JPH09161990A - X-ray generator - Google Patents

Abstract

(57) Abstract: A filament characteristic change due to a filament thinning due to the use of an X-ray tube is corrected. SOLUTION: When a switch 41, 51 is turned on at the time of aging to operate a tube current feedback control system and a desired tube current can be stably obtained, a resistor 2 is provided.
The current value flowing through 7 is captured by the timing circuit 42 and the A / D converter 43 and stored in the memory 33, and the set tube current value read from the memory 32 at the time of actual X-ray exposure after aging is completed. The initial adjustment value of the filament heating current corresponding to the
In step 4, the set value signal is sent to the comparator 37 based on the corrected data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generator, and more particularly to improvement of a filament heating current control system for an X-ray tube.

[0002]

2. Description of the Related Art In a conventional X-ray generator, a filament heating current of an X-ray tube is usually detected, and the detected value is compared with a set value of the filament heating current so that the detected value matches the set value. A constant current control method of feedback control is adopted, and the X-ray tube current is set to a desired value by controlling the filament heating current in this way. Also, the actual X-ray tube current value during X-ray exposure is measured, the difference between this measured value and the set tube current value is extracted, and the filament heating current is feedback-controlled according to the difference, and the tube current value is In some cases, a control circuit for adjusting the set tube current value is used.

[0003]

However, the filament heating current control method as described above has a problem that a desired tube current cannot be obtained. That is, the filament of the X-ray tube evaporates during use and becomes gradually thin.
Therefore, even if the same current value is applied, the filament temperature of the thin filament becomes higher than that before the thin filament. As a result, even if the same filament heating current is passed, the tube current gradually increases with the lapse of years of use.

That is, the correspondence relationship between the filament heating current and the tube current was initially represented by the characteristic as shown by the solid line 61 in FIG. 2, but after a lapse of years, the correspondence relationship shifts. As a result, the characteristic becomes as shown by the dotted line 62 in FIG. Therefore, even if the same filament heating current as in the initial stage is passed, the desired tube current cannot be obtained.

In this case, if the actual X-ray tube current value during X-ray irradiation is actually measured and the filament heating current is feedback-controlled in accordance with the actual value, the tube is heated regardless of the error due to the thinness of the filament as described above. It can be said that it is possible to set the current to a desired set value, but when irradiating X-rays in a pulse shape such as in cine photography, the pulse width may be several msec, so feedback control can be performed. It takes a long time for the tube current to stabilize, and the set value cannot be set. Since such tube current feedback control requires several tens of msec until the tube current becomes stable, even when X-rays are continuously exposed, the waveform of the tube voltage or the tube current is disturbed at the time of start, etc. It may cause malfunction.

In view of the above, the present invention improves the controllability of the tube current due to the thinning of the filament over time due to the use of an X-ray tube, and particularly in the case of pulse X-ray irradiation. An object is to provide a suitable X-ray generator.

[0007]

In order to achieve the above object, in an X-ray generator according to the present invention, an X-ray tube, a high voltage supply circuit for applying a high voltage between its anode and filament, and a filament are provided. A filament heating current supply circuit for supplying a flowing current; a current detector for detecting a current flowing through the filament; a first storage circuit for storing an initial adjustment value of the filament heating current for obtaining a predetermined tube current; A second memory circuit for storing the current value of the filament heating current for obtaining the tube current, a tube current setter for arbitrarily setting the tube current, and the above-mentioned initial adjustment value corresponding to the set value of the tube current. An arithmetic circuit for correcting the current value, and a control circuit for controlling the filament heating current supply circuit by comparing the corrected value with the value detected by the current detector. Is the distinctive feature that is provided.

At the present moment, a filament heating current for obtaining a predetermined tube current is obtained and stored in the second memory circuit. When the tube current is set to a certain value, an initial adjustment value corresponding to the set value is read from the first memory circuit, and this value is used as the filament current value stored in the second memory circuit. It is corrected by the heating current. This correction is performed, for example, by an operation such as multiplying the ratio of the current filament heating current to the filament heating current at the time of initial adjustment in order to obtain the same tube current. By this correction, an error due to the thinness of the filament is corrected, so that an accurate tube current can be obtained. This is done without relying on a tube current feedback control system, which detects the tube current and feeds it back to set the tube current, so the set tube current can be obtained from the start of X-ray exposure. Therefore, it is suitable for pulse X-ray exposure.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, a high voltage is applied between the anode and the cathode (filament) of the X-ray tube 13 from the high voltage supply circuit 12 connected to the AC power supply 11. A filament heating current is supplied from a filament heating current supply circuit 14 to the filament of the X-ray tube 13. Although not shown in the figure, the high-voltage supply circuit 12 includes, for example, a rectifying / smoothing circuit for rectifying / smoothing an alternating current, an inverter circuit for switching a direct current obtained by the rectifying / smoothing circuit at a predetermined high frequency, and its high frequency. Can be composed of a step-up transformer for converting into a high voltage and a rectifying / smoothing circuit for rectifying / smoothing the output of the step-up transformer again to obtain a direct current having a very high voltage.

