JP2014182879A - Fluoroscopic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluoroscopic apparatus capable of determining whether or not grid control operates normally.SOLUTION: A fluoroscopic apparatus comprises: a grid control detection unit 43 for detecting a waveform of tube voltage to detect propriety or existence of grid control, in order to make it possible to determine whether or not the grid control operates normally from a result obtained by the grid control detection unit 43 detecting the waveform of the tube voltage; and a grid control unit 44 for adjusting grid bias voltage to be applied to a grid electrode on the basis of the waveform of the tube voltage detected by the grid control detection unit 43, in order to make the grid bias voltage increase in the negative direction in the case that the grid control does not operate normally on the basis of the waveform of the tube voltage and perform fluoroscopy with grid bias voltage at time of the determination after the time in the case that the grid control operates normally on the basis of the waveform of the tube voltage.

Description

  The present invention relates to a fluoroscopic imaging apparatus that performs fluoroscopy or radiography, and particularly relates to a technique that includes a triode X-ray tube having a grid electrode.

  Conventionally, as this type of device, grid control for controlling a grid electrode is known in a triode X-ray tube having three electrodes of a cathode electrode, an anode electrode, and a grid electrode (for example, Patent Documents 1 to 7). reference). In Japanese Patent Application Laid-Open No. 2008-73115 of Patent Document 1, in order to shorten the waiting time between photographing (dual energy) at high tube voltage and low tube voltage, the same current can be obtained by controlling the grid electrode. It is disclosed. In Japanese Patent Application Laid-Open No. 2004-139790 of Patent Document 2, a negative voltage (also referred to as “cut-off voltage”) is applied to the grid electrode in order to suppress and control the jumping of the thermoelectrons from the cathode electrode filament. Is disclosed.

  Patent Documents 3 to 5 mainly disclose contents related to the grid control circuit. Japanese Patent Application Laid-Open No. 2002-33064 of Patent Document 3 discloses that the grid control circuit is reduced in size and price in the technique for suppressing and controlling the jumping of thermoelectrons from the filament described above. Japanese Patent Application Laid-Open No. 2000-82594 of Patent Document 4 discloses that the grid control circuit is protected by short-circuiting between the grid electrode and the cathode electrode. Japanese Patent Laid-Open No. 11-204289 of Patent Document 5 discloses that a grid X-cathode electrode is short-circuited (conducted), and a stable pulse X-ray is output at the time of overshoot.

  Japanese Patent Application Laid-Open No. 5-188018 of Patent Document 6 discloses that the deterioration or lifetime of an X-ray tube is grasped by monitoring a grid bias voltage applied to a grid electrode. Japanese Patent Application Laid-Open No. 2007-42516 of Patent Document 7 discloses that the current of the grid electrode is compared with a predetermined threshold value, and the deterioration of the X-ray tube is determined based on the comparison result.

  In particular, the grid control in Japanese Patent Application Laid-Open No. 2004-139790 of Patent Document 2 will be described in detail. The grid control here is to suppress and control jumping out of thermoelectrons by applying a cut-off voltage (for example, −2000 V to −3000 V) lower than that of the cathode to the grid electrode on the cathode electrode (cathode) side. Is. Note that the X-ray tube and the grid control unit having the function of performing the grid control cause an increase in cost, and thus are usually used for a relatively high-function (high price range) apparatus.

  On the other hand, in an X-ray tube having no grid control function, as shown in the timing chart relating to the waveform in FIG. 7A, when performing pulse fluoroscopy, a pulsed high voltage (in FIG. When the “apparatus output” is applied, a pulsed X-ray is output in synchronism with it (denoted by “X-ray output” in FIG. 7). When the high voltage is cut off, the discharge of the charge charged in the high voltage cable becomes an X-ray output, and a lot of low tube voltage components (soft X-rays) are included. In this way, in an X-ray tube that does not have a grid control function, the X-ray output after the high voltage is cut off is called a “wave tail component”, and the wave tail component contains a lot of soft X-rays. (See hatched hatching in FIG. 7).

  On the other hand, in an X-ray tube having a function of performing grid control, a cutoff voltage is applied to the grid electrode at the same time as the high voltage is cut off, as shown in the timing chart regarding the waveform in FIG. As a result, jumping out of the thermal electrons is suppressed. As a result, the wave tail component of the X-ray output is not output.

As described above, the purpose of performing the grid control includes the following two points in the case of a medical fluoroscopic apparatus.
(1) In pulse fluoroscopy that does not have a function of performing grid control, extra exposure due to a wave tail component occurs when pulse fluoroscopy is interrupted (when high voltage is interrupted). By performing grid control, there is no deterioration in image quality due to soft X-rays, and X-ray exposure to the subject (patient) can be reduced.
(2) In pulsed fluoroscopy that does not have a grid control function, the wave tail component is input to the X-ray tube, so the tube rating of the X-ray tube (the output of the high voltage device) is It was necessary to operate with the rating of the included X-ray tube. This may be 10% or more of the output not including the wave tail at the maximum voltage. By performing grid control, it is possible to increase the output by the amount of the wave tail component compared to when grid control is not performed.

