JP4648678B2 - X-ray tube filament heating device - Google Patents

Description

  The present invention relates to an X-ray tube filament heating apparatus, and more particularly to an X-ray tube filament heating apparatus capable of heating a filament at high speed.

X-rays are obtained by applying a high DC voltage (hereinafter referred to as tube voltage) between the anode and cathode of an X-ray tube, and thermionic electrons emitted from the filament, which is a cathode heated to a high temperature, collide with the anode. However, at this time, an apparatus for heating the filament to a high temperature is an X-ray tube filament heating apparatus.
The X-ray dose generated from the X-ray tube is the current flowing between the anode and cathode of the X-ray tube (hereinafter referred to as the tube current) and the time during which this current flows under the same tube voltage. The tube current is determined by the filament temperature.
Since the filament temperature is determined by the current flowing through the filament (hereinafter referred to as the filament current), the X-ray dose can be controlled by the filament current.

  As described above, a filament heating apparatus that controls the X-ray dose by heating the filament of the X-ray tube generally converts the direct current from the direct current power source into high frequency alternating current by the inverter circuit and transforms the output alternating voltage of the inverter circuit. The transformer is insulated (this transformer is called a heating transformer), and the output of the heating transformer controlled by at least one of the DC power source and the inverter circuit is supplied to the filament of the X-ray tube. A method of heating the filament of the tube is adopted.

In the filament heating device, when there is a time delay from the start of imaging, that is, from the start of X-ray emission until the filament temperature of the X-ray tube reaches a predetermined high temperature, it will be impossible to image at the optimal imaging timing. The filament temperature needs to be heated to reach a predetermined temperature as soon as possible.
In particular, in recent years, X-ray diagnostic equipment uses X-ray fluorescence intensifiers and TV cameras, as well as X-ray detectors, instead of taking X-ray photographs on X-ray films that have been widely used. Since a system using a flat panel detector is becoming widespread, an imaging system using them eliminates the time for replacing the film and the time for transporting the film to the imaging position that occurred in the X-ray film system. Therefore, a further increase in speed is required for the filament heating.

Conventionally, the technique disclosed in Patent Document 1 or Patent Document 2 has been adopted to increase the filament heating speed.
The filament heating device disclosed in Patent Document 1 obtains a filament resistance from the filament voltage and current and controls the heating power so that the filament resistance value becomes a target resistance value.
Further, the filament heating device disclosed in Patent Document 2 is intended to increase the heating speed by overshooting the voltage applied to the filament at the start of heating of the filament.
Japanese Patent No. 3447012 Japanese Patent Laid-Open No. 8-195294

In the method of controlling the resistance value of the filament disclosed in Patent Document 1, since the filament temperature and the filament resistance value have an exponential function relationship, this is converted into a linear function, and the converted filament temperature and Since the filament resistance value must be controlled, the controlled filament temperature is lower than the actual filament temperature.
Therefore, the X-ray dose is insufficient and the image quality of the X-ray image is deteriorated.

On the other hand, in the method of overshooting the voltage applied to the filament at the start of heating of the filament disclosed in Patent Document 2, the overshoot value of the voltage applied to the filament is an appropriate value. Otherwise, the following problems will occur.
That is, when the overshoot value is increased, the filament is heated at a high speed. However, when the overshoot value is excessively increased, the X-ray dose becomes greater than a predetermined value.
Conversely, if the overshoot value is small, X-rays are emitted before the filament temperature reaches the predetermined temperature, and the X-ray dose becomes insufficient.
Therefore, unless the overshoot value is set to an appropriate value, the image quality of the X-ray image is deteriorated. In particular, in the case of continuous imaging or the like, it causes a variation in image quality.

As described above, in the method using the overshoot, it is necessary to set the overshoot value to an appropriate value, but this overshoot value varies depending on the X-ray imaging conditions corresponding to the imaging region and the imaging technique, It depends on the type of X-ray tube and X-ray imaging system components such as the X-ray detector.
Therefore, since an appropriate overshoot value must be prepared corresponding to the various conditions, the heating control of the filament has been complicated.

