JP2018206582A - X-ray image capturing apparatus and X-ray tube - Google Patents

Abstract

To provide an x-ray image capturing apparatus and an x-ray tube capable of reducing the temperature rise of a target of an X-ray tube.SOLUTION: An x-ray image capturing apparatus according to an embodiment includes a target that generates X-rays by collision of thermal electrons irradiated from a filament, a drive unit that supports the target and varies a distance between the target and the filament, and an adjustment unit that adjusts an irradiation angle of the thermal electrons with respect to the target such that a focal position with respect to a driving direction of the target does not change on the basis of the distance between the target and the filament.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to an X-ray imaging apparatus and an X-ray tube.

  As an X-ray imaging apparatus that acquires an image from X-rays that have passed through a subject, for example, an X-ray CT (Computed Tomography) apparatus, an X-ray TV bed apparatus, an X-ray cardiovascular diagnostic system, and the like are known. An X-ray tube used in this type of X-ray imaging apparatus is emitted from a filament by, for example, applying a DC high voltage between the cathode and the anode and heating the cathode with a filament current to emit thermoelectrons. X-rays are emitted by focusing the hot electrons on the anode target. The target is configured using, for example, tungsten. The thermoelectrons emitted from the filament are focused by the focusing electrode, accelerated by a high voltage, and collide with the target.

  The target of the anode is overheated at one point of collision by the collision of the thermionic beam. Therefore, in order to prevent this local overheating of one point, some X-ray tubes include a rotating anode that rotates a target. The rotating anode has an umbrella-shaped target facing the cathode, and supports the target rotatably. The thermoelectrons are focused on the inclined surface of the target (the surface facing the cathode) to form a focal point on the target.

  Since the X-ray tube including the rotating anode can rotate the target, it is possible to avoid local focusing of the thermal electrons.

JP 2010-63758 A

  However, only by rotating the target, the locus of the focal point on the target always follows the same position, so that the temperature of the region of this locus is extremely increased and overheated.

  The problem to be solved by the present invention is to reduce the temperature rise of the target of the X-ray tube.

  An X-ray imaging apparatus according to an embodiment includes a target that generates X-rays by the collision of thermoelectrons irradiated from a filament, a drive unit that supports the target and varies the distance between the target and the filament. And an adjusting unit that adjusts an irradiation angle of the thermoelectrons with respect to the target so that a focus position with respect to a driving direction of the target does not change based on a distance between the target and the filament.

The block diagram which shows an example of the X-ray CT apparatus containing the X-ray tube which concerns on this embodiment. The schematic block diagram which shows the structural example of an X-ray tube, and the implementation | achievement function example by the processor of the processing circuit of the X-ray tube control apparatus of a gantry apparatus. (A) is a side view of the rotating anode for explaining the locus of the conventional focal position, (b) is a front view of the target of the rotating anode 151. (A) is a side view of the rotating anode for explaining the locus of the focal position according to the present embodiment, (b) is a front view of the target of the rotating anode. The figure for demonstrating the method to adjust the irradiation angle of a thermoelectron with an adjustment mechanism so that the focus position in the drive direction of a target may not change. (A) is a front view of the target for demonstrating the relationship between the spiral locus | trajectory adjacent on a target, and a focus size, (b) is a side view of a target.

  An X-ray imaging apparatus and an X-ray tube according to embodiments will be described with reference to the accompanying drawings.

(Schematic configuration of X-ray CT system)
FIG. 1 is a block diagram showing an example of an X-ray CT apparatus 1 including an X-ray tube 11 according to the present embodiment. In the following description, an example in which the X-ray CT apparatus 1 is used as an example of the X-ray imaging apparatus according to the embodiment will be described. In the present embodiment, the axis of rotation of the rotating frame 13 in the non-tilt state or the longitudinal direction of the top plate 33 of the bed apparatus 30 is orthogonal to the z-axis direction and the z-axis direction and is horizontal to the floor surface. Are defined as an y-axis direction and an axial direction perpendicular to the x-axis direction and z-axis direction and perpendicular to the floor surface, respectively (see FIG. 1).

