JPS6160560B2 - - 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 period 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 differences in X-ray control time depending on changes in the body thickness of the subject.
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 required exposure amount 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 that hold the X-ray film and turn the X-ray image into an optical image, helping expose the X-ray film, has improved. 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 present invention has been made in view of the above circumstances, and includes a detection device that detects X-rays that have passed through an object and converts them into electrical signals, and a delay of a predetermined period of time for an X-ray exposure start signal that commands the start of X-ray exposure. a delay circuit that switches the electrical signal conversion efficiency of the detection device according to the output of the delay circuit, an integrator that integrates the signal output from the detection device, and an integral value of the integrator that is set in advance. The device is composed of a comparator that outputs an X-ray cutoff signal when a reference value is reached, and the X-ray exposure is stopped by the cutoff signal, thereby correcting the cutoff delay of the X-ray device and providing accurate An object of the present invention is to provide an X-ray automatic exposure control device that can perform exposure control.

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 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; CR is the setting of the tube voltage and tube current of the X-ray tube. The X-ray controller H, which outputs an X-ray exposure start signal and an X-ray cutoff signal at the same time, is operated by this X-ray exposure start signal and generates the tube current and tube voltage set by this X-ray controller CR. This is a high voltage generator that is applied to the X-ray tube XT to cause it to emit X-rays, and stops its output in response to the X-ray cutoff signal to cut off the X-ray exposure. The above is X
This is the configuration of the wire device part. 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 an electric signal corresponding to the intensity and outputs the same, and includes a delay circuit to be described later. Get the output from and convert the conversion efficiency to e.g. 1/
It has a conversion efficiency switching circuit that converts the conversion efficiency into 2 and outputs the output. 2 is an integrator that integrates the output signal of this X-ray detection device 1; 3 is an integrator that compares the integrated value of the integrator 2 with reference to a preset reference value; when this integrated value reaches the reference value, a cutoff signal is generated; The X-ray controller CR receives the cutoff signal output from the comparator 3 and outputs an X-ray cutoff signal. 4 is the X output from the X-ray controller CR
This is a delay circuit that delays a radiation exposure start signal by a predetermined time and provides it to the X-ray detection device 1.

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 provides a high voltage output to the X-ray tube XT, which corresponds to the previously set tube voltage and tube current. As a result, the X-ray tube XT emits X-rays toward the subject P. 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
The X-ray exposure start signal from the CR is also sent to the delay circuit 4. After being delayed for a predetermined time by this delay circuit 4, the signal is input to the X-ray detection device 1.

The X-ray detection device 1 converts the incident X-rays into an electrical signal with a predetermined conversion efficiency and supplies it to the integrator 2.
When the X-ray exposure start signal is received via the delay circuit 4, the conversion efficiency is switched to 1/2 and output of the signal is started. Upon receiving the output of the X-ray detection device 1, the integrator 2 integrates it. 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 and supplies it to the X-ray controller CR. Then this X-ray controller CR is
A line cutoff signal is generated and applied to the 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 _V0 . Figures 2 and 3 show the input signal of the integrator 2 and its integrated output voltage when the conversion efficiency of the X-ray detection device 1 is constant as before, and the output of the integrator 2 at time t ₀ . reaches V ₀ .

On the other hand, the conversion efficiency of the X-ray detection device 1 that converts X-rays into electrical signals I is set to α times the predetermined value when X-rays begin to be irradiated, and τ hours after the start of X-rays irradiation. When the delay circuit output is returned to a predetermined value, the output I of the X-ray detection device 1 becomes as shown in FIG. 4, and the integrator output V becomes as shown in FIG. Therefore, in this case, V reaches V ₀ at t=t ₀ ', and the third
The comparator output is generated t ₀ −t ₀ ' earlier than in the case shown in the figure. As is clear from Figure 4, the shaded areas are equal, so (αI ₀ −I ₀ )・τ=(t ₀ −t ₀ ′)・I ₀ ∴(α−I)・τ=t ₀ −t ₀ ′ becomes. Therefore, as shown by the dotted line in Fig. 5, when viewed from the integrator output, it appears that the signal after the time of -(α-1)·τ is obtained regardless of the value of the input signal _I0 . It turns out. Incidentally, it is desirable to set τ to a time shorter than t ₀ ' in anticipation of interruption delay depending on various X-ray conditions, but in practice this will be determined experimentally depending on the individual apparatus.

