JPH07204189A - X-ray ct system - Google Patents

Abstract

PURPOSE:To reduce the influence of noise by providing a means increasing and decreasing the X-ray energy from an X-ray tube according to its rotation angle and increasing and decreasing the energy according to the X-ray transmission thickness of a testee. CONSTITUTION:An X-ray tube 2 and an X-ray detecting device 3, opposite each other, are rotated around a testee 4. The rotation is performed by a driving device 6 driven by a scanning part controller 7. The device 7 controls an X-ray controller 5 corresponding to the rotation angle, performing the start of X-ray radiation of the X-ray tube 2 and the increase and decrease of the X-ray radiation amount. It is driven by an output signal from a picture processor 10. When the X-ray tube 2 arranged at the top of a gantory 1 is taken as 0 deg. and the angle is increased clockwise, the X-ray is irradiated from the side of the testee 4 if the rotation angle theta is 90 deg. or 270 deg.. The X-ray does becomes highest when the width of X-raying to the testee is highest. If the rotation angle theta is 0 deg. or 180 deg., the X-ray does becomes the smallest.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an X-ray CT apparatus.

[0002]

2. Description of the Related Art An X-ray CT apparatus includes an X-ray tube arranged to face each other with a subject in between, and an X-ray detector for detecting X-rays emitted from the X-ray tube and passing through the subject. Equipped with
The X-ray tube and the X-ray detector are rotated about the subject while facing each other, and a cross-sectional image of the subject is created based on the output obtained from the X-ray detector. .

Conventionally, the X-ray dose irradiated from the X-ray tube is set to an optimum value in consideration of the adverse effect on the subject, and is a constant value even during the rotation of the X-ray. It was

[0004]

However, the X-ray CT apparatus constructed as described above has a structure in which the X-ray detector is at a predetermined angle in the output sequentially obtained from the rotating X-ray detector. It has been pointed out that noise is generated.

That is, while the X-ray tube having a constant X-ray dose is rotating, the transmission amount of X-rays to the subject is usually the most often the front and back surfaces of the subject.
It becomes the smallest when it penetrates the side. This is because the cross section of the subject is almost elliptical.

Therefore, in the detector for detecting the X-rays that have passed through the subject, the output becomes the smallest when detecting the X-rays that have passed through the side surface of the subject, and the influence on noise becomes large. It will be.

The present invention has been made under these circumstances, and an object of the present invention is to provide an X-ray CT apparatus capable of reducing the influence of noise.

[0008]

In order to achieve such an object, the present invention is basically based on an X-ray tube and an X-ray tube which are arranged so as to face each other with a subject interposed therebetween. And an X-ray detector that detects X-rays that have passed through the subject, and the X-ray detector rotates while centering on the subject while the X-ray tube and the X-ray detector face each other. In an X-ray CT apparatus that creates a cross-sectional image based on the output obtained from the X-ray tube, its X
A means for increasing or decreasing the X-ray energy from the X-ray tube is provided, and the X-ray energy is increased or decreased in accordance with the X-ray transmission thickness of the subject.

[0009]

According to the X-ray CT apparatus having such a structure, first, as the X-ray tube rotates, X-rays of energy corresponding to the rotation angle are emitted.

The energy of X-rays from the X-ray tube is adapted to increase or decrease in accordance with the X-ray transmission thickness of the subject which changes according to the rotation of the X-ray tube.

That is, when the X-ray transmission thickness of the subject is large, the energy of the X-rays emitted from the X-ray tube becomes large, and when the X-ray transmission thickness is small, the energy of the X-rays becomes small. Has become.

Therefore, the output of the X-ray detector corresponding to the energy of the detected X-rays does not become particularly small at a specific angle in the rotation of the X-ray tube, and the influence on noise can be reduced. Like

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a schematic configuration diagram showing an embodiment of an X-ray CT apparatus according to the present invention.

In FIG. 1, first, there is a gantry 1.
A hole is formed in the center of the gantry, and the subject 4 is inserted and arranged in the hole as the bed 13 is driven.

An X-ray tube 2 and an X-ray detector 3 are provided in the gantry 1.
The X-ray tube 2 and the X-ray detector 3 are arranged to face each other with the subject 4 in between. The X-ray tube 2 is adapted to irradiate the subject 4 with X-rays in a fan shape under the control of the X-ray controller 5, and the X-ray detector 3 has an arc shape accordingly. In addition, this X-ray detector 3
Has a large number of X-ray detection elements arranged along the arc surface.

