JPS637438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray diagnostic apparatus equipped with an automatic imaging condition setting circuit.

In general, as a special imaging method using X-ray diagnostic equipment, a contrast agent is injected into blood vessels and the state of the contrast agent flowing through the blood vessels is observed (dynamic observation) to discover abnormalities in the vascular system. There is a method called angiography. In this case, the flow of the contrast agent injected into the blood vessel is fast, and in order to dynamically observe the flow, it is necessary to obtain a large amount of information by taking a large number of images within a few seconds, so the X-ray film can be transferred at high speed. There are continuous photographing devices and X-ray photographing devices that transfer images created by image intensity onto a photographic film. In the case of continuous imaging, images are taken for several seconds, so in order to minimize X-ray exposure to the subject, continuous pulses are synchronized with the imaging device. Setting the shooting conditions becomes a problem. That is, if continuous shooting is performed with a device set with incorrect shooting conditions, the contrast and sharpness of the photos will deteriorate, and all the photos taken may be wasted.
In the angiography method, the subject is exposed to a large amount of X-rays, and surgery is required, making it difficult to take images again, so setting the imaging conditions is particularly important.

By the way, the quality of the photograph in the photographing process is determined by the density of the photograph. Therefore, an automatic exposure control device called a photo timer is used in the X-ray generator, which stops the X-ray exposure when the photographic density of the film reaches the optimum value. This phototimer outputs a current proportional to the X-ray dose rate irradiated by a photomal for X-ray dose detection, integrates the output current with an integrator, and detects when the integrated value exceeds a predetermined value. , X-ray exposure is stopped to obtain an X-ray photograph with optimal imaging density (optimum exposure). The optimal exposure in this case is proportional to the product of the imaging time and the X-ray dose rate. Here, since the angiography is dynamic imaging, the imaging time should be given top priority among the imaging conditions, and the imaging time must be 0.01 seconds or less. Therefore, in order to obtain optimal exposure in a short time, it is necessary to increase the X-ray exposure dose rate, that is, the tube current.
However, the maximum value of the tube current is determined by the X-ray tube used, and it cannot take a large value. Therefore, it is important to first determine the photographing time and, in relation to this, to find the tube current value for obtaining the optimum exposure.

Conventional diagnostic equipment has a circuit that determines whether the tube current setting when setting the imaging time is appropriate, and a single X-ray is emitted based on the output of this determination circuit. A device is added that displays the amount on a light meter to determine the degree of exposure. When determining the shooting conditions using this method, set the tube current value allowed by the shooting conditions, emit a single X-ray, check the exposure level with a light meter, and continue using this until the optimum exposure is achieved. I try to repeat operations like this. That is, as shown in Fig. 1, if the exposure level at the first exposure (N ₁ ) at an arbitrary tube current does not reach the optimum exposure, then increase the tube current and repeat the exposure for the first time (N 1 ). The second exposure (N ₂ ) is carried out, and if the exposure level in this case exceeds the optimal exposure, the next exposure is carried out (N ₃ ), and the same operation is repeated until the nth exposure (Nn ) to obtain the optimum exposure.

Therefore, in such a method, it takes time to set the tube current to obtain the optimum exposure, and there is a problem in that the exposure dose increases accordingly.

The present invention has been made to solve the above-mentioned problems, and is an X-ray system that can automatically obtain the tube current value to obtain the optimal exposure for the imaging time by performing one preliminary exposure. The purpose is to provide a diagnostic device.

The present invention will be specifically explained below using Examples.

First, before explaining specific embodiments of the present invention, the basic principle of the present invention will be explained.

The optimal exposure for a photograph is proportional to the integrated dose of exposed X-rays, as described above. Therefore, in the present invention,
In contrast to the imaging conditions (short-time exposure, large canal current) set in actual continuous imaging, the imaging conditions for the first preliminary exposure are set as canalicular current value and long-time exposure. This is because preliminary exposure does not require information on the flow of the contrast medium and only the exposure level is a concern, so exposure at the canalicular current value is sufficient. It is possible to accurately measure the exposure time required to obtain the desired results. In this case, the irradiation conditions may be converted using the following equations (1) and (2).
In addition, D is an integrated dose, Δt is a unit exposure time, ΔmA is a unit tube current, and m and n are integers.

