JP2737203B2 - X-ray automatic exposure control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the field of X-rays, and relates to an automatic X-ray exposure control device for automatically controlling a film density during X-ray photography to an appropriate value. .

(Prior art)

The X-ray automatic exposure control device includes a detector for detecting transmitted X-ray intensity, an integrator for integrating an output signal of the detector, and a reference signal for defining an output of the integrator and a film density to an appropriate value. And a controller including a comparator that outputs an X-ray cutoff signal and shuts off X-ray exposure, and is usually combined with an X-ray fluoroscope.
Detects part of the output light of an image intensifier (hereinafter referred to as an image tube) that converts a line image into a visible image, and when photographing, the density of the film placed on the input side of the image tube becomes an appropriate value Control.

FIG. 3 is a block diagram showing a schematic configuration of an X-ray fluoroscopic apparatus (X-ray television apparatus) provided with an X-ray automatic exposure control apparatus.

In the drawing, an X-ray generated from an X-ray tube (1) is irradiated with a subject (3) with an irradiation field regulated by an aperture (2).

The transmitted X-rays of the subject (3) are converted into a brightness-multiplied visible image by an image tube (12), and the output image is converted into a video signal by a TV camera (imaging tube) (14), and the TV monitor An X-ray fluoroscopic image is displayed at (15).

A snap-shot unit for storing film during X-ray photography (6)
Is inserted between the subject (3) and the input surface of the image tube (12) as shown.

The quick copy section (6) includes intensifying screens (7) and (9) disposed before and after the film (8), and the intensifying screen (7).
(9) A crimping mechanism (10) for holding and crimping between the two, a lead thin plate (11) for removing backscattered radiation, and the above-mentioned fluoroscopy section (6) during fluoroscopy are moved in the direction of the arrow to form an image tube (12). It comprises a moving mechanism (not shown) for removing from the front of the input surface.

In the state shown in the figure, the X-rays from the X-ray tube (1) pass through the rapid imaging section (6) containing the subject (3) and the film (8), and the transmitted X-rays are transmitted to the image tube (12) behind the X-ray tube. And is converted into a variable image.

Part of the output light of the image tube (12) is collected by the prism (13), converted into an electric signal by a detector (photomultiplier tube) (16), and the output is integrated by an integrator (17). The output is compared by a comparator (18) having one input as a reference value for adjusting the film density to an appropriate value. When the integrated value reaches the reference value, the X-ray high voltage device (19) sends the X-ray to the X-ray high voltage device (19). A cutoff signal is issued, X-rays are cut off, and the X-ray exposure time is controlled so that the film density becomes an appropriate value.

In general, the detector (16) also serves as a detector for automatically adjusting the luminance of transmitted X-rays displayed on the TV monitor (15) during fluoroscopy. (4) in the figure is a top plate,
(5) is a grid for removing scattered radiation.

[Problems to be solved by the invention]

Since the X-ray automatic exposure device described above detects the transmitted X-ray dose of the film and controls the X-ray exposure, it seems that an appropriate value of the film density is always obtained. However, the following problems occur. is there.

The reason that the film (8) is exposed during X-ray photography is mainly due to the light emission of the phosphor used for the front and rear intensifying screen sandwiching the film.

Phosphors generally have a so-called tube voltage dependency in which light emission characteristics vary depending on the tube voltage. Therefore, in the X-ray automatic exposure control apparatus shown in FIG. 3, even if the film density can be exposed to an appropriate value at a certain tube voltage, if the tube voltage changes, an appropriate film density cannot be obtained. Becomes particularly dark.

This disadvantageous tendency of the tube voltage dependency becomes greater in the case of an automatic exposure control device of the type detecting the output light of the image tube as shown in FIG.

That is, as described above, the light that is exposed to the film is the light emitted from the phosphor of the intensifying screen, and the light that is detected by the photomultiplier tube (12) is the pressure bonding mechanism (10) behind the film, )
The output light of the image tube (12) transmitted through the image tube and the fluorescent characteristics of the input fluorescent screen of the image tube. However, even if the X-ray exposure time is controlled so that the output light amount of the image tube is constant, the film density greatly varies depending on the tube voltage.

Therefore, an X-ray automatic exposure control device in which one reference value of the comparator is changed according to the tube voltage as shown in FIG. 4 so that an appropriate film density can be obtained irrespective of the change in the tube voltage. Proposed.

In FIG. 4, (16) is a photomultiplier tube, (17) is an integrator, (18) is a comparator, and the output of the integrator (17) is connected to one input terminal and the other input terminal is connected to the tube. For example, the output of a reference voltage generating circuit (20) for generating a reference voltage having the characteristics shown in FIG. 5 according to the voltage signal is input.