  It should be noted that if some failure occurs in the X-ray tube and system having the function of performing grid control and the grid control cannot be performed, or if the grid bias voltage cannot be applied due to a failure of the grid control unit, X It can be used in the same manner as an X-ray tube that does not have a function of performing grid control by setting the grid electrode of the tube to a cathode potential.

JP 2008-73115A (page 4-6, FIG. 1 and FIG. 2) JP 2004-139790 A (page 4-6, FIG. 2, FIG. 4 and FIG. 5) JP 2002-33064 A (page 3-5, FIGS. 1 and 2) JP 2000-82594 A (page 4-7, FIGS. 1 to 7) Japanese Patent Laid-Open No. 11-204289 (page 3-5, FIG. 1, FIG. 2, FIG. 4 and FIG. 5) JP-A-5-188018 (page 3, FIGS. 1, 3 and 6) JP 2007-42516 A (Page 5-9, FIG. 3, FIG. 6 and FIG. 7)

  However, if these grid faults occur and the grid electrode is set to the cathode potential, the wave tail cannot be cut off, resulting in the disadvantages shown in the above (1) and (2). Conventionally, for determining whether the grid control is functioning effectively (operating normally), a method of monitoring the grid bias voltage as disclosed in Japanese Patent Application Laid-Open No. 5-188018 is considered. However, in practice, it is difficult to directly measure the grid bias voltage. Therefore, it has not been detected (determined) whether the grid control is actually functioning, that is, whether the wave tail of the X-ray output is normally cut off.

  In addition, even when the grid bias voltage is set low due to a problem in installation adjustment, there is a problem that grid control for blocking the wave tail is not sufficiently performed. The grid bias voltage is a problem in installation adjustment. For example, when the grid bias voltage changes according to the tube and the voltage to be set is -2000V, the power supply of the grid control unit is set to -1500V. You may have forgotten.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a fluoroscopic imaging apparatus that can determine whether or not grid control operates normally.

  As a result of earnest research to solve the above problems, the inventors have obtained the following knowledge.

  That is, when grid control is not performed including failure, etc., the charge charged in the high voltage cable is released from the X-ray tube and becomes X-ray output (wave tail output). It was found that the tube voltage waveform of the X-ray tube dropped to almost “0”. On the other hand, when grid control is performed, it has been found that since the charge charged in the high-voltage cable is hardly released, the tube voltage waveform of the X-ray tube hardly drops even after the X-ray output is cut off.

  Therefore, by paying attention to the above points, it is possible to detect (determine) whether the grid control is operating normally by detecting the tube voltage waveform of the X-ray tube after the X-ray output is cut off. I got the knowledge.

The present invention based on such knowledge has the following configuration.
That is, a fluoroscopic imaging apparatus according to the present invention includes a triode X-ray tube having a grid electrode, and performs fluoroscopy or imaging in order to acquire an X-ray image based on X-rays emitted from the triode X-ray tube. A fluoroscopic imaging apparatus that includes a waveform detection unit that detects a waveform of a tube voltage of the triode X-ray tube in order to detect whether the grid control for controlling the grid electrode is correct or not. Is.

  [Operation / Effect] According to the fluoroscopic imaging apparatus of the present invention, the waveform detecting means is provided, and the waveform detecting means can detect whether the grid control is correct or not by detecting the waveform of the tube voltage. Specifically, as described in the knowledge, when grid control is not performed including failure, etc., the charge charged in the high voltage cable is released from the X-ray tube, and after the X-ray output is cut off, the X-ray is discharged. The tube voltage waveform of the tube falls to almost “0”. On the other hand, when grid control is performed, the electric charge charged in the high voltage cable is hardly released, so that the tube voltage waveform of the X-ray tube hardly drops even after the X-ray output is cut off. By utilizing this phenomenon, it is possible to determine whether or not the grid control operates normally when the waveform detecting means detects the tube voltage waveform.

  The fluoroscopic imaging apparatus according to the present invention described above preferably includes bias voltage adjusting means for adjusting the grid bias voltage applied to the grid electrode based on the waveform of the tube voltage detected by the waveform detecting means. If the grid control is not operating normally based on the tube voltage waveform, the grid bias voltage is increased in the negative direction. As a result of increasing the grid bias voltage in the negative direction, when the grid control operates normally based on the waveform of the tube voltage, fluoroscopy or imaging is performed with the grid bias voltage thereafter. Therefore, it is possible to normally suppress the wave tail component (wave tail cutoff).