The filament heating current supply circuit 14 includes a rectifier circuit 21 connected to the AC power supply 11, a smoothing capacitor 22, a current control transistor 23, and a capacitor 24 connected to the output side of the transistor 23. Prepare The output that has been rectified and smoothed into a direct current is switched at high speed in the inverter circuit 25 to have a high frequency, and is supplied to the filament of the X-ray tube 13 through the insulating transformer 26.

The input current to the inverter circuit 25 is converted into a voltage by the current detecting resistor 27 and sent to the comparator 37, compared with the set value signal of the filament heating current from the set value signal generating circuit 36, and the comparator. 37
Is sent to the base of the transistor 23 via the transistor base control circuit 38. Therefore, by detecting the current on the input side of the inverter circuit 25 and feeding it back, the filament heating current is controlled so as to match the setting value signal of the filament heating current from the setting value signal generating circuit 36. become.

The filament heating current set value signal is basically the value read from the memory 32 in accordance with the tube current set by the tube current setting unit 31 and the D / A converter 35. The setting value signal creating circuit 36 is created from the analog signal converted by. That is, the tube current setting device 3
1, when the tube current is set to a desired value, the value of the filament heating current that allows the tube current to flow is stored in the memory 32.
Is read from.

A filament heating current corresponding to the tube current is previously stored in the memory 32. For example, the tube current is adjusted at the time of installation, and the filament heating current value required to flow the tube current (usually 6 positions) set for some tube voltages (eg, 60 kV, 90 kV, 120 kV) is actually measured. . As a result, FIG.
The respective filament heating current values I1 to I for flowing the six tube current values mA1 to mA6 as shown in FIG.
6 is measured. These filament heating current values I1
Data representing each of I to I6 is stored in the memory 32 as an initial value.

When actually used later, the tube current value mAx
When (x is an arbitrary number from 1 to 6) is set, the corresponding Ix is read from the memory 32, D / A converted, and passed through the filament heating current set value signal generation circuit 36 to set the filament heating current. Comparator 3 as a value signal
7 This filament heating current set value signal is compared with the filament heating current value If detected by the current detection resistor 27, and the transistor base control circuit 38 is then compared.
Is sent to the base of the transistor 23 via
The control is performed so that f coincides with the set value signal, whereby the actual tube current value becomes the set tube current value mAx.

However, even if the filament becomes thin and thin with the passage of time of use of the X-ray tube 13 and the same filament heating current is passed, the filament temperature rises and the tube current increases. That is, the characteristic representing the relationship between the filament heating current and the tube current changes from the solid line 61 to the dotted line 62.
become that way. Therefore, for example, assuming that the tube current value mA6 is set in the tube current setting unit 31 and the filament heating current value I6 corresponding thereto is read from the memory 32 and the filament heating current is controlled to match this, the actual tube heating value I6 is controlled. The current becomes considerably larger than mA6.

In this case, a tube current feedback control system for detecting the tube current actually flowing and feeding it back to the filament heating current control system is provided. This tube current feedback control system includes, for example, a tube current detection circuit 52 for detecting a tube current flowing between the high voltage supply circuit 12 and the anode / filament of the X-ray tube 13, a comparator 53, and a tube as shown in FIG. And a current feedback circuit 54. In the comparator 53, the detection signal of the tube current detected by the tube current detector 52 and the tube current setting device 3
1 is compared with a signal representing the set value of the tube current, and an output corresponding to the difference is sent to the filament heating current set value signal generating circuit 36 via the tube current feedback circuit 54, and the difference is the above-mentioned filament. It is added to or subtracted from the heating current set value. Therefore, since the actual tube current value is detected and feedback control is performed so that it matches the set value, the actual tube current value comes to match the set value.

However, in this tube current feedback control system, since it takes time for the filament temperature to equilibrate and stabilize, the response speed is slow, and it takes several tens of msec for the tube current to stabilize at the set value. Since the response speed of the tube current feedback control system is slow in this way, the disturbance of the tube voltage and tube current occurs immediately after the start of continuous X-ray exposure, which causes an error, and the pulse X-ray exposure with a short pulse width. During irradiation, the X-ray irradiation ends before the tube current stabilizes, and the desired tube current cannot be obtained.

Therefore, as shown in FIG. 1, in addition to the memory 32 for storing the initial value of the filament heating current value, another memory 33 is provided to store the data of the current filament heating current value. For example, assuming that the filament heating current value required to obtain the tube current mA6 is I'6 as shown in FIG. 2, data representing this I'6 is stored in the memory 33.

When a desired tube current value mAx (x is 1 to 6) is set by the tube current setting unit 31 and Ix is read from the memory 32, the following calculation is performed by the arithmetic circuit 34. Done. Ix · (I′6 / I6) This calculation result is sent to the filament heating current set value signal generation circuit 36 through the D / A converter 35. As a result, the initial value Ix is linearly corrected, and the comparator 37 compares the corrected set value signal with the detection signal to perform control such that the filament heating current matches the corrected set value. Be done.