  The X-ray CT apparatus 1 includes a gantry device 10, a bed device 30, and a console device 40. FIG. 2 is a schematic block diagram showing a configuration example of the X-ray tube 11 and an example of functions realized by the processor of the processing circuit 21 of the X-ray tube control device 20 of the gantry device 10.

  The X-ray CT apparatus 1 includes a Rotate / Rotate-Type (third generation CT) in which an X-ray tube and a detector are integrally rotated around a subject, and a large number of X-ray detection elements arrayed in a ring shape. There are various types such as Stationary / Rotate-Type (fourth generation CT) in which only the X-ray tube rotates around the subject, and any type is applicable to the present embodiment. In the following description, an example in which a third generation Rotate / Rotate-Type is employed as the X-ray CT apparatus 1 according to the present embodiment will be described.

  The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13 having an opening 13 a in which an imaging region is inherent, an X-ray high voltage device 14, a gantry controller 15, a wedge 16, a collimator 17, and data collection. An X-ray tube control device 20 having a circuit (DAS: Data Acquisition System) 18 and a processing circuit 21 is provided.

  As shown in FIG. 2, the X-ray tube 11 includes a rotating anode 51 and a filament (cathode) 61.

  For example, the X-ray tube 11 receives supply of a high voltage from the X-ray high voltage device 14 and irradiates thermoelectrons from the filament (cathode) 61 toward the target 52 of the rotary anode 51. In this embodiment, the present invention can be applied to a single-tube type X-ray CT apparatus, and a so-called multi-tube type X-ray in which a plurality of pairs of an X-ray tube and a detector are mounted on a rotating ring. It can also be applied to a line CT apparatus.

  The X-ray detector 12 includes, for example, a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction along one arc with the focal point of the X-ray tube 11 as the center. The X-ray detector 12 has a structure in which a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction are arranged in the slice direction. The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passed through the subject (for example, a patient) P, and outputs an electrical signal corresponding to the X-ray dose to the DAS 18.

  Moreover, the X-ray detector 12 is an indirect conversion type detector comprised of a grid, a scintillator array, and an optical sensor array, for example. The scintillator array is composed of a plurality of scintillators, and the scintillator is composed of a scintillator crystal that outputs a photon amount of light corresponding to the incident X-ray dose. The grid is an X-ray shielding plate that is disposed on the surface on the X-ray incident side of the scintillator array and has a function of absorbing scattered X-rays. The photosensor array has a function of converting into an electrical signal corresponding to the amount of light from the scintillator, and is composed of a photosensor such as a photomultiplier tube, for example.

  Note that the X-ray detector 12 may be a direct conversion type detector constituted by a semiconductor element that converts incident X-rays into electrical signals.

  The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so as to face each other and rotates the X-ray tube 11 and the X-ray detector 12 by a gantry controller 15 described later. In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 further includes and supports an X-ray high voltage device 14 and a DAS 18.

  Note that the detection data generated by the DAS 18 is a photo provided on a non-rotating portion of the gantry device 10 such as a fixed frame (not shown) by optical communication from a transmitter having a light emitting diode (LED) provided on the rotating frame 13. It is transmitted to a receiver having a diode and transferred to the console device 40. The detection data transmission method from the rotating frame 13 to the non-rotating portion of the gantry device 10 is not limited to the optical communication described above, and any method may be adopted as long as it is a non-contact type data transmission. A fixed frame (not shown) is a frame that rotatably supports the rotating frame 13.