  Even if the grid bias voltage is increased in the negative direction, if the grid control still does not operate normally based on the waveform of the tube voltage, an X-ray condition adjusting means for adjusting the X-ray condition as described below is provided. preferable. Note that the aspect including the X-ray condition adjusting means does not necessarily need to adjust the grid bias voltage, and includes a case where the X-ray condition is adjusted without adjusting the grid bias voltage.

  Specifically, it is preferable to include an X-ray condition adjusting unit that adjusts the X-ray condition when the grid control is not operating normally based on the waveform of the tube voltage detected by the waveform detecting unit. For example, when the grid bias voltage is adjusted as described above, the grid bias voltage is increased in the negative direction, for example, up to the tube rating of the X-ray tube or the output voltage of the grid controller. If the grid control does not operate normally based on the voltage waveform, the grid bias voltage cannot be increased in the negative direction.

  Therefore, X-ray condition adjusting means for adjusting the X-ray conditions is provided. By providing the X-ray condition adjusting means for adjusting the X-ray condition, even if the grid control is not operating normally, it can be used in the same manner as an X-ray tube that does not have a function to perform grid control. Is possible.

  In the case where the X-ray condition adjusting means for adjusting the X-ray condition is provided, the X-ray condition adjusting means may adjust by reducing the tube current when the grid control is not operating normally. Thereby, the maximum subject (patient) exposure and the load on the tube of the X-ray tube can be reduced.

  Further, when the X-ray condition adjusting means for adjusting the X-ray condition is provided, the X-ray condition adjusting means reduces the maximum tube voltage setting for setting the tube voltage to the maximum when the grid control is not operating normally. You may adjust it. Thereby, even if it raises to the vicinity of the maximum tube voltage, the maximum subject (patient) exposure and the load on the tube of the X-ray tube can be reduced.

  Further, in the case where the X-ray condition adjusting means for adjusting the X-ray condition is provided, the X-ray condition adjusting means is configured to turn on or off the voltage applied to the triode X-ray tube when the grid control is not operating normally. It may be adjusted by reducing the pulse rate, which is the number of pulses per unit time. It is known that the influence of the wave tail component becomes larger as the load of the tube of the X-ray tube is higher (that is, the number of pulses per unit time is larger). Therefore, the influence of the wave tail component can be reduced by adjusting the pulse rate by reducing it.

  Further, in the case where the X-ray condition adjusting means for adjusting the X-ray condition is provided, the X-ray condition adjusting means is a time during which the voltage applied to the triode X-ray tube is on when the grid control is not operating normally. You may adjust by reducing the pulse width which is a width | variety. X-ray output can be suppressed by reducing the pulse width. Thereby, even if it raises to the vicinity of the maximum tube voltage, the maximum subject (patient) exposure and the load on the tube of the X-ray tube can be reduced.

  In addition, when the X-ray condition adjusting means for adjusting the X-ray condition is provided, the X-ray condition is set such that the tube current and the tube voltage are set to the maximum, the maximum tube voltage setting, and the voltage applied to the triode X-ray tube Alternatively, the pulse rate that is the number per unit time that is turned off or the pulse width that is the time width that the voltage applied to the triode X-ray tube is on, and the X-ray condition adjustment means that the grid control operates normally. If not, it may be adjusted by reducing at least two or more from the tube current, maximum tube voltage setting, pulse rate or pulse width.

  According to the fluoroscopic imaging apparatus according to the present invention, it is possible to detect whether the grid control is correct or not by providing the waveform detection means and detecting the waveform of the tube voltage by the waveform detection means. As a result, it is possible to determine whether the grid control operates normally by detecting the waveform of the tube voltage by the waveform detection means.

1 is a block diagram of a fluoroscopic apparatus according to an embodiment. It is the schematic of the triode X-ray tube which concerns on an Example. It is a flowchart regarding adjustment of a series of tube voltage waveforms, adjustment of a grid bias voltage, and fluoroscopy conditions according to an embodiment. It is a timing chart regarding the tube voltage waveform which concerns on an Example. FIG. 5 is a schematic diagram relating to detection of a fluoroscopic tube voltage in an enlarged tube voltage waveform of the timing chart of FIG. 4. It is a schematic diagram regarding the tube voltage waveform accompanying a change (adjustment) of a grid bias voltage. It is a timing chart regarding the conventional waveform.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of a fluoroscopic apparatus according to the embodiment, and FIG. 2 is a schematic diagram of a triode X-ray tube according to the embodiment. In the present embodiment, description will be made by taking, as an example, pulse fluoroscopy in which fluoroscopy is performed while repeatedly applying a pulsed high voltage at a pulse rate of 30 pps. Here, the unit is pps (pulse per second) as the number of pulses per second as the pulse rate.

