JP2010225461A - High-voltage device and x-ray computer tomograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an X-ray computer tomograph for scanning in a short time by high-speed rotation to operate with power supplied from a power source with a small power capacity. <P>SOLUTION: A DC/AC inverter 14c converts a first DC voltage into AC voltage. A high-voltage generator 14d uses the AC voltage obtained with the DC/AC inverter 14c to generate AC power for giving birth to X-ray irradiation by an X-ray tube 11a provided at the X-ray computer tomograph. An electric double-layer capacitor 14b accumulates electric energy by a second DC voltage, and the electric energy thus accumulated is output as a third DC voltage. An AC/DC converter 14a makes the electric double-layer capacitor 14b accumulate electric energy during a period when the X-ray irradiation is not carried out, and generates a second DC voltage, during a period when the X-ray irradiation is carried out, so as to be able to obtain the first DC voltage by composition with the third DC voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high voltage apparatus and an X-ray computed tomography apparatus which are applied to an X-ray computed tomography apparatus and generate a high voltage for X-ray irradiation.

  In recent years, an X-ray computed tomography apparatus (CT apparatus) for medical diagnosis has been improved in scanning speed and can be used for cardiac diagnosis. However, further improvement in scanning speed is required.

  Now, in order to obtain an image with little noise and high utility value for medical diagnosis, it is necessary that a certain amount or more of X-rays reach the X-ray detector. However, when the scanning speed is increased, the X-ray dose reaching the X-ray detector is decreased, and thus the S / N of the signal generated by the X-ray detector is decreased. In order to prevent this, it is necessary to compensate for a decrease in the X-ray dose due to a shortened diagnosis time by increasing the X-ray emission intensity from the X-ray tube.

JP 2000-348894 A

  When the output Po [kW] of the X-ray high voltage apparatus, the efficiency η [%] of the X-ray high voltage apparatus, and the power factor of the X-ray high voltage apparatus are Cosφ, the input power Pi [kVA] is expressed by the following equation. The

Pi = 100 Po / (η · Cosφ)
That is, when the output of the X-ray high voltage apparatus exceeds 100 [kW], the input power is likely to have a large power capacity exceeding 150 [kWA]. For this reason, in order to use the conventional CT apparatus, a special power source with a large power capacity is required, and installation of the CT apparatus has been an obstacle to the introduction, such as a large-scale construction. Also, it has been difficult to use in countries and regions where power supply conditions are not good.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to supply an X-ray computed tomography apparatus capable of scanning in a short time by high-speed rotation from a power source having a small power capacity. It is to be able to operate with electric power.

  A high voltage apparatus according to a first aspect of the present invention is a high voltage apparatus that generates alternating current power for causing X-ray irradiation by an X-ray tube provided in an X-ray computed tomography apparatus. Conversion means for converting a DC voltage into an AC voltage, generation means for generating the AC power using the AC voltage obtained by the conversion means, electric energy is accumulated by the second DC voltage, and this accumulated Storage means for outputting electrical energy as a third direct current voltage; electrical energy stored in the storage means during a period when the X-ray irradiation is not performed; and the third direct current voltage during a period when the X-ray irradiation is performed. Generating means for generating the second DC voltage so that the first DC voltage can be obtained by combining with.

  An X-ray computed tomography apparatus according to a first aspect of the present invention includes a high-voltage circuit that generates AC power, an X-ray tube that generates X-rays when supplied with the AC power, and generated by the X-ray tube The X-ray detector that detects X-rays transmitted through the subject, and the X-ray tube and the X-ray detector are rotated around the subject while facing each other with the subject interposed therebetween. A rotation mechanism; and reconstructing means for reconstructing a tomographic image of the subject based on the detection state of the X-ray by the X-ray detector while being rotated by the rotation mechanism, and the high voltage The circuit stores a first DC voltage smaller than the AC power into an AC voltage, stores electric energy using the second DC voltage, and outputs the stored electric energy as a third DC voltage. Do not perform storage with the X-ray irradiation In the period, electric energy is accumulated in the accumulating means, and in the period in which the X-ray irradiation is performed, the second DC voltage is set so that the first DC voltage is obtained by combining with the third DC voltage. Generating means for generating.

