JP7134713B2 - X-ray high voltage device and power supply - Google Patents

Description

Embodiments of the present invention relate to X-ray high voltage devices and power supplies.

X-ray CT (Computed Tomography) equipment is equipped with so-called dual energy imaging in which the X-ray tube voltage is rapidly switched between a low voltage (e.g. 80 kV) and a high voltage (e.g. 140 kV) during scanning. There is something configured. According to this type of X-ray CT apparatus, it is possible to visualize the difference in the constituent elements of the subject by acquiring images with X-ray beams having different energy distributions. Images of blood vessels by agents can be separated.

One of the methods of obtaining X-ray beams having such different energy distributions is a method of changing the tube voltage at high speed while the rotating gantry is rotating (hereinafter referred to as high-speed kV switching method). In the high-speed kV switching method, the operation of raising the tube voltage from a low voltage to a high voltage and the operation of lowering the tube voltage from a high voltage to a low voltage are completed within a predetermined time. If it is not completed within the predetermined time, it becomes difficult to obtain an accurate image.

In order to drop the tube voltage from a high voltage to a low voltage at high speed, it is necessary to rapidly discharge the high-voltage capacitor. However, although the inverter supplies AC power to the high voltage generating circuit, it does not contribute to the discharge of the high voltage capacitor. Therefore, the discharge of the high-voltage capacitor cannot be controlled by inverter control, and depends largely on the tube current of the X-ray tube. This means that when the tube current changes, the falling speed of the tube voltage also changes. However, the magnitude of the tube current is determined by the imaging region and the imaging sequence. For this reason, when shooting with a tube current below a predetermined value, the discharge speed of the high-voltage capacitor becomes insufficient, and the tube voltage cannot be lowered within a predetermined time, making it impossible to perform dual energy shooting. .

Japanese Patent Application Laid-Open No. 2001-230098

The problem to be solved by the present invention is to drop the output voltage of the high voltage circuit at high speed.

In order to solve the above-described problems, an X-ray high-voltage apparatus according to an embodiment of the present invention includes: a high-voltage circuit including a plurality of capacitors; A voltage control unit and a discharge control unit that discharges a part of the capacitors of the high voltage circuit in synchronization with the timing at which the output voltage drops.

1 is an overall configuration diagram showing an example of a power supply device according to an embodiment of the present invention; FIG. Explanatory drawing which shows an example of a high voltage generation circuit. (a) is an explanatory diagram showing an example of the falling speed of the tube voltage when the tube current is large, and (b) is an explanatory diagram showing an example of the falling speed of the tube voltage when the tube current is small. FIG. 4 is an explanatory diagram showing an example of operation timings of an inverter and a discharge circuit; The figure which shows the 1st structural example of a discharge circuit. The figure which shows the 2nd structural example of a discharge circuit. (a) is a diagram for explaining the first discharge method when the tube current is large, and (b) is a diagram for explaining the first discharge method when the tube current is small. (a) is a diagram for explaining the second discharge method when the tube current is large, and (b) is a diagram for explaining the second discharge method when the tube current is small. (a) is a diagram for explaining the third discharge method when the tube current is large, and (b) is a diagram for explaining the third discharge method when the tube current is small. The figure which shows the 3rd structural example of a discharge circuit. The figure which shows the 4th structural example of a discharge circuit.

Embodiments of the X-ray high voltage device and the power supply device will be described in detail below with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an example of a power supply device according to one embodiment of the present invention. The power supply device according to the present embodiment may be configured so that the output voltage output from the high voltage circuit to the load is variable. It can be used as a power supply device for applying voltage. In the following description, an example in which the power supply device is the X-ray high voltage device 10 that outputs voltage to be applied to the X-ray tube is shown.

As shown in FIG. 1 , an X-ray high-voltage device 10 as an example of a power supply device has a high-voltage circuit 20 that outputs voltage to an X-ray tube 11 and a processing circuit 30 that controls the high-voltage circuit 20 .