  The X-ray high voltage device 14 includes an electric circuit such as a transformer and a rectifier, and the X-ray tube 11 irradiates a high voltage generator having a function of generating a high voltage to be applied to the X-ray tube 11. An X-ray control device that controls the output voltage according to the X-ray to be performed. The high voltage generator may be a transformer system or an inverter system. The X-ray high voltage device 14 may be provided on the rotating frame 13 or on the fixed frame side of the gantry device 10.

  The gantry control device 15 includes a processor and a storage circuit, and a driving mechanism such as a motor and an actuator. The gantry control device 15 has a function of receiving an input signal from an input interface attached to the console device 40 or the gantry device 10 and controlling the operation of the gantry device 10. For example, the gantry control device 15 performs control for receiving the input signal to rotate the rotating frame 13, control for tilting the gantry device 10, and control for operating the bed device 30 and the top plate 33.

  Note that the tilt control of the gantry device 10 is controlled by the gantry control device 15 about the axis parallel to the X-axis direction based on the tilt angle (tilt angle) information input by the input interface attached to the gantry device 10. This is realized by rotating 13. The gantry control device 15 may be provided in the gantry device 10 or in the console device 40.

  The wedge 16 is a filter for adjusting the X-ray dose irradiated from the X-ray tube 11. Specifically, the wedge 16 transmits and attenuates the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the subject P have a predetermined distribution. It is a filter. For example, the wedge 16 (wedge filter, bow-tie filter) is a filter obtained by processing aluminum so as to have a predetermined target angle and a predetermined thickness.

  The collimator 17 is a lead plate or the like for narrowing the irradiation range of X-rays transmitted through the wedge 16, and forms a slit by a combination of a plurality of lead plates or the like.

  The DAS 18 includes at least an amplifier that performs amplification processing on an electric signal output from each X-ray detection element of the X-ray detector 12 and an A / D converter that converts the electric signal into a digital signal. Generate data. The detection data generated by the DAS 18 is transferred to the console device 40.

  The X-ray tube control device 20 includes at least a processing circuit 21 and a memory. The processing circuit 21 of the X-ray tube control device 20 is a processor that executes processing for reducing the temperature rise of the target 52 of the X-ray tube 11 by reading and executing a program stored in the memory. Further, the X-ray tube control device 20 may be provided in the gantry device 10 or may be provided in the console device 40.

  The couch device 30 is a device for placing and moving the subject P to be scanned, and includes a base 31, a couch driving device 32, a top plate 33, and a support frame 34.

  The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction (y direction). The couch driving device 32 is a motor or actuator that moves the top plate 33 on which the subject P is placed in the long axis direction (z direction) of the top plate 33. The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed.

  The couch driving device 32 may move the support frame 34 in the long axis direction (z direction) of the top plate 33 in addition to the top plate 33. Further, the bed driving device 32 may be moved together with the base 31 of the bed device 30. When the present invention can be applied to standing CT, a method of moving a patient moving mechanism corresponding to the top board 33 may be used. Further, when performing a scan that involves a relative change in the positional relationship between the imaging system of the gantry 10 and the top plate 33, such as a helical scan or a positioning scan, the relative change in the positional relationship is driven by the driving of the top plate 33. May be performed by running the pedestal or by combining them.

  The console device 40 includes an input interface 41, a display 42, a memory 43, and a processing circuit 44.

  The input interface 41 receives various input operations from the user, converts the received input operations into electrical signals, and outputs them to the processing circuit 44. For example, the input interface 41 receives from the operator collection conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-processed image from a CT image, and the like. . The input interface 41 is realized by, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a numeric keypad, or the like.

  The display 42 displays various information. For example, the display 42 outputs a medical image (CT image) generated by the processing circuit 44, a GUI (Graphical User Interface) for receiving various operations from the user, and the like. For example, the display 42 includes a liquid crystal display, a CRT (Cathode Ray Tube) display, an OLED (Organic Light Emitting Diode) display, or the like.