  According to the present invention, it is possible to operate an X-ray computed tomography apparatus capable of scanning in a short time by high-speed rotation with power supplied from a power source having a small power capacity.

The figure which shows the structure of the principal part of CT apparatus which concerns on one Embodiment of this invention. The block diagram which shows the structure of the high voltage generation | occurrence | production part in FIG. The figure which shows the electric power supply condition in the implementation state of the scan in a short time by high speed rotation.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of main parts of a CT apparatus 100 according to the present embodiment. This CT apparatus includes a scan gantry 1 and a computer apparatus 2. The scan gantry 1 is a component for collecting projection data related to a subject. The projection data collected by the scan gantry 1 is used for processing such as image reconstruction in the computer device 2.

  The scan gantry 1 includes a bed 10, an X-ray tube device 11, an X-ray detector 12, a gantry rotation drive unit 13, a high voltage generation unit 14, a bed drive unit 15, and a data collection unit 16.

  In the scan gantry 1, the X-ray tube device 11 and the X-ray detector 12 are mounted on an annular rotary mount (not shown) in an opposing relationship. The rotating gantry is driven to rotate by the gantry rotation driving unit 13. At this time, the X-ray tube device 11 and the X-ray detector 12 rotate around the same rotation axis RA. The scan gantry 1 forms a cavity (imaging port) inside the rotation trajectory of the X-ray tube device 11 and the X-ray detector 12.

  The X-ray tube device 11 includes an X-ray tube 11a and an X-ray filter 11b. The X-ray tube 11 a receives power supply from the high voltage generator 14 and emits X-rays toward the X-ray detector 12. The X-ray filter 11b removes low energy components to reduce exposure. The high voltage generator 14 includes a high voltage transformer, a filament current generator, and a rectifier. In addition to this, the high voltage generator 14 includes a tube voltage switch, a filament current switch, and the like in order to adjust the tube voltage and the filament current arbitrarily or stepwise.

  The X-ray detector 12 is configured by arranging a plurality of X-ray detection element arrays in a direction along the rotation axis RA. The X-ray detector 12 detects incident X-rays and outputs an electrical signal corresponding to the intensity.

  The subject is placed on the top 10 a of the bed 10. The bed 10 is driven by the bed driving unit 15 to move the top plate 10a in the longitudinal direction (left and right direction in FIG. 1). Usually, the bed 10 is installed such that the longitudinal direction thereof is parallel to the rotation axis RA. Usually, the subject is placed on the top board 10a so that the body axis is along the rotation axis RA. Thus, the subject is inserted into the cavity of the scan gantry 1 as the top plate 10a moves.

  The data collection unit 16 collects the output of the X-ray detector 12 and supplies it to the computer apparatus 2. Note that an interface using slip ring, optical communication, or the like is interposed between the X-ray detector 12 and the data collection unit 16. As a result, the data collection unit 16 can collect the output of the X-ray detector 12 while continuously rotating the rotary mount.

  The computer apparatus 2 includes a gantry control unit 21, a preprocessing unit 22, an image reconstruction unit 23, a display unit 24, and a console 25. The gantry control unit 21, the preprocessing unit 22, the image reconstruction unit 23, the display unit 24, and the console 25 are connected to each other via a data / control bus 26.

  Data supplied from the scan gantry 1 to the computer apparatus 2 is supplied as projection data to the image reconstruction unit 23 via the preprocessing unit 22. The image reconstruction unit 23 reconstructs tomographic image data based on the projection data. The tomographic image data is displayed on the display unit 24 and also supplied to the gantry control unit 21, and is used for processing for determining the timing of starting the main scan.

