JP2019118699A - X-ray diagnostic apparatus - Google Patents

Abstract

To facilitate the handling of an X-ray diagnostic apparatus as to changing of a focal size.SOLUTION: An X-ray diagnostic apparatus 1 comprises: an X-ray tube 21; a signal switching unit 44a; a focal size changing unit 44b; and a filament current setting unit 44c. The X-ray tube 21 comprises an anode with a target, a cathode with filaments, and a grid electrode for restricting electrons from the filaments to thereby generate X-rays. The signal switching unit 44a operates in conjunction with a use state at a diagnosis and switches a focal size change signal which indicates a change of the focal size of a focal point formed on the target. The focal size changing unit 44b changes a grid bias in response to switching of the focal size change signal to thereby change the focal size. The filament current setting unit 44c sets a filament current corresponding to a desired grid bias target value when the focal size change signal is switched.SELECTED DRAWING: Figure 1

Description

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

  In the X-ray diagnostic apparatus, the X-ray tube is provided with a grid electrode, the focal spot size is set before X-ray irradiation, and the focal spot size is changed by applying a grid bias corresponding to the focal spot size to the grid electrode There is something. This type of X-ray diagnostic apparatus is capable of finely setting the focal spot size. In addition, since this type of X-ray diagnostic apparatus does not need to switch a plurality of filaments, it is possible to change the focal spot size at high speed without depending on the thermal inertia of the filaments.

  By the way, when the input (tube voltage and tube current) to the X-ray tube is the same, the image quality (sharpness) of the X-ray image is improved as the focal point size is smaller. However, the smaller the focal spot size, the higher the temperature of the focal spot on the target of the X-ray tube, so the input to the X-ray tube is limited to the extent that the target does not melt.

  Usually, the focus size to be used is predetermined according to the examination. Specifically, when the tube current capable of securing the dose necessary for the inspection is determined, the focal point size to which the tube current can flow is determined. The focal spot size is set larger in favor of the dose because if the dose is insufficient during the examination, an X-ray image suitable for diagnosis can not be generated.

  However, if there is a change in subject thickness due to a change in the examination site or a required change in image quality during the examination, the focus size set before the examination may not be an appropriate value. If the focal spot size does not reach an appropriate value, the dose necessary for the inspection can not be secured, and either the image quality may deteriorate or the sharpness may deteriorate due to the focal spot size being too large. Occurs. On the other hand, when it is desired to change the focal point size so as to minimize the image quality deterioration while securing the dose necessary for the inspection, the focal point size is checked during the inspection in consideration of the relationship between the anode heat quantity and the overload protection. The operator's operation may be complicated because it is necessary to reset the input conditions to the X-ray tube. In other words, when it is desired to change the focal point size during the examination, it is necessary to reset the setting appropriately by the operation of the operator, which makes it difficult to handle the X-ray diagnostic apparatus with respect to the focal point change.

JP-A-61-218100

  The problem to be solved by the present invention is to facilitate the handling of the X-ray diagnostic apparatus with respect to changes in focal spot size.

  According to the embodiment, the X-ray diagnostic apparatus includes an X-ray tube, a grid bias power supply circuit, a filament heating circuit, a signal switching unit, a focus size changing unit, and a filament current setting unit. The x-ray tube comprises an anode with a target, a cathode with a filament, and a grid electrode which limits electrons from the filament and generates x-rays. The grid bias power supply circuit applies a grid bias to the grid electrodes. The filament heating circuit heats the filament by supplying the filament current to the filament. The signal switching unit switches the focus size change signal indicating the change of the focus size of the focus formed on the target in conjunction with the use condition at the time of diagnosis. The focus size changing unit changes the focus size by changing the grid bias in response to the switching of the focus size change signal. The filament current setting unit sets a filament current corresponding to a desired target value of the grid bias when switching the focus size change signal.

FIG. 1 is a schematic view showing the configuration of the X-ray diagnostic apparatus according to the first embodiment. FIG. 2 is a schematic view showing the configuration of the X-ray high voltage generator and the X-ray tube in the embodiment. FIG. 3 is a flowchart for explaining the operation in the embodiment. FIG. 4 is a timing chart for explaining the operation in the embodiment. FIG. 5 is a schematic view showing the configuration of the X-ray diagnostic apparatus according to the second embodiment. FIG. 6 is a timing chart for explaining the operation in the embodiment.

  Hereinafter, each embodiment will be described with reference to the drawings. In each embodiment, elements which are the same as or similar to the described elements are given the same or similar reference numerals, and redundant explanations are omitted, and elements which are not described yet are mainly described.

First Embodiment
FIG. 1 is a block diagram showing a configuration example of the X-ray diagnostic apparatus 1 according to the first embodiment. The X-ray diagnostic apparatus 1 includes a bed having an X-ray high voltage generator 10, an X-ray generator 20, an X-ray detector 30, a support frame 31, and a top 32, an image generation circuit 41, and a display 42. , Input interface 43, control circuit 44, storage circuit 45, and communication interface 46. The X-ray generator 20 also includes an X-ray tube 21 and an X-ray movable stop 22.