  The object of the present invention is to solve the above-mentioned conventional problems of image quality deterioration due to insufficient heating of the filament and complicated heating control of the filament, and to heat the unheated filament to the optimum temperature at high speed. It is to provide a filament heating device for a tube.

  The above objective is accomplished by controlling the filament temperature of the x-ray tube to match the target filament temperature. Specifically, this is achieved by the following means.

(1) A direct current power supply, an inverter circuit that converts direct current from the direct current power supply into alternating current, a heating transformer that insulates the output alternating voltage of the inverter circuit, and at least one of the direct current power supply and the inverter circuit An X-ray tube filament heating apparatus for supplying power to the filament of the X-ray tube by supplying an output of the heating transformer to the filament of the X-ray tube, wherein the filament is brought to a predetermined temperature. The filament temperature setting means for heating, the filament temperature detection means for detecting the temperature of the filament, and the target set temperature set by the filament temperature setting means and the temperature detected by the filament temperature detection means match. Filament heating control signal generating means for generating a control signal for controlling the power, and the power control means And it controls the power supplied to the filament based on the item.

In this way, the filament temperature detecting means and the filament temperature setting means are provided, and the power supplied to the filament so that the target set temperature set by the filament temperature setting means matches the temperature detected by the filament temperature detecting means. To control.
Therefore, the filament temperature has a one-to-one relationship with the target filament temperature, and the target value of the filament temperature may be set to a value according to the shooting conditions. The reduction and the complicated heating control of the filament are eliminated, and the unheated filament can be heated to the optimum temperature at high speed.

  The filament temperature may be detected by providing a temperature detection means in the vicinity of the filament of the X-ray tube container, or may be detected by other methods, and if the temperature equivalent to the filament temperature can be detected, Any means can be used.

(2) In Claim 1, the X-ray tube further includes a filament that forms at least two focal points of a small focus filament and a large focus filament, and the small focus filament and the large focus filament The filament heating power controlled based on the control signal generated by the filament heating control signal generating means is supplied to one of the filaments.

The X-ray tube with two filaments, the small focus filament and the large focus filament, uses a small focus filament to increase the sharpness of the image when framing the region of interest by X-ray fluoroscopy, and flows to the X-ray tube during imaging. Large focal filaments are used to increase current and increase X-ray dosage.
The same effect can be obtained by using the method (1) in the X-ray fluoroscopic imaging system using the X-ray tube that forms two focal points of the small focus and the large focus.

However, in this case, the following means are required.
1) The filament temperature setting means is provided with two temperature setting means for small focus and for large focus.
2) The filament heating transformer has two heating transformers, a small focus heating transformer and a large focus heating transformer, which are switched according to fluoroscopy and photographing, and the outputs of the two heating transformers are respectively changed. A focus selection circuit is provided for feeding the corresponding filaments.

(3) In any one of claims 1 and 2, the filament temperature detecting means is a temperature detecting filament equivalent to the filament of the X-ray tube for detecting a temperature proportional to the temperature of the filament of the X-ray tube The temperature of the temperature detecting filament is detected.

An example of the temperature detecting filament and temperature detecting means will be described below.
1) The temperature detecting filament has the same impedance as that of the filament of the X-ray tube, and has the same material as that of the filament of the X-ray tube.
2) The temperature detection filament is sealed in a vacuum glass container, and the temperature in the vicinity of the container is detected with a radiation thermometer or light emitted from the filament, and the X-ray tube is contactlessly detected. Detects the temperature equivalent to the filament.
3) The heating transformer is provided with a winding insulated from the filament of the X-ray tube, and power output from the winding is supplied to the temperature detecting filament.

  In this way, a temperature detection filament is provided, and this filament is heated with electric power corresponding to the electric power for heating the filament of the X-ray tube to detect a temperature equivalent to the filament of the X-ray tube. , X-ray tube filament temperature can be easily detected.

(3) The temperature detection filament is heated by using the output of the heating transformer. This is because the output of the inverter circuit is a temperature detection filament different from the heating transformer. It may be inputted to a heating transformer, and the output of this transformer may be supplied to the temperature detecting filament.
Even if comprised in this way, the effect similar to the above is acquired.

