JP6173700B2 - X-ray high voltage apparatus and X-ray CT apparatus - Google Patents

Description

  Embodiments described herein relate generally to an X-ray high voltage apparatus and an X-ray CT apparatus.

  Conventionally, in an X-ray CT (Computed Tomography) apparatus, an X-ray tube voltage is rapidly switched between a low voltage (for example, 80 kV) and a high voltage (for example, 135 kV) during scanning, and X-rays having different energy distributions There is an attempt to separate the calcified tissue portion from the blood vessel image by the contrast agent by visualizing the difference of the constituent elements of the subject by analyzing the image by the beam.

  As a method of obtaining an X-ray beam having such a different energy distribution, for example, an X-ray tube and an X-ray detector are arranged opposite to each other with a rotation center on a rotating mount, and the rotating mount is rotated at a high speed. There is a method of varying the tube voltage. As one method of an X-ray high voltage apparatus for high-speed KV switching CT by this method, a method of generating a triangular wave tube voltage by intermittently operating an inverter that supplies AC power to a high voltage generator is known. However, in the above-described prior art, the tube voltage waveform may change as the characteristics of the X-ray tube change.

JP 2012-10093 A

  The problem to be solved by the present invention is to provide an X-ray high voltage apparatus and an X-ray CT apparatus that can obtain a stable tube voltage waveform even if the characteristics of the X-ray tube change.

The X-ray high voltage apparatus according to the embodiment includes an output voltage changing unit, a detecting unit, an acquiring unit, and a correcting unit. The output voltage changing means changes the voltage value of the voltage output to the X-ray tube in synchronization with the rotation of the gantry. The detecting means detects the voltage whose voltage value has been changed by the output voltage changing means. The acquisition unit acquires a voltage value of the voltage detected by the detection unit. The correction unit corrects the filament current control in the X-ray tube according to the voltage value of the voltage detected by the detection unit. The obtaining means obtains the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage changes from falling to rising by the output voltage changing means in the voltage detected by the detecting means.

FIG. 1 is a diagram illustrating an example of the configuration of the X-ray CT apparatus according to the first embodiment. FIG. 2A is a diagram illustrating an example of a configuration of an X-ray high voltage apparatus according to the related art. FIG. 2B is a diagram for explaining an example of the high-speed KV switching operation. FIG. 3 is a diagram for explaining a change in the emission characteristics of the X-ray tube over time. FIG. 4 is a diagram for explaining a change in a triangular waveform in a high-speed KV switching operation accompanying a change in tube current. FIG. 5 is a diagram illustrating an example of the configuration of the X-ray high voltage apparatus according to the first embodiment. FIG. 6 is a diagram for explaining an example of sampling processing by S & H according to the first embodiment. FIG. 7 is a timing chart for explaining operation timings in the X-ray high voltage apparatus according to the first embodiment. FIG. 8A is a diagram for explaining stabilization of the tube voltage waveform by the X-ray high voltage apparatus according to the first embodiment. FIG. 8B is a diagram for explaining stabilization of the tube voltage waveform by the X-ray high voltage apparatus according to the first embodiment.

(First embodiment)
The X-ray CT apparatus irradiates a subject with X-rays from an X-ray tube, and detects X-rays transmitted through the subject with a detector, thereby reproducing an X-ray CT image indicating tissue morphology information in the subject. A device that performs the configuration. The configuration of the X-ray CT apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of a configuration of an X-ray CT apparatus 1 according to the first embodiment. As illustrated in FIG. 1, the X-ray CT apparatus 1 according to the first embodiment includes a gantry device 10, a couch device 20, and a console device 30.