The setting signal generation circuit (20) stores a potentiometer having a slider that moves in conjunction with a tube voltage setting device (not shown) and a tube voltage-setting voltage characteristic shown in FIG.
A memory addressed by a tube voltage signal. The integrator (17) is an operational amplifier (OP), integrating capacitor C, integrating resistor
R and a reset switch S.

However, in the device of FIG. 4, when the tube voltage is low,
There is a problem that the reference voltage of the comparator (18) becomes very low, and the operation of the X-ray automatic exposure control device becomes unstable.

In view of the above, it is an object of the present invention to provide an X-ray automatic exposure control device that operates stably without changing a reference value for defining a film density regardless of a change in a tube voltage.

[Means for solving the problem]

The present invention is configured as follows to achieve the above object.

That is, the present invention detects the X-ray dose transmitted through the film,
In an X-ray automatic exposure control device which shuts off X-ray exposure when it reaches a reference value, an integrated resistance of an integrator for detecting a transmitted X-ray amount through the light receiving element of a photocoupler comprising a light emitting element and a light receiving element. And the light emission intensity of the light emitting element is controlled according to the tube voltage.

[Action]

According to the present invention, the light emission intensity of the light emitting element of the photocoupler changes according to the tube voltage.

As a result, the resistance of the light receiving element acting as the integration resistance changes, and the time constant of the integrator changes according to the tube voltage. Therefore, the reference voltage may be maintained at a constant value that can ensure stable operation, and the operation of the X-ray automatic exposure control device does not become unstable.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG.
It is a figure for operation | movement description of a figure.

In FIG. 1, (P) is a photocoupler composed of a light emitting diode LED (light emitting element) and a CdS cell (light receiving element).
The resistance value of the dS cell changes according to the light emission intensity of the LED, that is, the current value of the LED.

The CdS cell is connected to the position of the integrating resistor R in FIG. 4, the LED is connected to the photocoupler current control circuits P and C, and the photocoupler current control circuit pC controls the supply current of the LED according to the tube voltage signal. .

In the drawing, the same parts as those in FIG. 4 are denoted by the same reference numerals. Next, the operation of the above circuit will be described.

The photomultiplier tube (16) is an image tube (1
It is placed behind the output light of (2) or behind the film (8) sandwiched between intensifying screens (7) and (9), and detects X-rays transmitted through the film.

When X-ray photography is started, the photocurrent from the photomultiplier tube (16) is passed through the CdS cell of the photocoupler P to the integrator (1).
7) The integration capacitor C is charged.

This voltage is compared with the reference voltage by the comparator (18), and when it reaches the reference voltage, an X-ray cutoff signal is issued, and X-ray irradiation is cut off.

The current value supplied to the LED of the photocoupler P is controlled by the photocoupler current control circuit pc according to the tube voltage value.
For example, when the tube voltage is low, the resistance of the CdS cell is reduced by controlling the supply current of the LED to be large, and the time constant of the integration capacitor C is reduced by reducing the time constant of the integration circuit (17). It is corrected to be shorter.

As a result, as shown in FIG. 2, as the tube voltage becomes lower, the time required for the integrated voltage to reach the reference voltage becomes earlier, so that the correction is made so that the X-ray is cut off earlier.

It should be noted that the reference voltage for specifying the film density supplied to one input terminal of the comparator (18) is set to a predetermined voltage at which the automatic exposure control is stably performed.

〔effect〕

According to the present invention, since the reference value that defines the film density as an appropriate value does not change, stable X-ray automatic exposure control can be performed regardless of changes in the tube voltage.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of the present invention. FIG. 2 is a diagram for explaining the operation. FIG. 3 is a block diagram showing a schematic configuration of an X-ray fluoroscopic apparatus having an X-ray automatic exposure control device. FIG. 4 is a circuit diagram showing a configuration of a conventional device, and FIG. 5 is a characteristic diagram for explanation of FIG. 16: photomultiplier tube (detector), 17: integrator (op) ... operational amplifier, C ... integrating capacitor, R ... integrating resistor, S ... reset switch 18: comparator, P: photocoupler (LED …… Light-emitting diode (light-emitting element), CdS …… CdS cell (light-receiving element), PC …… Photocoupler current control circuit.

Claims (1)

(57) [Claims] 1. A detector for detecting the intensity of transmitted X-rays of a film, an integrator for integrating an output signal of the detector, an output signal of the integrator is compared with a reference value, and an X-ray cutoff signal is output. And a photocoupler comprising a light-emitting element and a light-receiving element whose resistance varies according to the light-emitting intensity of the light-emitting element, and the light-emitting intensity of the light-emitting element is set to a tube voltage. An X-ray automatic exposure control device, wherein a control circuit for controlling the exposure is provided, and the light receiving element is an integral resistor of the integrator.