  According to the present invention, the filament heating power is controlled so that the filament temperature of the X-ray tube is detected and the detected temperature matches the target filament temperature. Image quality deterioration due to insufficient heating and complicated heating control of the filament are eliminated, and the unheated filament can be heated to the optimum temperature at high speed.

  Hereinafter, preferred embodiments of an X-ray tube filament heating apparatus according to the present invention used in an X-ray diagnostic imaging apparatus will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an overall configuration of an X-ray generator in which an X-ray tube filament heating device according to the present invention is applied to heating an X-ray tube filament having filaments that form two large and small focal points.

The X-ray generator shown in FIG. 1 includes an X-ray high-voltage device 1 that generates a DC high voltage, a small-focus filament 2S that emits X-rays by applying an output voltage of the X-ray high-voltage device 1, and a large focus. The X-ray tube 2 having two filaments 2L, the filament heating device 3 of the X-ray tube of the present invention for heating the filament of the X-ray tube 2, and the two 2S and 2L according to fluoroscopy and imaging And a console 4 for outputting a focus selection signal for selecting one of the filaments and a filament temperature setting value for heating the filament to a target temperature.
The X-ray generator configured in this way is mainly used for digestive system diagnosis such as stomach and large intestine and circulatory system diagnosis such as coronary arteries and cerebral blood vessels of the heart. Used in fluoroscopic systems.

  In the X-ray high voltage device 1, the high voltage transformer 9 described later is reduced in size and the pulsation of a high voltage (tube voltage) of DC applied between the anode and the cathode of the X-ray tube 2 is reduced. In order to improve the generation efficiency of X-rays radiated from the tube 2, an inverter type X-ray high voltage device is generally used.

This inverter type X-ray high voltage apparatus 1 converts a commercial AC power source 5 into a direct current with a first rectifier circuit 6 as shown in the figure, smooths this with a capacitor 7 and uses the first inverter circuit 8 to The AC voltage having a higher frequency than that of the power source is converted, the converted high-frequency AC voltage is boosted to a voltage at which a predetermined tube voltage is obtained by the high voltage transformer 9, and the boosted AC voltage is increased to a high voltage rectifier circuit. The voltage is converted into a high DC voltage by 10 and this voltage is applied between the anode and cathode of the X-ray tube 2 via the high voltage cable 11.
At least one of the first rectifier circuit 6 and the first inverter circuit 8 has a power control function, and this control function is configured to obtain a tube voltage according to the photographing conditions. ing.

In order to emit a required X-ray dose from the X-ray tube, it is necessary to heat the filament of the X-ray tube at a high speed to a temperature at which the X-ray dose can be obtained.
For this purpose, the filament heating device 3 of the X-ray tube according to the present invention is configured as shown. That is, the AC power source 5 is insulated by the transformer 12, and the alternating current obtained by this insulation is converted into direct current by the second rectifier circuit 13, which is smoothed by the capacitor 14 and then converted by the second inverter circuit 15. The high-frequency alternating current is converted, and this alternating current is input to the small-focus heating transformer 17 or the large-focus heating transformer 18 selected by the focus selection circuit 16, and the outputs of these heating transformers are respectively corresponding to the filaments 2S. Alternatively, the filament is heated by supplying 2 L.

The focus selection circuit 16 selects a small focus filament 2S during fluoroscopy and a large focus filament 2L during radiographing based on the focus selection signal output from the console 4 for setting various operation signals. When the small focus filament 2S is selected, the heating transformer 17 primary winding 17F, when the shooting large focus filament 2L is selected, the heating transformer 18 primary winding 18F, The output of the second inverter circuit 15 is input.
Then, the voltage of the secondary winding 17SS of the heating transformer 17 is applied to the small focus filament 2S, the voltage of the secondary winding 18SL of the heating transformer 18 is applied to the large focus filament 2L, respectively. The filaments are heated.

  The present invention includes a temperature detecting filament 19a for detecting a temperature equivalent to the temperature of the filaments 2S and 2L of the X-ray tube 2, and a radiation thermometer for detecting the temperature of the temperature detecting filament 19a in a non-contact manner. 20 and the heating transformers 17 and 18 are respectively provided with tertiary windings 17TS and 18TL, and the voltage of the tertiary winding is applied to the temperature detection filament 19a so that the temperature detection filament 19a is the X The temperature detecting filament 19a is heated so as to be equivalent to the filament temperature of the wire tube 2.

