JPS61208797A - X-ray device - Google Patents

Abstract

PURPOSE:To produce stable pulse X-rays and greatly improve the rate of dose reduction by storing the heating voltage at the end of the preceding exposure as a predetermined voltage level and applying a voltage of the predetermined level to a filament as soon as exposure is completed to preliminary heat the filament. CONSTITUTION:The heating voltage at the end of X-ray exposure is maintained over the period of nonexposure by using a heating voltage detection resistance 6 to detect heating voltage during X-ray exposure and by charging a capacitor 10 through a relay contact 12. After X-ray exposure is completed, a relay 9a is switched to close the circuit and even during the period of nonexposure filament-heating voltage is maintained at the same level as the voltage of the capacitor 10 at the end of X-ray exposure. Due to the above structure, there is no possibility that the heating level increases to the maximum during the period of nonexposure. Therefore, stable X-rays can be produced and the rate of dose reduction can be greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a heating circuit for an X-ray tube, and more particularly to an XSI device in which the preheating level can be optimally automatically controlled.

[Technical background of the invention and its problems] In an X-ray device, the X-ray weight and radiation quality vary depending on the tube current and tube voltage. In X-ray photography and fluoroscopy, in order to obtain good images, it is necessary to set appropriate tube current and tube voltage values according to the body thickness of the subject and the region to be diagnosed. The tube voltage value of an X-ray tube is determined by the voltage value applied between the anode and cathode of the X-ray tube, and the tube current value is approximately determined by the temperature of the filament of the X-ray tube. The filament temperature is determined by the filament voltage.

By the way, even if the tube current of an X-ray tube is set to have a constant heating amount, the load current tends to decrease over time. This occurs due to the combination of gas generated within the X-ray tube and thermoelectrons generated from the filament, and is a well-known fact as published in literature.

Therefore, XI! In a system in which the heating circuit of the apparatus (i.e., the circuit that controls the voltage applied to the filament of the X-ray tube) maintains a constant voltage and current, the tendency for the tube current to decrease over time is unavoidable.

In X-ray photography, the exposure time for X-rays is usually short, less than 1 second, and the effect is slight, so it is not a problem.
X1! In the case of fluoroscopy, since it is used for a long time, it is necessary to correct changes in the load current using a regulator as needed.

Therefore, in devices that mainly perform fluoroscopy, such as surgical Xm devices, the load current (secondary current), which is the tube current, is used as a feedback signal for the heating circuit, and the comparison between this and the tube current set value is performed. The method used is to change the heating level according to the load current by changing the filament voltage, thereby keeping the load current (tube current) constant. The circuit that achieves this is called a secondary current feedback type heating circuit.

On the other hand, in recent years, with the development of image storage devices, devices aimed at temporarily storing images, reducing noise by adding reproduced images, etc. have appeared and are put into practical use.

This device has various functions, and is capable of storing images at any timing during fluoroscopy, or storing final images and reproducing them.

There is also an X-ray apparatus that uses this image storage device to perform pulse fluoroscopy for the purpose of reducing dose.

This is a method that irradiates X-rays in pulses to obtain an X-ray image, stores the image, and replays and displays this stored image during the period when X-ray exposure is paused. The shorter the pulse width, the higher the dose reduction rate, so this is an effective method, especially for observing objects with little movement, since it can reduce the exposure dose without degrading the image quality.

By the way, when performing pulse fluoroscopy, the image reading time of the image storage device is about 100m5 (time required for several frames), so the X-ray exposure time should only be for this period, but in reality The required X-ray exposure time is the time taken for the X-rays to rise and stabilize, as well as the time taken into account the rise time and afterimage time of the imaging tube. Therefore, the shorter this time, the better the dose reduction rate.

Therefore, in order to accelerate the rise time of X-rays, in the case of ordinary X-ray equipment, a current considerably lower than that in the steady state is passed through the filament of the X-ray tube during the X-ray exposure pause period to preheat the filament. XI when entering clairvoyance! A method is adopted in which the filament current is raised to the steady level required for fluoroscopy at the same time as the exposure begins. However, even in this method, the rise time of X-rays requires several hundred ms.

Therefore, in order to further speed up the rise time of X-rays, it is best to always keep the heating in a steady state when selecting the pulse fluoroscopy mode, but by feeding back the secondary current and adjusting the tube current setting value. In the secondary current feedback type heating circuit as described above, which maintains the tube current at a constant (set value) based on comparison with the The heating level will rise to the highest level as if it were not there. Therefore, in this state
When radiation exposure is started, a dose overshoot occurs at the initial stage of X-ray exposure.