  The X-ray high voltage generator 10 generates a DC high voltage to be applied to the X-ray tube 21 and controls the magnitude of the DC high voltage, the application time, and the amount of current flowing. Specifically, as illustrated in FIG. 2, the X-ray high voltage generator 10 includes an X-ray control circuit 11, a high voltage generation circuit 12, a grid bias power supply circuit 13, and a first filament heating circuit 14. , And a second filament heating circuit 15. The X-ray tube 21 also includes a cathode having a first filament 21a, a second filament 21b, and a grid electrode 21c, and an anode having a target 21d. The X-ray tube 21 may have at least one filament.

  The X-ray control circuit 11 is a processor that controls the high voltage generation circuit 12, the grid bias power supply circuit 13, the first filament heating circuit 14, and the second filament heating circuit 15. The X-ray control circuit 11 receives an X-ray condition (a value of a tube voltage, a value of a tube current, an irradiation time, a focal point size, etc.) from the control circuit 44. The X-ray control circuit 11 controls the high voltage generation circuit 12, the grid bias power supply circuit 13, the first filament heating circuit 14, and the second filament heating circuit 15 based on the X-ray condition.

  The high voltage generation circuit 12 applies a high voltage (tube voltage) suitable for X-ray imaging and X-ray fluoroscopy to the X-ray tube 21 under the control of the X-ray control circuit 11. When a tube voltage is applied to the X-ray tube 21, a tube current corresponding to the heating state of the first filament 21 a or the second filament 21 b is supplied to the X-ray tube 21.

  The grid bias power supply circuit 13 applies a grid bias to the grid electrode 21 c under the control of the X-ray control circuit 11. As the grid bias, for example, a negative voltage is used with respect to a cathode terminal in which one side of the first filament 21a and the second filament 21b is common. By applying a negative voltage to the grid electrode 21c as a grid bias, electrons (tube current) emitted from the filament can be restricted or cut off. In the present specification, unless otherwise stated, a negative voltage is applied as a grid bias.

  The first filament heating circuit 14 heats the first filament 21 a by supplying a filament current to the first filament 21 a under the control of the X-ray control circuit 11. The amount of heating of the first filament 21a is controlled in order to obtain tube currents respectively suitable for radiography and radioscopy.

  The second filament heating circuit 15 heats the second filament 21b by supplying a filament current to the second filament 21b under the control of the X-ray control circuit 11. The amount of heating of the second filament 21b is controlled in order to obtain tube currents respectively suitable for radiography and radioscopy.

  The X-ray tube 21 generates X-rays based on the tube voltage applied by the high voltage generation circuit 12 and the tube current supplied from the high voltage generation circuit 12. The X-ray generated from the X-ray tube 21 is irradiated to the subject P. The X-ray tube 21 has a mechanism that can change the focal point size during X-ray irradiation, such as pulse fluoroscopy.

  The first filament 21a is, for example, a filament with a small focal spot size (small focal spot filament). The first filament 21 a is heated by the filament current supplied from the first filament heating circuit 14. The first filament 21a emits electrons when a tube voltage is applied by heating.

  The second filament 21b is, for example, a filament (large focus filament) having a large focus size. The second filament 21 b is heated by the filament current supplied from the second filament heating circuit 15. The second filament 21b emits electrons when a tube voltage is applied by heating.

  Electrons emitted from the first filament 21a (or the second filament 21b) form a focus at the target 21d.

  The grid electrode 21 c restricts electrons emitted from the first filament 21 a (or the second filament 21 b) by the grid bias applied by the grid bias power supply circuit 13. Specifically, by applying a negative voltage, the grid electrode 21c suppresses the electrons emitted from the first filament 21a (or the second filament 21b), and the amount of electrons colliding with the target 21d is It can be reduced.

  The grid electrode 21c has a structure for limiting the direction (direction of electron flow) of electrons emitted from the first filament 21a (or the second filament 21b). The electrons emitted from the filament are focused by the lens action of the electric field to form a focal point at the target 21d, which is an X-ray generation point.

  That is, the grid electrode 21c can control the focal spot size by restricting the direction of the electrons emitted from the filament by the grid bias.

  The target 21d generates X-rays by collision of the electrons emitted from the first filament 21a (or the second filament 21b).

  The X-ray movable restrictor 22 limits the radiation field of X-rays generated by the X-ray tube 21. The X-ray movable diaphragm 22 can irradiate X-rays only to the imaging region (or imaging range) desired by the operator by limiting the X-ray irradiation field. That is, the X-ray movable diaphragm 22 can prevent unnecessary exposure to a part (or range) different from the imaging part (or range). In addition, the X-ray movable stop 22 can reduce scattered X-rays and remove off-focus X-rays.

  The X-ray detector 30 detects X-rays generated from the X-ray tube 21 and transmitted through the subject P. The X-ray detector 30 includes, for example, a flat panel detector (FPD) capable of detecting X-rays. The FPD has a plurality of semiconductor detection elements. The semiconductor detection element is classified into an indirect conversion type and a direct conversion type. The indirect conversion type is a type in which incident X-rays are converted into light by a scintillator such as a phosphor and the converted light is converted into an electrical signal. Direct conversion is a form of converting incident X-rays directly into electrical signals.