D=mΔt×nΔmA ……(1) =nΔt×mΔmA ……(2) Here, if m<n, then (1)
The formula is the shooting conditions for actual continuous shooting, and is (2)
The formula corresponds to that in the preliminary exposure. Therefore, in preliminary exposure, X-ray exposure is performed at a unit tube current, and the exposure time (hereinafter also referred to as preliminary exposure time) to obtain the optimum exposure is measured, and the equations (1) and (2) Find the values of integers m and n that satisfy . For example, if the value of n in conditional expression (2) for preliminary exposure is set to n = 1, the value of m can be calculated using the exposure time to obtain the optimal exposure obtained by preliminary exposure. can. If we find the values of integers m and n in this way, we get
Since it is possible to clarify the relationship between the exposure time when performing imaging (hereinafter also referred to as exposure time for imaging) and tube current, it is possible to clarify the relationship between the exposure time for imaging (hereinafter also referred to as exposure time for imaging) and the tube current. This allows the tube current value for optimal exposure to be automatically set.

A circuit diagram of an embodiment of a device for realizing such a concept is shown in FIG. 2 and will be described. In the figure, 1 is an X-ray tube that emits X-rays, 2 is a subject, and 3
4 is an integrator that integrates the output current of the detector; 5 is an optimal exposure setting device that outputs a signal corresponding to the optimal exposure; 6 is a detector that detects X-rays that have passed through the subject;
is a comparator that compares the output of the integrator 4 and the optimum exposure signal, and inverts the output when the two match;
7 is the first signal that is output in synchronization with the X-ray exposure start signal.
An oscillation start signal generator for starting the oscillation of the oscillator 8; 9 is a first counter that counts the output pulses of the oscillator; 10 is a counter that latches the output of the first counter and controls the exposure when actually performing continuous imaging; The second parameter used when calculating the tube current value for the irradiation time
11 is a third counter in which a time series obtained by dividing the exposure time used in continuous imaging by the oscillation cycle time of the oscillator 8 is input, and the output is fed back to the input; 12 is a third counter used for calculations. a second oscillator that outputs clock pulses to the second and third counters; _G0 is a gate circuit whose two inputs are the output of the third counter and the output of the second counter;
A fourth counter 3 receives the output of the gate circuit, counts the number of output pulses, and generates a predetermined output from the four weighted output terminals. Transistors each controlled by the output of the output terminal
Q ₁ to _{Q 4} and a tube current setting device 15 that outputs a different current depending on the ON operating state of this transistor.
16 is a filament heating circuit that receives the output signal of the tube current setting device and outputs a filament heating control signal; 16 compares a preset overload signal with the output signal from the gate circuit G ₀ and determines that the two match; An overload determiner 17 generates an output when the overload determiner 17 performs a display circuit that displays the output of the overload determiner.

Next, the operation of the circuit will be explained with reference to the timing chart of FIG. First, a preliminary exposure is performed by setting an arbitrary tube current value (smaller than the actual imaging value). X-rays are emitted from the X-ray tube 1 in response to the X-ray exposure start signal, the X-rays pass through the subject 2 and are detected by the detector 3, and the detected current is integrated by an integrator. The value and the output of the optimum exposure setter 5 are compared, and when the two match, an X-ray exposure stop signal is output from the comparator 6, and the X-ray exposure is stopped. The time from the start of X-ray exposure until the output of the comparator 6 is reversed is the exposure time for obtaining the optimum exposure at the set tube current value.

The first oscillator 8 operates based on the X-ray exposure start signal, and outputs oscillation pulses having intervals corresponding to the minimum exposure time. The first counter 9 counts this oscillation output, and depending on the count, a pulse output is generated that rises every second oscillation pulse from the 1st bit, and from the 2nd bit, the pulse output is divided by 2. From the third bit, pulse outputs obtained by dividing the frequency by two are sequentially output (time t ₁ in FIG. 3). and,
When the output of the comparator 6 is inverted, the oscillator 8 stops oscillating (time t ₂ ). Therefore, the value obtained by multiplying the oscillation period of the oscillator by the value counted by the first counter 9 corresponds to the exposure time for obtaining the optimum exposure. That is, the count value of the first counter 9 becomes a value representing the relationship between the optimum exposure time and the tube current.