Since the electrons accumulated in the image pickup tube during this overshoot period remain as an afterimage, a completely stable state is not achieved until the influence of this afterimage disappears. The time it takes for the X-rays to reach this completely stable state is several hundred milliseconds after the X-rays stabilize.
Therefore, in order to cover this,
It becomes necessary to lengthen the radiation exposure time, and the dose reduction rate during pulsed fluoroscopy deteriorates accordingly. Therefore, the advantage of pulsed fluoroscopy, which is the reduction in exposure dose, is not fully demonstrated.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide an X-ray apparatus using a secondary current feedback type heating circuit, in which pulsed It is an object of the present invention to provide an X-ray apparatus that can shorten the exposure time and thereby sufficiently reduce the dose rate.

[Summary of the Invention] In other words, in order to achieve the above object, the present invention has a pulse fluoroscopy mode in which X-rays are emitted in a pulsed manner, and
In addition, in an X-ray apparatus having a secondary current feedback heating circuit that controls the filament heating voltage of the X-ray tube so that the load current reaches a set value by referring to the load current of the X-ray tube, A memory means for storing the filament voltage of a switching means for supplying the set value at the time of irradiation;
The pre-heating level of the filament during pulsed fluoroscopy, in which X-rays are irradiated in pulses, is determined by storing the heating voltage of the X-ray tube filament at the previous end, and setting this to the set voltage of the heating circuit at the same time as the end of X-ray pulse irradiation. The preheating level is stabilized by using this as a reference for preheating.
It is characterized by suppressing the occurrence of overshoot at the time of the next Xla@ shot.

[Embodiments of the invention] An embodiment of the present invention will be described below.

The present invention detects the heating level during Xfa@ irradiation from the heating voltage or current when the pulse fluoroscopy mode is selected, and maintains the heating state at the same level during the X-ray irradiation pause period. This method prevents a decrease in secondary current and also prevents overshoot at the rise of pulsed X-rays.

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings.

The figure is a circuit diagram showing the configuration of this apparatus, and in the figure 1 is an X-ray tube, here a dipole X-ray tube is shown. 1a is the anode of this X-ray tube 1, and 1b is a filament which becomes the cathode of this X-ray tube 1.

A high voltage transformer 2 generates a tube voltage to be applied between the @ pole and cathode of the X-ray tube 1. 3 is a filament heating transformer; 3a is a primary winding of the filament heating transformer 3;
b is a secondary winding of the filament heating transformer 3; 4 is a secondary current detection circuit which extracts current from the secondary winding of the high voltage transformer 2 to obtain a load current value. Reference numeral 5 denotes a heating switching transistor, which is an inverter switch that switches the direction of the current applied to the primary winding 3a of the filament heating transformer 3. Due to this switching of the transistor 5, a secondary output corresponding to the switching frequency and time width is generated from the secondary winding 3b of the filament heating transformer 3 and is applied to the filament. A heating voltage detection resistor 6 divides and extracts the voltage applied to the primary winding 3a of the filament heating transformer 3. Further, 7 is a transistor for the filament heating voltage IIJtll, and the layer 8! The voltage from E is controlled and applied to the primary winding 3a of the filament heating transformer 3. 8 is a differential amplifier,
9a and 9b are first and second contacts of a relay that operates when X-rays are irradiated; 10 is a capacitor that stores the heating voltage; 11
12 is a tube current setting device for setting a tube current value, and 12 is a relay contact for detecting heating voltage, which is turned on when X-rays are irradiated.

The capacitor 10 receives a divided voltage of the voltage applied to the primary winding 3a of the filament heating transformer 3 extracted by the heating voltage detecting resistor 6 via the heating voltage detecting relay contact 12, and charges the capacitor 10. Further, the differential amplifier 8 has the first contact 9a at its one input terminal during XI exposure.
The secondary winding current value of the high voltage transformer 2 extracted by the secondary current detection circuit 4 is inputted as a voltage signal through the secondary current detection circuit 4, and the tube current setting value is inputted to the input side through the second contact 9b. The tube current setting value of the device 11 is inputted, and a difference output between the two is generated. Further, when the X-ray exposure is stopped, the differential amplifier 8 connects the primary winding 3a of the filament top heating transformer 3 which is extracted by the heating voltage detection resistor 6 via the first contact 9a to one input terminal of the differential amplifier 8. A divided voltage of the applied voltage is inputted, and a charging voltage of the capacitor 10 is inputted to the input side through the second contact 9b, and a difference output between the two is generated. The output of the differential amplifier 8 is applied to the base of a transistor 7 for controlling the filament heating voltage.