The high voltage circuit 20 has a high voltage generation circuit 21 and a discharge circuit 22 . The high voltage generation circuit 21 has a Cockcroft-Walton circuit (hereinafter referred to as a CW circuit) 21cw composed of a plurality of capacitors and a plurality of diodes.

The discharge circuit 22 has a switch 22sw and is a circuit for discharging a part of the capacitors of the high voltage generation circuit 21 . Some capacitors of the high voltage generation circuit 21 discharged by the discharge circuit 22 are preferably preferentially selected from capacitors located on the AC power input side of the CW circuit 21cw.

The processing circuit 30 has a processor and a memory circuit. The processor of the processing circuit 30 is a processor that reads out and executes a program stored in a memory circuit, thereby executing processing for rapidly lowering the output voltage of the high voltage circuit 20 . The processor of the processing circuit 30 implements an output voltage control function 31 and a discharge control function 32 . Each of these functions is stored in the storage circuit in the form of a program.

The output voltage control function 31 controls the output voltage from the high voltage circuit 20 to the X-ray tube 11 so as to enable dual energy imaging with the first tube voltage (eg −80 kV) and the second tube voltage (−140 kV). is changed between the first tube voltage and the second tube voltage.

The discharge control function 32 discharges some capacitors of the CW circuit 21cw in synchronization with the timing at which the output voltage of the high voltage circuit 20 drops.
Here, the discharge circuit 22 will be described.

FIG. 2 is an explanatory diagram showing an example of the high voltage generation circuit 21. As shown in FIG. A DC voltage (for example, about 500 V) input to the inverter 21i from a DC power supply (not shown) is converted into a high-frequency AC voltage by the inverter 21i, input to the primary winding P1 of the high-voltage transformer TX1, and boosted. A high voltage (eg, about 10 kV) is developed across the secondary winding S1. The output of the secondary winding S1 is input to a Cockcroft-Walton circuit (CW circuit) 21cw composed of a plurality of capacitors and a plurality of diodes. FIG. 2 simply shows an example in which the CW circuit 21cw is composed of six capacitors C1-C6 and six diodes D1-D6.

The output voltage of the CW circuit 21cw is given by multiplying twice the peak-to-peak value of the input voltage by the number of stages. In the example shown in FIG. 2, when the secondary winding S1 outputs −10 kV, the high voltage generating circuit 21 applies an output voltage of −60 kV to the X-ray tube 11. In the example shown in FIG. Therefore, for example, when a four-stage first CW circuit and a three-stage second CW circuit are connected in series to the secondary winding S1 that outputs -10 kV, from the final stage of the first CW circuit, - A high voltage of 80 kV can be taken out as an output voltage, and a high voltage of -60 kV can be taken out as an output voltage from the final stage of the second CW circuit. Therefore, the output voltage control function 31 can easily realize dual energy imaging of −80 kV and −140 kV by appropriately combining the output voltages of the first CW circuit and the second CW circuit.

FIG. 3(a) is an explanatory diagram showing an example of the falling speed of the tube voltage when the tube current is large, and FIG. 3(b) is an explanation showing an example of the falling speed of the tube voltage when the tube current is small. It is a diagram.

In order to raise the tube voltage, which is the output voltage of the high voltage generation circuit 21 of the high voltage circuit 20, from a low voltage to a high voltage, the high voltage capacitor of the CW circuit 21cw of the high voltage generation circuit 21 should be rapidly charged. . Rapid charging of the high-voltage capacitor can be easily realized, for example, by increasing the frequency of the inverter 21i that supplies AC power to the high-voltage generating circuit or by lengthening the ON time of the inverter 21i.

On the other hand, in order to drop the tube voltage from a high voltage to a low voltage at high speed, it is necessary to rapidly discharge the high-voltage capacitor. However, the inverter 21i only supplies AC power to the high voltage generating circuit 21 and does not contribute to the discharge of the capacitor. Therefore, the discharge of the capacitor cannot be controlled by the inverter 21i, and depends largely on the tube current of the X-ray tube 11. FIG. Therefore, when the tube current changes, the falling speed of the tube voltage also changes. For example, when the tube current is high, the discharge speed of the capacitor is fast and the tube voltage falls quickly (see Fig. 3(a)). The falling speed of the voltage also slows down (see FIG. 3(b)).