The filament heating current is 1 to 4 for X-ray irradiation.
It is washed away for about a second. At this time, the filament heating current is detected by the resistor 27, compared with the set value signal by the comparator 37, and the transistor base control circuit 38
A filament heating current control system, which controls the transistor 23 via the above, operates. In this way, since the filament heating current is controlled before the X-ray irradiation, the filament heating current is stable at the set value at the time of the X-ray irradiation. Therefore, even in the case of pulsed X-ray irradiation, it is possible to control to a desired tube current. Further, in the case of continuous X-ray irradiation, a desired tube current can be obtained from the start point of X-ray irradiation at the time of rising, and malfunctions at the start point of continuous X-ray irradiation can be prevented.

The data to be stored in the memory 33 may be obtained by periodically measuring the filament heating current required to obtain a certain tube current, but a tube current feedback control system is provided. In that case, it can be used to obtain the data and store it in the memory 33. In that case, as shown in FIG. 1, a timing circuit 42 and an A / D converter 43 are provided as a data fetch circuit for fetching the current value of the filament heating current.

The switches 41 and 51 are turned on to operate the data acquisition circuit and the tube current feedback control system. Then, a certain tube current value (for example, mA6) is set by the tube current setting device 31, and X-rays are continuously emitted. This is performed for a long time to some extent, and when the tube current is stabilized by the tube current feedback control, the actual filament heating current at that time is sent to the A / D converter 43 through the timing circuit 42, digitized, and stored in the memory 33.
Write to. At this point, the tube current feedback control system has stabilized to mA6, and if the filament characteristics at this point are as shown by the dotted line 62 in FIG. 2, the filament heating current is I'6, and the data Will be written in the memory 33.

The X-ray generator usually performs aging by continuously irradiating X-rays for a relatively long time at the start of daily use (that is, every morning). Therefore, it is practically convenient to store the data regarding the actual filament heating current of the day in the memory 33 by utilizing this aging. That is, the switches 41 and 51 are turned on during aging, and when the tube current becomes stable as described above, the actual filament heating current is fetched and written in the memory 33.

In this description, the actual filament heating current value at the present time is stored in the memory 33 with only one value (I'6 in the above), and linear correction is performed using this value. The current value of the filament heating current value may be stored, and the correction calculation is not limited to the linear calculation. However, aging is usually performed only with one large tube current value, and one practical filament heating current value obtained by that is also taken in and linear correction is used to obtain a practically useful correction. Therefore, it can be said that it is actually suitable to perform such work during aging.

Further, although the tube voltage is not mentioned above, since the aging is usually performed by gradually increasing the voltage from a low voltage to a high voltage, the current values of the filament heating current for a plurality of tube voltages are written in the memory 33. It is easy to do so, which enables more accurate correction. Further, when the X-ray tube 13 has a plurality of filaments, if the filaments are sequentially subjected to aging, the current value of the filament heating current for each filament can be obtained and written in the memory 33. Correction is possible for each filament.

[0026]

As described above, according to the X-ray generator of the present invention, it is possible to correct the increase in the tube current due to the thinning of the filament of the X-ray tube over time. As a result, it is possible to prevent an overload on the X-ray tube caused by an increase in the tube current, and it becomes possible to use the X-ray tube stably for a long period of time. In particular, it is effective during pulsed X-ray irradiation where the tube current cannot be stabilized by the tube current feedback control system, and when the tube current feedback control is performed during continuous X-ray irradiation, the waveform It is also effective in suppressing turbulence and stabilizing in the short term to prevent malfunction.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between filament heating current and tube current.

[Explanation of Codes] 11 AC power supply 12 High voltage supply circuit 13 X-ray tube 14 Filament heating current supply circuit 21 Rectifier circuit 22 Smoothing capacitor 23 Current control transistor 24 Capacitor 25 Inverter circuit 26 Insulation transformer 27 Current detection resistor 31 Tube current Setting device 32 Filament heating current initial adjustment value memory 33 Filament heating current current value memory 34 Arithmetic circuit 35 D / A converter 36 Filament heating current set value signal creation circuit 37, 53 Comparator 38 Transistor base control circuit 41, 51 Switch 42 timing circuit 43 A / D converter 52 tube current detector 54 tube current feedback circuit 61 initial characteristics of filament 62 characteristics after aging of filament

Claims (1)

[Claims] 1. An X-ray tube, a high voltage supply circuit for applying a high voltage between its anode and filament, and a filament heating current supply circuit for supplying a current flowing through the filament.
A current detector for detecting a current flowing through the filament, a first storage circuit for storing an initial adjustment value of the filament heating current for obtaining a predetermined tube current, and a current filament heating current for obtaining the predetermined tube current. A second storage circuit for storing the value; a tube current setting device for arbitrarily setting the tube current;
The above-mentioned filament heating current is calculated by comparing the corrected value and the value detected by the above current detector with an arithmetic circuit that corrects the above initial adjustment value corresponding to the set value of the tube current with the above current value. An X-ray generator comprising: a control circuit that controls a supply circuit.