  The console 25 is provided for the operator to input various information such as scanning conditions and various instructions. The console 25 includes an operation screen.

  The gantry control unit 21 controls the operation of the scan gantry 1 so that scanning is performed so that projection data necessary for diagnosis is obtained.

  FIG. 2 is a block diagram showing the configuration of the high voltage generator 14 in FIG.

  As shown in FIG. 2, the high voltage generator 14 includes an AC / DC converter 14a, an electric double layer capacitor 14b, a DC / AC inverter 14c, and a high voltage generator 14d.

  The high voltage generator 14 is supplied with an AC voltage from an input power supply. The input power source is, for example, a device that is installed in a medical facility where the CT apparatus 100 is installed and supplies power to an electrical device in the medical facility.

  The AC / DC converter 14a receives a commercial frequency AC voltage supplied from an input power source. The AC / DC converter 14a includes a rectifier circuit and a DC / DC converter circuit. The AC / DC converter 14a rectifies the input AC voltage with a rectifier circuit, and then outputs a DC voltage of an arbitrary level obtained by adjusting the level with the DC / DC converter circuit. As the DC / DC converter, for example, a known step-down chopper circuit can be adopted. In this case, the output voltage of the DC / DC converter is controlled to be lower than √2 times the voltage of the input power supply. The output voltage can be adjusted by the ratio of turning on / off the switching element of the chopper circuit.

  The electric double layer capacitor 14b is charged by the output voltage from the AC / DC converter 14a during a period when there is no power consumption in the DC / AC inverter 14c. The electric double layer capacitor 14b outputs a DC voltage with the accumulated energy during a period when the required power amount in the DC / AC inverter 14c exceeds the output power amount of the AC / DC converter 14a.

  The DC / AC inverter 14c operates by receiving a DC voltage from the AC / DC converter 14a alone or from the AC / DC converter 14a and the electric double layer capacitor 14b, and outputs an AC voltage of several tens of kHz. Thus, the frequency of the output voltage of the DC / AC inverter 14c is increased from several hundred times to about one thousand times the commercial frequency. This is to make the high voltage generator 14d small.

  The high voltage generator 14d includes a step-up transformer and a high-voltage rectifier circuit. The high voltage generator 14d boosts the AC voltage output from the DC / AC inverter 14c to an acceleration voltage (generally 80 kV to 140 kV) necessary for the X-ray tube 11a to generate X-rays. Rectified and smoothed to obtain DC high voltage. The high DC voltage obtained by the high voltage generator 14d is applied between the anode and cathode of the X-ray tube 11a.

  Next, the operation of the CT apparatus 100 configured as described above will be described.

  The CT apparatus 100 can operate in various modes provided in known CT apparatuses.

  When operating in a mode with a relatively low scanning speed, the X-ray emission intensity from the X-ray tube 11a may be relatively low. When the DC / AC inverter 14d can generate the amount of power required by the high voltage generator 14d to obtain the required acceleration voltage by the output AC voltage from the AC / DC converter 14a, the AC / DC The converter 14a outputs a direct current voltage having an appropriate amount of power for the DC / AC inverter 14d to generate the amount of power required by the high voltage generator 14d in order to obtain a required acceleration voltage. Therefore, since all of the required electric energy is supplied to the DC / AC inverter 14c from the AC / DC converter 14a, no DC voltage is output from the electric double layer capacitor 14b.

  Thus, in this state, a DC high voltage can be stably obtained based on the input power supply, and X-rays can be generated for a long time.

  On the other hand, when the DC / AC inverter 14d cannot generate the amount of power required by the high voltage generator 14d to obtain the required acceleration voltage by the AC voltage output from the AC / DC converter 14a, X-ray irradiation Is performed intermittently with a certain pause.

  During the period when X-ray irradiation is not performed, the DC / AC inverter 14d stops operating, but the AC / DC converter 14a continues to output a DC voltage. Accordingly, the DC voltage output from the AC / DC converter 14a is applied to the electric double layer capacitor 14b, and the electric double layer capacitor 14b is charged.

