JPH0113640B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an automatic X-ray exposure control device.

Generally, an automatic X-ray exposure control device converts the X-rays that have passed through the object into an electrical signal, integrates this electrical signal, and when it reaches a predetermined reference value, issues an X-ray cutoff signal to stop X-ray exposure. This controls the exposure of the X-ray film and maintains the degree of darkening in the X-ray photograph at a predetermined density. If there is a certain amount of cut-off delay before it is stopped, this cut-off delay will cause the degree of blackening of the film to be uneven due to the difference in X-ray control time depending on changes in the body thickness of the subject, so the required exposure amount will be It is necessary to make a correction so that the X-ray cutoff signal is emitted earlier by this cutoff delay time than the time when the X-ray cutoff signal is reached.

Conventionally, the time it takes for an electromagnetic switch to operate in the X-ray cutoff method using an electromagnetic switch is considered to be approximately several tens of milliseconds as the cutoff delay time, so switching to a thyristor switching method that uses a thyristor instead of an electromagnetic switch is considered. It is said that the delay in shutoff has been eliminated, but in reality, until X-ray exposure is stopped, especially before the effect on the degree of blackening is completely eliminated, the high-voltage cable that leads the high voltage to the X-ray tube must be charged. Including the effects of voltage discharge, etc., there is still a time difference of several milliseconds.

This is not a problem when controlled over a relatively long period of time, but in recent years, the sensitivity of intensifying screens has been improved to help expose the X-ray film by sandwiching the X-ray film and converting the X-ray image into an optical image. With the increase in the capacity of the control device that controls the X-ray exposure of three-phase X-ray equipment, etc.
As short-term imaging is now performed, correction of the X-ray cutoff delay has become an important issue.

The conventional shutoff delay correction method converts the X-rays into an electrical signal Io as shown in Fig. 8, and then integrates it using an integrator as shown by the dotted line ₁₁ , and at the same time calculates a correction value proportional to the electrical signal. By adding to the integral value, an integrator output as shown by straight line 1 ₂ is obtained. Therefore, while the normal time for the integral value to reach the predetermined reference value Vo is to,
Since a correction value proportional to the electric signal is added to the integral value, the time to reach the predetermined reference value Vo is to', thereby advancing the time to reach the predetermined reference value by a certain period of time. However, in general, an X-ray apparatus often generates a surge-like noise as shown in FIG. 8S at the start of X-ray exposure, which affects the electrical signal. If surge-like noise is integrated, it will not affect the integral value, but since the above correction value is an electrical quantity proportional to the electrical signal, when surge-like noise appears, it momentarily exceeds the reference value Vo. This can easily lead to malfunctions. In order to achieve accurate operation, it is necessary to create a correction value that completely removes surge-like noise, but in the case of short-time control as mentioned above, a surge-like noise removal circuit is installed to eliminate surge-like noise. When X-rays are cut off, the amount of correction becomes dull due to this removal circuit, and appropriate correction cannot be performed.

The present invention has been made in view of the above circumstances, and includes a detection device that detects X-rays that have passed through a subject and converts them into electrical signals, an integrator that integrates the signal output from the detection device, and an X-ray exposure device. a delay circuit that delays an X-ray exposure start signal that commands the start for a predetermined time; a device that switches an integral constant of the integrator according to the output of the delay circuit; and a reference value that the integral value of the integrator is set in advance. and a comparator that outputs an X-ray cutoff signal when the X-ray cutoff signal is reached.
An automatic X-ray exposure control device that corrects the shut-off delay of the X-ray device by stopping radiation exposure and allows accurate exposure control without being affected by surge noise. The purpose is to provide.

An embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a block diagram showing the basic configuration of this device, where XT is an X-ray tube and P
is the subject, F is the X-ray film that is exposed to the X-rays from the X-ray tube XT that has passed through the subject P, and takes an X-ray image of the subject P, and CR is the setting of the tube voltage and tube current of the X-ray tube XT. an X-ray controller that outputs an X-ray exposure start signal and an X-ray cutoff signal;
H is a high voltage generator that provides driving power to the X-ray tube XT based on the tube current, tube voltage, and opening/closing control set by the X-ray controller CR. The above is the configuration of the X-ray device section. Reference numeral 1 denotes an X-ray detection device that detects the X-rays from the X-ray tube XT that have passed through the subject P and the X-ray film F, and converts the X-rays into electrical signals corresponding to the intensity thereof and outputs the signals. Reference numeral 2 denotes an integrator that integrates the output signal of the X-ray detection device 1, and has an integral constant switching circuit that reduces the integral constant to 1/2, for example, and outputs the output from a delay circuit, which will be described later. . Reference numeral 3 denotes a comparator that compares the integral value of the integrator 2 with a preset reference value as a reference, and generates a cutoff signal when this integral value reaches the reference value. Vessel 3
The X-ray cutoff signal is output in response to the cutoff signal output by the X-ray cutoff signal. Reference numeral 4 denotes a delay circuit that delays the X-ray exposure start signal output from the X-ray controller CR by a predetermined time and supplies it to the integrator 2.