  As shown in FIG. 1, the fluoroscopic apparatus according to the present embodiment includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates the subject M with X-rays, and a subject M. And a flat panel X-ray detector (FPD) 3 for detecting X-rays transmitted through the. As shown in FIG. 2, the X-ray tube 2 is a triode X-ray tube having three electrodes: a cathode electrode C, an anode electrode A, and a grid electrode G. The X-ray tube 2 corresponds to the triode X-ray tube in this invention.

  In addition, the fluoroscopic apparatus includes an X-ray control unit 4 as shown in FIG. The X-ray control unit 4 includes a fluoroscopy condition setting unit 41, a high voltage output unit 42, a grid control detection unit 43, and a grid control unit 44. A high voltage cable 5 is electrically connected between the X-ray tube 2 and the high voltage output unit 42, and a grid control unit 44 is interposed in the negative high voltage cable 5. The X-ray tube 2 and the high voltage output unit 42 are electrically connected by the positive high voltage cable 5 and the negative high voltage cable 5. Specific functions of the fluoroscopic condition setting unit 41, the high voltage output unit 42, the grid control detection unit 43, and the grid control unit 44 will be described later. The fluoroscopy condition setting unit 41 corresponds to the X-ray condition adjusting unit in the present invention, the grid control detecting unit 43 corresponds to the waveform detecting unit in the present invention, and the grid control unit 44 corresponds to the bias voltage adjusting unit.

  Further, the fluoroscopic imaging apparatus includes a control unit (not shown) that controls driving of the top board 1, the X-ray tube 2, and the FPD 3, and an image processing unit that performs various processes based on the X-ray detection signal output from the FPD 3. (Not shown) and a monitor (not shown) for displaying a processed X-ray image or the like. Since the control unit, the image processing unit, the monitor, and the like are not related to the feature part or the feature part of the present embodiment, detailed description thereof is omitted.

As shown in FIG. 2, the tube voltage between the cathode electrode C · the anode electrode A of the X-ray tube 2 and V _1, the grid bias voltage between the cathode electrode C · grid electrode G and V _2. The electron beam B emitted from the cathode electrode C passes through the grid electrode G that is a lattice electrode and collides with the anode electrode A that is a target to generate X-rays (denoted by “Xray” in FIG. 2).

As mentioned in the section of "Problems that the Invention is to solve", in practice it is difficult to measure the grid bias voltage V ₂ directly. Therefore, by measuring the tube voltage V _1, the tube voltage signal that is a measurement result high-voltage output unit 42 (see FIG. 1) is that the feed to the grid controller detection unit 43 (see FIG. 1), the grid-control detection The unit 43 detects the tube voltage waveform.

  Returning to the description of FIG. 1, the high voltage output unit 42 applies a voltage to each electrode of the X-ray tube 2 via the high voltage cable 5 to generate X-rays from the X-ray tube 2. When imaging is performed, a voltage is applied to each electrode of the X-ray tube 2 so as to obtain a normal dose, and the subject M is irradiated once with X-rays from the X-ray tube 2. In the case of performing fluoroscopy as in the present embodiment, a voltage is applied to each electrode of the X-ray tube 2 so that the dose is smaller than that during imaging, and X-rays are emitted from the X-ray tube 2 to the subject M. Pulse irradiation is continuously performed at a frame rate of 30 pps. Before irradiating the subject M with X-rays, the subject M is not placed on the top board 1 and, as shown in the timing chart of FIG. Applying “apparatus output”), a tube voltage waveform (indicated by “tube voltage waveform” in FIG. 4) is detected, and whether the grid control is correct or not is detected.

  In order to detect whether the grid control is correct or not, the grid control detection unit 43 detects the waveform of the tube voltage. The grid control detection unit 43 detects the waveform of the tube voltage from the high voltage output unit 42 and sends a grid control signal based on the detection result to the grid control unit 44, so that the grid control unit 44 is the grid control detection unit 43. Based on the detected waveform of the tube voltage, the grid bias voltage applied to the grid electrode G is adjusted. In addition, when the grid control is not operating normally based on the waveform of the tube voltage detected by the grid control detection unit 43, the grid control detection unit is used to adjust the fluoroscopy condition as the X-ray condition in this embodiment. 43 sends a setting command signal to the fluoroscopy condition setting unit 41.

  If the grid bias voltage is within the rated range of the tube of the X-ray tube 2, the grid control unit 44 can operate the grid control normally by adjusting the grid bias voltage. Since the grid control unit 44 is electrically connected to the high voltage output unit 42 and the X-ray tube 2 by the minus side high voltage cable 5, the grid bias voltage applied to the grid electrode G of the X-ray tube 2 is adjusted. be able to.

