JPH029439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tetrode-controlled X-ray generator.

[Conventional technology]

Conventionally, for examinations of circulatory system diseases such as the heart, especially examinations of dynamic function, pulsed X-rays of several milliseconds are generated at a high speed of approximately 20 to 400 pulses (number of times)/second, and each pulsed X-ray is High-resolution X-ray images
(Image Intensifier) Received at tube,
The so-called X-ray cine photography examination, in which this is photographed with a cine camera, is becoming effective and widely used. One of the configurations of such an X-ray inspection device is one that generates X-rays by combining a tetrode tube and a dipole
(See Publication No. 159691). Such tetrode control type
The drawback of the ray generator is that it cannot generate stable X-rays depending on the situation of the subject.

[Problem to be solved by the invention]

This will be explained in detail below.

Dynamic examinations take pictures of areas that are in motion. Because there is movement, high-speed shooting is required. The imaging method for this purpose is the pulse drive method. The pulse drive method uses pulsed X-rays of several milliseconds 20 to 400 times/
This is a method in which images are generated a number of times at high speeds of seconds, and moving parts are imaged each time.

In this pulse drive method, the period during which pulsed X-rays are emitted (ON period) is short;
It is necessary to emit a predetermined amount of X-rays during the ON period. For this reason, in each ON period, the ON
The problem is how quickly the imaging conditions can be set up immediately after the start of radiation, which is the starting point.

The photographing conditions will be described below. Various feedback controls are performed during X-ray photography. II constant brightness control,
Constant darkening degree control, constant tube voltage control, etc. are called this feedback control. Among these, constant brightness control II is the main feedback control. This feedback control is performed during the period when X-rays are being emitted, that is, during the ON period, and is not performed during the period when X-rays are not being emitted, that is, during the OFF period. The reason why the feedback operation is performed during the ON period is that the feedback operation targets the luminance II, and the luminance II is obtained during the ON period. Of course, there are feedback controls that are unrelated to X-ray radiation, so all feedback controls are turned on.
It does not necessarily take place during the period.

When feedback control is performed during the ON period, there is a problem in that if the convergence time for feedback control is prolonged, it causes variations in photographic image quality (deterioration in quality). Conventionally, these things were not taken into consideration.

Let's talk about variations in photographic image quality. FIG. 6 is an explanatory diagram for this purpose. FIG. 6A is an example of two ON periods. FIG. 6B shows the case where the feedback control is applied. Normally, conditions for X-ray radiation should be established from the rise of the ON period as shown in A, but since feedback control is applied at the start of the ON period, the convergence time τ to converge to the target value is ₁ , the original X-ray emission (period τ ₁₀ ) will occur. However, this does not mean that X-rays are not emitted during this convergence time τ ₁ . For example, in the feedback operation for controlling the brightness of II to be constant, X-rays are still being emitted although the brightness of II is not constant. In feedback control for constant tube voltage control, X-rays are emitted even though the tube voltage is not constant.
That is, the emitted X-rays are unstable during the τ ₁ period. The amount of transmission (ray quality) is determined by the sum of the convergence period τ ₁ and the post-convergence stable period τ ₁₀ (τ ₁ + τ ₁₀ ).Therefore, the presence of τ ₁ causes deterioration of image quality, and (τ ₁ +
The image quality determined by τ ₁₀ ) leads to variations in image quality. Incidentally, the maximum allowable value of the ON period (τ ₁ +τ ₁₀ ) is about 5 msec, whereas τ ₁ =0.5 to 1 msec, which shows that it cannot be ignored.

This kind of thing also occurs during the next ON period. τ ₃ is the convergence time in the next ON period. Generally, τ ₁ =τ ₂ , but if the body position changes between the first and second times, for example, τ ₁ ≠ τ ₂ may occur because the convergence is made to match the body position.

FIG. 6C shows another example of feedback convergence. Although FIG. 6B shows an example in which the signal converges with a first-order lag or second-order lag rise, there is also an example in which the feedback converges while causing ringing. This is Figure 6C. According to FIG. 6C, since the emitted X-rays become larger than the target constant value, variations in image quality occur in a different sense from FIG. 6B. τ ₃ and τ ₄ are convergence times, and τ ₃ =τ ₄ or τ ₃ ≠τ ₄ as in FIG. 6B.