As described above, 1, 2, 3, and 4 constitute an X-ray automatic exposure control device.

Next, the operation of this apparatus having the above configuration will be explained. Exposure conditions such as the tube voltage and tube current of the X-ray tube are set in the X-ray controller CR according to the part of the subject P to be imaged and the body thickness. Thereafter, when an X-ray exposure command is given, the X-ray controller CR generates an X-ray exposure start signal.
Then, the high voltage generator H receives this signal and applies high voltage output to the X-ray tube XT, which results in the previously set tube voltage and tube current, and the X-ray tube XT emits X-rays toward the subject P. Ru. As a result, the X-rays pass through the subject P, expose the X-ray film F, and are further incident on the X-ray detection device 1. On the other hand, the X-ray controller CR
The X-ray exposure start signal from is also sent to the delay circuit 4. After being delayed for a predetermined time by this delay circuit 4, it is input to the integrator 2 as an integration constant switching signal.

The X-ray detection device 1 converts the incident X-rays into an electrical signal, integrates it by doubling the integral constant until a predetermined time (τ) has elapsed from the start of X-ray exposure, and integrates it by doubling the integral constant.
give to When a predetermined time (τ) has elapsed from the start of X-ray exposure, the delay circuit 4 doubles the integral constant of the integrator 2, which has been doubled in advance, and returns it to the original integral constant.
Therefore, the integrator 2 integrates the output of the X-ray detection device 1 with a slope that is half the previous value. This integrated value is then compared with a reference value by a comparator 3. When the integral value reaches the reference value, the comparator 3 generates a cutoff signal,
Give to X-ray controller CR. Then this X-ray controller
CR generates an X-ray cutoff signal and supplies it to high voltage generator H. This causes the high voltage generator H to cut off its output, and the X-ray tube XT to stop emitting X-rays. The above operations are performed to automatically control the exposure of the X-ray film F. The operation of this device will be explained in more detail.

Now, assuming that the output of the X-ray detection device 1 is I and the output of the integrator 2 is V, the comparator 3 issues an output signal when V reaches the reference value Vo. Figures 2 and 3 show the input signal of the integrator 2 and its integrated output voltage when the integral constant is constant as before.
At time to, the integrator 2 output reaches Vo.

On the other hand, when the X-rays start to be irradiated, the integration constant of the integrator 2 that integrates the output signal of the X-ray detection device 1 that converts the X-rays into an electric signal I is set to α of a predetermined value K.
The electrical signal αIo is input to the integrator 2 until the time τ has elapsed since the start of X-ray irradiation. , the original Io after τ time elapses
When inputting the electric signal back to the electric signal, the integrator output V becomes as shown in FIG. Note that α is a value larger than 1 and is an arbitrarily set value. On the other hand, when the value of α is set to a small value, the time τ becomes shorter, and conversely, when the value of α is set to a large value, the time τ becomes longer. For this reason, the time τ needs to be set to a time shorter than the time to' when shutting off in anticipation of the shutoff delay time (to-to') specific to the X-ray device, so a value of 2 to 3 is desirable for α. .
Therefore, in this case, V reaches Vo at t=to', and the third
Compared to the case shown in the figure, the comparator output is issued earlier to-to' time.

In this case, the output voltage Vτ of the integrator 2 obtained by integrating the electric signal of αIo over τ becomes Vτ=αK∫〓 _p Idt=αKIτ (1) if the input voltage is DC. Next, as shown in FIG. 3, in order to obtain the output voltage Vτ with a conventional integrator having a predetermined integral constant K, it takes time t', as is clear from FIG. 4. Therefore, Vτ＝K∫ ^t _p ′Idt＝KIt′ ……(2) Therefore, from equations (1) and (2), αKIτ＝KIt′, and ∴ατ＝t′ ……(3) Also, As is clear from FIG. 4, the correction amount (to-to') according to the present invention is t'-τ=to-to' (4). Therefore, from equations (3) and (4), (α−1)・τ=to−to′. Therefore, as shown by the dotted line in FIG. 4, when viewed from the integrator output, it appears that a signal after the time point -(α-1)·τ is obtained. Note that it is desirable to set τ to a time shorter than to' in anticipation of interruption delays depending on various X-ray conditions, but in practice this is determined experimentally depending on the individual apparatus. As described above, according to the present invention, the electric signal input to the integrator 2 is multiplied by α by the time τ elapses from the start of X-ray irradiation.
The delay can be corrected at the front stage of the integrator by an amount equivalent to the area of PQRS, but even if surge noise enters the X-ray detection device that detects X-rays and converts them into electrical signals, the output of integrator 2 There is no effect. In other words, even if a surge-like noise S as shown in FIG. It becomes only a small value. Therefore, as in the present invention, τ from the start of X-ray exposure
The electric signal input to the integrator 2 is multiplied by α before the time elapses, and the cut-off delay is corrected at the front stage of the integrator 2. This is the comparison with the reference value Vo to determine whether the corrected exposure has been reached. Since this is performed using the output value of the integrator 2, even if the surge-like noise 7 occurs, it is possible to avoid malfunctions caused by exceeding the reference value Vo as in the conventional case.

