JP7086622B2 - X-ray computer tomography equipment - Google Patents

Description

Embodiments of the present invention relate to an X-ray computer tomography apparatus.

In X-ray computer tomography equipment, tube voltage modulation is required to reduce the exposure dose. When the tube voltage is simply modulated, the emission characteristics of the tube current due to the tube voltage change, so that the tube current value and the focal size change.

As a method for solving this problem, for example, Patent Document 1 divides a tube voltage to generate a focus voltage, and modulates the focus size with the generated focus voltage. Since the focus electrode holds the ground potential and the tube voltage and the focus voltage are in a proportional relationship, the focus size can be kept stable even if the tube voltage pulsates.

However, when the tube voltage value fluctuates greatly as in tube voltage modulation, the proportional relationship between the tube voltage and the focus voltage is broken. Therefore, in the technique of Patent Document 1, it is difficult to arbitrarily control the focal size while performing tube voltage modulation.

Japanese Patent Application Laid-Open No. 2003-163098 Special Table No. 11-502357 Gazette Japanese Patent Application Laid-Open No. 2003-332098

The problem to be solved by the invention is to arbitrarily control the focal size.

The X-ray computer tomography apparatus according to the embodiment includes an X-ray tube, a high voltage power supply, and a focal size control circuit. The X-ray tube has a cathode that emits electrons, an anode that receives electrons from the cathode to generate X-rays, and a deflector that deflects the electrons from the cathode. The high voltage power supply path generates a tube voltage applied between the cathode and the anode. The focus size control circuit is deflected based on the tube voltage value of the tube voltage and the predetermined size in order to form a focus of a predetermined size on the anode during the period when the tube voltage is applied by the high voltage power supply. By applying a deflection voltage of a voltage value to the deflector, the size of the focal point formed on the anode is controlled.

FIG. 1 is a diagram showing a configuration of an X-ray computer tomography apparatus according to the present embodiment. FIG. 2 is a diagram showing a configuration of an X-ray generation system composed of an X-ray tube and an X-ray high voltage device according to the present embodiment. FIG. 3 is a diagram showing the internal configuration of the X-ray tube of FIG. FIG. 4 is a diagram showing an example of an X-ray tube characteristic value table stored in the table storage circuit of FIG. FIG. 5 is a diagram showing a graph of a tube voltage set value in the tube voltage modulation according to the present embodiment. FIG. 6 is a diagram showing a graph of a focal size and a deflection voltage associated with tube voltage modulation according to the present embodiment.

Hereinafter, the X-ray computer tomography apparatus according to the present embodiment will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an X-ray computer tomography apparatus according to the present embodiment. As shown in FIG. 1, the X-ray computer tomography apparatus according to the present embodiment has a gantry 10 and a console 100. For example, the gantry 10 is installed in the CT examination room, and the console 100 is installed in the control room adjacent to the CT examination room. The gantry 10 and the console 100 are connected to each other so as to be able to communicate with each other. The gantry 10 is equipped with an imaging mechanism for CT imaging of the subject P with X-rays. The console 100 is a computer that controls the gantry 10.

As shown in FIG. 1, the gantry 10 has a substantially cylindrical rotating frame 11 in which an opening is formed. The rotating frame 11 is also called a rotating portion. As shown in FIG. 1, an X-ray tube 13 and an X-ray detector 15 arranged so as to face each other with an opening interposed therebetween are attached to the rotating frame 11. The rotating frame 11 is a metal frame formed in an annular shape by a metal such as aluminum. As will be described later, the gantry 10 has a main frame made of a metal such as aluminum. Mainframes are also called fixed parts. The rotating frame 11 is rotatably supported by the main frame.

The X-ray tube 13 generates X-rays. The X-ray tube 13 is a vacuum tube that holds a cathode that generates thermions and an anode that receives thermions flying from the cathode and generates X-rays. The X-ray tube 13 is connected to the X-ray high voltage device 17 via a high voltage cable.

The X-ray high voltage device 17 can be applied to any type such as a transformation type X-ray high voltage device, a constant voltage type X-ray high voltage device, a condenser type X-ray high voltage device, and an inverter type X-ray high voltage device. .. The X-ray high voltage device 17 is attached to, for example, a rotating frame 11. The X-ray high voltage device 17 adjusts the tube voltage, tube current, and X-ray focus size applied to the X-ray tube 13 according to the control by the gantry control circuit 29. The X-ray high voltage device 17 according to the present embodiment adjusts the X-ray focus of the X-ray tube 13 to an arbitrary size. The X-ray high voltage device 17 performs tube voltage modulation that modulates the tube voltage during X-ray irradiation. During the period of tube voltage modulation, the X-ray high voltage device 17 can adjust the X-ray focus of the X-ray tube 13 to any size. Details of the X-ray tube 13 and the X-ray high voltage device 17 will be described later.