On the other hand, even for the same specimen, the convergence time varies depending on the body position of the subject (thickness and object), breathing of the subject, injection of contrast medium, and movement of the subject.

Conventionally, this convergence time was ignored. but,
Considering that the convergence time is a parameter that determines whether the image quality is good or bad, it is not a good idea to ignore it.

The purpose of the present invention is to reduce the convergence time by using the convergence results obtained during the previous ON period as they are during the current ON period, instead of starting from the initial state and converging for each ON period. The present invention provides a pulse-driven X-ray imaging apparatus that attempts to reduce variations in image quality.

[Means for Solving the Problems] The present invention samples and holds the converged feedback amount obtained during the previous ON period at the end of the ON period, and gives this as the initial feedback amount for the current ON period. This is what I did. Here, the amount of feedback refers to the amount of feedback for constant brightness control of II.

[Effect]

According to the present invention, the converged feedback amount obtained during the previous ON period is given as the initial feedback amount for the next ON period.

〔Example〕

FIG. 1 shows an embodiment of the present invention. X-ray controller 3
0 is a timer circuit 204, a tube voltage indicator circuit 205,
High voltage application switch 50 and tube voltage indicator circuit 20
The slide autotransformer 101 is controlled by the output of No. 5. The high voltage generator 31 includes a high voltage transformer 51 and a high voltage rectifier 52. The tetrode unit 32 includes a smoothing capacitor 102 and a gate interface circuit 10.
7,107A, isolation transformer 108, voltage divider 10
6. It consists of two tetrode tubes 103 and 104, and controls the operation of an X-ray tube 105 as an external load.

Gate interface circuit 107, 107A
is controlled by a control input signal applied from the outside via a transformer 108, and controls the gates G1 and G2 of the tetrode tubes 103 and 104. The voltage divider 106 is a tetrode tube 10
It is provided on the output side of the Make use of it.

The timer circuit 204 generates a timer output signal under external control as described later. The timer output signal is used to control the tetrode tubes 103 and 104. The tube voltage pre-indication circuit 205 is provided for determining the radiation quality of generated X-rays (tube voltage control). This tube voltage control is performed by specifying the voltage on the primary side of the high voltage generator 31 and assuming the voltage generated on the secondary side.

Voltage is applied to the tetrode tubes 103 and 104 as a result of turning on the power switch 50, rectifying the AC input to a high voltage through the high voltage generator 31, and outputting it. On the other hand, in the tetrode tubes 103 and 104, the voltage of the gate G1 is about -
It is in a cut-off state when the voltage is 800V (DC), and becomes conductive when the voltage of gate G1 is approximately 0V (DC). When the voltage of the gate G2 is changed, the internal impedance of the tetrode tubes 103 and 104 changes, and the internal drop changes. +500V~+
For a voltage change of 1000V at the gate G2, the voltage between the cathodes and the plates of the tetrode tubes 103 and 104 changes by about 12KV. Such gates G1, G2
is controlled by a control signal carried on a high frequency carrier wave applied from the outside via an isolation transformer 108.

II (Image Intensifier) Tube 1
11 has a function of receiving X-rays from the X-ray tube 105 that have passed through the subject 110 and converting them into an optical image;
A light image is formed on the secondary phosphor screen. The photographing camera consists of three types: a television camera 36, a rapid sequence camera 34, and a cine camera 35, each of which takes in an optical image obtained through a lens 39 and a half mirror 37, and uses it for recording and photographing.

Next, the control system 33 will be explained. Control system 33
has various reference settings. The standard settings include
Operating point setting value V ₁ of the side tetrode 104, operating point setting value V ₂ of the side tetrode 103, brightness setting value V ₃ for setting the brightness of the exit side light of the II tube 111, film blackening degree setting value V There are ₄ . Each setting value is a setting device (potentiometer) 200, 20
1,207,208. Furthermore,
External inputs to the control system 33 include the timer output of the timer circuit 204, the output of the tube voltage indicator circuit 205, the divided voltage output of the voltage divider 106, and the prism 38.
This is the output light from the secondary phosphor screen of II tube 111 which is detected as an electrical signal by photomultitube 52 via . Outputs from the control system 33 to the outside include control outputs for the timer circuit 204 and control outputs for the gate interface circuits 107 and 107A.