  The fluoroscopy condition setting unit 41 uses the fluoroscopy condition as an X-ray condition when the grid control is not operating normally based on the waveform of the tube voltage detected by the grid control detection unit 43 (grid control signal based on the detection result). Adjust. The fluoroscopy condition setting unit 41 is configured to set the fluoroscopy condition by adjusting the fluoroscopy condition based on the X-ray detection signal (luminance signal) output from the FPD 3. The fluoroscopy condition setting unit 41 sends a fluoroscopy condition setting command signal to the high voltage output unit 42, and the high voltage output unit 42 actually adjusts the fluoroscopy conditions, so that the fluoroscopy condition setting unit 41 can adjust the fluoroscopy conditions. it can. The perspective condition setting unit 41, the grid control detection unit 43, and the grid control unit 44 are configured by a central processing unit (CPU) and the like.

  Next, specific tube voltage waveform, grid bias voltage adjustment and fluoroscopy condition adjustment will be described with reference to FIGS. FIG. 3 is a flowchart regarding a series of tube voltage waveforms, grid bias voltage adjustment, and fluoroscopy condition adjustment according to the present embodiment, FIG. 4 is a timing chart regarding tube voltage waveforms according to the embodiment, and FIG. FIG. 6 is a schematic diagram related to detection of the fluoroscopic tube voltage in the tube voltage waveform obtained by enlarging the timing chart of FIG. 4, and FIG.

(Step S1) Detection of Tube Voltage Waveform The grid control detector 43 (see FIG. 1) detects the tube voltage waveform from the high voltage output unit 42 (see FIG. 1). A timing chart in the case of performing grid control with or without grid control is as shown in FIG. On the other hand, the timing chart when the grid control is not performed with or without the grid control is as shown in FIG. FIG. 4B also shows a timing chart when the grid control is not effectively functioning (normally operating) even when the grid control is performed, that is, when the grid control is not operating normally when the grid control is right or wrong. As shown in

  As shown in the timing chart of FIG. 4, when a pulsed high voltage (indicated as “high voltage device output” in FIG. 4 as in FIG. 7) is applied, a pulsed X-ray is output in synchronization with it. . In addition, a tube voltage is also output in synchronization with the application of a pulsed high voltage (shown as “tube voltage waveform” in FIG. 4). When grid control is performed and it is operating normally, the charge charged in the high voltage cable 5 (see FIG. 1) is not released when the high voltage is cut off, so the timing chart of FIG. As shown in Fig. 4, the tube voltage waveform hardly falls.

  On the other hand, when the grid control is not performed or when the grid control is not performed normally even when the grid control is performed, when the high voltage is cut off, the charge charged in the high voltage cable 5 is changed to the X-ray tube. 2 (see FIG. 1 and FIG. 2), and after a high voltage interruption (after X-ray interruption) at a certain time, as shown in the timing chart of FIG. The waveform drops to almost 0V. Therefore, the discharge of the charge charged in the high voltage cable 5 becomes a wave tail component and contains a lot of soft X-rays, as in the X-ray output in FIG. 7A (see hatched hatching in FIG. 4).

(Step S2) Is grid control operating normally?
Focusing on this point, in order to detect the correctness of the grid control including the presence or absence of the grid control, the grid control detection unit 43 detects the waveform of the tube voltage and determines whether or not the grid control operates normally. To detect. When the grid control operates normally, the series of processes is terminated. If the grid control does not operate normally, the process proceeds to the next step S3.

  Specifically, as shown in FIG. 5, the tube when a certain time t [ms] has elapsed after the high voltage interruption of pulse fluoroscopy (after X-ray interruption) (indicated as “output interruption” in FIG. 5). A voltage is acquired (indicated as “tube voltage acquisition” in FIG. 5). The acquisition of the tube voltage may be performed only once, or an average value obtained by sampling a plurality of times until the next pulse (high voltage output) may be used.

The value of the tube voltage acquired in this way is determined as follows to detect whether the grid control is correct or not.
(1) If the acquired tube voltage is 80% or more of the fluoroscopic tube voltage, it is determined that the grid control has been normally operated (a series of processes is terminated).
(2) If the acquired tube voltage is less than 80% of the fluoroscopic tube voltage, it is determined that the grid control is not operating normally because the grid bias voltage (voltage for performing grid control) is insufficient (next step) (Transition to S3).
The percentage value in the cases (1) and (2) described above (80% in the cases (1) and (2) above) is an example. You may change suitably with the pulse rate mentioned later, the kind of tube of the X-ray tube 2, and fluoroscopic tube voltage.

(Step S3) Adjustment of Grid Bias Voltage In the case of (2) where it is determined that the voltage for performing grid control is insufficient, the user or service person is notified of an abnormality with a message or the like, and grid control which is a grid control unit The unit 44 (see FIG. 1) is instructed to increase the grid bias voltage in the negative direction. FIG. 5 shows an operation example at that time.

  In the present embodiment, it is determined that the grid bias voltage is insufficient (for example, at −2000 V) based on the tube voltage waveform detected by the grid control detector 43, and after the next pulse (high voltage output). For example, the grid control unit 44 changes the grid bias voltage to −2200 V (indicated as “grid bias voltage change” in FIG. 5).