  The gantry device 10 irradiates the subject P with X-rays, detects the X-rays transmitted through the subject P, and outputs the detected X-rays to the console device 30. The gantry device 10 includes an X-ray high voltage device 11, an X-ray tube 12, an X-ray detector 13, a data collection unit 14, a rotating frame 15, a gantry driving unit 16, and a gantry bed control unit 17. Have

  The X-ray high voltage apparatus 11 supplies a high voltage to the X-ray tube 12 according to control by the gantry bed control unit 17. The X-ray tube 12 is a vacuum tube that generates X-rays with a high voltage supplied from the X-ray high-voltage device 11, and irradiates the subject P with X-rays as the rotating frame 15 rotates. That is, the X-ray high voltage apparatus 11 adjusts the X-ray dose irradiated to the subject P by adjusting the tube voltage and tube current supplied to the X-ray tube 12.

  Here, the X-ray high voltage apparatus 11 and the X-ray tube 12 according to the present embodiment function as an X-ray generation apparatus 100 as shown in FIG. The X-ray generation apparatus 100 according to the present embodiment changes the voltage value of the voltage output to the X-ray tube 12 in synchronization with the rotation of the gantry (the rotation of the rotating frame 15). That is, the X-ray generation apparatus 100 is an X-ray generation apparatus applied to the dual energy type X-ray CT apparatus 1. Details of the X-ray generator 100 will be described later.

  The X-ray detector 13 is a two-dimensional array type detector (surface detector) that detects X-rays that have passed through the subject P, and has a detection element array in which X-ray detection elements for a plurality of channels are arranged. A plurality of rows are arranged along the body axis direction of the specimen P (Z-axis direction shown in FIG. 1). Specifically, the X-ray detector 13 in the first embodiment has X-ray detection elements arranged in multiple rows such as 320 rows along the body axis direction of the subject P. For example, the subject P It is possible to detect X-rays transmitted through the subject P over a wide range such as a range including the lungs and the heart.

  The data collection unit 14 generates projection data using the X-rays detected by the X-ray detector 13, and transmits the generated projection data to the image processing unit 34 of the console device 30. The rotating frame 15 is an annular frame that rotates continuously at high speed around the subject P, and the X-ray tube 12 and the X-ray detector 13 are arranged to face each other.

  The gantry driving unit 16 drives the gantry according to the control by the gantry bed control unit 17. Specifically, the gantry driving unit 16 continuously rotates the rotating frame 15 at a high speed by driving a motor, and continuously rotates the X-ray tube 12 and the X-ray detector 13 on a circular orbit around the subject P. . The gantry bed control unit 17 controls the X-ray high voltage apparatus 11, the gantry driving unit 16, and the couch driving unit 21 according to control by a scan control unit 36 described later.

  The couch device 20 is a table on which the subject P to be imaged is placed, and includes a couch driving unit 21 and a top plate 22. The couch drive unit 21 continuously reciprocates the top plate 22 in the body axis direction of the subject P by driving the motor according to the control by the gantry couch control unit 17. The top plate 22 is a plate on which the subject P is placed.

  The console device 30 receives an operation of the X-ray CT apparatus 1 by the operator and reconstructs an X-ray CT image from the projection data collected by the gantry device 10. Specifically, the console device 30 includes an input unit 31, a display unit 32, a system control unit 33, an image processing unit 34, an image data storage unit 35, and a scan control unit 36.

  The input unit 31 includes a mouse and a keyboard used by the operator of the X-ray CT apparatus 1 to input various instructions and various settings, and transfers instructions and setting information received from the operator to the system control unit 33. . For example, the input unit 31 receives an operation for calculating the degree of tumor invasion from the operator, an input operation for reconstruction conditions when reconstructing an X-ray CT image, and the like. The display unit 32 is a display such as an LCD (Liquid Crystal Display) and displays various types of information. For example, the display unit 32 displays an X-ray CT image stored in the image data storage unit 35, a GUI (Graphical User Interface) for receiving various instructions from the operator, and the like.

  The system control unit 33 controls the entire X-ray CT apparatus 1 by controlling the gantry device 10, the couch device 20, and the console device 30. For example, the system control unit 33 controls the scan control unit 36 to collect 3D projection data. For example, the system control unit 33 controls the image processing unit 34 to reconstruct an X-ray CT image from the three-dimensional projection data.