  Electrical signals generated by the plurality of semiconductor detection elements upon incidence of the X-ray are output to an analog to digital converter (A / D converter) not shown. The A / D converter converts the electrical signal into digital data. The A / D converter outputs digital data to the image generation circuit 41.

  The support frame 31 movably supports the X-ray generator 20 and the X-ray detector 30 disposed to face each other. Specifically, the support frame 31 corresponds to an overtube type frame in which the X-ray generator 20 is installed above the surface of the top plate 32. The support frame 31 may be an under-tube type frame in which the X-ray generator 20 is installed below the surface of the top plate 32. Also, the support frame 31 may have a C-arm and Ω-arm structure. Furthermore, the support frame 31 may have a structure with two arms (for example, robot arms etc.) that independently support the X-ray generator 20 and the X-ray detector 30.

  The not-shown bed has a top 32 (also referred to as a lying position table) on which the subject P is placed. The subject P is placed on the top 32.

  The driving device (not shown) drives the support frame 31 and the bed under the control of the control circuit 44, for example. At the time of X-ray fluoroscopy and X-ray imaging, the subject P placed on the top 32 is disposed between the X-ray generator 20 and the X-ray detector 30. Also, the drive device drives the X-ray movable restrictor 22 under the control of the control circuit 44, for example. The driving device may rotate the X-ray detector 30 with respect to the X-ray generator 20 under the control of the control circuit 44.

  The image generation circuit 41 generates an X-ray image based on digital data output from the X-ray detector 30 via the A / D converter. The image generation circuit 41 outputs the generated X-ray image to the storage circuit 45 and an external storage device (not shown).

  The display 42 displays the X-ray image (or fluoroscopic image) generated by the image generation circuit 41. The display may use the whole or part of the display as a display window for displaying an X-ray image (or fluoroscopic image), or may switch the whole or part. The display may display an input screen related to the input of the fluoroscopic / imaging position, the X-ray irradiation condition, and the like.

  The input interface 43 is an X-ray condition such as an X-ray imaging condition desired by the operator and an X-ray fluoroscopy condition, a fluoroscopic / imaging position, an irradiation field, and a region of interest in the X-ray image. ) Etc. at the instruction of the operator. The input interface 43 takes various instructions from the operator, instructions, information, selection, and settings into the X-ray diagnostic apparatus 1.

  The input interface 43 includes a joystick for setting a region of interest, a track ball, a switch button, a mouse, a keyboard, a touch pad for performing an input operation by touching the operation surface, and a display screen and touch pad integrated with each other. It is realized by a touch panel display, a foot switch for photographing, a microphone for voice recognition, and the like. The input interface 43 is connected to the control circuit 44, converts an input operation received from the operator into an electrical signal, and outputs the signal to the control circuit 44.

  In the present specification, the input interface 43 is not limited to one having physical operation parts such as the mouse and the keyboard described above. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the control circuit 44 is also included in the example of the input interface 43. .

  The control circuit 44 is a processor that controls each circuit, the driving device, and the like in the X-ray diagnostic apparatus 1. The control circuit 44 temporarily stores information (for example, X-ray conditions) such as an instruction of the operator input from the input interface 43 in a memory (not shown). The control circuit 44 controls the X-ray high voltage generator 10, the X-ray tube 21, the driving device and the like to execute X-ray imaging and X-ray fluoroscopy in accordance with the operator's instruction stored in the memory. . The control circuit 44 also controls X-ray image generation processing and the like in the image generation circuit 41.

  Furthermore, the control circuit 44 executes each function related to control of changing the focus size while keeping the dose constant according to the instruction of the operator stored in the memory. Each of the above functions includes, for example, a signal switching function 44a (signal switching section), a focus size changing function 44b (focus size changing section), a filament current setting function 44c (filament current setting section), and a use limit indicating function 44d (use limit There are instruction parts).

  The signal switching function 44a switches a focus size change signal indicating a change of the focus size of the focus formed on the target 21d in conjunction with the use condition at the time of diagnosis. Switching of the focus size change signal is arbitrarily set in accordance with the use situation. For example, when the focus size change signal is turned on, the signal switching function 44a may switch the focus size change signal to reduce the focus size, or the focus size to increase the focus size. The change signal may be switched.

  The usage state is, for example, an operation by the operator for the expansion of the field of view, an operation for the use of the high definition detector, and an operation for the High Level Control (HLC) fluoroscopy. The above operation includes, for example, an operation performed by the operator via the input interface 43, an operation in which the operator moves some device (for example, a high definition detector), and the like. The use state includes ending the above operation and returning to the state before the operation.

  An operation relating to the enlargement of the visual field is performed, for example, by the operator when it is desired to magnify and observe an X-ray image. When the field of view is enlarged, for example, the focal spot size needs to be reduced in order to prioritize the sharpness of the X-ray image.