The X-ray tube 2 and the X-ray detector 3 can rotate about the subject 4 while facing each other, and this rotation is driven by the scanning unit controller 7. It is designed to be done by the device 6.

As will be described in detail later, the scanning unit control device 7 controls the X-ray control device 5 in accordance with the scanning (rotation angle) to start X-ray irradiation of the X-ray tube 2 and X-ray irradiation. The dose of radiation is increased or decreased. Further, the scanning control device 7 is driven by an output signal from the image processing device 10.

Further, the output from the X-ray detector 3 is converted into an analog signal by an A / D converter 9 via an amplifier 8 and input to the image processing apparatus 10.

The information image-processed by the image processing device 10 is displayed on the display 11 or stored in the recording device 12.

1A and 1B show the X-ray tube 2 described above.
6 is a diagram showing that the X-ray irradiation amount from is increased or decreased corresponding to the rotation angle θ in the rotation of the X-ray tube 2. FIG.

In FIG. 1A, the case where the X-ray tube 2 is arranged on the top of the gantry 1 is set to 0 °, and the angle is gradually increased clockwise in the figure.

In such a case, when the X-ray tube 2 is positioned on the right side surface of the subject 4, the rotation angle becomes 90 °, and when it is positioned directly below the subject 4, the rotation angle becomes It becomes 180 degrees. Further, the rotation angle becomes 270 ° when it is positioned on the left side surface of the subject 2 and 360 ° when it is positioned right above.

FIG. 1B shows a graph in which the vertical axis represents the change in the X-ray dose from the X-ray tube 2 when the horizontal axis represents the rotation angle θ.

As is apparent from the figure, the rotation angle θ is 9
In the case of 0 ° or 270 °, the X-ray dose from the X-ray tube 2 is maximum. The reason for this is that X-rays are emitted from the side surface of the subject 4 and the X-ray transmission thickness of the subject is maximized. Needless to say, the maximum amount of X-rays is such that X-rays do not adversely affect the subject 4.

When the rotation angle θ is 0 ° (360 °) or 180 °, the X-ray dose from the X-ray tube 2 is minimum. This is because X-rays are irradiated from the front and back sides of the subject 4 and the X-ray transmission thickness of the subject is minimized.

According to the X-ray CT apparatus thus constructed, the X-ray tube 2 is irradiated with X-rays of a dose corresponding to the rotation angle of the X-ray tube 2 as it rotates.

The X-ray dose from the X-ray tube 2 is adapted to increase or decrease in accordance with the X-ray transmission thickness of the subject 4 which changes according to the rotation of the X-ray tube 2.

That is, when the X-ray transmission thickness of the subject 4 is large, the X-ray dose irradiated from the X-ray tube 2 is large,
When the X-ray transmission thickness is small, the X-ray dose is small.

Therefore, the output corresponding to the detected X-ray dose of the X-ray detector 3 does not become particularly small at a specific angle in the rotation of the X-ray tube 2, and the influence on noise can be reduced. become able to.

In the above-described embodiment, the X-ray dose is smoothly increased and decreased with the rotation of the X-ray tube 2. However, the X-ray dose is not necessarily limited thereto. This is because the object of the present invention can be achieved even if it is changed with a certain degree of discontinuity.

In the above-described embodiment, the X-ray dose is increased / decreased as the X-ray tube 2 rotates.
It goes without saying that not only the dose but also other factors such as the X-ray tube pressure may be used. The point is that the X-ray energy may be increased or decreased. The reason is that the change in the output of the X-ray detector is
This is because it is determined by the magnitude of the input X-ray energy.

[0032]

As is apparent from the above description,
The X-ray CT apparatus according to the present invention can reduce the influence of noise.

[Brief description of drawings]

1 (a) and 1 (b) are main part configuration diagrams showing an embodiment of an X-ray CT apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of an X-ray CT apparatus according to the present invention.

[Explanation of symbols]

 1 Gantry 2 X-ray tube 3 X-ray detector 4 Subject

Claims (1)

[Claims] 1. An X-ray tube comprising: an X-ray tube which is arranged to face each other with a subject in between; and an X-ray detector which detects X-rays emitted from the X-ray tube and passing through the subject. An X-ray CT apparatus, which rotates a tube and an X-ray detector while facing each other around a subject, and creates a sectional image based on an output obtained from the X-ray detector. Is provided with a means for increasing or decreasing the X-ray energy from the X-ray tube in accordance with the rotation angle in the rotation of the X-ray, and increasing or decreasing the X-ray energy according to the X-ray transmission thickness of the subject. X-ray CT device.