  The image processing unit 34 performs various processes on the three-dimensional projection data received from the data collection unit 14. Specifically, the image processing unit 34 performs preprocessing such as sensitivity correction on the 3D projection data received from the data collection unit 14, and performs backprojection processing on the 3D projection data after the preprocessing. A three-dimensional X-ray CT image (hereinafter sometimes referred to as “volume data”) is reconstructed. Then, the image processing unit 34 stores the reconstructed volume data in the image data storage unit 35. In addition, the image processing unit 34 generates an X-ray CT image having a stereoscopic effect by, for example, an SVR (Shaded Volume Rendering) method or the like, or generates a cross-sectional image of an arbitrary surface, thereby generating the generated X-ray CT image. Is stored in the image data storage unit 35.

  The image data storage unit 35 stores volume data reconstructed by the image processing unit 34, an X-ray CT image, and the like. The scan control unit 36 controls the gantry bed control unit 17 based on the scan condition instructed from the system control unit 33.

  The example of the configuration of the X-ray CT apparatus 1 according to the first embodiment has been described above. Under such a configuration, the X-ray CT apparatus 1 according to the first embodiment can obtain a stable tube voltage waveform even if the characteristics of the X-ray tube 12 are changed by the X-ray high voltage apparatus 11 described later. It is configured to be able to. In the X-ray generator 100 according to the present embodiment, a voltage (hereinafter referred to as tube voltage) supplied to the X-ray tube 12 disposed opposite to the X-ray detector 13 across the rotation center of the rotary frame 15 is used. A high-speed KV switching CT X-ray high voltage apparatus that changes at high speed is applied. Specifically, the high-speed KV switching CT X-ray high-voltage apparatus applied to the X-ray generator 100 intermittently operates an inverter that supplies AC power to the high-voltage generator to generate a triangular wave tube voltage. Device.

  Here, in the conventional X-ray high voltage apparatus, a case will be described in which the tube voltage waveform changes as the characteristics of the X-ray tube change. FIG. 2A is a diagram illustrating an example of a configuration of an X-ray high voltage apparatus according to the related art. As shown in FIG. 2A, the X-ray high voltage apparatus according to the prior art includes an inverter, a high voltage generator, a filament heating circuit, and a filament transformer, and the inverter is intermittently operated by an inverter control circuit (not shown). A triangular wave tube voltage is generated.

  That is, in the X-ray high voltage apparatus shown in FIG. 2A, the inverter control circuit transmits a timing signal for generating an AC voltage to the inverter. The inverter supplies an AC voltage to the high voltage transformer of the high voltage generator in accordance with the timing signal received from the inverter control circuit. The high voltage generator boosts the voltage with a high voltage transformer, rectifies and smoothes it with a rectifier and a capacitor, and supplies a DC high voltage to the X-ray tube.

  Here, the filament of the X-ray tube is heated to a temperature at which the filament current (If) flows by the output from the filament heating circuit via the filament transformer and emits thermoelectrons. When a high DC voltage is applied in such a state, the X-ray tube emits X-rays. In such an X-ray high-voltage apparatus, the high-speed KV switching operation is controlled by a timing signal transmitted from the inverter control circuit to the inverter.

  FIG. 2B is a diagram for explaining an example of the high-speed KV switching operation. The upper diagram in FIG. 2B shows a time change graph of the tube voltage with the vertical axis representing the tube voltage (kV) and the horizontal axis representing the time (t). The lower diagram in FIG. 2B shows the operation cycle of the inverter for generating the tube voltage in the upper time change graph. As shown in FIG. 2B, in the high-speed KV switching operation that generates a triangular wave-shaped tube voltage, the tube voltage rises when the inverter is operating, and the tube voltage decreases when the inverter is stopped. For example, in the high-speed KV switching operation, as shown in FIG. 2B, a triangular wave-like tube voltage is generated when switching between the tube voltage kV1 and the tube voltage kV2 at a high speed. At this time, the fall time until the tube voltage reaches kV1, that is, the inverter stop period is adjusted in advance.