  The high definition detector corresponds to, for example, a micro angio detector. The high definition detector is a detector that can confirm minute parts by making the pixel size smaller than that of a normal FPD. The high-resolution detectors include ones that are separate from the normal FPD and ones that are embedded (integrated) in part of the normal FPD. Therefore, the operation relating to the use of the high definition detector may be replaced with the operation relating to switching between the normal FPD and the high definition detector. During use of high definition detectors, for example, it is necessary to reduce the focal spot size in order to prioritize the sharpness of the x-ray image.

  High dose rate control fluoroscopy is a method of fluoroscopy that requires more doses than normal fluoroscopy. During high dose rate control fluoroscopy, for example, the focal spot size needs to be increased to prioritize the dose.

  More specifically, the signal switching function 44a switches the focus size change signal so as to reduce the focus size in conjunction with the operation related to the expansion of the visual field. Further, the signal switching function 44a switches the focus size change signal so as to reduce the focus size in conjunction with the operation related to the use of the high definition detector. Further, the signal switching function 44a switches the focus size change signal so as to increase the focus size in conjunction with the operation regarding the high dose rate control fluoroscopy.

  Note that the signal switching function 44a is a focal point size of the focal point formed on the target 21d in conjunction with a predetermined imaging protocol and a geometric change of the mechanical unit such as the angle of the support (the support frame 31 etc.). A focus size change signal may be toggled to indicate a change. For example, the signal switching function 44a switches the focal point size change signal to correspond to the thickness of the cross section to be radiographed when the C-arm angle changes while the imaging region included in the imaging protocol is fixed. You may

  The focal spot size changing function 44b changes the focal spot size by gradually changing the value of the grid bias or the time width of the bias pulse toward the desired target value in response to the switching of the focal spot size changing signal. The focus size changing function 44b may change the value of the grid bias stepwise, for example, while keeping the time width of the bias pulse of the grid bias constant. Also, the focus size changing function 44b may change the time width of the bias pulse of the grid bias stepwise, for example, by changing the value of the grid bias instantaneously and making it constant. The desired target value is the value of the grid bias corresponding to the target value of the focal spot size and the bias pulse time width of the grid bias corresponding to the application time of the high voltage. Here, the target value of the focus size is set in advance according to the above-mentioned use situation.

  In addition, the focal point size changing function 44b steps the grid bias (or the value of the grid bias) to a desired target value to correspond to the thermal inertia of the first filament 21a (or the second filament 21b). The focus size may be changed by changing it. Here, thermal inertia means the degree of response of the filament temperature to the increase or decrease of the filament current. The response of the filament temperature is, for example, the time it takes for the filament temperature to reach a temperature corresponding to a certain value when the filament current is set to a certain value, and usually takes about several hundred ms.

  More specifically, the focal spot size changing function 44b reduces the focal spot size by increasing the grid bias applied to the grid electrode 21c toward a desired target value. Here, "increase the grid bias toward the desired target value" is synonymous with "increase the negative voltage toward the desired target value". Thus, the electrons emitted from the filament can be reduced.

  In addition, the focal spot size changing function 44b may increase the focal spot size by decreasing the grid bias applied to the grid electrode 21c toward a desired target value (or, the focal spot size may be set to the original size). May return). Here, "reducing the grid bias toward the desired target value" is synonymous with "reducing the negative voltage toward the desired target value (or to zero)".

  When it is desired to make the focal point size larger than usual, it is conceivable to use a positive voltage as the grid bias. The electrons emitted from the filament can be increased by applying a positive voltage to the grid electrode 21c as a grid bias. However, the positive voltage of the grid bias is lower than the tube voltage.

  The filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias when switching the focus size change signal. Further, the filament current setting function 44c may set the filament current corresponding to the desired target value of the grid bias so that the value of the tube current supplied to the X-ray tube 21 becomes constant.

  For example, increasing the grid bias to reduce the focal spot size limits the emission of electrons from the filament. If the filament current is constant despite the fact that the grid bias is increased, the emission of electrons from the filament is limited, so the tube current decreases. The reduction in tube current may reduce the dose and prevent the production of the desired x-ray image. Therefore, the filament current setting function 44c also needs to increase the filament current when the grid bias is increased in order to prevent a decrease in dose.

  The use limit instruction function 44d instructs notification of the use limit of the focus of the X-ray tube 21 by changing the focus size. In addition, the use limit instructing function 44d may instruct the focus size changing function 44b to increase the focus size when instructing notification of the use limit of the focus in a state where the focus size is small. The use limit may be determined, for example, based on the use conditions of the x-ray tube, or may be determined by calculating the input to the anode of the x-ray tube. In addition, about the instruction | indication of a notification, before reaching a use limit, a warning display may be displayed on the display 42, and an alarm may be sounded from a speaker (not shown).

  The memory circuit 45 includes a memory for recording electrical information such as a hard disk drive (HDD), and peripheral circuits such as a memory controller and a memory interface attached to the memory. The memory is not limited to HDD, but SSD (solid state drive), magnetic disk (floppy (registered trademark) disk, hard disk, etc.), optical disk (CD, DVD, Blu-ray (etc.)), semiconductor memory, etc. As appropriate.