As shown in FIG. 1, the rotary frame 11 receives power from the rotary drive device 21 and rotates around the central axis Z at a constant angular velocity. Any motor such as a direct drive motor or a servo motor is used as the rotation drive device 21. The rotation drive device 21 is housed in, for example, a gantry 10. The rotation drive device 21 receives a drive signal from the gantry control circuit 29 and generates power for rotating the rotation frame 11.

A FOV is set in the opening of the rotating frame 11. A top plate supported by the bed 23 is inserted into the opening of the rotating frame 11. The subject P is placed on the top plate. The bed 23 movably supports the top plate. A bed driving device 25 is housed in the bed 23. The bed drive device 25 receives a drive signal from the gantry control circuit 29 and generates power for moving the top plate back and forth, up and down, and left and right. The bed 23 positions the top plate so that the imaging portion of the subject P is included in the FOV.

The X-ray detector 15 detects the X-rays generated from the X-ray tube 13. Specifically, the X-ray detector 15 has a plurality of detection elements arranged on a two-dimensional curved surface. Each detection element has a scintillator and a photoelectric conversion element. The scintillator is formed by a substance that converts X-rays into photons. The scintillator converts the incident X-rays into a number of photons according to the intensity of the incident X-rays. The photoelectric conversion element is a circuit element that amplifies a photon received from a scintillator and converts it into an electric signal. As the photoelectric conversion element, for example, a photomultiplier tube, a photodiode, or the like is used. The detection element may be an indirect conversion type that converts X-rays into photons and then detects them, or may be a direct conversion type that directly converts X-rays into electrical signals.

A data acquisition circuit 19 is connected to the X-ray detector 15. The data acquisition circuit 19 reads an electric signal corresponding to the intensity of the X-ray detected by the X-ray detector 15 from the X-ray detector 15 according to an instruction from the gantry control circuit 29, and reads the read electric signal for a view period. The data acquisition circuit 19 for collecting raw data having a digital value corresponding to the dose of X-rays is realized by, for example, an ASIC (Application Specific Integrated Circuit) equipped with a circuit element capable of generating raw data.

As shown in FIG. 1, the gantry control circuit 29 has an X-ray high voltage device 17, a data acquisition circuit 19, and a rotation drive device 21 in order to execute X-ray CT imaging according to the imaging conditions from the arithmetic circuit 101 of the console 100. And the sleeper drive device 25 are controlled synchronously. As hardware resources, the gantry control circuit 29 includes a processing device (processor) such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit) and a storage device (a storage device) such as a ROM (Read Only Memory) and a RAM (Random Access Memory). It has a memory). Further, the gantry control circuit 29 includes an ASIC, a field programmable gate array (FPGA), another complex programmable logic device (CPLD), and a simple programmable logic device (Simple Programmable Logic Device). : SPLD) may be realized.

As shown in FIG. 1, the console 100 includes an arithmetic circuit 101, a display 103, an input interface 105, and a memory 107. Data communication between the arithmetic circuit 101, the display 103, the input interface 105, and the memory 107 is performed via a bus.

The arithmetic circuit 101 has a processor such as a CPU, an MPU, or a GPU (Graphics Processing Unit) as a hardware resource. The arithmetic circuit 101 realizes a preprocessing function 111, a reconstruction function 113, an image processing function 115, and a system control function 117 by executing various programs. The preprocessing function 111, the reconstruction function 113, the image processing function 115, and the system control function 117 may be mounted by the arithmetic circuit 101 of one board, or may be distributed and mounted by the arithmetic circuits 101 of a plurality of boards. May be done.

In the preprocessing function 111, the arithmetic circuit 101 performs preprocessing such as logarithmic conversion on the raw data transmitted from the gantry 10. Raw data after preprocessing is also called projection data.

In the reconstruction function 113, the arithmetic circuit 101 generates a CT image expressing the spatial distribution of CT values with respect to the subject P based on the raw data after the preprocessing. As the image reconstruction algorithm, an existing image reconstruction algorithm such as an FBP (filtered back projection) method or a successive approximation reconstruction method may be used.

In the image processing function 115, the arithmetic circuit 101 performs various image processing on the CT image reconstructed by the reconstruction function 113. For example, the arithmetic circuit 101 performs three-dimensional image processing such as volume rendering, surface volume rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing on the CT image to display an image. To generate.