  At this time, when the voltage of the input power supply is 400 [V] and the maximum voltage of the electric double layer capacitor 14b is 500 [V], the AC / DC converter 14a outputs the output voltage from 0 [V] to a maximum of 500 [V]. To change. As described above, when the power is turned on, the output voltage of the AC / DC converter 14a is gradually increased, so that the electric double layer capacitor 14b is slowly charged and the inrush current of the input power supply can be suppressed.

  Next, the operation during X-ray irradiation will be described.

  At the start of X-ray irradiation, the electric double layer capacitor 14b is charged to its maximum voltage of 500 [V]. By gradually lowering the output voltage of the AC / DC converter 14a during X-ray irradiation, the electric charge accumulated in the electric double layer capacitor 14b can be taken out.

  For example, the capacitance of the electric double layer capacitor 14b is 3.48 [F], the voltage of the electric double layer capacitor 14b at the end of X-ray irradiation is 250 [V], and the X-ray high voltage device sets 100 [kW]. Consider the case of outputting for 5 seconds.

  When the total efficiency ηg of the DC / AC inverter 14c and the high voltage generator 14d is 87 [%], the required input power of the DC / AC inverter 14c is obtained by the following equation.

100 [kW] × 100 / 87≈115 [kW]
In order to supply this electric power for 5 seconds, energy of 115 [kW] × 5 [seconds] = 575 [kJ] is required.

  When the electric double layer capacitor 14b is charged to the maximum voltage, the stored energy Ec is obtained by the following equation.

Ec = C · V2 / 2 = 3.48 × 5002/2 = 435 [kJ]
If the voltage of the electric double layer capacitor 14b is set to 250 [V] which is 1/2 of the initial value at the end of the X-ray irradiation, 75% of the energy Ec can be extracted, and thus the electric power Pc that can be supplied from the electric double layer capacitor 14b. Is represented by the following equation.

Pc = 0.75 Ec / 5 [seconds] = 0.75 × 435 [kJ] / 5 [seconds] = 65.25 [kW]
That is, about 65 [kW] can be supplied from the electric double layer capacitor 14b. The power supply of 50 [kW] may be received from the AC / DC converter 14a. Assuming that the efficiency of the AC / DC converter 14a is 92 [%], the power supplied from the input power supply can be 54.3 [kW], the power factor can be 0.8, and the input capacity can be 68 [kVA]. FIG. 3 is a diagram showing the power supply status at this time.

  During the X-ray irradiation, the output voltage V of the AC / DC converter 14a is controlled to be expressed by the following formula as a quadratic function of the time t from the start of the X-ray irradiation. Electric power can be taken out.

V = V0 (1−Kd · t2)
Here, V0 is a voltage at the start of X-ray irradiation. Kd is a coefficient determined by the discharge depth of the capacitor and the output time, and is 0.02 in the above example.

  In the description so far, it is assumed that the AC / DC converter 14a is configured using a combination of a capacitor input rectifier circuit and a step-down DC / DC converter. However, the AC / DC converter 14a may have a power factor correction control (PFC) function. In this case, a booster type or a buck-boost type is used for the converter. By providing the AC / DC converter 14a with the PFC function, the power factor becomes approximately 1, and the input power (apparent power) further decreases.

  In diagnosis by the CT apparatus 100, it is common to perform several scans for one patient. This is because imaging is performed while changing the state such as absence or presence of a contrast medium.

  The voltage of the electric double layer capacitor 14b that has decreased in one scan must be recovered until the next scan. At this time, control is performed to gradually increase the output voltage of the AC / DC converter 14a. Realize with.