  The storage circuit 45 also includes various X-ray images generated by the image generation circuit 41, a system control program of the X-ray diagnostic apparatus 1, a diagnostic protocol executed by the control circuit 44, and operations sent from the input interface 43. It stores various data groups such as instructions from the user, imaging conditions for X-ray imaging, fluoroscopy conditions for X-ray fluoroscopy, error information, and various data sent via a network. In addition, the memory circuit 45 stores a table having a target value of focus size and a target value of grid bias associated with the use situation at the time of diagnosis, and a table having each value indicating the use limit of the X-ray tube. You may

  The communication interface 46 includes, for example, a circuit related to a network and an external storage device (not shown). An X-ray image or the like obtained by the X-ray diagnostic apparatus 1 can be transferred to another apparatus via the communication interface 46 and the network.

  Next, the operation of the X-ray diagnostic apparatus 1 configured as described above will be described using the flowchart of FIG. 3 and the timing chart of FIG. 4 and the like. The following description mainly describes the control by the control circuit 44, and in particular, the control for changing the focal spot size while keeping the dose constant.

  4 (a) is a waveform of a fluoroscopic signal showing switching of X-ray fluoroscopy, FIG. 4 (b) is a waveform showing on / off of high voltage output showing output of high voltage pulse to the X-ray tube 21; Fig. 4 (c) is a waveform of the focus size changing signal, Fig. 4 (d) is a plot of the size of the focus size, Fig. 4 (e) is a waveform showing the set value of the filament current, and Fig. 4 (f) is FIG. 4 (g) is a waveform showing the value of grid bias, FIG. 4 (h) is a waveform of tube current supplied to the X-ray tube 21, FIG. 4 (i) ) Is a waveform of a tube voltage applied to the X-ray tube 21.

  First, the subject P is placed on the couch top 32 of the bed. In the X-ray diagnostic apparatus 1, X-ray conditions are set by the operation of the operator. In the present embodiment, the X-ray diagnostic apparatus 1 is set to perform, for example, X-ray fluoroscopy. Then, in the standby state before the X-ray fluoroscopy (before time t0), the preheating current 50 is supplied to the filament. The preheating current 50 is set, for example, to such a value that electrons do not emit from the filament even when the tube voltage is applied.

(Step S1)
At time t0, the fluoroscopic signal is switched on by the instruction of the operator. When the fluoroscopic signal is turned on, the value of the filament current is set to the first fluoroscopic heating current 51, the grid bias is cut off, and preparation for X-ray irradiation is made.

(Step S2)
When the filament temperature reaches a suitable value at time t1, high voltage output by the high voltage generation circuit 12 is started, and a high voltage pulse is applied to the X-ray tube 21. During a period in which the high voltage pulse is applied, the X-ray tube 21 outputs pulsed X-rays.

(Step S3)
At the moment when pulsed X-rays are output, the value of the grid bias is set to zero. Also, the value of the grid bias may be a value that allows the tube current to flow. That is, the value of the grid bias only needs to maintain the value of the tube current which can ensure the desired dose. Note that the value of the grid bias is not limited to this while the focus size change signal is on.

(Step S4)
At time t2, a request for changing the focus size (for example, reducing the focus size) occurs depending on the use state at the time of diagnosis. The signal switching function 44a switches a focus size change signal indicating a change of the focus size of the focus formed on the target 21d in conjunction with the use condition at the time of diagnosis. Simultaneously with the switching of the focus size change signal, the control circuit 44 stores the target value of the focus size (focus size 52) and the target value of the grid bias (grid bias 53) associated with the use state at the time of diagnosis in the storage circuit 45. Read from the stored table.

(Step S5)
From time t2 to time t3 when the filament temperature reaches a suitable value, the focus size changing function 44b changes the focus size by changing stepwise from the current grid bias value to the grid bias 53. Do. Specifically, the focal spot size changing function 44b changes the focal spot size by stepwise changing the grid bias 53 so as to correspond to the thermal inertia of the first filament 21a (or the second filament 21b).

  In other words, the focal spot size changing function 44b changes the grid bias stepwise from 0 V to the grid bias 53 corresponding to the focal spot size 52 in accordance with the rise period of the filament temperature.

(Step S6)
The filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias at time t2 (ie, at the time of switching of the focus size change signal). In FIG. 4, the value of the filament current is set to the second perspective heating current 54 when the focus size change signal is turned on.

(Step S7)
At time t4, a request for changing the focal spot size (for example, increasing the focal spot size) occurs depending on the use state at the time of diagnosis. The signal switching function 44a switches the focus size change signal in conjunction with the use state at the time of diagnosis. Simultaneously with the switching of the focus size change signal, the control circuit 44 stores the target value of the focus size (focus size 55) and the target value of the grid bias (grid bias 56) before the focus size change (for example, at time t1). It reads from the circuit 45.

(Step S8)
From time t4 to time t5 when the filament temperature reaches a suitable value, the focal spot size changing function 44b changes the focal spot size by stepwise changing over the grid bias 56. Specifically, the focal spot size changing function 44b changes the focal spot size by stepwise changing the grid bias 56 so as to correspond to the thermal inertia of the first filament 21a (or the second filament 21b).