Next, an explanation will be given of the operation of a circuit that calculates, from the ratio of the optimum irradiation time and the tube current value as described above, how many times the unit tube current value is set in the preliminary irradiation. The count value stored in the first counter 9 is transferred to the second counter 10, and by the output of the oscillator 12, the second counter 10 and a value corresponding to the exposure time used in continuous exposure are preset. The respective third counters 11 are caused to count down. Since the set value of the third counter 11 is smaller than the numerical value of the second counter 10 as is clear from the relationship of equations (1) and (2) above, the output of the third counter 11 reaches zero first. become. At this time, the fourth counter 13 is sequentially incremented from zero based on the output of the gate circuit _G0 . The set value is again input to the third counter 11, and the second and third counters 10 and 11 are caused to count down by the clock pulse. This process is repeated until the content of the second counter 10 becomes zero.
This causes the initial value of the second counter 10 to change to the third
How many times the set value entered in the counter of
That is, it is possible to calculate how many times the exposure time to obtain the optimum exposure obtained in the preliminary exposure corresponds to the exposure time set in continuous shooting. Note that the repetitive operation of the counter is automatically stopped when the content of the second counter 10 becomes zero. Here, when the content of the second counter 10 becomes zero, the fourth counter 13 is always incremented by one, but this is because there is no surplus when calculating the coefficient of the exposure time. This is to make it possible to obtain a tube current value that sufficiently reaches the optimum exposure during actual photographing by adding the surplus when this occurs.

The value obtained by multiplying the count value of the fourth counter 13 by the unit tube current value set in the preliminary exposure becomes the tube current value for obtaining the optimum exposure in continuous shooting. That is, by turning on one of the transistors of the tube current setting device 14 using the count signal of the fourth counter 13, the tube current setting signal is supplied as a control signal to the filament heating circuit 15 and used for continuous imaging. The tube current value is automatically set to obtain the optimal exposure corresponding to the exposure time.
All subsequent photographs in continuous shooting will be taken clearly.

In addition, in the process of calculating the exposure time coefficient, the output of the gate circuit G ₀ is input to the overload determiner 16, so this output is compared with the overload state set value, and the overload state is determined. If so, an output is applied to the display circuit 17 to display that fact. Therefore, in such a case, it is sufficient to adjust the time setting value for the third counter 11 and calculate the time coefficient again, making it possible to prevent continuous shooting under overload.

According to the present invention described in detail above, it is possible to automatically set the tube current value corresponding to the optimum exposure with only one preliminary exposure, thereby shortening the time for setting imaging conditions and reducing the exposure dose. Since the preliminary exposure is performed at a low tube current value, it is possible to provide an X-ray diagnostic apparatus that can more accurately set the imaging conditions for optimum exposure.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional photographing condition setting method, FIG. 2 is a circuit diagram of an embodiment of the device of the present invention, and FIG.
The figure is a timing chart for explaining its operation. DESCRIPTION OF SYMBOLS 1... X-ray tube, 2... Subject, 3... Detector, 4... Integrator, 5... Optimal exposure condition setter, 6... Comparator, 7
...Oscillation start signal generator, 8, 12...Oscillator, 9,
10, 11, 13... Counter, 14... Tube current setting device, 15... Filament heating circuit, 16... Overload determination device, 17... Display circuit.

Claims (1)

[Claims] 1 An automatic exposure control circuit that compares the integrated dose value of the X-rays that have passed through the subject and the integrated dose value for obtaining the preset optimal exposure, and outputs an X-ray exposure stop signal when the two match. A circuit for determining the preliminary exposure time to obtain the optimum exposure when preliminary exposure is performed at a low tube current value, and a circuit for calculating the preliminary exposure time and the actual imaging. a circuit for calculating a multiple of the preliminary exposure time to the exposure time for photography by determining a ratio with the set exposure time for photography; An X-ray diagnostic device characterized in that an optimum tube current value is automatically set by multiplying the current value.