JPH05329144A - X-ray ct system - Google Patents

Abstract

PURPOSE:To avoid mixing of noises from a switching electric source into an X-ray detector during taking a picture of X-ray image. CONSTITUTION:A condenser 26 is provided between an Xe gas detector 12 and the output of an electric source circuit consisting of a commerical electric source 20, the first rectification circuit 21 which rectifies the electric voltage of the alternative current and converts it to an electric voltage of a direct current, an inverter circuit 22 which switches the direct electric voltage by high-frequency to obtain a high-frequency alternative current with several hundreds to several KHz, a transformer 23 which elevates the voltage of the high- frequency alternative current and the second rectification circuit 24 which rectifies the output of the transformer 23 and obtains an electric voltage of a direct current. An electromagnetic relay 25 which separates the commercial electric source 20 from the first rectification circuit 21 based on an input of an X-ray exposure signal from an operation table 27, is provided. When an X-ray picture is taken, the Xe gas detector 12 is actuated by the electric discharge voltage of the condenser 26. As the electric source circuit and the Xe gas detector 12 are separated from each other, there is no possibility of mixing of noises therefrom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus for tomography of a subject, and more particularly to a power supply circuit for an X-ray detector for converting the intensity of transmitted X-rays of the subject into an electric signal. Regarding

[0002]

2. Description of the Related Art As an X-ray detector of this type, for example, Xe
There is a gas ionization chamber type detector (hereinafter, abbreviated as Xe gas detector). A large number of electrode plates such as tungsten that do not transmit X-rays are arranged in an arc shape so as to face the X-ray focal point, housed in a hermetically sealed aluminum container, and Xe gas is sealed in the container. The X-rays that have passed through the subject enter the Xe gas detector and ionize the internal Xe gas to generate positive and negative ion pairs. The generated ion pairs are attracted to the electrode plates having opposite polarities, and an ionizing current flows between the electrode plates. By measuring this, the intensity of the transmitted X-ray is detected as an electric signal.

FIG. 3 shows a schematic structure of a power supply circuit for applying a voltage to the electrode plate. In the figure, reference numeral 1 is a bias electrode as the electrode plate, 2 is a signal electrode metallized on both sides of an insulator, and outputs the signal due to the ionization current to the outside. DC voltage (about 300 to 1000 [V] to bias electrode 1
The power supply circuit for applying the bias voltage of 1) is as follows.

First, the input voltage from the commercial power supply 3 is rectified by the rectifier circuit 4 to obtain a DC voltage. This DC voltage is applied to the switching operation of the inverter circuit 5 by several hundreds to several KHz.
Is converted into high-frequency AC, and the voltage is boosted in addition to the transformer 6. Then, the output of the transformer 6 is converted into a DC voltage by the rectifier circuit 7 and given to the bias electrode 1. The operating frequency of the inverter circuit 5 is changed to control the energization period to the transformer 6 to obtain a required DC voltage (the above bias voltage of about 300 to 1000 [V]).

[0005]

However, the energization of the bias electrode 1 as described above is always performed during the photographing period, and is generated by the switching operation of the inverter circuit 5 and amplified by the transformer 6, for example. Pulsating wave (ripple)
Or noise of electromagnetic waves radiated from the transformer 6 is Xe
There is a problem in that the gas detector or the data acquisition unit that amplifies and digitizes the output signal from the detector enters the gas detector, disturbs the waveform of the detection signal, and consequently deteriorates the image quality of the reconstructed tomographic image. is there.

The present invention has been made in view of such circumstances, and an object thereof is to provide an X-ray CT apparatus which does not give noise from the power supply circuit to an X-ray detector or the like. There is.

[0007]

In order to achieve the above object, the present invention has the following constitution. That is, the present invention is an X-ray CT apparatus including an X-ray tube for X-ray irradiation and an X-ray detector that converts the intensity of transmitted X-rays into an electric signal, and supplies power to the X-ray detector. A charging element is provided between the power source section and the X-ray detector, and the power source section and the charging element are switched to a posture in which the charging element is disconnected based on the input of an X-ray exposure signal that causes the X-ray tube to operate X-ray irradiation. It is characterized in that a switching device that replaces it is provided.

[0008]

The function of the present invention is as follows. When the X-ray exposure signal is not input and the X-ray is not emitted from the X-ray tube, the switching unit connects the power supply unit and the charging element, and the charging element stores the electric power from the power supply unit. .. When an X-ray exposure signal is input to the switching device during X-ray photography, the switching device switches to a posture in which the power supply unit and the charging element are separated, the charging element starts discharging, and power is supplied to the X-ray detector. To supply. Thus, X
Since electric power is supplied to the X-ray detector from the charging element, not from the power supply unit during radiography, noise from the power supply unit does not affect the detection signal.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an X-ray CT apparatus (third generation X-ray CT apparatus) according to this embodiment. An X-ray tube 11 for X-ray irradiation, an X-ray detector 12 for converting a transmitted X-ray into an electric signal, and an X-ray detection on a ring-shaped rotary frame 10 having a center axis in the body axis direction of the subject M. A data collection unit 13 that amplifies the output signal of the container 12 and converts it into a digital signal is attached in a state of facing. An endless belt 16 is laid between the peripheral surface of the rotating frame 10 and a pulley 15 attached to the output shaft of the electric motor 14. The rotating frame 10 is rotated by the driving force of the electric motor 14, and the X-ray is directed from the X-ray tube 11 toward the subject M during the rotation.
A line is irradiated to obtain a tomographic image.