  Then, in order to detect whether or not the waveform of the tube voltage becomes normal by increasing the grid bias voltage to −2200V (see “◯” in FIG. 5), a pulse ( The tube voltage is obtained when a certain time t [ms] has elapsed after the high voltage output (after high voltage output) is cut off (after X-ray cutoff). FIG. 5 shows an operation example when the grid control operates normally as a result of increasing the grid bias voltage to −2200V.

(Step S4) Is grid control operating normally?
As a result of increasing and adjusting the grid bias voltage in the negative direction in step S3, whether the grid control is correct or not is detected as in step S2, including the presence or absence of the grid control. When it is determined that the grid control has been operated normally (in the case of the above-described case (1)), the series of processes is terminated. Thereafter, pulse fluoroscopy is operated to perform fluoroscopy with the grid bias voltage. If it is determined that the voltage for performing the grid control is insufficient (in the case of (2) above), the process proceeds to the next step S5.

(Step S5) Within the rated range?
Even if the grid bias voltage is increased and adjusted in the negative direction in step S3, it is determined that the voltage for performing the grid control is insufficient. In the case of (2), the grid bias voltage is equal to that of the tube of the X-ray tube 2. Determine if it is within the rated range. When there is a grid bias voltage within the range of the rated tube voltage of the X-ray tube 2 or the output possible voltage of the grid control unit 44, the process returns to step S3 and steps S3 to S5 are repeated so that the rated range is satisfied. In Step 1, the adjustment to increase the grid bias voltage in the negative direction is continued until the grid control operates normally.

  If the grid control voltage does not operate normally based on the tube voltage waveform even though the grid bias voltage is increased in the negative direction within the rated range (for example, −3800 V), the grid bias voltage is negative. Cannot be raised in the direction of Therefore, in order to reduce the output of the tube of the X-ray tube 2, the grid control detection unit 43 sends a fluoroscopy condition setting command signal to the fluoroscopy condition setting unit 41 (see FIG. 1), and further the fluoroscopy condition setting unit 41. Adjusts the fluoroscopic condition by feeding the high voltage output unit 42.

(Step S6) Adjustment of fluoroscopy conditions As a method for controlling the X-ray output of pulse fluoroscopy (adjustment of fluoroscopy conditions), fluoroscopy tube current, fluoroscopy tube voltage, pulse rate and pulse width can be mentioned. When grid control is not functioning effectively (operating normally), the output of the tube of the X-ray tube 2 in fluoroscopy (pulse fluoroscopy) is adjusted by adjusting at least one of these or a combination of two or more thereof. X-ray output).

  Recent fluoroscopic imaging apparatuses have an automatic brightness adjustment function that automatically adjusts the brightness. Therefore, X-ray conditions (perspective conditions and imaging conditions) are set so that an appropriate brightness can be obtained even if X-ray output is suppressed. Is determined. For this reason, even if an attempt is made to automatically make the brightness appropriate, there is an effect of suppressing the X-ray output in a region where it cannot be set (a point at which the X-ray dose reaches the maximum output). That is, if the luminance is automatically adjusted, the X-ray output is naturally determined. Conversely, if the X-ray output is first determined, the luminance cannot be freely adjusted.

  This seemed good if the body of the subject M (see FIG. 1) has a body thickness of 30 cm (or the subject M), but the grid control function is not functioning effectively. When the line output is limited, for example, it means that only a part having a body thickness of 28 cm (or subject M) can be seen well. However, in order to prevent an increase in subject (patient) exposure and an overload of the tube of the X-ray tube 2, it is necessary to limit the fluoroscopic conditions (suppression of X-ray output) as in this embodiment.

* Limit the fluoroscopic tube current. For example, if the maximum load fluoroscopic tube current is 200 mA (peak value of pulse fluoroscopy) and the grid control is not functioning effectively, 10% depending on the tube voltage. It can be reduced by about 20%. Thereby, the fluoroscopic output can be reduced by about 10% to 20%, and the maximum subject (patient) exposure and the load on the tube of the X-ray tube 2 can be reduced. In addition, the tube current is greatly reduced to about 50%, and at the same time, the BH filter (soft X-ray removal filter) composed of a metal filter is changed to a thin one in order to perform beam hardening correction processing. To do. As a result, even if the tube current is greatly reduced, the deterioration of the image quality can be somewhat suppressed.

* Limit the fluoroscopic tube voltage If the maximum tube voltage (maximum tube voltage) for fluoroscopy is 120 kV, change it so that it can only be set up to 110 kV. Thereby, even if it raises to the maximum tube voltage vicinity by automatic brightness adjustment, the maximum subject (patient) exposure and the load of the tube | tube of the X-ray tube 2 can be reduced. Even in this case, the image quality deterioration in a thick subject can be somewhat suppressed by changing the BH filter to a thin one instead of lowering the maximum tube voltage.