In the system control function 117, the arithmetic circuit 101 comprehensively controls the X-ray computer tomography apparatus according to the present embodiment. Specifically, the arithmetic circuit 101 reads out the control program stored in the storage circuit 107, expands it on the memory, and controls each part of the X-ray computer tomography apparatus according to the expanded control program.

The display 103 displays various data such as CT images. As the display 103, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art can be appropriately used.

The input interface 105 inputs various commands from the user. Specifically, the input interface 105 has an input device. The input device receives various commands from the user. As an input device, a keyboard, a mouse, various switches and the like can be used. The input interface 105 supplies the output signal from the input device to the arithmetic circuit 101 via the bus.

The memory 107 is a storage device such as a RAM, ROM, HDD, SSD, or an integrated circuit storage device that stores various information. Further, the memory 107 may be a drive device or the like that reads and writes various information to and from a portable storage medium such as a CD-ROM drive, a DVD drive, and a flash memory. For example, the memory 107 stores a control program or the like related to CT imaging according to the present embodiment.

Next, an X-ray generation system including an X-ray tube 13 and an X-ray high voltage device 17 according to the present embodiment will be described. FIG. 2 is a diagram showing a configuration of an X-ray generation system including an X-ray tube 13 and an X-ray high voltage device 17 according to the present embodiment. The X-ray tube 13 shown in FIG. 2 is an anode grounded type. The X-ray tube 13 according to the present embodiment is not limited to the anode grounding type, and can be applied to any type such as the neutral point grounding type. FIG. 3 is a diagram showing the internal configuration of the X-ray tube 13.

As shown in FIGS. 2 and 3, the X-ray tube 13 houses the cathode 131, the anode 133, the grid electrode 135 and the deflector 137. The cathode 131 has, for example, a filament formed of a metal such as tungsten or nickel having a fine wire shape. The cathode 131 is connected to the X-ray high voltage device 17 via a cable or the like. The cathode 131 generates heat and emits thermions by receiving the application of the cathode voltage from the X-ray high voltage device 17 and the supply of the filament current.

The anode 133 is an electrode having a disk shape formed of a heavy metal such as tungsten or molybdenum. The anode 133 rotates with the rotation of the rotor around the axis (not shown). A high voltage tube voltage is applied between the cathode 131 and the anode 133 by the X-ray high voltage device 17. The thermions emitted from the cathode 131 collide with the anode 133 due to the action of the tube voltage. The anode 133 receives thermions and generates X-rays. The range where thermions on the anode 133 collide is called the actual focal point, and the apparent actual focal point from the X-ray detector side is called the effective focal point. When the actual focus and the effective focus are not particularly distinguished, they are simply called the focal points.

The grid electrode 135 is arranged between the cathode 131 and the anode 133. A grid voltage with respect to the cathode potential is applied to the grid electrode 135 by the X-ray high voltage device 17. The amount of thermions flying from the cathode 131 to the anode 133 is adjusted by applying a grid voltage. As a result, the tube current value is controlled to an arbitrary value.

The deflector 137 is arranged between the grid electrode 135 and the anode 133. The deflector 137 is realized by an electrode or a coil. A deflection voltage is applied to the deflector 137 by the X-ray high voltage device 17. When the deflector 137 is an electrode, the deflector 137 applies a deflection electric field to the flight path of thermions in response to the application of the deflection voltage. When the deflector 137 is a coil, the deflector 137 applies a deflection magnetic field to the flight path of thermions in response to the application of the deflection voltage. The orbit of thermions flying from the cathode 131 to the anode 133 is deflected by the application of a deflection electric field or a deflection magnetic field. This adjusts the size of the focal point. The size of the focal point is defined by a combination of the width of the effective focal point in the column direction (vertical width) of the X-ray detector 15 and the width of the effective focal point in the channel direction (horizontal width).

In the X-ray tube 13 shown in FIG. 2, the grid electrode 135, the deflector 137, and the anode 133 are arranged in order from the cathode 131. However, this embodiment is not limited to this. For example, the cathode 131, the deflector 137, the grid electrode 135, and the anode 133 may be arranged in this order.

As shown in FIG. 2, the X-ray high voltage device 17 includes a high voltage power supply 31, a filament power supply 33, a grid voltage generation circuit 35, a deflection voltage generation circuit 37, a tube voltage detection circuit 39, a tube current detection circuit 41, and a tube voltage. It has a comparison circuit 43, a tube voltage control circuit 45, a tube current comparison circuit 47, a grid voltage control circuit 49, a filament control circuit 51, a focal size control circuit 53, and a table storage circuit 55.