As described above, according to the present invention, the cut-off delay correction of (α-1)·τ time can be performed by waveform processing before the integrator, and can be performed regardless of the value of the input signal _I0 . Accurate correction can be made without regard to changes in the input signal I ₀ caused by changing the X-ray conditions in response to changes in body thickness.

FIG. 6 shows a specific embodiment of the present invention, where CR is an X-ray controller H is a high voltage generator, and XT is an X-ray tube 11.
12 is an X-ray detector that converts the X-rays transmitted through the subject P and the X-ray film F into light, and 12 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 13b.
Output resistors 13c and 13d connected in parallel
switch element 1 for separating resistor 13c from
Consists of 3e. 14 is an integrator that integrates the output amplified by this amplifier circuit 13;
4 is an operational amplifier 14a and an integrating capacitor 14b
Consists of. 15 is a comparator that outputs a cutoff signal when the integrated value of the integrator 14 reaches a preset reference value _V0 , and this cutoff signal is sent to the amplifier 1.
6 to the X-ray controller CR.
The ray controller CR outputs an X-ray cutoff signal to stop X-ray exposure. The switch element 13e is normally closed when X-ray exposure starts, and the resistor 13c is connected in parallel with the resistor 13d. Reference numeral 18 denotes a delay circuit, which outputs an output τ time after the X-ray exposure start signal sent from the X-ray controller CR, closes the switch element 13e, and disconnects the resistor 13c from the circuit. By operating this switch, the amplification degree of the amplifier 13 becomes 1/α after τ time from the start of X-ray exposure, as described above (α
-1) - τ time can be corrected.

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 . 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 electrical signal by the photoelectric conversion element 12, and the amplification circuit 13
sent to. Then, this amplifier circuit 13 amplifies this and outputs it. A resistor 13 is included in the amplifier circuit 13.
Since the parallel circuits c and 13d are connected as output resistors, the amplified output is input to the integrator 14 via the parallel connected resistors.

On the other hand, the X-ray exposure start signal output from the X-ray controller CR is delayed for a predetermined time by the delay circuit 17 and then applied to the switch element 13e. Then, this switch element 13e operates and opens the circuit. As a result, the resistor 13c connected in series with the switch element 13e is disconnected from the output side of the amplifier circuit 13, so that the output resistance of the amplifier circuit 13 is changed to the resistor 13d.
As a result, the resistance value increases. Therefore, since the output current to the integrator 14 is suppressed at this point, 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.

In this way, the switch element 13e is in a normally closed state at the start of X-ray exposure, and the resistor 13c is connected to the resistor 1.
3d is connected in parallel. Then, the delay circuit 17 delays the X-ray exposure start signal sent from the X-ray controller CR by τ time, and then the switch element 13c is opened to disconnect the resistor 13c from the circuit. By operating this switch, the amplification degree of the amplifier circuit 13 is adjusted after τ time from the start of X-ray exposure.
1/α, and the (α-1)·τ time can be corrected as described above. Letting the resistance values of the resistors 13c and 13d be Rc and Rd, respectively, α=Rd/RcRd=Rc+Rd/Rc.

Figure 7 shows the waveforms of the integrator input current I and integrator output voltage V when combined with a three-phase X-ray controller, and Figure 8 shows the integrator input when combined with a single-phase X-ray controller. These are the waveforms of current I and output voltage V.

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 integrated value 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 increasing the electrical signal conversion efficiency of the detection output at the time, and delaying the X-ray exposure start signal by a predetermined time in a delay circuit, the electrical signal conversion efficiency is returned to a steady value with this delayed output,
While ensuring the input signal I to obtain the optimum degree of blackening of the film, the integral value is increased in advance by an amount equivalent to the cut-off delay time when X-ray exposure is cut off, so that the exposure during the cut-off delay time is corrected. The amount is corrected in advance and integrated. Therefore, when the detected output integral value reaches a predetermined value, at that point, an X-ray cutoff signal is output with the exposure amount corresponding to the cutoff delay time remaining, and the cutoff operation is started. Therefore, since the necessary exposure amount is reached when the cut-off actually ends, accurate automatic exposure control can be performed taking into account the cut-off delay time.

