JP2005013311A - Grid for stereo-radiography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scattered ray removing grid without cut-off in either two vessel positions in stereo-radiography. <P>SOLUTION: This grid has a grid screen of a first shading member and a grid screen of a second shading member disposed/layered with a gap T in-between in the front/rear relative to incident radiation, and is structured to accommodate to two focal positions FA and FB disposed parallel to the grid apart from the flat plane of the grid by the focal distance (f). The grid satisfies the following expressions when the distance between FA and FB is (d) and the grid densities of the first screen and the second screen are N1 and N2: f=N1×d×T, and N2=(N1×d-1)/d. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stereo shooting grid.
[0002]
[Prior art]
Conventionally, radiographic apparatuses have been used in various fields such as medical diagnosis of subjects and non-destructive inspection of substances. Many radiographic apparatuses operate on the principle of irradiating a subject with radiation emitted from a point light source and converting the density distribution of the transmitted radiation into an image with a receiver.
[0003]
In the radiation imaging apparatus, in some cases, the scattered radiation generated when the radiation enters the subject is removed, and the scattered radiation removal grid is used to obtain a good image. A typical grid has a structure in which a large number of lead foils, which are radiation shielding members, are laminated in parallel to the radiation from a point light source with a gap. Radiation that travels straight from the point light source while passing through the subject passes through the gap in the lead foil and reaches the receiver. Of the radiation that is scattered within the subject and changes direction, it is no longer parallel to the lead foil. The object cannot be passed through the gap and is shielded with lead foil. In order to support the physical structure of the grid, the gap is filled with a radiation transmitting member such as wood or aluminum. The ratio of the length along the light beam direction of the gap to the width of the gap is called a lattice ratio, and is one of the parameters representing the efficiency of removing scattered radiation.
[0004]
Since the lead foil of the grid has a layer structure so as to converge toward the point light source, even if the radiation is shifted, the grid may not be able to pass through the grid (cut off) in some cases. 09-066054). For example, in a grid in which planar lead foils are stacked in a striped pattern, radiation from the light source cannot pass through the grid if the light source shifts in a direction perpendicular to the stacking surface. However, such a problem does not occur when the light source moves parallel to the laminated surface because the parallel relationship between the light beam and the lead foil is not broken.
[0005]
Some radiographic apparatuses are characterized in that the positional relationship between the light source and the receiver changes. For example, stereo photography and tomography are characterized in that a plurality of images are taken or multiple exposure is performed while changing the positional relationship between the light source and the receiver.
[0006]
[Problems to be solved by the invention]
In the stereo imaging method, a stereoscopic effect is obtained by irradiating radiation from two light source positions, obtaining images for each, and observing separately with both eyes. In order to obtain a good binocular parallax, it is desirable that a certain distance can be secured between the two light source positions. Further, it is desirable that the blur of the image in the parallax direction is reduced as much as possible.
[0007]
If the scattered radiation removal grid is to be used during such shooting, there is a problem that there are a plurality of light source positions. When the parallax direction and the laminated surface of the grid are parallel, no cut-off occurs depending on the light source position, but since the scattered rays parallel to the laminated surface cannot be removed as described above, the blur in the parallax direction cannot be reduced. In the case where the parallax direction and the grid stacking plane are orthogonal to each other, the grid cut-off occurs due to the movement of the light source. If the grating ratio is lowered in order to reduce the cutoff to ensure the parallax, the scattered radiation removal efficiency is deteriorated, and the cutoff cannot be completely eliminated.
[0008]
The present invention provides a grid that is useful in the above-described case and that has no cut-off with respect to a plurality of focal positions and is capable of removing scattered radiation in a direction parallel to the focal direction.
[0009]
[Means for Solving the Problems]
The scattered radiation removal grid that solves the above problem has the following characteristics. It has a lattice screen of a first shielding member and a lattice screen of a second shielding member, which are arranged so as to be overlapped with a gap of T before and after the incident radiation. The two focal positions FA and FB, which are arranged in parallel to the grid at a focal distance f away from the plane of the grid, are matched. When the distance between FA and FB is set to d and the lattice density of the first screen and the second screen is set to N1 and N2,
f = N1 × d × T
N2 = (N1 × d−1) / d
Meet.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view of a bifocal grid according to the present invention. In the figure, the first shielding member screen of the present invention is formed on the upper side, and the second shielding member screen is formed on the lower side. The radiation is emitted from the upper focal point FA or FB in the drawing, passes through a subject (not shown), passes down the grid, and forms an image on a receiver (not shown).
[0011]
The light beam from the focal point FA passes through the gaps 1, 2, 3,... Of the first shielding member screen, and passes through the gaps 1, 2, 3,. The light beam from the focal point FB passes through the gaps 2, 3, 4,... Of the first shielding member screen, and passes through the gaps 1, 2, 3,.
[0012]
Looking back at this process, it can be seen that the gap 1 of the second shielding member screen receives light from the gaps 1 and 2 of the first shielding member screen, and the other rays are shielded. . Further, in a normal grid, when the light source is located at a position other than the focal point, cutoff occurs. However, according to the grid of the present invention, the shielding area is minimized when the light source position is both FA and FB, and the cutoff is reduced. Disappear.
[0013]
【The invention's effect】
As described above, according to the scattered radiation removal grid of the present invention, the cutoff can be eliminated at the two focal positions, and the ability to remove scattered radiation scattered in the focal parallax direction can be provided. By disposing an X-ray tube at these focal positions and performing stereo imaging, resolution of images in the parallax direction can be improved.
[Brief description of the drawings]
FIG. 1 is a principle diagram of a grid according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st shielding member screen 2 2nd shielding member screen

Claims (2)

A scattered radiation removal grid comprising a radiation shielding member disposed with a gap so as to transmit a part of radiation from a radiation source, and a radiation transmissive member filling the gap between the shielding members, The arrangement includes a first shielding member screen arranged in a stripe pattern or a grid pattern, and a stripe pattern or a grid slightly lower than the first screen on the side opposite to the radiation source with respect to the first screen. And a second shielding member screen arranged in a striped pattern or a grid pattern with a density of. The grid is optimized with respect to two focal positions arranged parallel to the grid surface, the distance between the two being d (cm), and the first screen and the second screen. When the interval is T (cm), the lattice density of the first screen is N1 (cm ⁻¹ ), the lattice density of the second screen is N2 (cm ⁻¹ ), and the focal length is f (cm). ,
f = N1 × d × T
N2 = (N1 × d−1) / d
The scattered radiation removal grid according to claim 1, wherein

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