In addition to the above-mentioned setting device, the control system 33 includes an oscillator 3,
AM modulators 4, 5, 8, voltage amplification amplifiers 6, 7,
9, addition amplifiers 11, 18, 19, sample and hold circuits 16, 17, analog switches 14, 1
5, differential amplifiers 12, 13, 22, integrator 21,
It has a comparator 22. In addition, switch 1, 2,
10 will be described later. The oscillator 3 is a high frequency oscillator and oscillates a carrier wave.

Next, the overall operation will be explained. When taking an X-ray image of the subject 110 using the cine camera 35 or rapid sequence camera 34, the Subject 1
10, the transmitted image is displayed on the secondary fluorescent screen of the II tube 111, and the lens 39 and half mirror 37
It is best to expose one sheet or one frame of film through a . (The reason is that continuous X from X-ray tube 105
If the continuous images displayed on the secondary phosphor screen of the II 111 were taken one frame or one film at a time with a cine camera or rapid camera, the images before and after the shooting would be wasted. ) This photosensitivity → degree of blackening is determined by the brightness and time of the image displayed on the secondary fluorescent screen of II111 (photographing time,
In this case, if the timer 204 is turned ON (the width of the bell) is constant, the degree of blackening will always be the same, but the contrast agent in the subject 110 (for imaging the circulatory system, etc., an iodine contrast agent is used in the blood) The brightness of the image changes due to the flow of the fluid (a fluid with poor X-ray transmission) and changes in body thickness caused by rotating the imaging system or the subject, and the degree of darkening changes from frame to frame or frame by frame. It becomes different. It is necessary to automatically keep this degree of blackening constant.

First, when the high voltage application switch 50 is closed, high voltage direct current is generated at both ends of the capacitor 102 and is applied between the plate of the tetrode 103 and the cathode of the tetrode 104. and timer circuit 204
When the timer signal becomes H level, a modulation signal is output from the modulator 8, and this modulation signal is amplified by the voltage amplifier 9 and sent to the gate interface circuit 10.
7,107A and is converted into DC, turning on the gates G1 of the tetrodes 103, 104. Modulators 4 and 5 also have operating point setters 200 and 201.
Tetrode 10 outputs a modulated signal with the amplitude that can be
3,104 G2 operating points are determined. Gate G
1 is turned ON, high voltage direct current is applied to the X-ray tube 105 and X-rays are emitted. When high voltage direct current is applied to the X-ray tube 105, a predetermined voltage is generated in the voltage divider 106. This voltage is applied from the differential amplifiers 12 and 13 to the analog switches 14 and 15 (when the timer signal is high).
(closed due to the level) and is input to adding amplifiers 18 and 19. Therefore, summing amplifier 1
The outputs of 8 and 19 become high or low, the G2 voltage becomes high or low, and the high voltage direct current applied to the X-ray tube is controlled to a predetermined voltage.

Next, input signals to the differential amplifiers 12 and 13 from sources other than the voltage divider 106 will be described. The input signal is an output obtained via the differential amplifier 20 and the summing amplifier 11. The differential amplifier 20 calculates the difference between the brightness detection signal obtained from the photo multiplexer 52 and the predetermined brightness set value _V3 of the brightness setter 207, and determines whether the actual brightness has not reached the brightness set value _V3 . Sometimes the difference between the two is positive, and if it exceeds the difference, a difference signal between the two is output and applied to the plus input terminal of the summing amplifier 11. The output of the summing amplifier 11 is applied to the positive input terminals of the differential amplifiers 12 and 13. As a result of this configuration, when the II tube output does not reach or exceeds the brightness set value, a feedback system is formed from the differential amplifier 20 to the summing amplifier 11 to the differential amplifiers 12 and 13, and the brightness set value is Work to converge.

On the other hand, the tube voltage pre-indication signal of the tube voltage pre-indication circuit is input to the plus input terminal of the summing amplifier 11 in a form corresponding to its level. Therefore, this tube voltage indication signal also serves as a set value, and the feedback system is operated in order to approach the set value.