Such a triangular waveform of the tube voltage changes depending on the filament current (If) flowing through the X-ray tube. Accordingly, by keeping the filament current constant, the triangular waveform of the tube voltage is kept constant. Here, the inclination when the tube voltage decreases in the waveform on the triangular wave is determined by the capacitance of the X-ray high voltage apparatus and the emission characteristics of the X-ray tube. The capacitance of the X-ray high-voltage device is the sum of the output capacitor capacitance “C ₀ ” of the X-ray high-voltage device and the stray capacitance “C _x ” in the high-voltage cable and X-ray tube, as shown in the following equation. It is.

1 / (1 / C ₁ + 1 / C ₂ ) + C _x = C ₀ + C _x

  The emission characteristics of the X-ray tube indicate the correspondence between the tube current “Ip” and the filament current “If”. Here, the emission characteristics of the X-ray tube change with the aging of the X-ray tube. FIG. 3 is a diagram for explaining a change in the emission characteristics of the X-ray tube over time. FIG. 3A shows changes in emission characteristics at the beginning of use of the X-ray tube. FIG. 3B shows a change in emission characteristics when the X-ray tube is used for a long time. 3A and 3B, the vertical axis indicates the tube current “Ip”, and the horizontal axis indicates the filament current “If”.

  For example, when the X-ray tube is first used, the electron emission ability from the filament of the X-ray tube is low, and therefore, as shown in FIG. The emission characteristics shift to the right. As a result, the tube current is reduced when the filament current is kept constant.

  On the other hand, when the X-ray tube is used for a long time, the filament of the X-ray tube is thinned, so that the emission characteristic shifts to the left as compared with the initial characteristic as shown in FIG. . As a result, the tube current increases when the filament current is kept constant.

  Thus, since the tube current changes depending on the usage history of the X-ray tube, the triangular waveform in the high-speed KV switching operation changes. FIG. 4 is a diagram for explaining a change in a triangular waveform in a high-speed KV switching operation accompanying a change in tube current. FIG. 4A shows a change in waveform when the tube current is reduced, that is, when the X-ray tube is first used. FIG. 4B shows a change in waveform when the tube current increases, that is, when the X-ray tube is used for a long period of time. 4A and 4B, the vertical axis indicates the tube voltage “kV”, and the horizontal axis indicates time “t”.

  For example, when the tube current is reduced at the beginning of use of the X-ray tube, as shown in FIG. 4A, when the tube voltage waveform decreases, the tube voltage does not fully decrease from kV2 to kV1, but increases. It exceeds kV2 at the upper end. That is, when the tube current is reduced, the triangular waveform in the high-speed KV switching operation is shifted upward.

  On the other hand, when the X-ray tube is used for a long time and the tube current increases, as shown in FIG. 4B, the tube voltage falls below kV1 and starts to rise and reaches kV2 at the upper end. do not do. That is, when the tube current increases, the triangular waveform in the high-speed KV switching operation shifts downward.

  As described above, in the conventional X-ray high voltage apparatus, the tube voltage waveform may change as the characteristics of the X-ray tube change. Therefore, the X-ray high voltage apparatus 11 according to the present embodiment is configured such that a stable tube voltage waveform can be obtained even if the characteristics of the X-ray tube change. FIG. 5 is a diagram illustrating an example of the configuration of the X-ray high voltage apparatus 11 according to the first embodiment.

  As shown in FIG. 5, the X-ray high voltage apparatus 11 includes an inverter control circuit 110, an inverter 120, a high voltage generator 130, a filament heating circuit 140, a filament transformer 150, an effective value / DC conversion circuit ( RMS / DC) 160, an error amplifier 170, an amplifier (Amp) 180, a sample and hold circuit (S & H) 190, a reference signal setting device 200, and a correction error amplifier 210. Supply high voltage.