Even when the electric double layer capacitor 14b is charged, the output voltage of the AC / DC converter 14a is controlled so as to be expressed by the following expression as a quadratic function of the time t from the start of charging, so that the power supplied from the input power supply is constant. Can be kept in. In addition,
V = V0 (1 + Kc · t2)
Here, V0 is a voltage at the start of charging. Kc is a coefficient determined by the charging start voltage, charging end voltage and charging time of the capacitor.

  As described above, according to the present embodiment, the high voltage generation unit 14 can generate an acceleration voltage larger than the acceleration voltage that can be obtained from the input power supply. Therefore, even if the performance of the input power supply is relatively low, scanning in a short time by high-speed rotation is possible. As a result, the CT apparatus 100 can be used even in a facility that does not have special power supply equipment. Therefore, a large-scale construction is not required for installation, the introduction is easy, and the power supply situation is not good. It can also be used in the region.

  In addition, according to the present embodiment, since the electric double layer capacitor 14b is used for energy storage, charging / discharging in a short time is possible, and waiting for repeated scanning in a short time by high-speed rotation is possible. You can save time.

  This embodiment can be variously modified as follows.

  Instead of the electric double layer capacitor 14b, another type of capacitor or a secondary battery can be used. However, it is desirable that the time required for charging / discharging is short, for example, a lithium ion capacitor is suitable.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Scan gantry, 2 ... Computer apparatus, 10 ... Bed, 11 ... X-ray tube apparatus, 11a ... X-ray tube, 11b ... X-ray filter, 12 ... X-ray detector, 13 ... Mount rotation drive part, 14 ... High Voltage generator, 14a ... AC / DC converter, 14b ... Electric double layer capacitor, 14c ... DC / AC inverter, 14d ... High voltage generator, 15 ... Bed drive unit, 16 ... Data collection unit, 21 ... Gantry control unit, DESCRIPTION OF SYMBOLS 22 ... Pre-processing part, 23 ... Image reconstruction part, 24 ... Display part, 25 ... Console, 26 ... Control bus, 100 ... X-ray computed tomography apparatus (CT apparatus).

Claims (6)

In a high voltage apparatus for generating alternating current power for generating X-ray irradiation by an X-ray tube provided in an X-ray computed tomography apparatus,
Conversion means for converting the first DC voltage into an AC voltage;
Generating means for generating the AC power using the AC voltage obtained by the conversion means;
Storage means for storing electrical energy with a second DC voltage and outputting the stored electrical energy as a third DC voltage;
Electric energy is stored in the storage means during a period when the X-ray irradiation is not performed, and the first DC voltage is obtained by combining with the third DC voltage during the period when the X-ray irradiation is performed. A high voltage apparatus comprising: generating means for generating the second DC voltage.   2. The high voltage apparatus according to claim 1, wherein the generation unit reduces the second DC voltage by a quadratic function of time during a period in which the X-ray irradiation is performed.   The high voltage apparatus according to claim 1, wherein the generation unit includes a power factor improvement function.   2. The high voltage device according to claim 1, wherein the storage means is a capacitor.   2. The high voltage device according to claim 1, wherein the storage means is an electric double layer capacitor. A high voltage circuit for generating AC power;
An X-ray tube that receives the supply of AC power and generates X-rays;
An X-ray detector for detecting X-rays generated by the X-ray tube and transmitted through the subject;
A rotation mechanism for rotating the X-ray tube and the X-ray detector around the subject while facing the subject with the subject interposed therebetween;
Reconstructing means for reconstructing a tomographic image of the subject based on the detection state of the X-ray by the X-ray detector while being rotated by the rotation mechanism;
And the high voltage circuit comprises:
Conversion means for converting a first DC voltage smaller than the AC power into an AC voltage;
Storage means for storing electrical energy with a second DC voltage and outputting the stored electrical energy as a third DC voltage;
Electric energy is stored in the storage means during a period when the X-ray irradiation is not performed, and the first DC voltage is obtained by combining with the third DC voltage during the period when the X-ray irradiation is performed. An X-ray computed tomography apparatus comprising: generating means for generating the second DC voltage.

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