The high voltage power supply 31 generates a tube voltage applied to the X-ray tube 13 according to the control by the tube voltage control circuit 45. For example, in the case of an inverter type X-ray high voltage device, the high voltage power supply 31 is an AC / DC converter that converts an AC voltage from a commercial power supply into a DC voltage, and an inverter that converts the DC voltage of the AC / DC converter into an AC voltage. It has a transformer that boosts the AC voltage from the inverter, and a high-voltage rectifying smoothing circuit that rectifies and smoothes the AC voltage boosted by the transformer to generate a high DC voltage. The DC high voltage from the high-voltage rectification smoothing circuit is applied as a tube voltage between the cathode 131 and the anode 133 of the X-ray tube 13.

The filament power supply 33 generates a filament current for heating the filament of the cathode 131 according to the control by the filament control circuit 51.

The grid voltage generation circuit 35 applies a grid voltage between the cathode 131 of the X-ray tube 13 and the grid electrode 135 according to the control by the grid voltage control circuit 49. Typically, a grid voltage is applied to the cathode potential of the cathode 131. The grid voltage generation circuit 35 may be realized by a step-down circuit that steps down the voltage generated by the high voltage power supply 31, or may be realized by a power supply system independent of the high voltage power supply 31.

The deflection voltage generation circuit 37 applies a deflection voltage to the deflector 137 of the X-ray tube 13 according to the control by the focus size control circuit 53. The deflection voltage generation circuit 37 is realized by a power supply system independent of the high voltage power supply 31. For example, the deflection voltage generation circuit 37 has an AC / DC converter that converts an AC voltage from a commercial power source into a DC voltage, an inverter that converts the DC voltage of the AC / DC converter into an AC voltage, and a step-down AC voltage from the inverter. It has a transformer for rectifying and smoothing an AC voltage stepped down by the transformer to generate a DC voltage. The DC voltage from the rectifying smoothing circuit is applied to the deflector 137 as a deflection voltage.

The tube voltage detection circuit 39 is connected between the high voltage power supply 31 and the X-ray tube 13. The tube voltage detection circuit 39 detects the voltage applied between the cathode 131 and the anode 133 as the tube voltage. The detected tube voltage value (hereinafter referred to as tube voltage detection value) signal (hereinafter referred to as tube voltage detection signal) is supplied to the tube voltage comparison circuit 43 and the focal size control circuit 53.

The tube current detection circuit 41 is connected between the high voltage power supply 31 and the X-ray tube 13. The tube current detection circuit 41 detects the current flowing due to thermionic flow from the cathode 131 to the anode 133 as the tube current. The detected tube current value (hereinafter referred to as tube current detection value) signal (hereinafter referred to as tube current detection signal) is supplied to the tube current comparison circuit 47 and the focal size control circuit 53.

The tube voltage comparison circuit 43 includes a signal (hereinafter referred to as a tube voltage setting signal) indicating a tube voltage set value (hereinafter referred to as a tube voltage set value) from the gantry control circuit 29 and a tube from the tube voltage detection circuit 39. Input the voltage detection signal. The tube voltage comparison circuit 43 generates a signal (hereinafter referred to as a differential voltage signal) indicating a difference value between the tube voltage set value and the tube voltage detection value by subtracting the tube voltage detection signal from the tube voltage setting signal. The differential voltage signal is supplied to the tube voltage control circuit 45.

The tube voltage control circuit 45 controls the high voltage power supply 31 based on the comparison between the tube voltage detection value and the tube voltage set value, that is, the difference voltage signal. More specifically, the tube voltage control circuit 45 feedback-controls the high voltage power supply 31 so that the tube voltage detection value converges to the tube voltage set value.

The tube current comparison circuit 47 includes a signal (hereinafter referred to as a tube current setting signal) indicating a tube current set value (hereinafter referred to as a tube current set value) from the gantry control circuit 29 and a tube from the tube current detection circuit 41. Input the current detection signal. The tube current comparison circuit 47 generates a signal (hereinafter referred to as a differential current signal) indicating a difference value between the tube current set value and the tube current detection value by subtracting the tube current detection signal from the tube current setting signal. The differential current signal is supplied to the grid voltage control circuit 49.

The grid voltage control circuit 49 controls the grid voltage generation circuit 35 based on the comparison between the tube current detection value and the tube current set value, that is, the difference current signal. More specifically, the grid voltage control circuit 49 feedback-controls the grid voltage generation circuit 35 so that the tube current detection value converges to the tube current set value.

The filament control circuit 51 generates a signal (hereinafter referred to as a filament current setting signal) indicating a filament current set value based on the tube voltage setting signal, the tube current setting signal, and the focal size information from the gantry control circuit 29. Then, the filament power supply 33 is controlled according to the filament current setting signal. The tube current is controlled, for example, by controlling the filament current by the filament control circuit 51. When tube voltage modulation is performed, the tube current may be controlled by controlling the filament current by the filament control circuit 51 and controlling the grid voltage by the grid voltage control circuit 49. Since the tube current cannot follow the modulated tube voltage only by controlling the filament current, the tracking delay is compensated by controlling the grid voltage.

