JPH0127559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic X-ray exposure control device having a function of automatically correcting offset voltage.

An overview of a conventional automatic exposure control system in an X-ray diagnostic system will be explained with reference to FIG. X
The X-rays emitted from the ray tube 1 pass through the subject 2 and
The line reaches the line detector 3. The transmitted X-rays are sent to the X-ray detector 3
The signal is converted into an electrical signal and applied to the automatic exposure control circuit section 4. Further, the X-rays transmitted through the X-ray detector 3 reach the X-ray film 5. The automatic exposure control circuit unit 4 integrates the electrical signal from the X-ray detector 3, compares this integrated value with a predetermined reference value, and generates an X-ray exposure stop signal when the two match. I'm starting to do that. This stop signal is the next stage
The signal is sent to the X-ray controller 6, and the X-ray exposure is stopped by the signal from the X-ray controller 6 at this time.

By the way, the X-ray detector 3 and the X-ray automatic exposure control circuit section 4 are specifically constructed as shown in FIG. 2, respectively. That is, the X-ray detector 3
A plurality of detection elements 3a to 3n arranged in a matrix on the line detection field, a current-voltage converter (I/V converter) group 3A connected to each element, and an output of each converter. Switch group 3 that can be selected in combination as appropriate
B, and an adder circuit 3C that adds the voltage signals obtained from the switch group. X
The line automatic exposure control circuit section 4 includes an input side switch circuit 4 for transmitting the output E _a of the adder circuit 3C.
0, an integrating circuit group 41 including a plurality of integrating circuits 41a to 41n provided corresponding to all the combinations of the matrix-shaped detection elements 3a to 3n, and an integral circuit group 41 having the same configuration as the input side switch circuit 40. and an output side switch circuit 42 that operates in conjunction with each other.
and a comparison circuit 43 that compares the output of the output side switch circuit 42 and a predetermined reference signal E _s and generates an output signal E ₀ when the two match. Here, the reason why multiple integration circuits are required corresponding to the number of combinations of detection elements is because the offset voltage differs depending on the state of each combination.
This is because the offset must be adjusted in response to this (usually done by adjusting a volume provided in the integrating circuit). With such a configuration, by selecting an arbitrary number of detection elements of the X-ray detector 3, corresponding portions of electric signals are applied to the addition circuit 3C and added. Then, this addition output is applied via the input side switch circuit 40 to one integrating circuit of the integrating circuit group 41 selected corresponding to the combination of the detection elements, and is integrated. This integrated value is applied to the comparison circuit 43 via the output side switch circuit 42, and is compared with the reference signal _Es .

However, in the device having the above configuration, as the detection field of view becomes wider, the number of detection elements increases accordingly, and the number of selected combinations increases accordingly. Therefore, the number of integrating circuits increases, which has the drawback of increasing the size and cost of the X-ray automatic exposure control circuit section 4.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an X-ray automatic exposure control device that can be made smaller and lower in price by reducing the number of integrating circuits in the automatic exposure control circuit section. It is something to do.

The present invention will be specifically explained below using Examples.

FIG. 3 is a block diagram showing one embodiment of the apparatus of the present invention. In the figure, numeral 3 is the aforementioned X-ray detector, and an adder circuit 3C is shown. 4 is an automatic exposure control circuit section. 7 is an integrator circuit that receives the output E _a of the adder circuit, and 8 is the output of the integrator circuit.
This is a comparison circuit that receives E _b , compares it with a predetermined reference signal E _s , and generates an output signal E ₀ when the two match. 20 is an offset voltage automatic correction circuit which constitutes a characteristic part of the device of the present invention;
A buffer circuit 9 that receives the output E _b of the adder circuit 7, a comparison circuit 10 that determines whether the output signal of the buffer circuit 9 is positive or negative, a D latch circuit 11 that receives the output of the comparison circuit 10, and the D latch circuit. an oscillation circuit 14 that generates pulses for driving the counters 12 and 13; a phase delay circuit 15 that delays the phase of the output pulses of the oscillation circuit 14; The output signal of the delay circuit 15 and the two counters 12,
A NAND gate circuit 1 which has two inputs of signals at connection points 13 and provides a control signal to the D latch circuit 11.
6, and a current value determining circuit 17 connected between the output points of the counters 12 and 13 and the input point of the integrating circuit 7. Here, the counters 12 and 13 are each constituted by a 4-bit up-down counter, and perform up or down based on the positive or negative output of the comparator circuit 10, and one of them, for example 12, is the lower 4 bits. On the other hand, for example, 13 is responsible for the upper 4 bits. Also, counter 12; 13
Resistors R ₁ to R ₈ are connected to each bit of
This resistance has a value corresponding to a binary value (1, 2,
4 and 8), the weighting changes stepwise. Therefore, the voltage generated at each bit of the counter is converted into a current by these resistors, and the current that changes in a stepwise manner is applied to the current value determining circuit 17. In this case, it is assumed that the generated current is set so that each step width is equal and has a desired variation width. Furthermore, both of these counters 12 and 13 are configured so that their output states are fixed by the X-ray exposure start signal. In addition, the D latch circuit 11,
The phase delay circuit 15 and the NAND gate circuit 16 output "1" or "0" from the comparator circuit 10 when the clock signal rises and when a carry signal is output between the counters 12 and 13. If a signal of This is a circuit provided for this purpose.