As the X-ray detector 12 of such a third generation X-ray CT apparatus, the Xe gas detector mentioned in the conventional example is used.
(Hereinafter, the X-ray detector 12 is referred to as a Xe gas detector 12) is used. As shown in the perspective view of FIG. 2, the Xe gas detector 12 is formed by metalizing the tungsten on both surfaces of a bias electrode 30 formed of a material such as tungsten that does not transmit X-rays and an insulator 31. The signal electrodes 32 are arranged facing each other in an arc shape so as to face the X-ray focal point, housed in a sealed aluminum container 33, and Xe gas is sealed in the sealed aluminum container 33.

The X-rays incident on the Xe gas detector 12 ionize the Xe gas between the bias electrode 30 and the signal electrode 32 to generate positive and negative ion pairs, and these ion pairs have opposite polarities. Ionizing current flows between the electrodes 30 and 32 by being attracted to the bias electrode 30 and the signal electrode 32. As shown in FIG. 1, this electrical signal is transmitted from the signal electrode 32 to the data collection unit.
It is given to 13 and sent to an image processing device (not shown). In order to attract the ion pairs to flow an ionizing current, it is necessary to apply a DC bias voltage to the bias electrode 30, and a power supply circuit for the bias electrode 30 will be described below.

Similar to the conventional power supply circuit, the commercial power supply 20, the first rectifier circuit 21 for rectifying the AC voltage of the commercial power supply 20 into the DC voltage, and the DC voltage is switched at a high frequency for several hundreds to several K.
The commercial power supply includes an inverter circuit 22 for obtaining a high frequency alternating current of Hz, a transformer 23 for boosting the output alternating current of the inverter circuit 22, and a second rectifying circuit 24 for rectifying the output of the transformer 23 to obtain a direct current voltage. An electromagnetic relay 25 for switching connection / disconnection between 20 and the first rectifier circuit 21 and a capacitor 26 for accumulating the output of the second rectifier circuit 24 and outputting it to the bias electrode 30 are newly added. There is.

The electromagnetic relay 25 is turned on and off by inputting an X-ray exposure signal from the operator console 27. When the X-ray exposure signal is input, the commercial power source 20 and the first rectifying circuit 21.
Is disconnected, and conversely, the commercial power supply 20 and the first rectifier circuit 21 are connected when the X-ray exposure signal is not input. This X-ray exposure signal is generated by the X-ray generator 28.
The X-ray generator 28 applies a high voltage for X-ray generation to the X-ray tube 11 when the X-ray exposure signal is input, and thereby the X-ray imaging is performed. Is to be done.

Next, the operation of the above power supply circuit will be described.
The electromagnetic relay 25 connects the commercial power supply 20 and the first rectifier circuit 21 when X-ray imaging is not performed. The first rectifier circuit 21 rectifies the AC voltage from the commercial power source 20 and converts it into a DC voltage, which is converted by the inverter circuit 22 into high-frequency AC of several hundreds to several KHz and the transformer 23 steps up the voltage. The exchange is second
Is converted into direct current by the rectifier circuit 24 and stored in the capacitor 26.

When performing X-ray photography, an X-ray exposure signal is output from the console 27 to the electromagnetic relay 25 and the X-ray generator 28. By inputting this X-ray exposure signal, the electromagnetic relay 25 disconnects the commercial power source 20 and the first rectifier circuit 21. Then, the capacitor 26 starts discharging, and the discharging voltage is applied to the bias electrode 30. On the other hand, the X-ray generator 28
A high voltage for X-ray generation is applied to the X-ray tube 11 to perform X-ray irradiation.

As described above, during X-ray photography, the commercial power source 20 and the first rectifier circuit 21 are separated from each other to stop the operation of the power source circuit which is the source of noise, and the bias voltage of the bias electrode 30 is generated by the discharge voltage of the capacitor 26. Since the bias voltage is applied to, the detection signal is not disturbed. In the above-described embodiment, the electromagnetic relay 25 is installed between the commercial power source 20 and the first rectifier circuit 21, but this is the second relay as shown by the dotted line in FIG.
It may be installed between the rectifier circuit 24 and the capacitor 26.
The X-ray detector is not limited to the above Xe gas detector, but may be a scintillation detector or a semiconductor detector.

[0017]

As is apparent from the above description, according to the X-ray CT apparatus of the present invention, the charging element is provided between the X-ray detector and the power supply section for supplying power to the X-ray detector. The power from the power supply unit is stored in the charging element, and the power supply unit and the charging element are separated when the X-ray irradiation signal for operating the X-ray irradiation is input, and the discharging power of the charging element is supplied to the X-ray detector. By doing so, noise from the power supply unit does not enter the X-ray detector or the like during X-ray photography, and therefore a tomographic image without image quality deterioration can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an X-ray CT apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the structure of a Xe gas detector which is an example of an X-ray detector.

FIG. 3 is a block diagram showing a configuration of a power supply circuit of a conventional X-ray detector.

[Explanation of symbols]

 11 ・ ・ ・ X-ray tube 12 ・ ・ ・ Xe gas detector 25 ・ ・ ・ Electromagnetic relay (switch) 26 ・ ・ ・ Capacitor (charging element)

Claims (1)

[Claims] 1. An X-ray CT apparatus comprising an X-ray tube for X-ray irradiation and an X-ray detector for converting the intensity of transmitted X-rays into an electric signal, and supplying power to the X-ray detector. A charging element is provided between the power source section and the X-ray detector, and the posture is switched to the disconnection state between the power source section and the charging element based on the input of the X-ray exposure signal for operating the X-ray tube for the X-ray irradiation. An X-ray CT apparatus having a switching device.