The focal size information is information indicating a desired focal size selected by the input interface 105 or the like. The focus size information is supplied from the gantry control circuit 29.

The focal size control circuit 52 is a tube voltage value of the tube voltage in order to form a focus of a predetermined size on the anode 133 during a period in which the tube voltage is applied between the cathode 131 and the anode 133 by the high voltage power supply 31. By applying a deflection voltage of a deflection voltage value based on the predetermined size to the deflector 137, the size of the focal point formed on the anode 133 is controlled. For example, the focus size control circuit 53 has a deflection voltage associated with the tube voltage value of the tube voltage in the table storage circuit 55 in order to form a focus of a predetermined size on the anode 133 during the period in which the tube voltage is modulated. Based on the value, the size of the focal point formed on the anode 133 is controlled. Specifically, the focal size control circuit 53 inputs a tube voltage detection signal, a tube current detection signal, a tube voltage set value, and a tube current set value. The focal size control circuit 53 inputs at least one of the tube voltage value of the tube voltage detection value indicated by the tube voltage detection signal and the tube voltage set value indicated by the tube voltage setting signal to the table storage circuit 55, and has a predetermined size. Determine the deflection voltage value required to form the focal point. The focal size control circuit 53 may determine the deflection voltage value based on at least one of the tube current detection value indicated by the tube current detection signal and the tube current setting value indicated by the tube current setting signal, in addition to the tube voltage value. .. The focus size control circuit 53 controls the deflection voltage generation circuit 37 in order to apply the deflection voltage of the determined deflection voltage value to the deflector 137.

The table storage circuit 55 stores each of the plurality of tube voltage values in association with the deflection voltage value applied to the deflector 137 in order to form a focal point of a predetermined size on the anode 133. When the deflection voltage is determined in consideration of the tube current value, the table storage circuit 55 stores the deflection voltage value in association with each combination of the plurality of tube voltage values and the plurality of tube current values. Hereinafter, the deflection voltage value shall be determined based on the tube voltage value and the tube current value. The table storage circuit 55 stores a LUT (Look Up Table) that defines the relationship between the combination of the tube voltage value and the tube current value and the deflection voltage value for each of the plurality of focal sizes. Hereinafter, the LUT will be referred to as an X-ray tube characteristic value table.

FIG. 4 is a diagram showing an example of an X-ray tube characteristic value table. As shown in FIG. 4, a deflection voltage value is associated with each combination of the input value to the X-ray tube characteristic value table and the set focal size [vertical width mm × horizontal width mm]. The input value is defined by a combination of the input tube voltage value [kV] and the input tube current value [mA]. As the input tube voltage value, the tube voltage set value or the tube voltage detection value is input. As the input tube current value, the tube current set value or the tube current detection value is input. The input tube voltage value is input in 1 kV increments, and the input tube current value is input in 1 mA increments, for example. The set focus size is set by the user via the input interface 105 or the like. The deflection voltage value is the deflection that should be applied to the deflector 137 to achieve the set focal size when a load defined by the combination of the input tube voltage value and the input tube current value is applied to the X-ray tube 13. It is a voltage value. For example, in order to realize the set focal size "L1 x W1" when the input tube voltage value "V1" and the input tube current value "A11" are applied to the X-ray tube 13, the deflection voltage is applied to the deflector 137. It is necessary to apply the value "BV111".

If the focal size control circuit 52 can adjust the focal size to an arbitrary selection value under the application of the tube voltage, the focal size control circuit 52 adjusts the focal size in the tube voltage constant period in which the tube voltage is not modulated by the tube voltage control circuit 45. It may be controlled, or the focal size may be controlled during the tube voltage modulation period in which the tube voltage is modulated by the tube voltage control circuit 45. Hereinafter, the focus size control circuit 52 uses the tube voltage value of the tube voltage modulated to form a focus of a predetermined size on the anode 133 during the period in which the tube voltage is modulated by the tube voltage control circuit 45, and the predetermined value. By applying a deflection voltage of a deflection voltage value based on the size of the anode 137 to the deflector 137, the size of the focal point formed on the anode 133 shall be controlled.

Next, an operation example of the X-ray computer tomography apparatus related to the control of the tube current and the focal size in the tube voltage modulation will be described.