* Limiting the pulse rate To the pulse rate that is the number of pulses per unit time when the voltage applied to the triode X-ray tube is turned on or off (in this example, the pulse rate that is the number of pulses per second) Add restrictions. It is known that the influence of the wave tail component increases as the rate of pulse fluoroscopy increases in the tube load of the X-ray tube 2 when grid control is not performed. If it is used at a pulse rate of 30 pps, it is automatically changed to 15 pps, so that fluoroscopy at a pulse rate of 30 pps cannot be performed.

* Limit the pulse width Limit the pulse width, which is the time width when the voltage applied to the triode X-ray tube is on. If the fluoroscopic tube current (peak value) of each pulse in pulse fluoroscopy is the same, X-ray output can be suppressed by reducing the pulse width when grid control is not functioning effectively. Thereby, even if it raises to the maximum tube voltage vicinity by automatic brightness adjustment, the maximum subject (patient) exposure and the load of the tube | tube of the X-ray tube 2 can be reduced.

  The fluoroscopic imaging apparatus according to the present embodiment includes the grid control detection unit 43, and the grid control detection unit 43 can detect whether the grid control is correct or not by detecting the waveform of the tube voltage. Specifically, as described in the knowledge, when grid control is not performed including failure, etc., the charge charged in the high voltage cable 5 is released from the X-ray tube 2 and after the X-ray output is cut off, The waveform of the tube voltage of the X-ray tube 2 falls to almost “0”. On the other hand, when grid control is performed, the electric charge charged in the high voltage cable 5 is hardly released, so that the waveform of the tube voltage of the X-ray tube 2 hardly drops even after the X-ray output is cut off. Using this phenomenon, the grid control detection unit 43 can detect whether the grid control operates normally by detecting the waveform of the tube voltage.

  In the present embodiment, it is preferable to include a grid control unit 44 that adjusts the grid bias voltage applied to the grid electrode G based on the waveform of the tube voltage detected by the grid control detection unit 43. If the grid control is not operating normally based on the tube voltage waveform, the grid bias voltage is increased in the negative direction. As a result of increasing the grid bias voltage in the negative direction, when the grid control operates normally based on the waveform of the tube voltage, fluoroscopy or imaging (in this embodiment, fluoroscopy) is performed with the grid bias voltage thereafter. . Therefore, it is possible to normally suppress the wave tail component (wave tail cutoff).

  Even if the grid bias voltage is increased in the negative direction, if the grid control still does not operate normally based on the waveform of the tube voltage, the fluoroscopy condition setting unit 41 that adjusts the X-ray condition (the fluoroscopy condition in this embodiment). Is preferably provided.

  Specifically, a fluoroscopy condition setting unit 41 that adjusts an X-ray condition (fluoroscopy condition) when the grid control is not operating normally based on the waveform of the tube voltage detected by the grid control detection unit 43 is provided. Is preferred. For example, in the case where the grid bias voltage is adjusted as described above as in the present embodiment, the grid bias voltage is increased in the negative direction to, for example, the rating of the tube of the X-ray tube 2 or the output possible voltage of the grid control unit 44. In spite of this, if the grid control does not operate normally based on the waveform of the tube voltage, the grid bias voltage cannot be increased in the negative direction.

  Therefore, a fluoroscopy condition setting unit 41 that adjusts X-ray conditions (fluoroscopy conditions) is provided. By providing a fluoroscopy condition setting unit 41 that adjusts X-ray conditions (fluoroscopy conditions), even if grid control is not operating normally, it is the same as an X-ray tube that does not have a function to perform grid control. It is possible to use.

  In the case where the fluoroscopy condition setting unit 41 that adjusts the X-ray condition (fluoroscopy condition) is provided, the fluoroscopy condition setting unit 41 may adjust by reducing the tube current when the grid control is not operating normally. . Thereby, the maximum subject (patient) exposure and the load on the tube of the X-ray tube 2 can be reduced.

  Further, in the case where the fluoroscopy condition setting unit 41 for adjusting the X-ray condition (fluoroscopy condition) is provided, the fluoroscopy condition setting unit 41 sets the maximum tube voltage when the grid control is not operating normally. The voltage (maximum tube voltage) setting may be reduced and adjusted. Thereby, even if it raises to the maximum tube voltage vicinity, the maximum subject (patient) exposure and the load of the tube | tube of the X-ray tube 2 can be reduced.

  Further, in the case where the fluoroscopy condition setting unit 41 for adjusting the X-ray condition (fluoroscopy condition) is provided, the fluoroscopy condition setting unit 41 is a triode X-ray tube (X-ray tube) when the grid control is not operating normally. It may be adjusted by reducing the pulse rate that is the number of pulses per unit time at which the voltage applied to 2) is turned on or off (in this embodiment, the pulse rate that is the number of pulses per second). It is known that the load on the tube of the X-ray tube 2 is more influenced by the wave tail component as the pulse rate is higher (that is, the number of pulses per unit time is larger). Therefore, the influence of the wave tail component can be reduced by adjusting the pulse rate by reducing it.