  The memory 43 has a configuration including a recording medium readable by a processor such as a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, and an optical disk. The memory 43 stores, for example, projection data and reconstructed image data. A part or all of the program and data in the recording medium of the memory 43 may be downloaded by communication via a network.

  The processing circuit 44 of the console device 40 controls the entire operation of the X-ray CT apparatus 1 in accordance with, for example, an electric signal for input operation output from the input interface 41.

  For example, the processing circuit 44 controls various functions of the processing circuit 44 based on an input operation received from the user via the input interface 41. Further, the processing circuit 44 generates data obtained by performing preprocessing such as logarithmic conversion processing, offset correction processing, interchannel sensitivity correction processing, and beam hardening correction on the detection data output from the DAS 18. Note that data before preprocessing (detection data output by the DAS 18) and data after preprocessing may be collectively referred to as projection data.

  Further, the processing circuit 44 performs a reconstruction process using a filtered back projection method, a successive approximation reconstruction method, or the like on the generated projection data to generate CT image data. Further, the processing circuit 44 converts the generated CT image data into tomographic image data or three-dimensional image data of an arbitrary cross section by a known method based on an input operation received from the user via the input interface 41.

(Configuration of X-ray tube 11)
Next, a configuration example of the X-ray tube 11 according to the present embodiment and an implementation function example of the processing circuit 21 of the X-ray tube control device 20 of the gantry device 10 will be described.

  As shown in FIG. 2, the processor of the processing circuit 21 of the X-ray tube control device 20 of the gantry device 10 includes a rotation control function 211, a drive control function 212, an irradiation angle control function 213, an aperture control function 214, and a synchronous control function. 215 is realized. Each of these functions is stored in the memory 43 in the form of a program.

As shown in FIG. 2, the rotating anode 51 of the X-ray tube 11 includes an umbrella-shaped target 52 that generates X-rays by collision of thermoelectrons, a rotor 53, a shaft 54, and a drive mechanism 55. Have The rotor 53 is attached to the shaft 54. The shaft 54 includes a bearing (not shown) that rotatably supports the rotor 53. The rotor 53 constitutes an electric motor together with a stator coil 71 disposed outside a glass bulb (not shown). The rotor 53 rotates at a high speed along the rotation axis (z axis) integrally with the target 52 by a rotating magnetic field or the like from the stator coil 71. The rotation control function 211 rotates the target 52 through the stator coil 71 and controls the rotation speed.
Here, problems of the conventional rotating anode 151 will be described.

  3A is a side view of the rotary anode 151 for explaining a conventional focal position locus 156, and FIG. 3B is a front view of the target 152 of the rotary anode 151. FIG.

  In general, when thermoelectrons generated in the filament 161 collide with the target 152, most of the energy is converted into heat, and high heat is generated at the focus of the target 152. For this reason, by rotating the target 152 around the shaft, the locus 156 of the focal position can be formed in a ring shape, so that one point of heat can be avoided. However, as is clear from FIG. 3, the locus 156 of the focal position causes the thermal electrons to collide with the original location again when the target 152 makes one round. For this reason, since the peak of heat generation in the entire target 152 eventually concentrates on the locus 156, the continuous output time of X-rays at a predetermined tube current and tube voltage is limited by the ring length of the locus 156.

  Thus, the X-ray tube 11 according to the present embodiment makes it possible to lengthen the X-ray continuous output time by lengthening the locus of the focal position.

  FIG. 4A is a side view of the rotating anode 51 for explaining the focal point locus 56 according to the present embodiment, and FIG. 4B is a front view of the target 52 of the rotating anode 51.

  The drive mechanism 55 supports the shaft 54 via the drive support portion 55a. In addition, the drive mechanism 55 drives the shaft 54, the rotor 53, and the target 52 in translation along the rotation axis (z axis) of the target 52 through the drive support portion 55a. As a result, the distance in the z-axis direction between the target 52 and the filament 61 varies. The drive control function 212 controls the translational movement amount and translational movement speed along the z-axis of the target 52 via the drive support part 55 a of the drive mechanism 55.