However, the magnitude of the tube current is determined by the imaging region and the imaging sequence. For this reason, in the case of imaging with a predetermined tube current or less, the discharge speed of the capacitor becomes insufficient, and the tube voltage cannot be lowered within the predetermined time, making it impossible to perform dual energy imaging. . That is, it is extremely difficult to adjust the falling speed of the tube voltage only with the high voltage generation circuit 21 .

Therefore, the power supply device according to this embodiment includes a discharge circuit 22 for discharging the capacitor of the high voltage generation circuit 21 .

FIG. 4 is an explanatory diagram showing an example of operation timings of the inverter 21i and the discharge circuit 22. As shown in FIG. 5 is a diagram showing a first configuration example of the discharge circuit 22. As shown in FIG.

As shown in FIG. 4, when the tube voltage is lowered, that is, when the output voltage of the high voltage generation circuit 21 is lowered, the inverter 21i stops operating. The discharge control function 32 controls the discharge of a part of the capacitors of the high voltage generation circuit 21 by controlling the switch 22sw provided in the discharge circuit 22 at this stop timing. Specifically, the discharge control function 32 discharges some capacitors of the CW circuit 21cw by controlling the switch 22sw of the discharge circuit 22 in synchronization with the timing at which the output voltage of the high voltage generation circuit 21 drops. Let

The discharge circuit 22 according to the first configuration example has at least discharge elements for discharging some of the capacitors selected from the capacitors close to the AC power input side of the CW circuit 21cw. In the following description, as shown in FIG. 5, the discharge circuit 22 has a diode D7, a resistor R1 as a discharge element, a photocoupler U1, and a switch 22sw1, and the first stage on the AC power input side of the CW circuit 21cw , a diode D8, a resistor R2 as a discharge element, a photocoupler U2, and a switch 22sw2, and a second-stage capacitor on the AC power input side of the CW circuit 21cw and a second discharge circuit element for mainly discharging C4. Note that the number of discharge circuit elements may be one, or three or more.

By discharging the capacitor of the high voltage generation circuit 21 by the discharge circuit 22, the output voltage of the high voltage generation circuit 21 can be lowered at a higher speed than when the discharge of the capacitor depends only on the tube current.

Further, when using an image while the output voltage of the high voltage generating circuit 21 is falling, it is preferable that the falling speed is a predetermined value regardless of the tube current. In this case, the discharge control function 32 controls the switches 22sw1 and 22sw2 so that the rate of decrease of the output voltage of the high voltage generation circuit 21 becomes a predetermined value. Specifically, the discharge control function 32 adjusts the output voltage according to the load to which the output voltage is applied, i. Therefore, the rate of decrease of the output voltage is corrected by controlling the switching timing of the switches 22sw1 and 22sw2 to control the discharge of some capacitors so that the rate of decrease of the output voltage is constant regardless of the tube current.

The switches 22sw1 and 22sw2 are controlled by the discharge control function 32 in the ON/OFF timing of the pulses input to the photocouplers U1 and U2, respectively. The discharge current can be controlled by controlling the duty ratio and frequency of the switches 22sw1 and 22sw2.

It should be noted that the capacitors discharged by the discharge circuit 22 may not be all the capacitors forming the CW circuit 21cw, but may be some of the capacitors. This is because, in dual energy photography, it is not necessary to drop the voltage from a high tube voltage (eg -140 kV) to 0V, and it is sufficient to drop the voltage to a low tube voltage (eg -80 kV). This is because there is no need to discharge to Also, some capacitors discharged by the discharge circuit 22 may be preferentially selected from capacitors closer to the AC power input side than the capacitor C6 farther from the AC power input side of the CW circuit 21cw. When discharging a capacitor close to the AC power input side, the potential is lower than that of a capacitor far from the AC power input side. can be used.