  Further, in the case where the fluoroscopy condition setting unit 41 for adjusting the X-ray condition (fluoroscopy condition) is provided, the fluoroscopy condition setting unit 41 is a triode X-ray tube (X-ray tube) when the grid control is not operating normally. The voltage applied to 2) may be adjusted by reducing the pulse width, which is the ON time width. X-ray output can be suppressed by reducing the pulse width. Thereby, even if it raises to the maximum tube voltage vicinity, the maximum subject (patient) exposure and the load of the tube | tube of the X-ray tube 2 can be reduced.

  Further, in the case where the fluoroscopy condition setting unit 41 that adjusts the X-ray condition (fluoroscopy condition) is provided, the X-ray condition includes the maximum tube voltage setting that sets the tube current and the tube voltage to the maximum, The pulse rate which is the number per unit time when the voltage applied to the tube 2) is turned on or off, or the pulse width which is the time width when the voltage applied to the triode X-ray tube (X-ray tube 2) is on. Thus, when the grid control is not operating normally, the fluoroscopy condition setting unit 41 may adjust the tube current, the maximum tube voltage setting, the pulse rate, or the pulse width by reducing at least two in combination. .

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, the pulse fluoroscopy in which fluoroscopy is performed while repeatedly applying a pulsed high voltage has been described as an example. However, the present invention is applied to pulse imaging in which imaging is performed by applying a pulsed high voltage. May be.

  (2) In the above-described embodiments, the grid bias voltage is adjusted, but it is not always necessary to adjust the grid bias voltage. X-ray conditions (transmission conditions and imaging conditions) may be adjusted without adjusting the grid bias voltage. In this case, in the flowchart of FIG. 3, if the grid control is not normally operated in step S2 without adjusting the grid bias voltage in steps S3 to S5, the process proceeds to step S6 unconditionally. The fluoroscopic conditions may be adjusted.

  (3) In the above-described embodiment, the pulse rate is the number of pulses per second, but is not limited to the number of pulses per second. For example, the number of pulses per unit msec may be used.

DESCRIPTION OF SYMBOLS 2 ... X-ray tube 41 ... Perspective condition setting part 43 ... Grid control detection part 44 ... Grid control part G ... Grid electrode

Claims (8)

A triode X-ray tube having a grid electrode;
A fluoroscopic imaging apparatus that performs fluoroscopy or imaging in order to acquire an X-ray image based on X-rays emitted from the triode X-ray tube,
A fluoroscopic imaging apparatus comprising waveform detection means for detecting a waveform of a tube voltage of the triode X-ray tube in order to detect whether the grid control for controlling the grid electrode is correct or not. The fluoroscopic apparatus according to claim 1,
A fluoroscopic imaging apparatus comprising bias voltage adjusting means for adjusting a grid bias voltage applied to the grid electrode based on a waveform of the tube voltage detected by the waveform detecting means. The fluoroscopic apparatus according to claim 1 or 2,
A fluoroscopic imaging apparatus comprising: an X-ray condition adjusting unit that adjusts an X-ray condition when the grid control is not operating normally based on a waveform of the tube voltage detected by the waveform detecting unit. . The fluoroscopic apparatus according to claim 3,
The fluoroscopic apparatus according to claim 1, wherein the X-ray condition adjusting unit adjusts by reducing a tube current when the grid control is not operating normally. The fluoroscopic apparatus according to claim 3,
The fluoroscopic imaging apparatus according to claim 1, wherein the X-ray condition adjusting unit reduces and adjusts a maximum tube voltage setting that sets a tube voltage to a maximum when the grid control is not operating normally. The fluoroscopic apparatus according to claim 3,
The X-ray condition adjusting means reduces a pulse rate that is the number of pulses per unit time at which a voltage applied to the triode X-ray tube is turned on or off when the grid control is not operating normally. A fluoroscopic imaging device characterized by adjusting. The fluoroscopic apparatus according to claim 3,
The X-ray condition adjusting means adjusts by reducing a pulse width which is a time width during which the voltage applied to the triode X-ray tube is on when the grid control is not operating normally. Perspective imaging device. The fluoroscopic apparatus according to claim 3,
The X-ray condition includes a tube current, a maximum tube voltage setting for setting the tube voltage to a maximum, a pulse rate that is the number per unit time at which the voltage applied to the triode X-ray tube is turned on or off, or the triode The voltage applied to the X-ray tube has a pulse width which is an ON time width, and
The X-ray condition adjusting means adjusts by reducing at least two or more of the tube current, the maximum tube voltage setting, the pulse rate or the pulse width when the grid control is not operating normally. A fluoroscopic imaging device characterized by:

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