As shown in FIG. 2, the temperature detecting filament 19a is made of the same material as the filaments 2S and 2L of the X-ray tube 2 and has a high melting point so as to have the same impedance as the filaments 2S and 2L of the X-ray tube 2. When processing into a coil shape, a material that does not easily break or crack, such as tungsten, is used.
The thread-like tungsten of such a material is processed into a coil shape, which is housed in a glass container 19, and a vacuum is drawn in a sealed state to mount the temperature detecting filament 19a on the glass container 19 in a vacuum state.

  In order to supply the temperature detection filament 19 with the same power as that supplied to the filaments 2S and 2L of the X-ray tube 2, the number of turns of the tertiary windings 17TS and 18TL of the heating transformer is the heating transformer. Use the same number of turns as the secondary windings 17SS and 18SL.

The temperature of the filament 19a for temperature detection thus heated is detected by the radiation thermometer 20, and a temperature equivalent to the filament temperature of the X-ray tube 2 is detected.
The reason for using the radiation thermometer 20 to detect the temperature of the temperature detection filament 19a is that the temperature of the temperature detection filament 19a is very high. You will have to take it.
If such measures are taken, the apparatus becomes complicated and expensive. To avoid this, as shown in FIG. 3, the glass surface of the glass container 19 containing the temperature detection filament 19a is irradiated with a radiation temperature. The radiation thermometer 20 is arranged so as to be in contact with the temperature detection surface of the total 20, and the temperature of the temperature detection filament 19a is detected in a non-contact manner.

  Constructed in this way, the temperature of the filament 19a for temperature detection detected by the radiation thermometer 20 and the filament temperature setting value for small focus or the filament temperature setting value for large focus output from the console 4 are heated with the filament. The temperature of the filament 19a for temperature detection equivalent to the temperature of the filament 2S or 2L of the X-ray tube 2 and the filament temperature setting value for small focus or a large value are input to the control signal generation circuit 21. A control signal that matches the focus filament temperature setting value is generated.

  Since the second rectifier circuit 13 and the second inverter circuit 15 have a power control function in at least one of these circuits, the control signal generated by the filament heating control signal generation circuit 21 Based on the temperature of the filament 2S or 2L of the X-ray tube 2 and the filament temperature setting value for the small focus or the filament temperature setting for the large focus in at least one of the second rectifier circuit 13 and the second inverter circuit 15 The heating power of the filaments 2S and 2L is controlled so that the values match.

  FIG. 4 shows the temperature of the filament 19a for temperature detection when the filament is heated by the filament heating device of the X-ray tube according to the present invention having the above configuration, the temperature of the filament of the X-ray tube (in the case of the large focal length filament 2L), the filament The relationship between the filament current (effective value) flowing through 2L and the tube current is shown.

By controlling the temperature of the temperature detection filament as described above, the temperature of the filament 2L becomes as shown in the figure.
Since the filament temperature is low at the start of heating, the filament current has a small filament resistance value, and a large current flows transiently to become an overshoot current.
When the filament is heated and the filament temperature rises, the filament resistance value gradually increases with time.
When the filament temperature reaches the target temperature, the resistance and current of the filament become constant values.
Thus, the filament current at the start of heating has an appropriate overshoot-like waveform, and the filament temperature reaches the target temperature at high speed.
The temperature of the small focal filament 2S is also controlled in the same manner as the large focal 2L, and the filament temperature reaches the target temperature at high speed.

  According to the first embodiment, the temperature detection filament is provided, the temperature of the filament is detected, and feedback control is performed so that the filament temperature of the X-ray tube becomes the target temperature. The temperature of the filament to be reached reaches the target temperature at high speed, and the image quality deterioration due to insufficient heating of the filament, which is a conventional problem, can be solved. In addition, it is only necessary to set the target value of the filament temperature to a value according to the imaging conditions, so that the overshoot value of the voltage applied to the filament for raising the filament temperature at a high speed as in the conventional method is used. This eliminates the need to set all X-ray imaging conditions, X-ray tube types, and X-ray detector components such as X-ray detectors, and eliminates the complexity of filament heating control.