FIG. 6 is a diagram showing a second configuration example of the discharge circuit 22. As shown in FIG. As shown in FIG. 6, as the discharge elements of the discharge circuit 22, coils L1 and L2 may be used instead of the resistors R1 and R2. When the coils L1 and L2 are used as discharge elements, the discharge control function 32 controls the frequencies of the currents flowing through the coils L1 and L2 by controlling the switches 22sw1 and 22sw2 to control the impedance of the coils L1 and L2. , and controls discharge of a part of the capacitors of the CW circuit 21cw to control the rate of decrease of the output voltage of the high voltage generation circuit 21 .

When the resistors R1 and R2 are used as the discharge elements (see FIG. 5), the resistors R1 and R2 need to be large and expensive elements because the loss in the discharge elements is large. On the other hand, when the coils L1 and L2 are used as the discharge elements (see FIG. 6), the loss in the discharge elements can be greatly reduced, so the cost of the discharge elements can be reduced.

Since the photocouplers U1 and U2 are switched at a high frequency, the impedances of the coils L1 and L2 are large and the current is limited. By changing the duty ratio of the switches 22sw1 and 22sw2 from this state, the amount of discharge current can be adjusted, and by changing the frequency of the switches 22sw1 and 22sw2, the impedance of the coils L1 and L2 can be changed. Therefore, the amount of discharge current can be adjusted.

Next, a method of discharging some capacitors of the CW circuit 21cw will be described.

FIG. 7A is a diagram for explaining the first discharge method when the tube current is large, and FIG. 7B is a diagram for explaining the first discharge method when the tube current is small.

A first method of discharging some of the capacitors of the CW circuit 21cw is to keep the operating frequencies of the switches 22sw1 and 22sw2 constant and change the duty ratio.

When the tube current is large, the discharge current from the discharge elements (for example, L1 and L2) of the discharge circuit 22 may be small. (See FIG. 7(a)). In this case, only the switch 22sw2 may be operated, or both the switches 22sw1 and 22sw2 may be operated at a low duty ratio.

On the other hand, when the tube current is small, the discharge current from the discharge circuit 22 is preferably large. In this case, the discharge control function 32 should operate both the switches 22sw1 and 22sw2 at a higher duty ratio than when the tube current is small. . At this time, it is preferable to shift the operation phases of the switches 22sw1 and 22sw2 by 180 degrees so as to reduce the ripple of the discharge current (see FIG. 7(b)).

FIG. 8A is a diagram for explaining the second discharge method when the tube current is large, and FIG. 8B is a diagram for explaining the second discharge method when the tube current is small.

A second method of discharging some capacitors of the CW circuit 21cw is to keep the duty ratios of the switches 22sw1 and 22sw2 constant and change the frequency. The constant duty ratio is preferably 50% so as to reduce the ripple of the discharge current.

When the tube current is high, the discharge current from the discharge elements (for example, L1 and L2) of the discharge circuit 22 may be small. Therefore, the discharge control function 32 operates only the switch 22sw1 at a low frequency, and does not operate the switch 22sw2. (See FIG. 8(a)). In this case, only the switch 22sw2 may be operated, or both the switches 22sw1 and 22sw2 may be operated at a low frequency.

On the other hand, when the tube current is small, it is preferable that the discharge circuit 22 discharges a large current. In this case, the discharge control function 32 should operate both the switches 22sw1 and 22sw2 at a higher frequency than when the tube current is small. At this time, it is preferable to shift the operation phases of the switches 22sw1 and 22sw2 by 180 degrees so as to reduce the ripple of the discharge current (see FIG. 8(b)).

FIG. 9A is a diagram for explaining the third discharge method when the tube current is large, and FIG. 9B is a diagram for explaining the third discharge method when the tube current is small.

A third method of discharging some of the capacitors of the CW circuit 21cw is to keep the OFF time constant and change the ON time when the switches 22sw1 and 22sw2 are operated.

When the switches 22sw1 and 22sw2 are OFF, the circuit is in a high impedance state and the voltage applied to the photocouplers U1 and U2 increases. In order to suppress this voltage rise, in the third discharge method, the OFF time is fixed and the ON time is changed to adjust the discharge current.