  The inverter control circuit 110 receives the projection data collection timing signal (View Timing) and the X-ray irradiation signal (X-RAY) from the gantry bed control unit 17, and sends a timing signal for controlling the operation timing of the inverter to the inverter 120. Send. Specifically, the inverter control circuit 110 performs the inverter control circuit 110 based on the projection data collection timing as a reference for collecting projection data in synchronization with the rotation of the gantry and the X-ray irradiation signal as a reference for irradiating X-rays. An inverter control timing signal for controlling start / stop of operation is transmitted to the inverter. For example, the inverter control circuit 110 transmits the inverter control timing signal at a frequency half that of the projection data collection timing signal.

  Here, the inverter control circuit 110 controls the stop of the inverter operation by stopping the transmission of the inverter control timing signal. This is because the tube voltage depends on the switching frequency of the tube voltage and the tube current at the time of switching. It is executed based on the rise time. That is, the inverter control circuit 110 stops the transmission of the inverter control timing signal according to a preset time. For example, as shown in FIG. 2B, the inverter control circuit 110 stops transmission of the inverter control timing signal in the time corresponding to 6 cycles of the inverter operation.

  The inverter 120 supplies an AC voltage to the high voltage generator 130 under the control of the inverter control circuit 110. For example, the inverter 120 starts supplying the AC voltage at a frequency half that of the projection data collection timing signal, and stops the supply according to a preset time.

  As shown in FIG. 5, the high voltage generator 130 includes a high voltage transformer, a high voltage rectifier, a high voltage capacitor, and an output voltage detection voltage dividing resistor, and supplies a DC high voltage to the X-ray tube 12. The high voltage transformer boosts the AC voltage supplied from the inverter 120. Specifically, in the high-voltage transformer, the primary coil on the input side of the AC voltage and the secondary coil on the output side to the high-voltage rectifier are wound around the core (iron core), and the AC voltage is applied to the primary coil. As a result, a fluctuating magnetic field is generated, and a voltage is generated in the secondary coil. Here, since the transformation ratio is proportional to the number of turns of the secondary coil and the primary coil, for example, by increasing the number of turns of the secondary coil to twice the number of turns of the primary coil, the AC voltage is boosted twice. Can do.

  The high voltage rectifier converts the AC voltage boosted by the high voltage transformer into a DC voltage. The high voltage capacitor smoothes the DC voltage converted by the high voltage rectifier. The output voltage detection voltage dividing resistor detects a DC high voltage supplied to the X-ray tube 12. That is, the output voltage detection voltage dividing resistor detects a voltage whose voltage value has been changed by the control of the inverter control circuit 110.

  The filament heating circuit 140 outputs a filament current for heating the filament of the X-ray tube. The filament transformer 150 is excited by the filament current output by the filament heating circuit 140 and emits thermoelectrons from the filament of the X-ray tube 12.

  The effective value / DC conversion circuit (RMS / DC) 160 converts the output current from the filament overheating circuit 140 detected by CT (Current Transformer) or the like into a DC voltage.

  The error amplifier 170 receives the filament current setting voltage whose output is controlled by the gantry bed control unit 17 and the output of the effective value / DC conversion circuit (RMS / DC) 160 and drives the filament heating circuit 140. Specifically, the error amplifier 170 increases the output current from the filament heating circuit 140 when the filament current setting voltage increases, and decreases the output current from the filament heating circuit 140 when the output of the RMS / DC 160 increases. Operate. That is, when the filament current setting voltage is constant, the error amplification circuit 170 receives the output of the RMS / DC 160 and performs an operation related to feedback control for keeping the filament current output from the filament heating circuit 140 constant. To do.

  Here, in the X-ray high voltage apparatus 11 according to the present embodiment, as shown in FIG. 5, the error amplifier 170 receives the output of the correction error amplifier 210 described later, and is output from the filament heating circuit 140. Vary the filament current. The output of the correction error amplifier 210 will be described later.

  The amplifier (Amp) 180 amplifies the output voltage of the high voltage generator 130 detected by the output voltage detection voltage dividing resistor of the high voltage generator 130 and outputs the amplified output voltage to the sample and hold circuit (S & H) 190. Specifically, Amp 180 outputs a triangular waveform of the tube voltage during the switching operation to S & H 190.

