detection circuit, and ht is a three-phase transformer with a similar configuration to the three-phase high voltage transformer HT (however, the secondary side is low voltage), with Y-connected primary windings l ₁ , Y and △-connected primary windings. The secondary windings _L21 and _L22 are each connected to a three _- phase rectifier _.
Connected to d ₁ and d ₂ respectively. Rectifier d ₁ , d ₂
The respective positive output terminals of are connected to the negative input terminals of comparator amplifiers AP ₁ and AP ₂ via capacitors C ₁ and C ₂ . The positive input terminals of the amplifiers AP ₁ and AP ₂ are grounded, and the input voltage is compared and amplified. The output terminals of the comparator amplifiers AP ₁ and AP ₂ are connected to the first and second input terminals of the NAND gate NG via inverters IN ₀₁ and IN ₀₂ , respectively, and diodes D ₀₁ and D ₀₂ are connected between the ground and the inverter. connected in each direction. The output terminal of the NAND gate NG is connected to the trigger input terminal of a mono multivibrator MM ₁ for phase adjustment. The mono multivibrator MM ₁ uses an external variable resistor to
The output pulse width (the ripple phase of the charging voltage at the start of charging) can be adjusted as appropriate. The output terminal of the mono-multivibrator _MM1 is connected to the set input terminal of a latch RS type flip-flop FF via a differential circuit for detecting a falling edge, which is composed of a capacitor _C3 and a resistor _R1 .

The Q output terminal of the flip-flop FF is the first NOR gate of the switching control circuit SC, which will be described later.
Connected to the second input terminal of NR ₁ .

CM is a comparator, AP ₇ is a comparison operational amplifier, and its inverting and non-inverting input terminals are connected to the output terminal of the summing operational amplifier AP ₆ and the reference voltage (+Es ₂ ) source (the high-voltage capacitor HC ₁ , a voltage corresponding to the charging setting voltage of HC ₂ ) are connected respectively. The output terminal of the amplifier AP ₇ is connected to the reset input terminal of the flip-flop FF, and also to the trigger input of the monomultivibrator MM ₂ via the differentiating circuit for detecting a falling edge consisting of a capacitor C ₆ and _a resistor R ₁₀ and an inverter IN 04. connected to each terminal,
Furthermore, it is connected to the second input terminal of the first AND gate _NR1 .

SC is a switching control circuit, NR ₁ NR ₂ are first and second AND gates, and the fourth input terminal of the first AND gate NR ₁ receives a charging command signal associated with pulsed X-ray irradiation. It is supplied from a signal source not shown. This charging command signal rises at the same time as the falling edge of the X-ray exposure pulse and indicates the end of charging (amplifier AP ₇
This is a pulse signal that falls at the same time as the signal is reversed (from positive to negative). In CT, for example, a photoelectric rotary encoder connected to a rotating mount (a mount for rotating an X-ray tube and an The pulses derived at each time are used as trigger signals to emit X-rays for a predetermined pulse width to obtain pulsed X-rays. Fall of this X-ray exposure pulse (end of exposure)
The charging command signal is generated from the charging command signal. Furthermore, the output terminal of the mono multivibrator MM ₂ is connected to the first input terminal of the second AND gate. The third input terminal of the first AND gate NR ₁ , the second input terminal of the second AND gate NR ₂
The input terminal of is connected to the Q output terminal of a pulse generator PG consisting of an unstable multivibrator, which derives an output pulse with a repetition period of, for example, 20 kHz. First and second AND gates NR ₁ , NR ₂
Each output terminal is connected to NPN via resistor _R2 and _R4 separately.
to the bases of type transistors TR ₁ and TR ₃ , and separately through inverters IN ₂ and IN ₃ and resistors R ₃ and R ₅ .
They are connected to the bases of NPN transistors TR ₂ and TR ₄ , respectively. The collectors of the transistors TR ₁ and TR ₃ are connected to the DC drive power supply +Vcc, and the emitters of the transistors TR 1 and TR 3 are connected to the primary windings of the pulse transformers PT ₁ and PT ₂ via the capacitors C ₄ and C ₅ , respectively.
They are connected to the collectors of transistors TR ₂ and TR ₄ , respectively. The emitters of transistors TR ₂ and TR ₄ are both grounded. pulse transformer
The output terminals of the secondary windings PT ₁ and PT ₂ are connected between the cathode gate terminals of the first and second thyristors SCR ₁ and SCR ₂ of the switching circuit SW shown in FIG. Switching circuit SW in Figure 1
is a three-phase rectifier D ₀ to which the isolated neutral terminal of the primary winding L ₁ of the high-voltage transformer HT is connected,
A first thyristor SCR ₁ for neutral point closing is connected in the forward direction between the output terminals of this rectifier D ₀ , and is connected in parallel to this first thyristor SCR ₁ in the forward direction via a diode D ₀ . a second thyristor SCR ₂ for opening the neutral point, and this second thyristor
It consists of a resonance inductance l ₀ and a capacitance C ₀ connected in parallel to SCR ₂ .