FIG. 5 is a diagram showing a graph of tube voltage set values in tube voltage modulation. The vertical axis of the graph of FIG. 5 is defined by the tube voltage [kV], and the horizontal axis is defined by the time [sec]. As shown in FIG. 5, in tube voltage modulation, the tube voltage value changes periodically so that the upper limit value V1 and the lower limit value V9 are alternately repeated. The upper limit value V1 and the lower limit value V9 may be set to any value.

As shown in FIG. 5, the tube voltage control circuit 45 controls the high voltage power supply 31 in order to change the tube voltage value so as to periodically repeat the upper limit value V1 and the lower limit value V9. The tube voltage modulation is performed, for example, as follows. The tube voltage comparison circuit 43 inputs a waveform of a tube voltage set value that alternately repeats the upper limit value V1 and the lower limit value V9 as shown in FIG. 5 from the gantry control circuit 29 during X-ray imaging. Further, the tube voltage comparison circuit 43 immediately inputs the tube voltage detection value, which is an output with respect to the tube voltage set value, from the tube voltage detection circuit 39. The tube voltage comparison circuit 43 calculates a difference value (tube voltage difference value) between the tube voltage set value and the tube voltage detection value during the period of tube voltage modulation, and the calculated tube voltage difference value is used as the tube voltage control circuit 45. Repeatedly give feedback to. The tube voltage control circuit 45 controls the high voltage power supply 31 according to the tube voltage difference value so that a voltage such that the tube voltage detection value becomes equal to the tube voltage set value is applied between the cathode 131 and the anode 133. This makes it possible to perform tube voltage modulation according to the tube voltage set value.

Next, tube current control will be described. When the tube voltage is modulated, the amount of thermions emitted from the cathode 131, that is, the tube current also fluctuates due to the emission characteristics of the filament of the cathode 131. The grid voltage control circuit 49 adjusts the amount of thermions emitted from the cathode 131 by applying a grid voltage to the cathode potential, and arbitrarily controls the tube current value.

Specifically, the tube current comparison circuit 47 calculates the difference value (tube current difference value) between the tube current set value and the tube current detection value during the period during which the tube voltage modulation is performed, and the calculated tube current. The difference value is repeatedly fed back to the grid voltage control circuit 49. The grid voltage control circuit 49 repeatedly controls the grid voltage generation circuit 35 according to the tube current difference value so that the tube current detection value becomes equal to the tube current set value. The grid voltage generation circuit 35 repeatedly applies a grid voltage corresponding to the tube current difference value between the cathode 131 and the grid electrode 135. In this way, the tube current detection value can be maintained at the tube current set value by repeatedly adjusting the grid voltage. For example, when the tube current set value is a constant value that does not fluctuate with time, the grid voltage control circuit 49 can maintain the tube current value at the constant value during the tube voltage modulation.

Next, focus size control will be described. FIG. 6 is a diagram showing a graph of a focal dimension and a deflection voltage associated with tube voltage modulation. Focus dimension is a general term for vertical width and horizontal width. The focal dimension is a dimension in one direction, either vertical or horizontal. The focal size is a combination of dimensions in two directions. The vertical width and the horizontal width are individually controlled by the focal size control circuit 53. The focal size is modulated in conjunction with the modulation of the focal dimension.

The left vertical axis of the graph of FIG. 6 is defined by the focal dimension [vertical width mm or horizontal width mm], the right vertical axis is defined by the deflection voltage [V], and the horizontal axis is defined by the time [sec]. Since the left vertical axis in FIG. 6 is one-dimensional, it cannot represent a two-dimensional focal size. Therefore, for simplicity, the left vertical axis is defined by the focal dimension. The thick and thin lines in FIG. 6 indicate the focal dimension, and the dotted line indicates the deflection voltage. As shown by the thick line in FIG. 6, when the tube voltage modulation is simply performed, the focal dimension fluctuates with the tube voltage modulation, and the image quality deteriorates. The focal size control circuit 53 according to the present embodiment uses the X-ray tube characteristic value table to maintain a constant focal dimension regardless of the tube voltage modulation as shown by the thin line in FIG. The generation circuit 37 is controlled.

As the focal size control method, there are a method of using the tube voltage detection value and the tube current detection value, and a method of using the tube voltage set value and the tube current set value. Hereinafter, they will be described in order.

In the method of utilizing the tube voltage detection value and the tube current detection value, the focus size control circuit 53 inputs the set focus size from the gantry control circuit 29 at the start of the X-ray CT imaging. It is assumed that the set focal size is a constant value that does not change with the passage of time. For example, as shown in FIG. 6, the set focal size is set to "L1 × W1" or the like. During the X-ray CT imaging, the tube voltage detection value is repeatedly fed back from the tube voltage detection circuit 39 to the tube current detection circuit 41, and the tube current detection value is repeatedly fed back to the focal size control circuit 53 from the tube current detection circuit 41.