  In other words, the focal spot size changing function 44 b changes the grid bias from the grid bias 53 to the grid bias 56 corresponding to the focal spot size 55 in accordance with the falling period of the filament temperature.

(Step S9)
The filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias at time t4 (ie, at the time of switching of the focus size change signal). In FIG. 4, the value of the filament current is set to the first perspective heating current 57 when the focus size change signal is turned off.

(Step S10)
At time t6, the fluoroscopic signal is switched off by the instruction of the operator. When the fluoroscopic signal is turned off, the value of the filament current is set to the preheating current 58. In addition, the high voltage output by the high voltage generation circuit 12 is ended when the fluoroscopic signal is turned off.

(Step S11)
From time t6 to time t7 when the residual voltage of the tube voltage becomes zero, the value of the grid bias is set to cutoff. By setting the grid bias to a cutoff, the emission of electrons is suppressed and unnecessary X-rays are not generated.

(Step S12)
At time t7, the grid bias is set to zero in response to the residual voltage of the tube voltage becoming zero.

  As described above, according to the first embodiment, the X-ray diagnostic apparatus switches the focus size change signal indicating the change of the focus size of the focus formed on the target, in conjunction with the use state at the time of diagnosis. The focal spot size is changed by changing the grid bias in response to the switching of the size change signal, and the filament current corresponding to the desired target value is set when switching the focal size change signal. As described above, since the focus size is changed by switching the focus size change signal in synchronization with the use condition at the time of diagnosis, the operator's operation regarding the change of the focus size is not required. Also, by changing the grid bias, the focus size can be changed, so that the focus size can be set to an appropriate value. Thus, the X-ray diagnostic apparatus can facilitate handling of changes in focal spot size.

  In addition, when the use condition is an operation related to the expansion of the field of view, the X-ray diagnostic apparatus switches the focus size change signal so as to reduce the focus size in conjunction with the operation related to the expansion of the field of view. Reduce the focal spot size. Therefore, the X-ray diagnostic apparatus can automatically change the focal spot size so as to minimize the image quality deterioration while securing the dose necessary for the inspection only by performing the operation regarding the expansion of the visual field.

In addition, when the use condition is an operation related to the use of the high definition detector, the X-ray diagnostic apparatus interlocks with the operation related to the use of the high definition detector to reduce the focus size change signal so as to reduce the focus size. Reduce focus size by switching and increasing grid bias. Therefore, the X-ray diagnostic apparatus can automatically change the focal spot size so as to minimize the image quality deterioration while securing the dose necessary for the inspection only by performing the operation related to the use of the high definition detector. it can.

  In addition, when the use condition is an operation related to high dose rate control fluoroscopy, the X-ray diagnostic apparatus switches the focus size change signal to increase the focus size in conjunction with the operation related to high dose rate control fluoroscopy, The focus size is increased by reducing the grid bias. Therefore, the X-ray diagnostic apparatus can automatically change the focus size so as to minimize the image quality deterioration while securing the dose necessary for the inspection only by performing the operation regarding the high dose rate control fluoroscopy .

  In addition, the X-ray diagnostic apparatus sets a filament current corresponding to a desired target value so that the value of the tube current supplied to the X-ray tube becomes constant. Thus, the X-ray diagnostic apparatus can reduce the change in tube current due to the application of the grid bias.

  Also, the x-ray diagnostic apparatus changes the focal spot size by stepwise changing the value of the grid bias to correspond to the thermal inertia of the filament. Therefore, the X-ray diagnostic apparatus can further reduce the change in tube current due to the application of the grid bias.

  In addition, the X-ray diagnostic apparatus can notify the use limit of the focus due to the change of the focus size. Therefore, the X-ray diagnostic apparatus can prevent the continuous use at the use limit of the focus.

  The X-ray diagnostic apparatus can also issue an instruction to increase the focal point size when the focal point use limit is notified in a state where the focal point size is small. Therefore, the X-ray diagnostic apparatus can prevent the continuous use at the use limit of the focus.

Second Embodiment
In the first embodiment, the case where the focal spot size is changed while the tube current is kept constant by stepwise changing the value of the grid bias has been described. In the second embodiment, the case where the dose per pulse of X-ray is made constant when changing the value of the grid bias will be described.

  FIG. 5 is a block diagram showing a configuration example of the X-ray diagnostic apparatus 1 according to the second embodiment. The X-ray diagnostic apparatus 1 of FIG. 5 differs from the X-ray diagnostic apparatus 1 according to the first embodiment in that the control circuit 44 includes a pulse width control function 44 e (pulse width control unit).

  The pulse width control function 44 e has a pulse width of a high voltage pulse (high voltage output) applied to the X-ray tube 21 so that the time product (tube current time product) of the tube current supplied to the X-ray tube 21 becomes constant. Control. The tube current time product is the product of the tube current value (mA) and the pulse width (s). When the pulse width of the high voltage pulse to the X-ray tube 21 is controlled, the filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias.

  Next, the operation of the X-ray diagnostic apparatus 1 according to the second embodiment will be described using the flowchart of FIG. 3 and the timing chart of FIG. The following description mainly describes the control by the control circuit 44, and in particular, the control for changing the focal spot size while keeping the dose constant.

