JPH02204999A - X-ray automatic exposure control device - Google Patents

Abstract

PURPOSE:To keep constant the reference value for specifying the film concentration regardless of varying tube voltage by using a photo-receiving element to constitute a photo-coupler as an integral resistance of an integrating device to sense the does of penetrative X-rays, and by controlling the intensity in light emission from photo-emitting element in accordance with the tube voltage. CONSTITUTION:The resistance value of a CdS cell of a photo-coupler P consisting of a CdS cell (photo-receiving element) and a light emitting diode LED (photo-emitting element) varies in compliance with the intensity in light emission from the LED, i.e. the current value of LED. The LED is connected with a photo-coupler current control circuit P.C. which controls the supply current to the LED in conformity to the tube voltage signal. Consequently a lower tube voltage provides an earlier time for attaining the reference voltage by the integral voltage to result in a correction so that the X-rays are shut earlier. The reference voltage to specify the film concentration supplied to one of the input ports of a comparator 18 is set to a certain voltage which ensures stable performance of automatic exposure control.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is used in the field of X-rays and relates to an automatic X-ray exposure control device for automatically controlling film density to an appropriate value during X-ray photography. .

[Prior art]

The automatic X-ray exposure control device includes a detector that detects the intensity of transmitted X-rays, an integrator that integrates the output signal of this detector, and the output of this integrator and film density? Comprising a comparator and a controller that compares the reference signal with a predetermined appropriate value, outputs the XIIAR@ signal, and shuts off the X-ray injection b2. and usually X
Combined with a radiographic imaging device, the detector detects a part of the output light of an image intensifier (hereinafter referred to as an image tube) that converts the transmitted XG image of the subject into a visible image, and The density of the film placed on the input side of the image tube is controlled to a proper value.

FIG. 3 is a block diagram showing the entire schematic configuration of an X-ray fluoroscopic imaging device (X-ray television screen device) equipped with an automatic X-ray exposure control device.

In the figure, the irradiation field of the Fj X-rays generated from the X#I tube (1) is regulated by the aperture (2), and is irradiated to the subject (3).

The transmitted Xtm of the object (3) is converted into a visible image with brightness multiplied by the image tube (b), and the output image is transmitted to the TV camera (
(image pickup tube) is converted into a video signal by α4 and sent to a TV monitor (g)
An X-ray fluoroscopic image is displayed.

X! I Snapshot section (6) that accommodates all the film when taking photos
is inserted between the subject (3) and the input surface of the image tube as shown.

The snapshot section (6) has intensifying screens (7) (9) arranged before and after the film (8), and a film (8)? Intensifying screen <7)
(9) Pressure 1 to be clamped and crimped between the mechanism QG and the thin lead plate α1 for removing backscattered radiation The mobile device FIt (not shown) is configured to be removed from the front side.

In the illustrated state, the X-rays from the X-ray tube (1) are aimed at the subject (3).

Film (8)? The photographing unit (6) that accommodates the image is completely transmitted, and this transmitted image X#I enters the image tube 03VC behind it and is converted into a variable image.

A part of the output light from the image tube @ is illuminated on the prism side,
The detector (photomultiplier tube) is converted into an electrical signal by the Q, the output is integrated by the integrator Oη, and the output is transferred to the film f.
Ik degree t - is compared by a comparator Q8 whose one input is a friend reference value for making the appropriate value, and when the integral value reaches the reference value,
An X-ray cutoff signal is sent to the X% high-voltage device 09 to cut off X1s and control the X-ray exposure time so that the film density becomes an appropriate value.

Generally, the detector M is the TV monitor (to) during fluoroscopy.
It also serves as a companion detector that automatically adjusts the brightness of transmitted X-rays displayed on the screen. Further, in the figure, (4) is a top plate, and (5) is a grid for removing scattered radiation.

[Problem to be solved by the invention]

The above-mentioned X-ray automatic exposure @ is the X-ray flk transmitted through the film.
Since the X-ray exposure is controlled by detecting the X-rays, it seems that the appropriate film density can always be obtained, but there are the following problems.

During X-ray photography, the film (3) is mainly exposed to light.
This was due to the discovery of the phosphor used in the intensifying screen after the a that holds the l.

Fluorescent materials generally have so-called tube voltage dependence, in which the emission characteristics differ depending on the tube voltage. Therefore, with the X-ray auto@exposure control device shown in Figure 3, even if the film density can be exposed to the full appropriate value at a certain tube voltage, if the tube voltage changes, the film density cannot be obtained at the appropriate value, and the tube tail pressure is low. The film density becomes special KM.

This disadvantageous tendency of tube voltage dependence becomes more pronounced in the case of an automatic exposure control device of the type that detects the output light of the image tube as shown in FIG.

That is, as mentioned above, the source of the film being exposed to light is the detection of the phosphor in the intensifying screen, and the source of detection by the photomultiplier tube (6) is the crimping mechanism (IG, thin lead plate C[] )
This is the output light of the image tube (A) that passes through the image tube (a), and together with the firefly source characteristics of the input firefly surface of the image tube, the X-ray tube voltage, that is, the quality of the The remaining power of the image tube varies, and even if the X-ray exposure time is controlled so that the output +i of the image tube is constant, the film density varies greatly depending on the tube voltage.