During X-ray CT imaging, the focus size control circuit 53 searches the X-ray tube characteristic value table using the set focus size, tube voltage detection value, and tube current detection value as search keys at predetermined time intervals, and sets the set focus size. Identify the deflection voltage value associated with the combination of the tube voltage detection value and the tube current detection value. For example, as shown in FIG. 4, in the case of the set focal size "L1 or W1", the tube voltage detection value "V2", and the tube current detection value "A21", the deflection voltage value "BV211" is specified. The focus size control circuit 53 controls the deflection voltage generation circuit 37 so as to apply the deflection voltage of the specified deflection voltage value to the deflector 137 each time the deflection voltage value is specified. Since the deflection voltage generation circuit 37 generates a deflection voltage by a power supply system independent of the high voltage power supply 31, the focal size control circuit 53 can control the deflection voltage independently of the tube voltage. .. Therefore, by applying the deflection voltage of the deflection voltage value determined by using the X-ray tube characteristic value table to the deflector 137, the focal size can be maintained at the set focal size even when the tube voltage is modulated. It will be possible.

In the method of utilizing the tube voltage set value and the tube current set value, the focus size control circuit 53 inputs the set focus size from the gantry control circuit 29 at the start of the X-ray CT imaging. The focal size control circuit 53 inputs a tube voltage set value and a tube current set value from the gantry control circuit 29 during X-ray CT imaging. As shown in FIG. 5, the tube voltage set value related to the tube voltage modulation changes periodically with the passage of time. It is assumed that the tube current set value and the set focal size are constant values that do not change with the passage of time.

During X-ray CT imaging, the focal size control circuit 53 searches the X-ray tube characteristic value table using the set focal size, tube voltage set value, and tube current set value as search keys at predetermined time intervals, and sets the set focal size. Identify the deflection voltage value associated with the combination of the tube voltage set value and the tube current set value. The focus size control circuit 53 controls the deflection voltage generation circuit 37 so as to apply the deflection voltage of the specified deflection voltage value to the deflector 137 each time the deflection voltage value is specified. Therefore, by applying the deflection voltage of the deflection voltage value determined by using the X-ray tube characteristic value table to the deflector 137, the focal size can be maintained at the set focal size even when the tube voltage is modulated. It will be possible.

The X-ray tube characteristic value table used may differ between the method of using the tube voltage detection value and the tube current detection value and the method of using the tube voltage set value and the tube current set value. That is, a first X-ray tube characteristic value table in which the input values are the tube voltage detection value and the tube current detection value, and a second X-ray tube characteristic value table in which the input values are the tube voltage set value and the tube current set value are created. , It is good that it is stored in the table storage circuit 55. In this case, a value different from the deflection voltage value in the first X-ray tube characteristic value table and the deflection voltage value in the second X-ray tube characteristic value table is associated with the same input value. This is because the tube voltage set value and the tube voltage detection value detected in response to the application of the tube voltage do not always match due to a response delay or the like.

When using the tube voltage set value and the tube current set value, it is preferable that the deflection voltage value in consideration of the tube voltage and the response delay of the tube current with respect to the set value is registered in the X-ray tube characteristic value table.

In the above embodiment, it is assumed that the focal size is kept constant at the time of tube voltage modulation. However, this embodiment is not limited to this. That is, as for the set focal size, the first size and the second size may be periodically repeated with the passage of time. Even in this case, the focal size control circuit 53 takes the waveform of the set focal size that is repeated periodically as an input, and sets the X-ray tube characteristic value table based on the combination of the set focal size, the tube voltage set value, and the tube current set value. It can be used to determine the deflection voltage value. As a result, the focus size control circuit 53 can control the focus size to an arbitrary value at the time of tube voltage modulation.

The focal size control circuit 53 controls the deflector 137 so as to realize the set focal size based on the combination of the tube voltage value and the tube current value. However, this embodiment is not limited to this. For example, the focus size control circuit 53 controls the deflection voltage generation circuit 37 so as to realize the set focus size based on the tube voltage value or the tube current value. In this case, in the X-ray tube characteristic value table, the tube voltage value or tube current value and the deflection voltage value are associated with each set focal size. The focal size control circuit 53 searches the X-ray tube characteristic value table using the tube voltage value or the combination of the tube current value and the set focal size as a search key, and identifies and identifies the deflection voltage value associated with the combination. The deflection voltage generation circuit 37 is controlled according to the deflection voltage value. This makes it possible to arbitrarily control the focal size based on either the tube voltage value or the tube current value.