Further, the present invention can also provide the following additional effects. That is, in general, X-ray equipment often generates a surge-like noise at the beginning of X-ray exposure, and for example, as in the technology disclosed in Japanese Patent Application Laid-Open No. 114892/1983, which has already been put into practical use. In the technology where an average value reading circuit takes the average of the incident X-ray dose and controls the reference value using this average value, when this surge-like noise appears, there is a risk of instantaneously exceeding the reference value and causing an error. . That is, as shown in FIG. 6 in Japanese Patent Application Laid-open No. 49-114892, X Detects the dose rate,
This average value is used to control the reference value of the reference voltage generator. Therefore, when a surge-like noise occurs, its peak value is held in the peak detection circuit, which may cause malfunction. However, according to the present invention described above, since an integral operation is performed, there is also an advantage that there is no adverse effect due to surges. Furthermore, in the case of high dose rate 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, correction can be easily and accurately performed in an extremely short period of time. It is possible to provide an X-ray automatic exposure control device having excellent features such as:

In this embodiment, the amplification degree of the amplifier is switched as the conversion efficiency, but any efficiency can be switched as long as it is between the X-ray detector and the integrator input. The same effect can be obtained by changing the sensitivity of the X-ray detector, or by changing the detection field area or transmittance of the X-ray detector.

For example, as shown in FIG. 9, when a photomultiplier tube (photomultiplier) PH is used as a photoelectric element, dynodes D ₁ , D ₂ , D ₉ are used to adjust the detection efficiency of the photomultiplier PH. This can also be done by adjusting the bias potential. That is, the dynode
Resistors Ra and Rb connected in parallel to the ground side ends of D ₁ , D ₂ ......D ₉ are connected in series, and a switch is connected in series to resistor Rb so that the resistance value can be selected.
A switch SWa is provided so that this resistor Rb can be disconnected from the circuit, and the bias potential is changed by turning on and off the switch SWa. With this, it is possible to change the detection efficiency of the photomul PH, and the same can be done even if the negative potential -HV applied to the cathode K of the photomul PH is varied.

Incidentally, FIG. 10 shows test results of automatic exposure control using the above-described apparatus of the present invention. In the figure, the vertical axis shows the degree of blackening, and the horizontal axis shows the exposure time, starting from 2 [msec].
This figure shows the results of automatic exposure of X-ray film at various exposure times over 1000 [msec], and the optimum value of the degree of blackening is expressed as 1. As is clear from the figure, in the conventional method indicated by A, 400
Unless the exposure is for a long time of [msec], the value does not approach the optimum value, and for short exposures, the control is completely inaccurate, but in the method of the present invention shown in B, it is almost averaged out, and this effect is particularly noticeable for short exposures.

[Brief explanation of the drawing]

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 an explanatory diagram of a conventional integrator output waveform. FIG. 5 is an explanatory diagram of the converted integrator input signal, and FIG. 6 is an explanatory diagram of the integrator output waveform according to the present invention.
The figure shows a specific embodiment of the present invention, Figure 7 is an integrator input/output waveform diagram when combined with a three-phase X-ray device, and Figure 8 is an integral diagram when combined with a single-phase X-ray device. FIG. 9 is a circuit diagram showing another example of the present invention, and FIG. 10 is a diagram for comparing control results between the device of the present invention and a conventional device. 1... X-ray detection device, 2... Integrator, 3... Comparator, 4, 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, 13e ... switch element, 15 ... voltage comparator, V ₀ ... setting reference value.

Claims (1)

[Claims] 1. An X-ray detection device with selectable conversion efficiency that detects X-rays that have passed through a subject, converts them into electrical signals, and outputs them; an integrator that integrates the output of this X-ray detection device;
The integrated value of this integrator is compared with a reference value, and when the integrated value reaches the reference value, a comparator outputs a cutoff signal instructing X-ray cutoff, and a signal delaying the signal commanding the start of X-ray exposure by a predetermined time. and a delay circuit that outputs the delayed signal as the conversion efficiency selection signal to the X-ray detection device, and outputs the X-ray dose corresponding to the X-ray cutoff delay time at the time of X-ray cutoff from the delay circuit. An X-ray automatic exposure control device characterized in that the conversion efficiency of the X-ray detection device is increased to a predetermined value and corrected in advance until a signal is output.