Therefore, the reference value of one of the comparators is changed according to the tube voltage as shown in FIG.
Automatic exposure control vi: is proposed.

In FIG. 4, αl19 is a charged premultiplier tube, a'? ) is an integrator, (G) is a comparator, and one input terminal has the output of the integrator ση, and the other input terminal has a reference voltage that generates a reference voltage having the characteristics shown in FIG. 5 by means of a tube voltage signal. The output of the generating circuit (1) is input.

The setting signal generating circuit (1) is a potentiometer with a slider kW that moves in conjunction with a tube voltage setting device (not shown);
Also, the tube voltage-setting voltage characteristics shown in Figure 5? A memory that stores and is addressed by the tube voltage signal. Also, integrator Q7
) is composed of an operational amplifier (op), an integrating capacitor C1, an integrating resistor R, and a reset switch S.

However, the device shown in Figure @4 has a problem in that when the tube voltage is low, the reference voltage of the comparator (G) becomes very low, making the operation of the automatic X-ray exposure control device unstable.

In view of the above, it is an object of the present invention to provide an X-ray automatic exposure control system which does not change the reference value that defines the total film density regardless of changes in tube voltage, and whose operation is stable.

[Defined means to solve problems]

Is this invention intended for the above purpose? To achieve this, it is structured as follows.

That is, this invention detects film transmission XMfi,
In an automatic exposure control device that cuts off X-ray exposure when the amount of radiation reaches a reference value, an integrating resistor of an integrator that detects the amount of X-rays transmitted through the light-receiving element of a photocoupler consisting of a light-emitting element and a light-receiving element is used. In addition, the light emitting intensity of the light emitting element is controlled according to the brass voltage.

[For production]

According to this invention, the light emission intensity of the light emitting element of the photocoupler changes depending on the tube voltage.

The resistance of the light-receiving element, which acts as a collective integral resistance, changes, and the time constant of the integrator changes in accordance with the tube voltage. Therefore, since the reference voltage need only be kept at a constant value that ensures stable operation, the operation of the automatic X-ray exposure control device will not become unstable.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of FIG. 1.

In Fig. 1, (P) is a photocoupler consisting of a source diode IJD (light emitting element) and a CdS SE/L/ (light receiving element). Change.

The CdS cell is connected to the position of the integral resistor R in Fig. 4, and the LED is connected to the photocoupler current control circuit P and CK, and the photocoupler current control circuits P and C control the supply current of the LED according to the tube voltage signal. Control.

Note that the same parts in the figure as in FIG. 4 are given the same reference numerals. Next, the operation of the above circuit will be explained.

As shown in Figure 1, the photomultiplier tube QQ is placed at the lighting position of the output source of the image tube (2) or behind the film (8) held between the intensifying screens (7) and (9). Detects X-rays.

When X-ray photography starts, the original current from the photomultiplier tube 0Q is CdS C/L/? of the photocoupler P. Through this, the integrating capacitor C of the integrator (b) is charged.

This voltage is compared with a reference voltage by a comparator (g), and when it reaches the reference voltage, an X@ cutoff signal is issued at a fixed time, and the Xls exposure is cut off.

The current value supplied to the LED of the photocoupler P is controlled according to the tube voltage value by photocoupler current control circuits p and c. For example, if the tube voltage is low, use LBD! [By controlling the current to increase, the resistance value of the CdS cell becomes small, and the time constant of the integrating circuit a force becomes small, so that the charging time of the integrating capacitor C is corrected to be shortened.

As a result, as shown in FIG. 2, when the tube voltage is low, the time for the integrated voltage to reach the reference voltage becomes faster, so the correction is made so that the X-rays are cut off sooner.

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

〔effect〕

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

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention; FIG. 2 is a diagram for explaining the operation; FIG. 3 is a block diagram showing the schematic configuration of an X-ray fluoroscopic imaging device equipped with an automatic X-ray exposure control device; FIG. 4 is a circuit diagram showing the configuration of a conventional device, and FIG. 5 is an explanatory characteristic diagram of FIG. 4. 16: Photomultiplier tube (detector L17: Integrator (Op...
・Operational amplifier, C...integrating capacitor, R...integrating resistor, S...reset switch) 18: Comparator, P:
Photocoupler (LED... Source diode (light emitting element)
. Cd8...Cd8/I/(light receiving element J), P
C---Photocoupler current control circuit. Patent applicant: Shimadzu Corporation EI:'
Illusion

Claims (1)

[Claims] (1) Comparison of a detector that detects the intensity of X-rays transmitted through the film, an integrator that integrates the output signal of the detector, and a comparison that compares the output signal of this integrator with a reference value and outputs an X-ray cutoff signal. In an automatic X-ray exposure control device, a photocoupler consisting of a light-emitting element and a light-receiving element whose resistance value changes according to the emission intensity of the light-emitting element is provided, and the emission intensity of the light-emitting element is adjusted according to the tube voltage. 1. An X-ray automatic exposure control device, characterized in that a control circuit is provided for controlling the exposure, and the light receiving element is used as an integrating resistor of the integrator.