In the above embodiment, the focus size control circuit 53 determines the deflection voltage value using the X-ray tube characteristic value table. However, this embodiment is not limited to this. For example, the focal size control circuit 53 determines a deflection voltage value corresponding to the input tube voltage value and the set focal size, or a deflection voltage value corresponding to the combination of the input tube voltage value and the input tube current value and the set focal size. , It may be calculated according to a predetermined algorithm, or it may be determined by machine learning or the like.

According to at least one embodiment described above, the focal size can be arbitrarily controlled.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

10 ... Stand, 11 ... Rotating frame, 13 ... X-ray tube, 15 ... X-ray detector, 17 ... X-ray high voltage device, 19 ... Data acquisition circuit, 21 ... Rotating drive device, 23 ... Sleeper, 25 ... Sleeper drive Device, 29 ... gantry control circuit, 31 ... high voltage power supply, 33 ... filament power supply, 35 ... grid voltage generation circuit, 37 ... deflection voltage generation circuit, 39 ... tube voltage detection circuit, 41 ... tube current detection circuit, 43 ... tube Voltage comparison circuit, 45 ... tube voltage control circuit, 47 ... tube current comparison circuit, 49 ... grid voltage control circuit, 51 ... filament control circuit, 53 ... focus size control circuit, 55 ... table storage circuit, 100 ... console, 101 ... Calculation circuit, 103 ... Display, 105 ... Input circuit, 107 ... Storage circuit, 111 ... Preprocessing function, 113 ... Reconstruction function, 115 ... Image processing function, 117 ... System control function, 131 ... Cathode, 133 ... Adenator, 135 ... grid electrode, 137 ... deflector.

Claims (7)

An X-ray tube having a cathode that emits electrons, an anode that receives electrons from the cathode and generates X-rays, and a deflector that deflects the electrons from the cathode.
A high voltage power supply that generates a tube voltage applied between the cathode and the anode,
A tube current control circuit that controls the tube current flowing through the X-ray tube,
With a table storage circuit that stores the deflection voltage value applied to the deflector in order to form a focal point of the size for each combination of a plurality of tube voltage values, a plurality of tube current values, and a plurality of focal sizes. ,
In order to form a focal point of a predetermined size on the anode during the period when the tube voltage is applied by the high voltage power supply, the tube voltage value of the tube voltage and the tube current value of the tube current flowing through the X-ray tube are used. A focus size control circuit that controls the size of the focal point formed on the anode by applying a deflection voltage of a deflection voltage value associated with the combination with the predetermined size to the deflector.
X-ray computer tomography apparatus equipped with. A tube voltage control circuit that inputs a set value of a tube voltage that changes in time series and modulates the tube voltage applied between the cathode and the anode based on the input set value is further provided.
The focal size control circuit applies a voltage having a deflection voltage value associated with the input set value , the tube current value of the tube current flowing through the X-ray tube, and the predetermined size to the deflector.
The X-ray computer tomography apparatus according to claim 1 . A detector for detecting the tube voltage applied between the cathode and the anode is further provided.
The focal size control circuit applies a voltage having a deflection voltage value associated with the detected value of the detected tube voltage, the tube current value of the tube current flowing through the X-ray tube, and the predetermined size to the deflector. do,
The X-ray computer tomography apparatus according to claim 1 . The second aspect of the invention, wherein the table storage circuit stores the plurality of tube voltage values and the plurality of tube current values in association with a deflection voltage value for forming a focal point of the same size as the predetermined size. X-ray computer tomography equipment. A tube voltage control circuit that modulates the tube voltage applied between the cathode and the anode,
A deflection voltage generation circuit that generates a deflection voltage applied to the deflector is further provided.
The tube voltage control circuit controls the high voltage power supply based on the tube voltage value.
The focus size control circuit controls the deflection voltage generation circuit based on the deflection voltage value.
The deflection voltage generation circuit generates the deflection voltage in an electric system independent of the high voltage power supply.
The X-ray computer tomography apparatus according to claim 1. Further provided with a tube voltage control circuit that modulates the tube voltage applied between the cathode and the anode.
The focal size control circuit includes a tube voltage value of the modulated tube voltage and the tube voltage value of the modulated tube voltage in order to form a focus of the predetermined size on the anode during a period in which the tube voltage is modulated by the tube voltage control circuit. A deflection voltage of a deflection voltage value based on the tube current value of the tube current flowing through the X-ray tube and the predetermined size is applied to the deflector.
The X-ray computer tomography apparatus according to claim 1. Each of the plurality of focal sizes is a combination of vertical width and horizontal width.
The focal size control circuit individually controls the vertical width and the horizontal width.
The X-ray computer tomography apparatus according to claim 1.

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