  The sample and hold circuit (S & H) 190 acquires the voltage value of the voltage detected by the output voltage detection voltage dividing resistor of the high voltage generator 130. Specifically, the S & H 190 acquires the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage is changed by the inverter control circuit 110 in the voltage detected by the output voltage detection voltage dividing resistor. For example, the S & H 190 acquires the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage changes from falling to rising by the inverter control circuit 110. Hereinafter, the voltage value at the timing when the flow changes from falling to rising may be referred to as valley voltage.

  As an example, the S & H 190 is based on the inverter control timing signal output from the inverter control circuit 110, and the voltage value at the timing when the triangular voltage waveform of the tube voltage during the switching operation output from the Amp 180 changes from falling to rising. To get. FIG. 6 is a diagram for explaining an example of sampling processing by the S & H 190 according to the first embodiment. In FIG. 6, the vertical axis represents the tube voltage (kV), and the horizontal axis represents time (t). FIG. 6 shows a case where the tube voltage changes in a triangular waveform between 80 kV and 135 kV.

  For example, the S & H 190 samples the voltage value of the tube voltage at the timing when the inverter control timing signal is output from the inverter control circuit 110, that is, the operation start timing of the inverter 120. The voltage value is acquired in synchronism with the timing when the shift from rising to rising. In other words, if there is no change in the tube voltage, the S & H 190 acquires a signal corresponding to 80 kV.

  Returning to FIG. 5, the reference signal setting unit 200 generates a reference value that serves as a reference for the voltage value of the voltage. Specifically, the reference signal setting unit 200 outputs a reference signal for calculating the deviation of the voltage value acquired by the S & H 190. For example, when the tube voltage changes with a triangular waveform between 80 kV and 135 kV, the reference signal setting unit 200 generates a signal corresponding to −80 kV. That is, by adding together with the positive voltage value acquired by the S & H 190, the voltage value information corresponding to the deviation of the voltage value acquired by the S & H 190 from 80 kV can be output to the correction error amplifier 210.

  For example, when the tube current is reduced and the tube voltage cannot be lowered to 80 kV, a positive voltage signal is input to the correction error amplifier 210, the tube current is increased, and the tube voltage falls below 80 kV. When the voltage drops, a negative voltage signal is input to the correction error amplifier 210.

  The correction error amplifier 210 corrects the filament current control in the X-ray tube 12 according to the voltage value of the voltage detected by the S & H 190. Specifically, the correction error amplifier 210 corrects the error amplifier 170 for controlling the filament current so as to increase the filament current when the valley voltage is higher than the setting, and the valley voltage is lower than the setting. When it is low, the filament current is corrected to be lowered.

  The X-ray high voltage apparatus 11 according to the present embodiment can obtain a stable tube voltage waveform even if the characteristics of the X-ray tube change due to the above-described configuration. Here, the operation timing in the X-ray high voltage apparatus 11 will be described. FIG. 7 is a timing chart for explaining operation timings in the X-ray high voltage apparatus 11 according to the first embodiment. 7 shows the projection data collection timing signal, the inverter control timing signal, the operation of the inverter, the tube voltage waveform during the KV switching operation, and the operation of the sample and hold circuit 190, with the horizontal direction as the time axis.

  For example, as shown in FIG. 7, the X-ray high voltage apparatus 11 outputs an inverter control timing signal at a frequency half that of the projection data collection timing signal to operate the inverter 120. At this time, the inverter control timing signal is output for a period set in advance based on the rise time of the tube voltage.

  The operation of the inverter is started from the rise of the inverter control timing signal, and is stopped when the inverter control timing signal is stopped. Here, the waveform of the tube voltage rises while the inverter is operating, and turns downward when the inverter stops. That is, the waveform of the tube voltage becomes a triangular wave waveform by repeatedly rising and falling according to the start and stop of the operation of the inverter. The S & H 190 samples the voltage value of the tube voltage when the inverter control timing signal rises, that is, when the inverter operation starts.