  6 (a) is a waveform of a fluoroscopic signal showing switching of X-ray fluoroscopy, FIG. 6 (b) is a waveform showing on / off of high voltage output showing output of high voltage pulse to the X-ray tube 21; 6 (c) is a waveform of the focus size change signal, FIG. 6 (d) is a plot of the size of the focus size, FIG. 6 (e) is a waveform showing the set value of the filament current, and FIG. FIG. 6 (g) is a waveform showing a grid bias value, FIG. 6 (h) is a waveform of a tube current supplied to the X-ray tube 21, FIG. ) Is a waveform of a tube voltage applied to the X-ray tube 21.

  First, the subject P is placed on the couch top 32 of the bed. In the X-ray diagnostic apparatus 1, X-ray conditions are set by the operation of the operator. In the present embodiment, the X-ray diagnostic apparatus 1 is set to perform, for example, X-ray fluoroscopy. Then, in the standby state before the X-ray fluoroscopy (before time t10), the filament is supplied with a preheating current 60. The preheating current 60 is set, for example, to such a value that electrons do not emit from the filament even when the tube voltage is applied.

(Step S1)
At time t10, the fluoroscopic signal is switched on by the instruction of the operator. When the fluoroscopic signal is turned on, the value of the filament current is set to the first fluoroscopic heating current 61, the grid bias is cut off, and preparation for X-ray irradiation is made.

(Step S2)
When the filament temperature reaches a suitable value at time t11, high voltage output by the high voltage generation circuit 12 is started, and a high voltage pulse is applied to the X-ray tube 21. During a period in which the high voltage pulse is applied, the X-ray tube 21 outputs pulsed X-rays.

(Step S3)
At the moment when pulsed X-rays are output, the value of the grid bias is set to zero. Also, the value of the grid bias may be a value that allows the tube current to flow. That is, the value of the grid bias only needs to maintain the value of the tube current which can ensure the desired dose. Note that the value of the grid bias is not limited to this while the focus size change signal is on.

(Step S4)
At time t12, a request for changing the focus size (for example, reducing the focus size) occurs depending on the use state at the time of diagnosis. The signal switching function 44a switches a focus size change signal indicating a change of the focus size of the focus formed on the target 21d in conjunction with the use condition at the time of diagnosis. Simultaneously with the switching of the focus size change signal, the control circuit 44 stores the target value of the focus size (focus size 62) and the target value of the grid bias (grid bias 63) associated with the use state at the time of diagnosis in the storage circuit 45. Read from the stored table.

(Step S5)
From time t12 to time t13 when the filament temperature reaches a suitable value, the focal point size changing function 44b instantaneously switches (changes) the current grid bias value to the grid bias 63 value, thereby focusing. Change the size. Further, the pulse width control function 44 e controls the pulse width of the high voltage output to the X-ray tube 21 so that the time product of the tube current supplied to the X-ray tube 21 becomes constant. The focus size changing function 44b changes the pulse width of the grid bias stepwise according to the pulse width of the high voltage output.

  In this embodiment, the tube current time product is made constant in order to change the focal spot size (or grid bias) instantaneously and to reduce the change in dose per pulse due to the change in the tube current. Thus, a method of controlling high voltage pulses to the X-ray tube 21 is used. By performing such a control method, a desired dose can be secured, and the image quality of the X-ray image can be made constant. In other words, the pulse width control function 44e controls the pulse width of the high voltage output to the X-ray tube 21 so that the time product of the tube current supplied to the X-ray tube 21 becomes constant.

  However, although the control method described above can change the focal spot size instantaneously, the pulse width of the high voltage output to the X-ray tube 21 may be broadened. When the pulse width of the high voltage output to the X-ray tube 21 is expanded, the time resolution is deteriorated. Therefore, it is desirable to apply the above-described control method to a portion where the movement of the object is small.

(Step S6)
The filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias at time t12 (ie, at the time of switching of the focus size change signal). Specifically, the filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias. In FIG. 6, the value of the filament current is set to the second perspective heating current 64 when the focus size change signal is turned on.

(Step S7)
At time t14, a request for changing the focus size (for example, increasing the focus size) occurs depending on the use state at the time of diagnosis. The signal switching function 44a switches the focus size change signal in conjunction with the use state at the time of diagnosis. Simultaneously with the switching of the focus size change signal, the control circuit 44 stores the target value of focus size (focus size 65) and the target value of grid bias (grid bias 66) before the focus size change (for example, at time t11). It reads from the circuit 45.

(Step S8)
From time t14 to time t15 when the filament temperature reaches a suitable value, the focal spot size changing function 44b instantaneously switches (changes) the current grid bias value to the grid bias 66 value, thereby focusing. Change the size. Further, the pulse width control function 44 e controls the pulse width of the high voltage output to the X-ray tube 21 so that the time product of the tube current supplied to the X-ray tube 21 becomes constant.

(Step S9)
The filament current setting function 44c sets the filament current corresponding to the desired target value of the grid bias at time t14 (ie, at the time of switching of the focus size change signal). In FIG. 6, the value of the filament current is set to the first perspective heating current 67 when the focus size change signal is turned off.