The first embodiment is an example in which the temperature of the temperature detection filament 19a is detected by the radiation thermometer 20, but since the temperature detection filament 19a is housed in the glass container 19, the temperature from the glass container is the temperature. It emits light with an illuminance proportional to the temperature of the detection filament 19a.
Therefore, by detecting the illuminance light with the illuminometer 22 and converting this output into temperature, a temperature equivalent to the temperature detecting filament 19a can be detected.

  In the second embodiment of the present invention, the temperature of the temperature detecting filament 19a is detected by an illuminance meter 22 and an illuminance-temperature conversion circuit 23, and this portion is shown in FIG.

In FIG. 5, the temperature detection filament 19a is heated in the same manner as in Example 1, and the illuminance meter 22 detects the illuminance proportional to the temperature of the filament 19a and converts this to the temperature by the illuminance-temperature conversion circuit 23. .
In order to efficiently detect the illuminance, as shown in FIG. 6, the illuminance meter 22 is arranged so that the glass surface of the glass container 19 containing the temperature detection filament 19a is in contact with the illuminance detection surface of the illuminance meter 22. Then, a temperature equivalent to the temperature of the temperature detection filament 19a is detected in a non-contact manner.

  A temperature value equivalent to the temperature detection filament 19a converted by the illuminance-temperature conversion circuit 23 is input to the filament heating signal generation circuit 21, and this is set to a small focus filament temperature setting value or a large focus filament temperature setting value. Is generated and output, and based on this control signal, at least one of the second rectifier circuit 13 and the second inverter circuit 15 (the second inverter circuit 15 in the example of FIG. 5) Then, the heating power of the filament is controlled so that the temperature of the filament 2S or 2L of the X-ray tube 2 matches the filament temperature setting value for small focus or the filament temperature setting value for large focus.

Also in Example 2, the relationship between the temperature of the temperature detection filament 19a, the temperature of the filament of the X-ray tube, the filament current (effective value) flowing through the filament, and the tube current is as shown in FIG. The filament current at the start of heating has a proper overshoot waveform, and the filament temperature reaches the target temperature at high speed.
As a result, in Example 2, the same effect as in Example 1, that is, the deterioration of image quality due to insufficient heating of the filament and the complicated heating control of the filament can be eliminated.

  In the first and second embodiments, the small-focus heating transformer 17 and the large-focus lens are used to supply the temperature detection filament 19a with the same power as that supplied to the small-focus filament 2S and the large-focus filament 2L. The heating transformer 18 is provided with tertiary windings 17TS and 18TL, respectively, and the output of these windings is supplied to the small focus filament 2S and the large focus filament 2L to heat the temperature detection filament 19a. The present invention is not limited to this, and any means may be used as long as the same output as that of the tertiary windings 17TS and 18TL can be obtained.

  Embodiment 3 of the present invention shown in FIG. 7 is provided with a heating transformer 24 of a temperature detecting filament different from the heating transformers 17 and 18, and the second inverter circuit is provided on a primary winding 24F of the transformer. The output of 15 is input, and the output of the secondary winding 24S of the heating transformer 24 for the temperature detection filament is supplied to the temperature detection filament 19a.

FIG. 7 shows an example in which the temperature of the temperature detection filament 19a is detected by the radiation thermometer 20, but it goes without saying that the same method using the illuminometer 22 and the illuminance-temperature conversion circuit 23 as in the second embodiment may be used.
Even with this configuration, the same effects as those of the first and second embodiments can be obtained.

  As mentioned above, although the said Example 1, 2, and 3 demonstrated the filament heating apparatus of the X-ray tube which has a filament with a small focus for fluoroscopy and two filaments with a large focus for imaging | photography, one filament for imaging | photography Of course, the present invention can also be applied to a filament heating apparatus for an X-ray tube having the above.