  The X-ray high voltage apparatus 11 has the configuration shown in FIG. 5 and, as shown in FIG. 7, by sampling the voltage value of the tube voltage, a stable tube can be obtained even if the characteristics of the X-ray tube change. A voltage waveform can be obtained. Hereinafter, stabilization of the tube voltage waveform by the X-ray high voltage apparatus 11 will be described with reference to FIGS. 8A and 8B. 8A and 8B are diagrams for explaining stabilization of the tube voltage waveform by the X-ray high voltage apparatus 11 according to the first embodiment. FIG. 8A shows stabilization of the tube voltage waveform when the X-ray tube 12 is first used. 8B shows stabilization of the tube voltage waveform when the X-ray tube 12 is used for a long period of time.

  Here, in FIG. 8A and FIG. 8B, in order to make the operation easy to understand, the correction operation is started from the state where the tube voltage waveform during the KV switching operation is deviated from the predetermined tube voltage waveform when the filament current is not corrected. Shows the transition to a predetermined tube voltage waveform.

  For example, as shown in FIG. 8A, when the emission characteristic of the X-ray tube 12 changes in the direction in which the emission of the thermal electrons decreases at the beginning of use of the X-ray tube 12, the tube current falls below a predetermined value. During the stop of 120, the tube voltage is less likely to decrease, and the valley voltage shifts upward. In such a case, the output voltage of the S & H 190 increases and the output voltage of the correction error amplifier 210 decreases. As a result, as shown in FIG. 8A, the output voltage of the error amplifier 170 for controlling the filament current increases, and the filament current increases. Thereby, the fall of the tube voltage while the inverter 120 is stopped is accelerated, the valley voltage is gradually lowered, and the KV switching waveform is controlled to change between the predetermined tube voltages.

  Further, for example, as shown in FIG. 8B, when the emission characteristic changes in a direction in which the emission of thermoelectrons increases after using the X-ray tube 12 for a long time, the tube current rises above a predetermined value. The tube voltage is likely to drop during the stop of the operation, and the valley voltage shifts downward. In such a case, the output voltage of the S & H 190 decreases and the output voltage of the correction error amplifier 210 increases. As a result, as shown in FIG. 8B, the output voltage of the error amplifier 170 for controlling the filament current decreases, and the filament current decreases. Thereby, the drop of the tube voltage while the inverter 120 is stopped is moderated, the valley voltage is gradually increased, and the KV switching waveform is controlled to change between the predetermined tube voltages.

  8A and 8B show a state of shifting from the state deviated from the tube voltage waveform to a predetermined tube voltage waveform by the correction operation, but actually, the emission characteristics of the X-ray tube 12 are shown. Since the change occurs slowly, the tube voltage waveform is corrected before the shift without shifting as shown in the figure. In addition, as shown in FIG. 5, by using a capacitor and a resistor, the response of the correction error amplifier 210 is set to be slow, so that it can stably coexist with the feedback control by the RMS / DC 160.

  As described above, according to the first embodiment, the inverter control circuit 110 changes the voltage value of the voltage output to the X-ray tube 12 in synchronization with the rotation of the gantry. The output voltage detection voltage dividing resistor of the high voltage generator 130 detects a voltage whose voltage value has been changed by the inverter control circuit 110. The S & H 190 acquires the voltage value of the voltage detected by the output voltage detection voltage dividing resistor. The correction error amplifier 210 corrects the filament current control in the X-ray tube 12 according to the voltage value of the voltage acquired by the S & H 190. Therefore, the X-ray high voltage apparatus 11 according to the first embodiment makes it possible to obtain a stable tube voltage waveform even if the characteristics of the X-ray tube 12 change over time.

  Further, according to the first embodiment, the S & H 190 detects the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage is changed by the inverter control circuit 110 in the voltage detected by the output voltage detection voltage dividing resistor. To get. Therefore, the X-ray high voltage apparatus 11 according to the first embodiment makes it possible to accurately acquire the voltage value of the tube voltage at the same location in the tube voltage waveform.