Next, the operation of this device will be explained. First, when X-ray exposure is not being performed, the offset voltages of the circuits connected to the selected detection elements in the X-ray detector 3 are added by the adding circuit 3C, and the output is
It is input to the integrating circuit 7 as E _a (added offset voltage). The integrating circuit 7 outputs a signal E _b having a value obtained by adding the added offset voltage E _a of the adding circuit 3C and the offset voltage of the integrating circuit 7 itself. The signal E _b obtained by adding the two types of offset voltages in this manner is applied to the comparator circuit 10 via the buffer circuit 9 in the automatic offset voltage correction circuit 20 , and is It is determined whether the signal is positive or negative. The comparison circuit 1
The positive/negative discrimination signal output from 0 is the D latch circuit 1.
1 to the counters 12 and 13, but at this time, the D latch circuit operates to latch without transmitting the signal at the rise of the pulse of the oscillation circuit 14 and when the counters 12 and 13 perform a carry operation. , after which the signal is transmitted after a predetermined time delay, thereby stabilizing the operation of the counter. The output of the D-latch circuit 11 causes the counters 12 and 13 to operate, and a current that changes stepwise according to the operating state of the counters 12 and 13 is outputted and applied to the current value determining circuit 17. Current value determination circuit 1
At step 7, the stepwise changing current value is converted into a current value required in the circuit system and applied to the input terminal of the integrating circuit 7. This current value determining circuit 1
The offset voltage of the integrating circuit 7 approaches zero volts in a stepwise manner due to the current flowing from the integrating circuit 7, and finally oscillates around zero volts with a predetermined voltage value amplitude. This voltage amplitude is determined by the values of the resistors R ₁ to _{R 8} provided in the counters 12 and 13 and the value setting of the current value determining circuit 17. In this way, just before X-rays are irradiated (before the X-ray exposure switch is pressed), the offset voltage of the integrating circuit 7 is in a state where it oscillates at a predetermined voltage value amplitude around zero volts. Become. This oscillating voltage value can be set in advance to a value that does not affect the operation of the circuit system.

Next, when the X-ray exposure start signal is input (the X-ray exposure switch is pressed), the counter 1
The operations of 2 and 13 are stopped, their output states are fixed, and a constant current flows into the input terminal of the integrating circuit 17 via the current value determining circuit 17 while X-ray exposure is performed. . As a result, integrating circuit 1
7, the output E _b is generated by subtracting the offset voltage from the normal integral value, and the influence of the offset voltage is eliminated. Therefore, it is possible to prevent adverse effects caused by changes in the offset voltage of the circuit system due to differences in the combination state of a plurality of detection elements in the X-ray detection circuit 3 or changes in the offset voltage due to aging, and to always maintain a constant voltage. Desired X-ray exposure becomes possible. Furthermore, when the X-ray exposure switch is turned off at the end of the operation as described above, the output fixed state of the counters 12 and 13 is released in the same way, and the offset voltage automatic adjustment circuit operates again, so that the offset voltage is automatically adjusted. Needless to say, the radiation level is adjusted to zero in order to prepare for the next X-ray exposure.

The above-mentioned automatic offset voltage correction circuit is not limited to the above-mentioned embodiment, and may be configured such that the number of counters is increased to further improve the correction accuracy. Further, the configuration is not necessarily limited to digital processing, and may be configured to process analog signals.

The device of the present invention described in detail above is provided with a correction circuit that automatically corrects to zero a change in the offset voltage of the integrating circuit based on a change in the number of selected combinations of detection elements, so only one integrating circuit is required. Furthermore, even if the offset voltage changes drastically over time, the responsiveness is good, so the offset voltage can be corrected very accurately. Therefore, an automatic X-ray exposure control device can be obtained that can be made smaller and less expensive.

[Brief explanation of drawings]

Figure 1 is a block diagram to explain the outline of the X-ray diagnostic system, and Figure 2 is the X-ray diagnostic system used in it.
FIG. 3 is a block diagram showing an example of the configuration of the automatic X-ray exposure control circuit section. FIG. 3 is a block diagram showing an embodiment of the automatic X-ray exposure control apparatus of the present invention. 3...X-ray detector, 3a to 3n...detection element,
3A...I/V converter group, 3B...Switch group,
3C...addition circuit, 4...X-ray automatic exposure control circuit section, 7...integration circuit, 8...comparison circuit, 9...buffer circuit, 10...comparison circuit, 11...D latch circuit, 12, 13... Counter, 14... Oscillation circuit, 15... Phase delay circuit, 16... NAND gate circuit, 17... Current value determining circuit, 20...
Offset voltage automatic correction circuit.

Claims (1)

[Claims] 1 X that detects X-rays obtained by passing through the subject
ray detection means, an integration circuit that integrates an electrical signal obtained based on the X-ray detection means, and a comparison circuit that compares an output signal of the integration circuit with a predetermined reference signal, the comparison circuit The X-ray automatic exposure control device that stops X-ray exposure based on the output signal of the integrating circuit includes a discrimination circuit that discriminates whether the offset voltage of the integrating circuit is positive or negative, and a discrimination circuit that discriminates whether the offset voltage of the integrating circuit is positive or negative, and A counter that increases or decreases the output signal, an oscillation circuit that generates a pulse for driving the counter, and a correction signal determining circuit that receives the output signal of the counter and provides a correction signal to the integrator, An X-ray automatic exposure control device, characterized in that the offset voltage is automatically subtracted from the output signal of the integrating circuit when performing radiation exposure.