Also, even if a surge-like noise occurs after τ time has passed, the reference value for determining whether proper exposure has been reached.
Since the comparison with Vo is made with the output value of integrator 2, as above, the output value of integrator 2 will not instantaneously exceed the reference value, so accurate correction for the cut-off delay can be made. I can do it.

FIG. 5 shows a specific embodiment of the present invention, where CR is an X-ray controller, H is a high voltage generator, XT is an X-ray tube,
11 is the object P and the X transmitted through the X-ray film F.
The X-ray detector 12 that converts rays into light is a photoelectric conversion element that converts the conversion output of the X-ray detector 11 into an electrical signal. 13 is an amplifier circuit that amplifies the signal converted by this photoelectric conversion element 12, and this amplifier circuit 13 includes an operational amplifier 13a and a feedback resistor 1.
3R1 and an output resistor 13R2. 14 is an integrator that integrates the output amplified by this amplifier circuit 13, and this integrator 14 is an operational amplifier 14a.
1. An integrating capacitor 14c1 connected between the input and output terminals of this amplifier 14a1, a capacitor 14c2 connected in parallel with this capacitor 14c1 via a switch element 14s1, and the amplifier 1
4a1 and an integrating capacitor 14c via a switch element 14s2 between the input and output terminals.
3 is connected, and the output terminal is the switch element 14s1.
It consists of an operational amplifier 14a2 connected to one end of a capacitor 14c2 via. Further, the switch elements 14s1 and 14s2 are connected to a delay circuit 17 which will be described later.
The opening and closing are controlled in conjunction with each other, and the state is normally as shown in the figure, and when the output signal is derived from the delay circuit 17, the opening and closing state is reversed. 15
is a comparator that outputs a cutoff signal when the integrated value of this integrator 14 reaches a preset reference value Vo, and this cutoff signal is sent to the X-ray controller CR via the amplifier 16 to The controller CR outputs an X-ray cutoff symbol to stop X-ray exposure. 17
is a delay circuit and the X sent from the X-ray controller CR
This circuit outputs an output τ time after the radiation exposure start signal and controls the open/close states of the switch elements 14s1 and 14s2. By operating this switch, the integrated output of the integrator 14 becomes 1/α after τ time from the start of X-ray irradiation, and the correction of (α−1)·τ time can be performed as described above.

Next, the operation of this apparatus having the above configuration will be explained. Basically, the operation is the same as the circuit shown in FIG. When the X-ray controller CR generates an X-ray exposure start signal, the high voltage generator H applies a high voltage to the X-ray tube XT, and the X-ray tube XT performs X-ray exposure. The emitted X-rays pass through the subject P and form an X-ray film F.
, and further enters the X-ray detector 11 . and,
The X-ray detector 11 converts the incident X-rays into light corresponding to the incident X-rays. This converted light is further converted into an electric signal by the photoelectric conversion element 12, and the amplification circuit 1
3 and input to the integrator 14 via the output resistor 13R2. In the integrator 14,
Since the switch elements 14s1 and 14s2 are in a non-operating state (the state shown in the figure) at the start of X-ray exposure, the capacitor 14c2 is connected to the amplifier 14a2, and the capacitor 14c3 is disconnected from the circuit. Here, capacitors 14c1, 14c2,
If the capacitances of capacitors 14c3 are C1, C2, and C3, then if the capacitances are determined as C1=C2=C3/2, then the current flowing through capacitors 14c1 and 14c2 will be equal and they will be charged to the same potential. go. On the other hand, the delay circuit 17 energizes the switch elements 14s1 and 14s2 after a time τ has elapsed since the X-ray exposure start signal sent from the X-ray controller CR, and the capacitors 14c1 and 14c2 are connected in parallel.
Also, capacitor 14c2 is disconnected from amplifier 14a2, and capacitor 14C3 is connected instead. At this time, since each capacitance is C1=C2=C3/2, (C1+C2)=C3, the capacitor 14c3
The current flowing to the capacitors 14c1 and 14c2
The currents flowing in the parallel circuits are equal. Therefore, α=
When (C1+C2)/C1, the integral constant of the integrator 14 becomes 1/α after τ time has elapsed from the start of X-ray exposure, and the correction of (α−1)·τ time can be performed as described above. In this example, C1=C2 is selected, so α=2, and the constant of integration becomes 1/ after the elapse of τ time.
It becomes 2. Therefore, the rate of increase in the integral value of the amplifier circuit output of the integrator 14 becomes low. The integral values integrated in this way are compared by a comparator 15, and when the integral value reaches a reference value, the comparator 15 outputs a cutoff signal, which is sent to the X-ray controller CR via an amplifier 16. . Then, this X-ray controller CR outputs an X-ray exposure stop signal and gives it to the high voltage generator H to stop the output. As a result, the X-ray exposure is stopped and the X-ray imaging is completed.