  In the above embodiment, a temperature detecting filament is provided, and this temperature is detected to detect a temperature equivalent to the temperature of the filament of the X-ray tube. However, the present invention is not limited to this. The temperature detection means may be provided in the vicinity of the filament of the container of the X-ray tube 2 or may be detected by other methods, as long as the temperature equivalent to the filament temperature can be detected. .

1 is a diagram showing an overall configuration of an X-ray generator to which an X-ray tube filament heating apparatus according to a first embodiment of the present invention is applied. FIG. 2 is a diagram showing an outline of a temperature detecting filament met in Example 1 and a glass container storing the same. FIG. 3 is a diagram showing the positional relationship between a temperature detection filament and a radiation thermometer of Example 1. FIG. 3 is a graph showing a relationship among temperature detection filament temperature, X-ray tube filament temperature, filament current (effective value), and tube current in Example 1. The figure which shows Example 2 of the filament heating apparatus of the X-ray tube by this invention which detects the temperature of the filament for temperature detection with an illuminometer. FIG. 4 is a diagram showing a positional relationship between a temperature detection filament and an illuminometer in Example 2. FIG. 6 is a diagram showing an embodiment 3 of the filament heating apparatus for an X-ray tube according to the present invention in which the temperature detection filament is heated by a temperature detection filament heating transformer.

Explanation of symbols

  1 Inverter X-ray high voltage device, 2 X-ray tube, 3 X-ray tube filament heating device, 4 console, 5 AC power supply, 6 first rectifier circuit, 8 first inverter circuit, 9 high voltage transformer 13 Second rectifier circuit, 15 Second inverter circuit, 17 Small focus filament heating transformer, 17TS Heating transformer 17 tertiary winding, 18 Large focus filament heating transformer, 18TL Heating transformer 18 tertiary Winding, 19a Temperature detection filament, 19 Glass container containing temperature detection filament 19a, 20 Radiation thermometer, 21 Filament heating control signal generation circuit, 22 Illuminance meter, 23 Illuminance-temperature conversion circuit, 24 Temperature detection filament Heating transformer

Claims (7)

DC power supply, inverter circuit for converting direct current from the direct current power supply into alternating current, a heating transformer for insulating the output alternating voltage of the inverter circuit, and at least one of the direct current power supply and the inverter circuit as power control means An X-ray tube filament heating device for heating the filament of the X-ray tube by supplying the output of the heating transformer to the filament of the X-ray tube,
Filament temperature setting means for heating the filament to a predetermined temperature, a temperature detecting filament equivalent to the filament of the X-ray tube for detecting a temperature proportional to the temperature of the filament of the X-ray tube, Filament temperature detection means for detecting the temperature of the filament for temperature detection, and a control signal for controlling the target set temperature set by the filament temperature setting means and the temperature detected by the filament temperature detection means to coincide with each other A filament heating control signal generating means for generating, and the power control means controls the power supplied to the filament based on the control signal.   2. The X-ray tube according to claim 1, further comprising a filament that forms at least two focal points of a small focal filament and a large focal filament, and one of the small focal filament and the large focal filament. A filament heating apparatus for an X-ray tube, wherein filament heating power controlled based on a control signal generated by the filament heating control signal generating means is supplied to the filament. 2. The temperature detecting filament according to claim 1, wherein the filament has an impedance equivalent to that of the filament of the X-ray tube and is capable of temperature detection without contact. Wire tube filament heating device. 4. The filament heating apparatus for an X-ray tube according to claim 3, wherein the filament for temperature detection has the same material as the filament of the X-ray tube, and the filament is sealed in a vacuum glass container. 5. A temperature equivalent to the filament of the X-ray tube is detected in a non-contact manner by detecting the temperature in the vicinity of the temperature detecting filament with a radiation thermometer or light emitted from the filament with an illuminometer. A filament heating apparatus for an X-ray tube. 6. The heating transformer according to claim 1, wherein a winding insulated from the filament of the X-ray tube is provided in the heating transformer, and power output from the winding is supplied to the temperature detection filament. An X-ray tube filament heating device. 6. The output of the inverter circuit according to claim 1, wherein the output of the inverter circuit is input to a temperature detection filament heating transformer different from the heating transformer, and the output of the transformer is supplied to the temperature detection filament. A filament heating apparatus for an X-ray tube.

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