Next, the operation of the above configuration will be explained with reference to FIG. 4. That is, in FIG. 1, a three-phase AC power supply 3φAC is supplied to the Y-connected primary winding L ₁ of the high-voltage transformer HT, and the output terminals of the Y-connected and △-connected secondary windings L ₂₁ and L ₂₂ are, for example, A high voltage of 120kVP is generated. This high voltage is a high voltage rectifier
Rectified by HD ₁ and HD ₂ , high voltage capacitor HC ₁ ,
Each is charged to HC ₂ . The output voltages of the rectifiers HD ₁ and HD ₂ each include ripples (6 ripples per cycle) with peaks every π/3,
The ripples of the output waveforms of the other side have a phase shift of π/6 from each other. Therefore the positive terminal of capacitor HC ₁ ,
The voltage waveform between the negative terminals of HC ₂ includes the same number of ripples as the ripples (12 ripples at every π/6 in one cycle). The output voltage between the positive and negative terminals _of both capacitors HC ₁ and _{HC 2 is} transferred to
It will be applied to the wire tube XT. On the other hand, the output voltage of both capacitors HC ₁ and HC ₂ is determined by the bleeder resistance.
Charge voltage detection resistor connected via R ₁₁ and R ₁₂
The charging pressure is detected by R ₂₁ and R ₂₂ respectively,
A signal is sent to the comparator CM, which will be described later. The tetrode tubes TT ₁ , TT ₂ are normally connected to the first grid with a suitable negative voltage -Eg ₂ for cut-off and also to the second grid.
An appropriate voltage +Eg ₂ is applied to each grid, and the voltage between the cathode and the first grid is controlled to zero or a voltage similar to that by a control signal from an X-ray exposure control circuit (not shown) so that conduction occurs. It's getting old. The filament of the X-ray tube XT is supplied with an appropriately controlled filament heating current If from a filament heating control circuit (not shown).

On the other hand, the Y-connected primary winding L ₁ of the high voltage transformer HT
Since the neutral points of the two are separated from each other, the opening and closing of the neutral points is controlled by a switching circuit SW for opening and closing the neutral points. Therefore, by controlling the opening and closing of the primary side circuit of the high voltage transformer HT, the charging operation of the high voltage capacitors HC ₁ and HC ₂ is controlled as a result.
In other words, the switching circuit SW for opening and closing the neutral point
closes the neutral point by firing the first thyristor SCR ₁ and by firing the second thyristor SCR ₂ causes a resonant action due to the inductance l ₀ and the capacitance C ₀ . , a reverse bias voltage is instantaneously applied to the thyristors SCR ₁ and SCR ₂ to extinguish the arc, thereby opening the neutral point. The ignition control gate terminals of the thyristors SCR ₁ and SCR ₂ are appropriately supplied from a switching control circuit SC, which will be described later, via pulse transformers PT ₁ and PT ₂ .