On the other hand, the comparator 22 compares the integrated value obtained from the output of the photomal 52 via the integrator 21 with the predetermined output V ₄ of the degree of blackening setter 208 . When the set value is large in proportion to both, an H level signal is sent to the timer circuit 204, and the timer circuit 204 outputs an H level signal, which is the generation state of the timer output at that time.
Maintain level output. When the output of the integrator 21 rises and matches the set value of the blackening degree setter 208, an L level signal is generated from the comparator 22,
The signal is sent to timer circuit 204. Timer circuit 204
When receiving an L level signal, it drops the current H level output to an L level signal. As a result, the analog switches 14 and 15 controlled by the output signal of the timer circuit 204 are turned off, and the input to the AM modulator 8 is also eliminated. Furthermore, this timer circuit 2
When the sample-and-hold command is given to the sample-and-hold circuits 16 and 17 by the output of the timer circuit 204 at the time when the state changes from H to L at 04, the sample-and-hold circuits 16 and 17 control the output of the differential amplifiers 12 and 13 at that time. Sample and hold the output.
During this hold period, the output of the timer circuit 204 is L.
This is the section where the level output is occurring.
When the output of this timer circuit 204 changes from L to H, the analog switches 14 and 15 are turned on again.
The output from the AM modulator 8 also controls the gate G1 of the tetrode tube. Also, at this time, the integrator 21 has been reset, and upon receiving the output of the photo multiplexer 52, the integrator 21 starts integrating again. Further, when the analog switches 14 and 15 are turned on, the inputs to the summing amplifiers 18 and 19 are the hold outputs of the sample and hold circuits 16 and 17, and a feedback system is formed using the hold outputs as initial values. Therefore, there is no need for a process to converge to various set values again, and stable cyclic operation with less fluctuation becomes possible.

That is, sample and hold circuits 16 and 17, and analog switches 14 and 15. During the ON period, the switches 14 and 15 are ON, and the outputs of the amplifiers 12 and 13 pass through the switches 14 and 15 and directly become the inputs of the amplifiers 18 and 19.
During the OFF period, switches 14 and 15 are OFF.
Sample and hold circuits 16 and 17 are interposed between amplifiers 12 and 18 and between amplifiers 13 and 19.

The operation is as follows. In the first ON period in which the first pulsed X-ray is generated, convergence takes a convergence time determined by the part of the circuit subject under normal feedback control. After this convergence, constant control is maintained and X-ray imaging is performed including the rest and ON period. next
Entering the OFF period. At the start of this OFF period, the switches 14 and 15 are turned OFF, so the outputs of the amplifiers 12 and 13 at that time (ie, the amount of convergence feedback) are sampled and held by the sample and hold circuits 16 and 17. This hold value is
Amplifier 18,1 as the initial value at the beginning of the ON period
This will be the input of 9. Therefore, in the next ON period, there is no need to perform the convergence operation from the beginning again, and it is sufficient to perform convergence in the current ON period using the hold value as an initial value, and the convergence time is shortened. This eliminates variations in image quality.

Next, the output of the timer circuit 204 will be described. The timer circuit 204 generates two types of timer outputs depending on at least shooting conditions (or depending on shutter conditions). The first one is suitable for photographing with the TV camera 36, and is a timer output with a high-speed pulse cycle synchronized with TV scanning. The second type is suitable for photographing with the cine camera 35, and generates a pulse signal synchronized with the photographing cycle of the cine camera. Figure 2 shows the situation during this period.

FIG. 2 is a diagram showing the output of the timer circuit 204, where T ₀ is the pulse period, and T ₀ at the TV camera.
is set smaller than T ₀ in a cine camera.
T ₁ , T ₂ , T ₃ , . . . are intervals in which the timer output is at the H level, and are times when the integrator output reaches the blackening degree set value. During this time, the X-ray generator
This is also the time when lines are generated. _T1 , _T2 , _T3 ,...
The fall from H to L is made by the output of the comparator 22.

Next, the embodiments of the present invention will be described in accordance with the time chart. FIG. 3 first shows sample and hold circuits 16 and 17 and analog switches 14 and 15.
Switches 1 and 2 are assumed to be on the output side of the circuit, and various signals are shown when the switches 1 and 2 are turned on.
When this switch is on, the so-called tetrode 10
This corresponds to the case where the switch 3,104 is used as a simple switch. This corresponds to the start-up operation at the time of startup of this embodiment. Therefore, the switch may actually exist. In such a state, summing amplifier 1
The outputs of 8 and 19 are constant value outputs according to the set values, and therefore the outputs of AM modulators 4 and 5 are also constant value outputs.
Outputs a signal with AM modulation. Next, the level is increased by voltage amplifiers 6 and 7, and the transformer 1
Gate interface circuit 10 through 08
7,107A and a constant voltage on gate G2
Apply 500V. On the other hand, between the H level of the output of the timer circuit 204, the carrier wave modulated at the H level via the AM modulator 8 and amplifier 9 is transmitted through the transformer 108, gate interface circuits 107 and 1.
07A, the gate G1 becomes approximately 0 (V), and the tetrodes 103 and 104 are turned on. still,
At this time, if a ripple occurs in the high voltage transformer 51, the X-ray tube voltage will also include ripples as shown in FIG. This ripple becomes a factor that deteriorates the photographed content.