Figure 6 shows the waveforms of the integrator input current I and integrated output voltage V when combined with a three-phase X-ray control device.
FIG. 7 shows the waveforms of the integrator input current I and output voltage V when combined with a single-phase X-ray control device. As shown by this waveform, by outputting the cutoff signal at time to' in anticipation of the cutoff delay, the X-rays are actually cut off at the appropriate time to obtain the appropriate degree of darkening.

In this way, the X-rays that have passed through the object are detected,
The detection output is integrated by an integrator, and when the output value of the integrator reaches a predetermined value, the X-ray exposure of the X-ray device is shut off to control the exposure of the X-ray film. , by delaying the X-ray exposure start signal for a predetermined time in a delay circuit during X-ray imaging, and switching the integration constant of the integrator to a predetermined value using the delayed output, a predetermined time has elapsed since the start of X-ray exposure. By multiplying the electric signal that is input to the integrator by a predetermined value until the end of the cutoff, the integral value is corrected in advance by the amount of cutoff delay time, so when the cutoff actually ends, the required exposure amount is reached, making it accurate. Automatic exposure control is possible.

Furthermore, according to the present invention, even if surge noise enters the signal processing system from the X-ray detector to the integrator as described above, a correction value proportional to the electrical signal converted based on the X-ray signal can be calculated. The electric signal input to the integrator is multiplied by a predetermined value until a predetermined time elapses from the start of X-ray exposure without using the X-ray beam, and the integration operation is performed by making a correction equivalent to the cut-off delay time. Since the surge-like noise is only integrated by the integrator, the output value of the integrator is not affected by the surge-like noise as in the conventional case, and accurate control is possible. Furthermore, in the case of high-dose irradiation using a three-phase X-ray control device, a cut-off delay of several milliseconds also affects the degree of blackening of the film, but according to the present invention,
It is possible to provide an X-ray automatic exposure control device having excellent features such as being able to easily and accurately perform correction in an extremely short period of time.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the present invention, Fig. 2 is an explanatory diagram of a conventional integrator input signal, Fig. 3 is an explanatory diagram of a conventional integrator output waveform, and Fig. 4 is a diagram according to the present invention. An explanatory diagram of the integrator output waveform, FIG. 5 is a diagram showing a specific embodiment of the present invention, FIG. 6 is an integrator input/output waveform diagram when combined with a three-phase X-ray device, and FIG.
The figure is an integrator input/output waveform diagram when combined with a single-phase X-ray device, and FIG. 8 is an integrator input/output waveform diagram of an X-ray device that performs a conventional shutoff delay correction. 1... X-ray detection device, 2... Integrator, 3... Comparator,
17...Delay circuit, CR...X-ray controller, XT...X-ray tube, P...subject, F...X-ray film, 11...X-ray detector, 12...photoelectric conversion element, 14s1, 14s
2... Switch element, 15... Voltage comparator, Vo... Setting reference value, 14c1, 14c2, 14c3... Integrating capacitor.

Claims (1)

[Claims] 1 An X-ray tube that irradiates X-rays toward a subject; an X-ray controller that determines the X-ray irradiation conditions of this X-ray tube and outputs an X-ray exposure start signal; an X-ray detection device that detects the X-rays transmitted through the subject and converts the X-rays into an electrical signal corresponding to the intensity thereof and outputs the same; an integrator that integrates the electrical signal output from the X-ray detection device; , a comparator that compares the integral value output from the integrator with a preset reference value and outputs a cutoff signal to the X-ray controller when the reference value is reached, the integral value of the integrator In the automatic X-ray exposure control device, the X-ray exposure start signal outputted from the X-ray controller is delayed by a predetermined time to adjust the integral constant. A delay circuit that outputs a switching signal and an electric signal output from the X-ray detection device are integrated by multiplying an arbitrary integral constant by a predetermined time from the start of X-ray exposure until the predetermined time elapses, and and an integrator that returns to the desired integration constant and integrates after the elapse of time based on the integration constant switching signal output from the delay circuit, An X-ray automatic exposure control device characterized in that the electric signal input to the integrator is multiplied by the predetermined value in between, thereby correcting the integrated value by an amount corresponding to the cutoff delay time.