In Figure 3, the three-phase AC is the high voltage transformer.
The voltage is stepped down appropriately by a three-phase transformer ht with a configuration similar to that of HT (however, the secondary side is low voltage), and a ripple voltage waveform similar to the output voltage waveform of the high voltage rectifiers HD ₁ and HD ₂ is generated by three-phase rectifiers d ₁ and d ₂ . A voltage waveform output including . The DC component of this voltage waveform is cut off by capacitors C ₁ and C ₂ , and the voltage waveform becomes a ripple waveform only (Figure 4 <a> shows the output waveform via capacitor C ₁ ). ₁ , it is compared and amplified with the ground potential at AP ₂ . The comparison operational amplifiers AP ₁ and AP ₂ cause the amplifier to close only when the voltage drops below the ground voltage, that is, near zero phase.
The output of AP ₁ and AP ₂ is changed from positive to negative diode D ₀₁ ,
is inverted via D ₀₂ , resulting in a pulse voltage being derived. (Figure 4 <c> shows the output of the amplifier AP ₁ and <d> shows the output of the amplifier AP ₂ shifted by π/6.)
The outputs of both amplifiers AP ₁ and AP ₂ are connected to inverters IN ₀₁ and
IN ₀₂ is supplied to mono multivibrator MM ₁ via NAND gate NG. Therefore, a pulse having a repetition period of π/6 (the pulse shown in FIG. 4 <d>) is introduced into the mono-multivibrator MM ₁ , and a pulse having an appropriate pulse width is derived every time a pulse is introduced. This pulse is differentiated by a capacitor C ₃ and a resistor R ₁ , and in synchronization with its trailing edge, an RS type flip-flop FF for latch is applied.
Give a set pulse to.

On the other hand, one of the output voltages S ₁ and S ₂ of the charge voltage detection resistors R ₂₁ and R ₂₂ is connected to the inverter operational amplifier AP ₅
The positive and negative values are inverted by the summing operational amplifier AP ₆ .
will be added at This addition output (voltage corresponding to the voltage applied to the X-ray tube XT) is connected to the reference voltage + _{Es 2 (} both high voltage capacitors
When the voltage reaches _{the reference voltage + Es 2 or} less, the output of _{the amplifier AP 7 is} reversed from positive to negative, the reset state of the flip-flop FF is released, and at the same time the AND gate NR is Open the first gate of ₁ . Therefore, flip-flop
FF is then set by the ripple zero-phase synchronization pulse (Fig. 4 <d>) introduced above,
Open the second gate of ANDGATE NR ₁ . This allows the output pulse from the pulse generator PG to pass through the AND gate NR ₁ to the NPN gate via the base resistor R ₂ .
At the base of type transistor TR ₁ , there is also an inverter
IN ₂ is alternately applied to the base of transistor TR ₂ via base resistor R ₃ . transistor
When TR ₁ conducts, transistor TR ₁ (collector to emitter) to capacitor C ₄ to pulse transformer
Current flows between the primary coil of PT ₁ and ground, and conversely, when transistor TR ₄ conducts, current flows between capacitor C ₅ - transistor TR ₃ (collector - emitter) - ground and the primary coil of pulse transformer PT ₂ . It should be noted that the purpose of alternately sending the phase-inverted pulses is to prevent the signal from being adversely affected by single excitation of the transformer _PT1 . ) This makes the pulse transformer
A pulse is derived from PT ₁ and supplied to the gate of thyristor SCR ₁ of the switching circuit SW mentioned above, which fires and switches the high _voltage transformer HT.
The neutral point of the primary winding L ₁ is closed, and as a result charging of the high voltage capacitors HC ₁ and HC ₂ begins.

When charging starts, charging pressure detection resistor R ₂₁ ,
The signal level obtained through R ₂₂ gradually increases and then the output of the amplifier AP ₆ (charging pressure level)
When reaches the reference voltage +Es ₂ , the output of amplifier AP ₇ is inverted from negative to positive, which resets flip-flop FF and closes the gate of AND gate NR ₁ to stop supplying pulses to transistors TR ₁ and TR ₂ . do. (Fig. 4 <e> shows the output of the amplifier AP ₇ ; <f> shows the output of the AND gate NR _1. ) At the same time, trigger the monomultivibrator MM ₂ via the capacitor C ₆ and the resistor R ₁₀ , AND gate NR ₂ gate for a predetermined time (Fig. 4 <g>
MonoMulti MM ₂ output pulse width shown in Figure 2). Therefore, the output pulse of the pulse generator PG passes through the AND gate NR ₂ for the predetermined time to the base of the transistor TR ₃ via the base resistor R ₄ ,
The pulses are supplied to the base of the transistor TR ₄ via the inverter IN ₃ and the base resistor R ₅ , and the pulses are derived from the pulse transformer PT ₂ . (Figure 4<
h> indicates the output of AND gate NR ₂ ). As a result, the thyristor of the switching circuit SW
igniting SCR ₂ and opening the neutral point of the primary winding L ₁ of the high voltage transformer HT, resulting in the high voltage capacitor HC ₁ ,
Stop charging HC ₂ . At this time, since there is a predetermined operation delay time "t ₂ " before the thyristor SCR ₂ actually turns off and charging completely stops, the charging time t ₁ of the high voltage capacitors HC ₁ and HC ₂ is shortened.
is the charging output (negative level) period ( _4th
t ₁ which is longer by the delay time “t ₂ ” than the illustrated <e>)
+t ₂ (fourth diagram <i>). however,
Since the charging start timing is at the predetermined phase (peak or zero phase) of the ripple, the integrated amount of charge charged to the high voltage capacitors HC ₁ and HC ₂ during the delay time "t ₂ " is constant. (The shaded area in <j> in the fourth diagram is the charging voltage.) Therefore, if there are no fluctuations in voltage and phase, the voltage that is repeatedly charged under the same set voltage will be stable without variation.