In addition to switches 1 and 2, Fig. 4 shows differential amplifier 2.
Assuming that the switch 10 short-circuits the output side of 0, the operation is shown under the condition that the switch 10 is turned on and the switches 1 and 2 described in FIG. 3 are turned off. This condition assumes a case in which the output of the actual II tube 111 is not taken in from the photomultitube 52 as a feedback signal. Since there are cases where the output of the II tube 111 is used without being fed back, the switch 10 may actually exist.

Under such conditions, the level-adjusted output of the tube voltage indicator circuit 205 is applied to the summing amplifier 11, and the output is applied to the positive terminal inputs of the differential amplifiers 12 and 13. Therefore, at this time, the voltage divider 106 is set to the set tube voltage.
Feedback is made to the differential amplifiers 12 and 13 via
The control system operates to converge to the tube voltage. The convergence operation in this control system is as follows. A DC signal proportional to the tube voltage preindication signal output from the summing amplifier 11 is applied to the positive input terminals of the differential amplifiers 12 and 13, and the deviation from the actual tube voltage signal from the voltage divider 106 is detected by the differential amplifier. This results in outputs of 12 and 13. The divided voltage output of the voltage divider 106 is the tetrode tube 103,1 which is turned on when the timer output is H.
04 output. When the divided voltage output is higher than the indicated voltage, a negative deviation output is output, and when it is lower, a positive deviation output is output. This output is sent to summing amplifiers 18 and 19 via analog switches 14 and 15. The summing amplifiers 18 and 19 combine the voltage from the operating point setters 200 and 201 with the differential amplifiers 12 and 1.
When the tube voltage is lower than the above, the output level of the adding amplifier increases, and when the tube voltage is high, the output voltage level decreases. The outputs of the oscillator 3 are modulated by the outputs of the summing amplifiers 18 and 19, and modulated outputs are obtained from the AM modulators 4 and 5. Thus, tetrode tube 103,10
The gate G2 bias voltage of No. 4 decreases in level when the tube voltage is high, and increases in level when the tube voltage is low. As a result, the X-ray tube voltage converges to the indicated voltage. On the other hand, the sample hold circuit 16,
17 follows the outputs of the differential amplifiers 12 and 13 during X-ray emission, and maintains the state immediately before turning off when the timer signal is at L level. Tetrode tube 103,1
04 is off and high voltage is not applied to the X-ray tube 105, the outputs of the differential amplifiers 12 and 13 are as follows.
Since there is no output from the voltage divider, the output is large in the positive direction, and when the timer signal is sent and the tetrode chains 103 and 104 are turned on, gate G2
This results in a large voltage swing. Therefore, the gate interface circuits 107, 107
Coupled with the time constant in A, this causes ripples to be included in the X-ray tube voltage, which is particularly problematic when X-rays are emitted continuously for a short period of time. Due to the function of the sample and hold circuits 16 and 17, fluctuations in the control signal of the gate G2 can be suppressed to a small level, and the tracking performance of the tube voltage is improved.

As is clear from the above explanation, due to the feedback control and sample hold function, even if the output of the high voltage generator 31 contains ripples,
A stable DC voltage can be supplied to the ray tube, and X-ray photographs with good diagnostic value can be obtained with good reproducibility. It goes without saying that the output of the high voltage generator needs to be higher than the voltage applied to the X-ray tube by at least (ripple) + (minimum drop in the tetrode).

Next, FIG. 5 shows a time chart under the condition that switches 1, 2, and 10 are all turned off. In addition to the above two operating modes, this mode adds a mode in which the output of the photomultitube is taken in and utilized, and is a mode that is related to all the operations of the embodiment shown in FIG.

