JP4896465B2 - X-ray image tube distortion correction method and apparatus - Google Patents

Description

  The present invention relates to an X-ray image tube distortion correction method and apparatus for correcting distortion of a visible light image excluding the influence of an external magnetic field.

  In general, in medical X-ray diagnostic apparatuses and industrial non-destructive inspection apparatuses using an X-ray image tube, the X-ray image from the X-ray tube is transmitted through the subject, and the X-ray image is visible through the X-ray image tube. The image is converted into a light image, the visible light image is captured by an imaging camera, and the captured image is projected on a monitor to enable observation.

  The parts other than the input surface of the X-ray image tube are covered with a magnetic shield made of a material that blocks the influence of magnetism such as permalloy, but the input surface is covered with a magnetic shield so as not to prevent the transmission of X-rays. Not covered. For this reason, there is a problem that an external magnetic field enters from the input surface of the X-ray image tube due to geomagnetism or magnetism generated from an external device, and the visible light image is distorted by the influence of the external magnetic field.

Therefore, in order to correct distortion due to an external magnetic field, a magnetic field detector and a coil are arranged on or near the input surface, and this magnetic field detector detects an external magnetic field that enters the input surface of the X-ray image tube from the outside. By flowing a current from the power supply unit to the coil so that a reverse magnetic field that cancels the detected external magnetic field is generated from the coil, the external magnetic field is canceled and the distortion of the visible light image is reduced. That is, the current flowing from the power supply unit to the coil is varied based on the external magnetic field detected by the magnetic field detection unit by feedback control (see, for example, Patent Document 1).
JP-A-7-65756 (page 3-4, Fig. 1-2)

  Generally, since feedback control is always performed in feedback control, the control of the power supply unit is always corrected in accordance with the fluctuation of the external magnetic field detected by the magnetic field detection unit, and the current flowing from the power supply unit to the coil is always varied. .

  However, compared to the time required to output a command for correcting the control of the power supply unit in response to the fluctuation of the external magnetic field detected by the magnetic field detection unit, the current flowing through the coil is varied by the power supply unit that has received the command. It takes a long time to complete. Therefore, before the current flowing through the coil in the power supply unit is completely varied, the correction of the control of the power supply unit is repeated in response to the fluctuation of the external magnetic field detected by the magnetic field detection unit. There is a problem that it takes a long time for this hunting to converge.

  The present invention has been made in view of the above points, and can correct the distortion of an X-ray image tube that can prevent the occurrence of hunting when correcting the influence of an external magnetic field and can correct the influence of the external magnetic field in a short time. It is an object to provide a method and apparatus.

The X-ray image tube distortion correction method of the present invention detects an external magnetic field that enters the X-ray image tube from the outside and generates a magnetic field that cancels the external magnetic field that enters the X-ray image tube from the outside. This method corrects the generation of a magnetic field that cancels the external magnetic field so that it returns to the reference range when the detected external magnetic field fluctuates beyond a preset reference range of the magnetic field strength . From the time when the external magnetic field fluctuates beyond the reference range of the preset magnetic field strength until the preset time elapses after correcting the generation of the magnetic field that cancels the external magnetic field so as to return to the reference range complement during the generation of a magnetic field to cancel the external magnetic field when varies within the intensity of the reference range of regulating the correction operation based on the external magnetic field detected during, the magnetic field detected stray field is preset Those that do not.

A distortion correction apparatus for an X-ray image tube according to the present invention generates a magnetic field detector that detects an external magnetic field that enters the X-ray image tube from the outside, and a magnetic field that cancels the external magnetic field that enters the X-ray image tube from the outside. A magnetic field generating unit, a power source unit that drives the magnetic field generating unit to generate a magnetic field, and controls the power source unit, and an external magnetic field detected by the magnetic field detecting unit has a preset magnetic field strength reference range. beyond the control of the power supply unit corrects back to the reference range when variation, when varies within reference range and a control unit that does not correct the control of the power supply unit, wherein the control unit, wherein the magnetic field A time set in advance after correcting the control of the power supply unit so that the external magnetic field detected by the detection unit fluctuates beyond the reference range of the magnetic field strength set in advance and returns to the reference range. Until During, it restricts the correction operation based on the external magnetic field detected by the magnetic field detector therebetween.

According to the present invention, when the detected external magnetic field fluctuates beyond a preset reference range of the magnetic field strength, the generation of the magnetic field that cancels the external magnetic field is corrected so as to return to the reference range. When the magnetic field fluctuates within the preset reference range of magnetic field strength, the generation of the magnetic field that cancels the external magnetic field is not corrected. Can be converged within the reference range in a short time. Further, after the detected external magnetic field fluctuates beyond a preset reference range of magnetic field strength, a preset time after correcting the generation of the magnetic field that cancels the external magnetic field so as to return to the reference range. Until the time elapses, the correction operation based on the external magnetic field detected in the meantime can be restricted, and the occurrence of hunting due to repeated correction within a short time loop can be prevented.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  In FIG. 2, 11 is an X-ray image tube. This X-ray image tube 11 has a vacuum envelope 12, and an input window 13 is formed on the X-ray incident side of the vacuum envelope 12. An output window 14 is formed on the opposite side to the input window 13. Inside the vacuum envelope 12, an input surface 15 for converting X-rays into an electron beam and emitting it is provided inside the input window 13, and the electron beam is converted into a visible light image and output inside the output window 14. An output surface 16 is provided.

