JPH04336044A - Grid structure of X-ray CT device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid structure for an X-ray CT apparatus that blocks scattered X-rays incident on an X-ray detector.

0002

2. Description of the Related Art Generally, in an X-ray apparatus, an X-ray tube emits X-rays, and an X-ray detector collects the X-rays after passing through a subject. At this time, the X-ray detector collects not only transmitted X-rays but also scattered X-rays scattered within the subject, which causes noise generation and deterioration of image quality. Therefore,
Conventionally, the following two methods have been used to remove these scattered X-rays.
Two methods have been devised.

FIG. 3 is an explanatory diagram showing the first method, in which a scattered X-ray detector 5 is installed near the side of the main detector 6. Scattered X-rays 3 obtained by scattering the X-rays emitted from the X-ray tube 1 within the subject 2 are detected by a scattered ray detector 5. Then, based on the amount of scattered X-rays 3, the amount of scattered X-rays to be collected by the main detector 6 is determined empirically. The amount of transmitted X-rays is determined by removing it.

FIG. 4 is an explanatory diagram showing the second method, in which a grid 8 is provided at each joint position of a plurality of scintillators 7. The transmitted X-rays 4 are transmitted between the grids 8 and collected by the scintillator 7, and the scattered X-rays 3 are incident on the grids 8 and absorbed. This removes the scattered X-rays 3.

[0005]

However, in the first method, the scattering detector 5 for detecting the scattered X-rays 3 and the calculation function for calculating the scattered radiation dose collected by the main detector 6 are (not shown), the installation requires a large space and increases costs.

Furthermore, in the second method, since the grid 8 is disposed between each scintillator, for example, the grid 8
If the thickness of the scintillator 7 is L1 and the pitch between the channels of the scintillator 7 is L2, then the width that can be collected by the grid 7 is (L2
-L1), resulting in a significant drop in geometric efficiency.

[0007] This invention was made in order to solve the conventional problems, and its purpose is to provide an X-ray system that can easily remove scattered X-rays without reducing the geometric efficiency. The object of the present invention is to provide a grid structure for a line CT device. [Structure of the invention]

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a grid for an X-ray CT apparatus that blocks scattered X-rays that inevitably enter an X-ray detector that collects X-rays after passing through a subject. In terms of structure, the X-ray detector is characterized in that it is composed of a plurality of detection elements arranged in parallel, and that a grid plate is provided for each of two or more detection elements. Further, in claim 1, the opening width and the depth of the grid plate are configured to have a predetermined ratio.

[0009]

[Function] With the above structure, the number of grid plates is smaller than when a grid plate is provided for each detection element, so the amount of transmitted X-rays blocked by the thickness of the grid plate is reduced. Therefore, the geometric efficiency improves by this amount,
The image quality of CT images is improved.

0010

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 an embodiment of the grid structure of an X-ray CT apparatus to which the present invention is applied.

A plurality of scintillators 7 shown in the figure are arranged in parallel to collect transmitted X-rays. Furthermore, each scintillator 7 is connected to a photodiode 9 that converts detected X-rays into electrical signals.

A grid 8 is provided for every three scintillators 7 on the X-ray incident side of the scintillator 7 . This grid 8 is made of metal such as molybdenum or tungsten, and is designed to absorb the irradiated X-rays.

[0013] Then, the grid structure shown in Fig. 1 (hereinafter,
The dimensions of the device (referred to as the example device) are determined as follows. That is, the thickness of the grid 8 is L1, the pitch between channels of the scintillator 7 is L2, and the depth distance of the grid 8 is L3.
, and the opening width of the grid 8 is assumed to be L4.

On the other hand, in order to compare the geometrical efficiency with the device of this embodiment, a conventional grid structure (hereinafter referred to as the conventional device) is shown in FIG. The opening width is determined to be L5. Next, the geometric efficiency of the embodiment device and the conventional device will be compared using FIGS. 1 and 2. Now, if the removal efficiency of scattered X-rays is made equal, the following equation (1) becomes the condition. 3・L2 /L3 =L2 /L6 ...(
1) Therefore, L3 = 3・L6
...(2) And the geometric efficiency E1 of the conventional device is E1 = L5 /L2 = (L2 - L1) / L2
=1-(L1/L2)
...(3) Also, the geometric efficiency E2 of the example device
is E2=L4/(3・L2)=(3・L2−L1)/(3・L2)=1−{L
1/(3・L2)} …(4)
Comparing the second term of equation (3) and the second term of equation (4), we find that L1 /L2 >L1 /(3・L2)...
Since the relationship (5) holds true, from equations (3) and (4), E1 < E2
...(6) is obtained, and it can be seen that the geometrical efficiency of the example device is better than that of the conventional device.

In this way, in this embodiment, the grid 8 is installed every three scintillators 7 to remove scattered X-rays. Therefore, it becomes possible to collect transmitted X-rays with higher geometric efficiency than before. In this embodiment, the grid 8 is provided for every three scintillators 7, but it goes without saying that the number may be two or more.

[0016]

As explained above, in the present invention, a grid plate is installed for each of a plurality of detection elements, and the grid plate is configured such that the depth and opening distance are in a predetermined ratio. Therefore, scattered X-rays can be removed with higher geometrical efficiency than in the past. As a result, it is possible to obtain a clear CT image that is not affected by scattered X-rays.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for determining the geometric efficiency of a conventional device.

FIG. 3 is a configuration diagram showing a conventional example.

FIG. 4 is a configuration diagram showing a conventional example.

[Explanation of symbols]

1. X-ray tube 2. Subject 3 Scattered X-rays 4 Transmission X-ray 7 Sintering 8 Grid

Claims (2)

[Claims] Claim 1: In a grid structure of an X-ray CT apparatus that blocks scattered X-rays that inevitably enter an X-ray detector that collects X-rays after passing through a subject, a plurality of the X-ray detectors are arranged in parallel. 1. A grid structure for an X-ray CT apparatus comprising detection elements, characterized in that a grid plate is provided for each of two or more detection elements. 2. The grid plate according to claim 1, wherein the opening width and the depth length of the grid plate are configured to have a predetermined ratio.
Grid structure of line CT device.