When the tube current is large, the discharge current from the discharge elements (for example, L1 and L2) of the discharge circuit 22 may be small. , and the switch 22sw2 is not operated (see FIG. 9A). In this case, only the switch 22sw2 may be operated, or both the switches 22sw1 and 22sw2 may be operated with a short ON time.

On the other hand, when the tube current is small, it is preferable that the discharge circuit 22 discharges a large current. 22sw2 should be operated together. At this time, it is preferable to shift the operation phases of the switches 22sw1 and 22sw2 by 180 degrees so as to reduce the ripple of the discharge current (see FIG. 8(b)).

According to the first to third discharge methods described above, the capacitor of the high voltage generation circuit 21 can be discharged by the discharge circuit 22. Therefore, the tube voltage of the X-ray tube 11 can be increased faster than when relying only on the tube current. can be lowered to Further, according to the first to third discharge methods, the drop rate of the X-ray tube voltage can be corrected to a predetermined value regardless of the state of the tube current of the X-ray tube 11. Therefore, the fall of the X-ray tube voltage The waveform is the same regardless of the tube current, and a uniform dual energy image can be obtained in any operation mode.

FIG. 10 is a diagram showing a third configuration example of the discharge circuit 22. As shown in FIG. As shown in FIG. 10, the discharge circuit 22 may use transformers TX2 and TX3 as discharge elements. In this case, the primary sides P2 and P3 of the transformers TX2 and TX3 are connected to the discharge circuit 22, and the secondary sides S2 and S3 are connected to the regenerative capacitor 22c via the diode D9.

Also in the third configuration example, the above-described first to third discharge methods can be used. Further, in the third configuration example, regardless of which of the first to third discharge methods is used, the discharge currents flowing through the primary sides P2 and P3 of the transformers TX2 and TX3 are distributed to the secondary sides S2 and S3. The regenerative capacitor 22c connected to is charged. The energy charged in the regeneration capacitor 22c is regenerated by the input capacitor c7 of the inverter 21i, and can be reused as energy for the tube voltage start-up operation of the inverter 21i. Therefore, according to the third configuration example of the discharge circuit 22, the discharge energy of a part of the capacitors of the CW circuit 21cw can be regenerated and used in the high voltage generation circuit 21. Overall energy efficiency can be improved.

FIG. 11 is a diagram showing a fourth configuration example of the discharge circuit 22. As shown in FIG. As shown in FIG. 11, the transformers TX2 and TX3 used in the third configuration example may be replaced with flyback transformers FBTX2 and FBTX3, respectively. The fourth configuration example of the discharge circuit 22 shown in FIG. 11 differs from the third configuration example shown in FIG. 10 in the timing of regenerating energy in the regeneration capacitor 22c.

In the fourth configuration example of the discharge circuit 22 shown in FIG. 11, when the switches 22sw1 and 22sw2 are turned on and the discharge current flows through the primary sides P2 and P3 of the flyback transformers FBTX2 and FBTX3, the secondary sides S2 and S3 are in the flyback configuration. Therefore, energy cannot be transmitted, and energy is accumulated in FBTX2 and FBTX3 themselves. The accumulated energy is charged in the regeneration capacitor 22c connected to the secondary sides S2 and S3 and regenerated to the input capacitor c7 of the inverter 21i while the switches 22sw1 and 22sw2 are OFF.

According to the fourth configuration example of the discharge circuit 22, the energy is released to the secondary sides S2 and S3 of the flyback transformers FBTX2 and FBTX3 during the period when the switches 22sw1 and 22sw2 are OFF when the circuit becomes high impedance. Therefore, overvoltage generated during the OFF period can be suppressed.

According to at least one embodiment described above, the output voltage of the high voltage circuit can be lowered at high speed.

The output voltage control function 31 and the discharge control function 32 of the processing circuit 30 in this embodiment are examples of the output voltage control section and the discharge control section, respectively, in the scope of claims.