  An electron lens that accelerates or focuses the electron beam is formed along the path of the electron beam traveling from the input surface 15 toward the output surface 16, and this electron lens is a cathode electrode that applies a negative voltage to the input surface 15. K and an anode electrode A that applies a high positive voltage to the output surface 16, and a plurality of electrodes such as a plurality of grid electrodes G1, G2, and G3 between the cathode electrode K and the anode electrode A.

  The periphery of the vacuum envelope 12 excluding the input surface 15 and the output surface 16 is covered with a magnetic shield 17 made of a material that blocks the influence of magnetism such as permalloy.

  Next, in FIG. 1, a distortion correction device 21 of the X-ray image tube 11 is shown. The distortion correction device 21 generates an external magnetic field that enters the X-ray image tube 11 from the outside due to geomagnetism or magnetism generated from an external device. Magnetic field detection unit 22 using a magnetoelectric transducer to detect, coil 23 as a magnetic field generation unit that generates a reverse magnetic field as a magnetic field that cancels an external magnetic field that enters X-ray image tube 11 from the outside, and current is passed through this coil 23 And a control unit 25 for controlling a current value flowing from the power supply unit 24 to the coil 23.

  The magnetic field detector 22 is disposed near the periphery of the input surface 15 between the vacuum envelope 12 and the magnetic shield 17, and the coil 23 is disposed between the vacuum envelope 12 and the magnetic shield 17. It is disposed along the periphery of the input surface 15.

  The control unit 25 corrects the control of the power supply unit 24 so that when the external magnetic field detected by the magnetic field detection unit 22 fluctuates beyond a reference range, which is a preset magnetic field strength stability range, it returns to the reference range. The function of not correcting the control of the power supply unit 24 when it fluctuates within the reference range, and the external magnetic field detected by the magnetic field detection unit 22 fluctuates beyond a preset magnetic field strength reference range. From time to time, after correcting the control of the power supply unit 24 to return to within the reference range, the correction operation based on the external magnetic field detected by the magnetic field detection unit 22 is regulated until a preset time elapses. It has a function to do.

  As shown in FIG. 3, the reference range of the magnetic field strength is an upper limit value and a lower limit value of a predetermined width with the detection value detected by the magnetic field detection unit 22 in a state where no external magnetic field enters the X-ray image tube 11 as a reference value. Is a range in which the influence is small even if the external magnetic field fluctuates. These reference value, upper limit value, lower limit value, reference range, and the like are stored in a storage unit (not shown) provided in the control unit 25.

  The control unit 25 includes an external communication means or setting means, and sets a reference value, an upper limit value, a lower limit value, a reference range, etc. according to a setting signal from the outside through the communication means or setting by the setting means. Settings and changes are possible.

  Next, the operation of the present embodiment will be described.

  First, in order to recognize the reference condition when the distortion correction device 21 is stable, the detection signal detected by the magnetic field detection unit 22 without being affected by the external magnetic field is input to the control unit 25. The detection signal of the magnetic field detection unit 22 is set as a reference value, and the upper limit value and lower limit value of the detection signal regarded as being in a stable state are set simultaneously, and the range between these upper limit value and lower limit value is set as a reference range that is a stable range Set.

  The reference range set by the control unit 25 is stored in the storage unit of the control unit 25, but can be set and changed by an external setting signal or setting unit through the communication unit. In addition to the parameters that can be set and changed, a sampling interval by the magnetic field detector 22 and the like are also included.

  Next, the distortion correction operation will be described with reference to the flowchart of FIG.

  Here, the description will be made assuming that the reference value, the upper limit value, the lower limit value, the reference range, the sampling interval, etc. have already been set.

  When the power is turned on, it is determined whether the magnetic field strength Ta of the external magnetic field detected by the magnetic field detection unit 22 is between the upper limit magnetic field strength Timax and the lower limit magnetic field strength Timin of the reference range, that is, within the reference range (step) 1). This determination is looped at a constant interval. Therefore, during operation, the output of the magnetic field detector 22 is also sampled at a constant interval of, for example, several tens of milliseconds or less.

  When the magnetic field strength Ta of the external magnetic field detected by the magnetic field detection unit 22 exceeds the magnetic field strength Timax of the upper limit value of the reference range (step 2), the magnetic field strength Ta of these external magnetic fields and the magnetic field strength of the reference value A difference Tb in magnetic field strength from Timax was obtained (step 3), and an electric signal (voltage or current) E for generating a reverse magnetic field in the coil 23 necessary to cancel the difference Tb in the magnetic field strength was obtained and obtained. The power supply unit 24 is controlled to output the electric signal E to the coil 23 (step 4). The electric signal E is obtained by the equation E = Tb × A, where A is an electric signal necessary for correcting the unit magnetic field.