As described above, according to the present invention, a high voltage pulse voltage obtained by charging and discharging a high voltage capacitor provided on the secondary side of a high voltage transformer is applied to an X-ray tube to obtain pulsed X-rays. In the X-ray generator, since the high-voltage capacitor can be charged from a predetermined position of the ripple of the charging voltage, it is possible to prevent variations in the charging voltage caused by a delay in the opening operation of the switching circuit for charging control.
In CT, the reliability of X-ray absorption data can be greatly improved.

Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, ripple waveforms of both the high voltage rectifiers HD ₁ and HD ₂ having a phase shift of π/6 from each other are obtained and each is extracted. and π/6
We tried to obtain a pulse synchronized with a predetermined phase for each phase, but if we obtain a ripple waveform for only one of them, the π/
It is also possible to obtain pulses synchronized with every 3 predetermined phases. In this case, the charging start timing must wait at most π/3 (π/6 in the above embodiment) after the charging command is issued, but at least
It has been confirmed that there are virtually no major problems with CT. Of course, other modifications may be made as appropriate without changing the gist.

[Brief explanation of the drawing]

Figure 1 is an electrical circuit diagram showing an example of a conventional X-ray generator for obtaining pulsed X-rays, and Figure 2 is an electrical circuit diagram of an example of a conventional
FIG. 3 is an electric circuit diagram showing the configuration of an embodiment of the main part of the X-ray generator for obtaining pulsed X-rays according to the present invention, and FIG. 4 is a signal waveform diagram for explaining the operation in the figure. 4 is a signal waveform diagram for explaining the operation of FIG. 3. FIG. SW...Switching circuit, PC...Ripple phase detection circuit, SC...Switching control circuit, HT
...High voltage transformer, HD ₁ , HD ₂ ...High voltage rectifier,
CH ₁ , CH ₂ ... High voltage capacitor, R ₂₁ , R ₂₂ ... Charging voltage detection resistor, ht ... Three-phase transformer, d ₁ , d ₂
... Rectifier, C ₁ to C ₅ ... Capacitor, AP ₁ to _{AP 7}
...Operation amplifier, NG...NAND gate, NR ₁ ,
NR ₂ ...and gate, MM ₁ , MM ₂ ... mono multivibrator, FF ... flip-flop,
TR ₁ to _{TR 4} ...transistor, PT ₁ to _{PT 2} ...pulse transformer, PG...pulse generator.

Claims (1)

[Claims] 1. A three-phase high-voltage transformer, a high-voltage capacitor to which a DC voltage containing ripples that has been boosted and rectified by the three-phase high-voltage transformer is applied, and a matching signal is generated when the charging voltage of this high-voltage capacitor is detected and reaches a reference voltage. a switching circuit that opens and closes a connection circuit between the high-voltage transformer and the AC power supply, and a first circuit that obtains a voltage waveform similar to the ripple-containing DC voltage charged in the high-voltage capacitor. , a second circuit that extracts and amplifies only the ripple portion of the output waveform of the first circuit, and a phase detection circuit that derives a pulse signal synchronized with a predetermined phase of the ripple amplified by the second circuit. and a switching control circuit for deriving a closing signal from the AND of the pulse signal and the charging command signal for the switching circuit, and deriving an opening signal from the coincidence signal of the comparator. Line generator.