The degree of blackening for each frame of film during cine shooting is determined by taking an image of the secondary phosphor screen of the II tube, so if the brightness of the secondary phosphor screen of the II tube is constant, the degree of blackening for each frame of the film is determined by a fixed timer. When opened and closed, the degree of blackening remains constant. However, if the X-ray absorption of the subject changes due to the flow of a contrast agent injected into a blood vessel or the rotation of the imaging system, the brightness naturally changes. The operation for keeping the brightness constant is as follows.

The difference between the output from the photomultitube 52 and the set value of the brightness setter 207 is detected by the differential amplifier 20. When the actual luminance is larger than the set value, the output of the differential amplifier 20 becomes a negative deviation, and conversely, when it is smaller, it becomes a positive deviation output. This deviation output is added to the pre-indication signal in the addition amplifier 11, and becomes a new pre-indication signal according to the situation of the subject (the subject's body position, the X-ray incident angle of the imaging system, or the condition of the contrast agent), and is then added to the pre-indication signal as described above. In a process similar to that described in FIG. 4, the bias voltage of G2 of the tetrode is controlled and converged to the set value.

On the other hand, the output of the photomultitube 52 is integrated by the integrator 21 and compared with the blackening degree setting value V ₄ by the comparator 22. When the two match, the timer circuit 204 in the X-ray controller 30 sends the X-RAY
Send the OFF signal, change the timer output from H to L,
Turn off the X-ray tube 105. As described above, as a result of simultaneously operating the voltage control of the tetrode tube and the timer control based on the set value comparison using the photomal output, the operation with the photomal timer (so-called phototimer) is performed while the change in the tetrode voltage is delayed. By supplementing, it is possible to make the degree of blackening uniform for each frame. In addition, in order to avoid using the X-ray tube beyond its allowable load,
The photo timer has a maximum time limit of up to the timer of the X-ray controller. That is, X-rays are cut off by the X-RAY OFF signal from either the timer or the photo timer, whichever is earlier. Incidentally, the integrator 21 is reset by the timer off signal.

〔Effect of the invention〕

According to the present invention, instead of converging from the beginning during the ON period, the previous converged feedback amount is used as the initial value of the current feedback amount, so the convergence time can be shortened. Variations in image quality can be reduced.

[Brief explanation of drawings]

Figure 1 is an embodiment of the present invention, Figure 2 is a waveform diagram of timer output, Figure 3 is a waveform diagram of tube voltage control, and Figure 4 is a waveform diagram of tube voltage control.
5 and 5 are control waveform diagrams using sample and hold results, and FIG. 6 is a diagram illustrating variations in image quality. 33...Control system, 12,13...Differential amplifier,
16, 17...sample hold circuit, 105...
...X-ray tube, 103,104...tetrode, 11
1...Image intensifier, 204...
timer circuit.

Claims (1)

[Claims] 1. A tube voltage indicator circuit, a high voltage generator that generates a DC voltage according to the support of the indicator circuit, and first and second gates each having a first gate and a second gate, respectively.
a tetrode connected in series between the first tetrode connected to the positive output terminal of the high pressure generator and the second tetrode connected to the negative output terminal of the high pressure generator; An X-ray tube that turns on when the second tetrode is turned on according to the first gate potential control, an II that takes in X-rays from the X-ray tube through the subject and converts them into optical signals, and photographs the II output. A tetrode-controlled X-ray generator comprising a camera, a photodetector for detecting the amount of light of the II output, a differential amplifier that takes the difference between the brightness setting value and the detection output of the photodetector, and 1. A voltage divider circuit that detects the voltage applied to the X-ray tube from the second tetrode, an added value of the output of the differential amplifier and the support value of the preceding circuit, and a detected value of the voltage divider circuit. a timer circuit that generates an intermittent pulse output for indicating an X-ray generation period when the same subject is imaged; control means for feedback-controlling the respective gate potentials of the first and second tetrodes on a carrier wave added to the set point so that the difference in the difference means becomes zero; and the timer circuit output. When the first and second tetrodes are turned off in response to an instruction from the X-ray tube and the X-ray tube is turned off, the first and second tetrodes are sampled and held for sample-holding the deviation at the time of turning off; Second
A tetrode-controlled X-ray generator comprising a setting means for setting the sample-held value as an initial value of the deviation in the control means when the X-ray tube is turned on by the tetrode-on.