  Further, according to the first embodiment, the S & H 190 acquires the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage starts to increase from the decrease by the output voltage detection voltage dividing resistor. Therefore, the X-ray high voltage apparatus 11 according to the first embodiment makes it possible to easily detect a change in tube voltage.

  In addition, according to the first embodiment, the reference signal setting unit 200 generates a reference value that serves as a reference for the voltage value of the voltage. The correction error amplifier 210 calculates a difference between the voltage value of the voltage acquired by the S & H 190 and the reference value generated by the reference signal setting unit 200, and the filament when the voltage value of the voltage is higher than the reference value. When the current is increased and the voltage value of the voltage is lower than the reference value, the filament current is decreased. Therefore, the X-ray high voltage apparatus 11 according to the first embodiment can correct the change in the tube voltage waveform more accurately.

(Second Embodiment)
Although the first embodiment has been described so far, the present invention may be implemented in various different forms other than the first embodiment described above.

  In the first embodiment described above, the case where the valley voltage is sampled to correct the filament current has been described. However, the embodiment is not limited to this, and may be a case where the filament current is corrected by sampling the voltage at the time when the tube voltage changes from rising to falling, for example.

  In such a case, the S & H 190 samples the voltage when the output of the inverter control timing signal is stopped. Further, the reference signal setting unit 200 outputs a voltage value set as a high voltage as a reference signal.

  Further, for example, the filament current may be corrected by sampling the voltage when the tube voltage is increased. In such a case, for example, the S & H 190 samples the voltage value based on the number of cycles in which the inverter control timing signal is output. For example, the S & H 190 samples the voltage value at the rising edge of the fourth cycle in the number of cycles of the inverter operation shown in FIG. 2B. The reference signal setting unit 200 outputs the voltage value reached at the rising point of the fourth cycle as a reference signal.

  As described above, according to the first and second embodiments, a stable tube voltage waveform can be obtained even if the characteristics of the X-ray tube change.

  Although several embodiments of the present invention have been described, these embodiments are presented 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 changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 11 X-ray high voltage apparatus 12 X-ray tube 13 X-ray detector 100 X-ray generator 110 Inverter control circuit 120 Inverter 130 High voltage generator 140 Filament heating circuit 150 Filament transformer 160 RMS / DC
170 Error Amplifier 180 Amplifier 190 Sample and Hold Circuit (S & H)
200 Reference signal setting device 210 Error amplifier for correction

Claims (3)

Output voltage changing means for changing the voltage value of the voltage output to the X-ray tube in synchronization with the rotation of the gantry,
Detecting means for detecting a voltage whose voltage value has been changed by the output voltage changing means;
Obtaining means for obtaining a voltage value of the voltage detected by the detecting means;
Correction means for correcting filament current control in the X-ray tube according to the voltage value of the voltage acquired by the acquisition means;
Equipped with a,
The obtaining means obtains the voltage value of the voltage in synchronization with the timing at which the voltage value of the voltage changes from falling to rising by the output voltage changing means in the voltage detected by the detecting means. X-ray high voltage device. Reference value generating means for generating a reference value serving as a reference for the voltage value of the voltage is further provided,
The correcting unit calculates a difference between the voltage value of the voltage acquired by the acquiring unit and the reference value generated by the reference value generating unit, and the voltage value of the voltage is higher than the reference value. the filament current is increased if, X-rays high voltage apparatus according to claim 1, characterized in that to reduce the filament current when the voltage value of the voltage is lower with respect to the reference value. Output voltage changing means for changing the voltage value of the voltage output to the X-ray tube in synchronization with the rotation of the gantry,
Detecting means for detecting a voltage whose voltage value has been changed by the output voltage changing means;
Obtaining means for obtaining a voltage value of the voltage detected by the detecting means;
Correction means for correcting filament current control in the X-ray tube according to the voltage value of the voltage acquired by the acquisition means;
I have a,
The X-ray high-voltage apparatus acquires the voltage value of the voltage in synchronism with the timing when the voltage value of the voltage changes from falling to rising by the output voltage changing unit in the voltage detected by the detecting unit An X-ray CT apparatus comprising:

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