  The drive support portion 55a only needs to be configured to support the shaft 54 and be translationally driven along the z-axis. For example, the drive support portion 55a can be configured by a screw mechanism or a pinion rack, and is provided in a recess on the shaft 54 side. It may be constituted by a linear motor type translational drive mechanism using the magnetic force between the magnetic body or electromagnet and the magnetic body or electromagnet provided on the convex portion side of the drive mechanism 55 fitted in the concave portion.

  The X-ray tube 11 includes an adjusting mechanism 62 that focuses the thermoelectrons generated from the filament 61 on the target 52 and adjusts the irradiation angle of the thermoelectrons on the target 52. The adjusting mechanism 62 is configured by, for example, a four-divided focusing electrode, and can individually control the voltage applied to each electrode element to control the irradiation angle of the thermoelectrons with respect to the target 52 and change the focal spot size. be able to. The irradiation angle control function 213 adjusts the irradiation angle of the thermoelectrons on the target 52 via the adjustment mechanism 62.

  The thermoelectrons generated in the filament 61 of the X-ray tube 11 are accelerated by a high voltage, focused as an electron beam by the adjusting mechanism 62, and collide with the target 52, whereby X-rays are generated at the focal point of the target 52.

  The adjustment mechanism 62 is designed such that the reference angle for adjusting the irradiation angle is a non-parallel angle with respect to the rotation axis (z axis) of the target 52. This reference angle is determined by calculating back from the size of the X-ray detector 12 (width in the z direction), the distance from the target 52 to the X-ray detector 12, the inclination angle of the umbrella-shaped portion of the target 52, and the like. .

  By irradiating the target 52 with thermoelectrons non-parallel to the translation drive direction (z-axis direction) of the target 52, the target 52 is translated and the distance in the z-axis direction between the target 52 and the filament 61 varies. The locus 56 of the focal position of the thermoelectrons on the target 52 draws a spiral (see FIG. 4B). As a result, the locus 56 of the focal position according to the present embodiment can be made significantly longer than the locus 156 of the conventional focal position, and concentration of the overheated portion on the target 52 can be prevented.

  FIG. 5 is a diagram for explaining a method for adjusting the irradiation angle of the thermal electrons by the adjusting mechanism 62 so that the focal position in the driving direction of the target 52 does not change.

  As shown in FIG. 5, when the target 52 translates along the rotation axis (z-axis), the focal position 81 changes to the focal position 82. The focal position 81 and the focal position 82 differ in the position of the target 52 in the driving direction (z-axis direction), and therefore the focal position expected by the X-ray detector 12 differs. Therefore, as shown in FIG. 5, the adjusting mechanism 62 prevents the focus position with respect to the drive direction of the target 52 from changing based on the distance in the drive direction between the target 52 and the filament 61, that is, the thermoelectrons at the focus position 83. Adjust the irradiation angle of the thermoelectrons so that they collide.

  More specifically, the synchronization control function 215 has a rotation control function so that the focal position of the target 52 with respect to the driving direction does not change and the locus 56 of the focal position of the thermoelectrons on the target 52 draws a spiral. The rotation speed control of the target 52 by 211, the translation speed control of the target 52 by the drive control function 212, the irradiation angle control of the thermoelectrons by the irradiation angle control function 213, and the aperture width control of the opening 72 of the collimator 17 by the aperture control function 214. Synchronous control is recommended.

  The aperture control function 214 may control the opening width of the opening 72 of the collimator 17 based on the distance in the driving direction between the target 52 and the filament 61.

  FIG. 6A is a front view of the target 52 for explaining the relationship between the spiral trajectories 56n and 56n + 1 adjacent to each other on the target 52 and the focal point sizes 91n and 91n + 1. It is a side view.