In such a configuration, when an X-ray exposure command is generated, the relay contacts 9a and 9b are activated, and the set voltage of the tube current setting device 11 is applied to the positive side of the operational amplifier 8 as the tube current set value. At the same time, a voltage corresponding to the load current is input from the secondary current detection circuit 4 to one input terminal of the operational amplifier 8 as a load current detection output. When a difference occurs between the setting side voltage and the load voltage, the output of the operational amplifier 8 corresponds to the difference. Therefore, the transistor 7, which uses the output of the operational amplifier 8 as its base current, converts the output of the power supply E into the corresponding one. The voltage is controlled to a value corresponding to the base current and sent to the primary winding side of the filament heating transformer 2.

Therefore, the filament voltage from the secondary winding 3b of the filament heating transformer 3 is corrected according to the load current value by the amount required to compensate for the difference from the set value. As a result, the temperature of the filament is adjusted by the voltage corrected, and the amount of thermoelectrons emitted from the filament is adjusted accordingly. As a result, the tube current value is controlled to be constant.

Further, the heating voltage during X-ray irradiation is detected by the heating voltage detection resistor 6, but this detection voltage is applied to the capacitor 10 via the relay contact 12, which is closed during the X-ray irradiation. It will be charged. and relay contact 12
is turned off at the end of the X-ray exposure, so the voltage of the capacitor 10 maintains the heating voltage at the end of the exposure.

When the X-ray exposure is completed, the relay 9a is switched to the normally closed state, so the voltage of the capacitor 10 is input to the input side of the differential amplifier 8.

At this time, since the filament heating voltage is input from the heating voltage detection resistor 6 to one input terminal of the operational amplifier 8, the operational amplifier 8 generates an output corresponding to the difference between the two and supplies it to the transistor 7. The transistor 7 adjusts the output of the power supply E to a voltage according to this difference output and applies it to the primary side of the filament heating transformer 3. The heating voltage of the filament will be controlled to maintain the same voltage as that of 10.

In this way, in the secondary current feedback type heating circuit, xi
The secondary current at the time of irradiation is memorized, and the filament voltage is adjusted to the voltage corresponding to this memorized value during the X-ray pause period, so it does not work like a conventional secondary current feedback type heating circuit. Since there is no load current during the X-ray exposure pause period, it becomes the same as when no heating is being performed, and the inconvenience that the heating level rises to the highest level is eliminated.
Therefore, the situation of overshooting the dose at the beginning of X1m radiation is eliminated, and the time required for the Ii image tube to stabilize is several hundred milliseconds until it reaches a completely stable state.
The X-ray exposure time can be shortened, and the dose reduction rate during pulsed fluoroscopy can be improved accordingly. Therefore, it becomes possible to fully utilize the effect of reducing exposure dose, which is an advantage of pulse fluoroscopy.

Incidentally, the present invention is not limited to the embodiments described above and shown in the drawings, and can of course be practiced with appropriate modifications within the scope of the gist thereof.
By dividing the zero voltage and adjusting the partial voltage value, it is possible to arbitrarily determine the heating voltage level of the filament during rest.

In other words, in order to make the imaging tube start up faster, the preheating level of the filament is raised above the steady state, and a dose overshoot is generated for a short period of time to suddenly give a certain amount of radiation. Therefore, it can be applied to such uses.

[Effects of the Invention] As detailed above, according to the present invention, in an X-ray apparatus using a secondary current feedback type heating circuit, stable pulse
It is possible to provide an X-ray device that can generate rays and has features such as a significantly improved dose reduction rate.

[Brief explanation of drawings]

The figure is a circuit diagram showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... X-ray tube, 1a... Anode, 1b... Filament (Is pole), 2... High voltage transformer, 3... Filament heating transformer, 3a... Filament heating transformer 3 Primary winding, 3b... Secondary winding of filament heating transformer 3, 4... Secondary current detection circuit,
5... Transistor for heating switching, 6...
bo Resistor for thermal voltage detection, 7... Transistor for filament heating voltage control, 8... Differential amplifier, 9a, 9
b... First and second contacts of relay, 10... Capacitor for storing heating voltage, 11... Tube current setting device, 1
2... Relay contact for heating voltage detection, E... Power supply.

Claims (1)

[Claims] A secondary current has a pulse fluoroscopy mode in which X-rays are emitted in a pulsed manner, and also controls the filament heating voltage of the X-ray tube by referring to the load current of the X-ray tube so that the load current becomes a set value. In an X-ray apparatus having a feedback heating circuit, there is provided a storage means for storing a filament voltage during X-ray irradiation, and a value stored in this storage means is replaced with the set value when X-ray irradiation is stopped in a pulse fluoroscopy mode. an X-ray apparatus comprising switching means for supplying the set value and supplying the set value at the time of X-ray irradiation.