  On the other hand, when the magnetic field strength Ta of the external magnetic field detected by the magnetic field detector 22 exceeds the magnetic field strength Timin of the lower limit value of the reference range, the magnetic field strength Ta of the external magnetic field and the magnetic field strength Timin of the reference value An intensity difference Tb is obtained (step 5), an electric signal (voltage or current) E for generating a reverse magnetic field in the coil 23 necessary to cancel the magnetic field intensity difference Tb is obtained, and the obtained electric signal E is obtained. The power supply unit 24 is controlled so as to output to the coil 23 (step 6).

  After the power supply unit 24 is controlled to output the electrical signal E thus obtained to the coil 23, it waits for a preset time to elapse (step 7). This preset time is determined from the time constants of the power supply unit 24 and the coil 23, and until the actual correction operation is stabilized in order to generate a reverse magnetic field in the coil 23 necessary to cancel the difference Tb in the magnetic field strength. However, it generally stabilizes at several tens of milliseconds.

  At this time, the control unit 25 controls the power supply unit 24 so that the external magnetic field detected by the magnetic field detection unit 22 fluctuates beyond a preset magnetic field strength reference range, and returns to the reference range. After the correction, until the preset time elapses, the correction operation based on the external magnetic field detected by the magnetic field detection unit 22 is restricted during that time, and the occurrence of hunting due to repeated correction within the short-time loop To prevent.

  When a preset time has elapsed, the correction result is confirmed (step 8). By checking the correction result, if the magnetic field strength Ta of the external magnetic field detected by the magnetic field detection unit 22 falls within the reference range, it is confirmed whether the correction is completed and the power is turned off (step 9). If the correction is insufficient or excessively corrected, the difference is further corrected by the same control.

  As described above, when the detected external magnetic field fluctuates beyond the preset reference range of the magnetic field strength, the generation of the magnetic field that cancels the external magnetic field is corrected so as to return to the reference range. Since the generation of a magnetic field that cancels the external magnetic field is not corrected when it fluctuates within a preset reference range of magnetic field strength, hunting can be prevented and fluctuations in the external magnetic field can be reduced compared to the case where feedback control is always performed. It can be converged within the reference range in time.

It is a block diagram of the distortion correction apparatus of the X-ray image tube which shows one embodiment of this invention. It is sectional drawing of an X-ray image tube same as the above. It is a graph which shows the relationship between the magnetic field intensity and time of an X-ray image tube same as the above. It is a flowchart which shows the distortion correction method of a X-ray image tube same as the above.

11 X-ray image tube
21 Distortion correction device
22 Magnetic field detector
23 Coil as magnetic field generator
24 Power supply
25 Control unit

Claims (4)

An X-ray image tube distortion correction method for detecting an external magnetic field that enters the X-ray image tube from the outside and generating a magnetic field that cancels the external magnetic field that enters the X-ray image tube from the outside,
When the detected external magnetic field fluctuates beyond a preset magnetic field strength reference range, the generation of a magnetic field that cancels the external magnetic field is corrected so as to return to the reference range,
After the detected external magnetic field fluctuates beyond a preset reference range of magnetic field strength, a preset time elapses after correcting the generation of the magnetic field that cancels the external magnetic field so that it returns to the reference range In the meantime, the correction operation based on the external magnetic field detected during that time is regulated,
A distortion correction method for an X-ray image tube, characterized in that generation of a magnetic field that cancels out an external magnetic field is not corrected when the detected external magnetic field fluctuates within a preset reference range of magnetic field strength. The reference range of the strength of the magnetic field is a range in which an upper limit value and a lower limit value are set with a detection value in a state where no magnetic field enters the X-ray image tube from the outside as a reference value. The distortion correction method of the X-ray image tube of description . A magnetic field detector that detects an external magnetic field that enters the X-ray image tube from the outside;
A magnetic field generator for generating a magnetic field that cancels an external magnetic field that enters the X-ray image tube from the outside;
A power supply unit that drives the magnetic field generation unit to generate a magnetic field;
Control the power supply unit, and when the external magnetic field detected by the magnetic field detection unit fluctuates beyond a preset magnetic field strength reference range, correct the control of the power supply unit to return to within the reference range, A control unit that does not correct the control of the power supply unit when it fluctuates within a reference range ,
The control unit corrects the control of the power supply unit so that the external magnetic field detected by the magnetic field detection unit fluctuates beyond a preset magnetic field strength reference range and then returns to the reference range. An X-ray image tube distortion correction apparatus , wherein a correction operation based on an external magnetic field detected by the magnetic field detection unit is regulated until a preset time elapses later . The reference range of the magnetic field strength is a range in which an upper limit value and a lower limit value are set with a detection value of the magnetic field detection unit in a state where an external magnetic field does not enter the X-ray image tube as a reference value. The distortion correction apparatus for an X-ray image tube according to claim 3 .

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