In the above embodiment, the word "processor" is, for example, a dedicated or general-purpose CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC), Circuits such as programmable logic devices (eg, Simple Programmable Logic Devices (SPLDs), Complex Programmable Logic Devices (CPLDs), and FPGAs) shall be meant. The processor implements various functions by reading and executing programs stored in the storage medium.

Further, in the above embodiments, an example of a case where a single processor of the processing circuit realizes each function is shown, but a processing circuit is configured by combining a plurality of independent processors, and each processor realizes each function. good too. Further, when a plurality of processors are provided, a storage medium for storing programs may be provided individually for each processor, or a single storage medium may collectively store programs corresponding to the functions of all processors. good too.

It should be noted that although several embodiments of the invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

10 X-ray high voltage device 11 X-ray tube 20 high voltage circuit 21 high voltage generation circuit 21cw Cockcroft-Walton circuit 21i inverter 22 discharge circuit 22c regeneration capacitor 22sw1 switch 22sw2 switch 30 processing circuit 31 output voltage control function 32 discharge control function

Claims (7)

a high voltage circuit comprising: a high voltage generation circuit including a plurality of capacitors; and a discharge circuit including a switch for discharging said part of the capacitors of said high voltage generation circuit ;
an output voltage control unit that changes the output voltage from the high voltage circuit to the X-ray tube;
a discharge control unit that discharges a part of the capacitor of the high voltage circuit in synchronization with the timing at which the output voltage drops;
with
The discharge control unit
controlling the discharge of the part of the capacitor of the high voltage generation circuit by controlling the switch of the discharge circuit ;
The high voltage generation circuit of the high voltage circuit comprises:
Having a Cockcroft-Walton circuit composed of the plurality of capacitors and a plurality of diodes,
the part of the capacitors of the high voltage generation circuit,
preferentially selected from capacitors located on the AC power input side of the Cockcroft-Walton circuit;
X -ray high voltage equipment. The discharge control unit
correcting the falling speed of the output voltage;
An X-ray high voltage apparatus according to claim 1. The discharge control unit
controlling discharge of the part of the capacitor according to the load to which the output voltage is applied so that the rate of decrease of the output voltage becomes a predetermined value regardless of changes in the load to which the output voltage is applied;
3. The X-ray high voltage apparatus according to claim 2 . The output voltage control unit
The output voltage from the high voltage circuit to the X-ray tube is set to the first voltage so as to enable dual energy imaging with a first tube voltage and a second tube voltage higher than the first tube voltage. Vary between the tube voltage and the second tube voltage,
The discharge control unit
according to the tube current of the X-ray tube so that the rate of decrease when decreasing the tube voltage from the second tube voltage to the first tube voltage becomes the predetermined value regardless of changes in the tube current of the X-ray tube. to control the discharge of said part of the capacitor,
4. The X-ray high voltage apparatus according to claim 3 . The discharge control unit
correcting the falling speed of the output voltage by changing the impedance of the coil based on the frequency of the current flowing through the coil of the high voltage circuit;
5. An X-ray high voltage apparatus according to any one of claims 2 to 4 . The discharge control unit
correcting the falling speed of the output voltage by regenerating the current energy flowing through the transformer of the high voltage circuit to the inverter circuit of the high voltage circuit;
5. An X-ray high voltage apparatus according to any one of claims 2 to 4 . a high voltage circuit comprising: a high voltage generation circuit including a plurality of capacitors; and a discharge circuit including a switch for discharging said part of the capacitors of said high voltage generation circuit ;
an output voltage control unit that changes the voltage output by the high voltage circuit;
a discharge control unit that discharges a part of the capacitor of the high voltage circuit in synchronization with the timing of the voltage drop;
with
The discharge control unit
controlling the discharge of the part of the capacitor of the high voltage generation circuit by controlling the switch of the discharge circuit ;
The high voltage generation circuit of the high voltage circuit comprises:
Having a Cockcroft-Walton circuit composed of the plurality of capacitors and a plurality of diodes,
the part of the capacitors of the high voltage generation circuit,
preferentially selected from capacitors located on the AC power input side of the Cockcroft-Walton circuit;
Power supply .

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