  The actual focus on the target 52 has a focus size 91n corresponding to the position 56n of the locus 56. For this reason, the synchronization control function 215 controls the rotation control function 211 to control the interval between the spirals 56n and 56n + 1 so that the actual focus does not overlap by a predetermined ratio (for example, half) or more according to the focus size 91n on the target 52. The drive control function 212, the irradiation angle control function 213, and the aperture control function 214 may be controlled synchronously. FIGS. 6A and 6B show an example in which synchronous control is performed so that the actual focal points do not overlap at all.

  The smaller the overlap of the real focal points between adjacent spiral trajectories 56, the more heat concentration can be prevented and the X-ray continuous output time can be made longer.

  According to at least one embodiment described above, the temperature rise of the target 52 of the X-ray tube 11 can be reduced.

  Note that the drive mechanism 55 and the adjustment mechanism 62 in the present embodiment are examples of the drive unit and the adjustment unit in the claims, respectively. In addition, the rotation control function 211, the aperture control function 214, and the synchronization control function 215 of the processing circuit 21 according to the present embodiment are examples of a rotation control unit, an aperture control unit, and a synchronization control unit, respectively, in the claims.

  In the above embodiment, the term “processor” means, for example, a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC). It shall mean a circuit such as a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and an FPGA). The processor implements various functions by reading and executing a program stored in the storage medium.

  In the above embodiment, an example in which a single processor of a processing circuit realizes each function has been described. However, a processing circuit is configured by combining a plurality of independent processors, and each processor realizes each function. Also good. Further, when a plurality of processors are provided, the storage medium for storing the program may be provided for each processor individually, or one storage medium stores the programs corresponding to the functions of all the processors in a lump. Also good.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus 11 ... X-ray tube 17 ... Collimator 52 ... Target 56, 56n ... Trajectory 61 ... Filament 72 ... Opening 81, 83 ... Focus position 91n ... Focus size 211 ... Rotation control function 212 ... Drive control function 213 ... Irradiation angle control function 214 ... Aperture control function 215 ... Synchronous control function

Claims (7)

A target that generates X-rays by collision of thermal electrons irradiated from a filament;
A drive unit that supports the target and varies a distance between the target and the filament;
An adjustment unit that adjusts the irradiation angle of the thermoelectrons with respect to the target based on the distance between the target and the filament so that the focal position with respect to the driving direction of the target does not change;
An X-ray imaging apparatus comprising: A collimator for limiting the X-ray irradiation area;
A diaphragm controller that controls the opening width of the collimator based on the distance between the target and the filament;
The X-ray imaging apparatus according to claim 1, further comprising: A rotation controller for rotating the target;
Further comprising
The drive unit is
By changing the distance of the target and the filament in the driving direction of the target by translationally driving the target with the direction along the rotation axis of the target as the driving direction of the target,
The X-ray imaging apparatus according to claim 1 or 2. The adjustment unit, the drive unit, and the rotation control unit are synchronized so that the focal position with respect to the drive direction of the target does not change and the locus of the focal position of the thermoelectrons on the target draws a spiral. A synchronous control unit to control,
The X-ray imaging apparatus according to claim 3, further comprising: The synchronization control unit
According to the focus size on the target, the adjustment unit, the drive unit, and the rotation control unit are synchronously controlled so as to control the space between the spirals so that the actual focus does not overlap.
The X-ray imaging apparatus according to claim 4. The thermoelectrons are
Colliding with the target at an irradiation angle non-parallel to the driving direction of the target,
The X-ray imaging apparatus according to any one of claims 1 to 5. A filament that emits thermal electrons;
A target that generates X-rays by the collision of the thermoelectrons irradiated from the filament;
A drive unit that supports the target and varies a distance between the target and the filament;
An adjustment unit that adjusts the irradiation angle of the thermoelectrons with respect to the target based on the distance between the target and the filament so that the focal position with respect to the driving direction of the target does not change;
X-ray tube with

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