(Step S10)
At time t16, the fluoroscopic signal is switched off by the instruction of the operator. When the fluoroscopic signal is turned off, the value of the filament current is set to the preheating current 68. Also, when the fluoroscopic signal is turned off, the high voltage output to the X-ray tube 21 by the high voltage generation circuit 12 is ended.

(Step S11)
From time t16 to time t17 when the residual voltage of the tube voltage is zero, the value of the grid bias is set to cutoff. By setting the grid bias to a cutoff, the emission of electrons is suppressed and unnecessary X-rays are not generated.

(Step S12)
At time t17, the grid bias is set to zero in response to the residual voltage of the tube voltage becoming zero.

  As described above, according to the second embodiment, the X-ray diagnostic apparatus can obtain the same effect as the X-ray diagnostic apparatus according to the first embodiment.

  In addition to this, the X-ray diagnostic apparatus controls the pulse width of the high voltage pulse applied to the X-ray tube so that the time product of the tube current supplied to the X-ray tube becomes constant. Therefore, this X-ray diagnostic apparatus can change the focus size instantaneously because it is not necessary to change the value of the grid bias stepwise.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

  DESCRIPTION OF SYMBOLS 1 ... X-ray diagnostic apparatus, 10 ... X-ray high voltage generator, 11 ... X-ray control circuit, 12 ... high voltage generation circuit, 13 ... grid bias power circuit, 14 ... 1st filament heating circuit, 15 ... 2nd filament Heating circuit 20 X-ray generator 21 X-ray tube 21a first filament 21b second filament 21c grid electrode 21d target 22 X-ray movable stop 30 X-ray detection 31 support frame 32 top board 41 image generation circuit 42 display 43 input interface 44 control circuit 44a signal switching function 44b focal point size changing function 44c filament current setting Function 44d Use limit instruction function 44e Pulse width control function 45 Memory circuit 46 Communication interface 50, 58, 60, 68 Heating current 51, 57, 61, 67 ... first perspective heating current, 52, 55, 62, 65 ... focal spot size, 53, 56, 63, 66 ... grid bias, 54, 64 ... second perspective heating current, P: Subject.

Claims (10)

An x-ray tube comprising an anode having a target, a cathode having a filament, and a grid electrode for limiting electrons from the filament, the x-ray tube generating x-rays;
A grid bias power supply circuit that applies a grid bias to the grid electrodes;
A filament heating circuit that heats the filament by supplying the filament current to the filament;
A signal switching unit that switches a focus size change signal indicating a change in focus size of the focus formed on the target in conjunction with a use condition at the time of diagnosis;
A focus size changing unit that changes the focus size by changing the grid bias in accordance with switching of the focus size change signal;
A filament current setting unit configured to set the filament current corresponding to a desired target value of the grid bias when switching the focus size change signal;
An X-ray diagnostic device equipped with The use condition includes an operation related to the expansion of the visual field,
The signal switching unit switches the focus size change signal so as to reduce the focus size in conjunction with an operation related to the expansion of the visual field.
The X-ray diagnostic apparatus according to claim 1, wherein the focal spot size changing unit reduces the focal spot size by increasing the grid bias. The use situation includes operations relating to the use of a high definition detector,
The signal switching unit switches the focus size change signal so as to reduce the focus size in conjunction with an operation related to the use of the high definition detector.
The X-ray diagnostic apparatus according to claim 1, wherein the focal spot size changing unit reduces the focal spot size by increasing the grid bias. The use situation includes operations relating to high dose rate control fluoroscopy,
The signal switching unit switches the focus size change signal to increase the focus size in conjunction with the operation related to the high dose rate control fluoroscopy.
The X-ray diagnostic apparatus according to claim 1, wherein the focus size changing unit increases the focus size by reducing the grid bias.   The filament current setting unit sets the filament current corresponding to a desired target value of the grid bias such that a value of a tube current supplied to the X-ray tube becomes constant. The X-ray diagnostic apparatus according to any one of the preceding claims.   The focal spot size changing unit according to any one of claims 1 to 5, wherein the focal spot size changing unit changes the focal spot size by stepwise changing the value of the grid bias to correspond to the thermal inertia of the filament. X-ray diagnostic equipment. And a pulse width control unit for controlling the pulse width of the high voltage pulse applied to the X-ray tube such that the time product of the tube current supplied to the X-ray tube is constant.
The X-ray diagnostic apparatus according to any one of claims 1 to 4.   The X-ray diagnostic apparatus according to claim 7, wherein the focal spot size changing unit changes the focal spot size by stepwise changing the pulse width of the grid bias in accordance with the pulse width of the high voltage pulse.   The X-ray diagnostic apparatus according to any one of claims 1 to 8, further comprising a use limit instruction unit for instructing notification of a use limit of the focus by changing the focus size.   10. The use limit instructing unit according to claim 9, wherein when the notification of the use limit of the focus is instructed in the state where the focus size is small, the use limit instructing unit instructs the focus size changing unit to increase the focus size. X-ray diagnostic equipment.