X-ray or gamma ray systems or devices – Beam control – Antiscatter grid
Reexamination Certificate
2000-03-20
2004-03-16
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Antiscatter grid
Reexamination Certificate
active
06707884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an X-ray scatter reducing grid and a fabrication method thereof which are used in an apparatus for X-ray imaging.
2. Description of the Related Art
In the radiation-transmitted image of a subject (such as human body or the like) by radiation transmitted through the subject, it is known that an X-ray scatter reducing grid, for absorbing rays scattered when radiation is transmitted through the subject, is employed in order to obtain a high quality transmitted image in which scattered radiations are reduced.
For the general configuration of the above-mentioned X-ray scatter reducing grid, radiation-absorbing portions and radiation-transmitting portions, which have width in the direction in which radiation travels, are alternately disposed in parallel and are formed into the shape of a flat plate as a whole. When radiation is transmitted through the subject, the scattered radiation travel obliquely and are absorbed and reduced by the radiation-absorbing portions, and only the primary radiation are transmitted through the subject and travel substantially linearly. The primary radiation, transmitted through the radiation-transmitting portions, reach a detector and form a radiation-transmitted image. The radiation-transmitting portions are formed from wood, aluminum or the like, while the radiation-absorbing portions are formed from lead or the like. These portions are alternately and closely disposed and maintain structural strength as a whole. It is desirable that the radiation-transmitting portions have a high transmittance so as not to reduce the transmission of the primary radiation.
As an example of an X-ray scatter reducing grid with its radiation-transmitting portion being air (i.e., a so-called air grid), an X-ray scatter reducing grid disclosed in Japanese Unexamined Patent Publication No. 10(1998)-5207 is known. This X-ray scatter reducing grid is provided with two support members
202
a
,
202
b
curved in the form of a circular arc with respect to focal point F, as shown by reference numeral
200
in
FIG. 17. A
plurality of paired grooves
204
,
206
extending along a Z-axis are formed in the inner surfaces of the support members
202
a
,
202
b
and are directed toward the focal point F (radiation source). Collimator plates
210
, which are composed of metal such as tungsten whose radiation (X-rays) absorption is great, are inserted in the paired grooves
204
,
206
along the Z-axis through the upper ends of the support members
202
a
,
202
b
and are fixed between the support members
202
a
,
202
b
, as shown in FIG.
17
A.
When fabricating the X-ray scatter reducing grid
200
which supports strips (collimator plates
210
) as radiation-absorbing members between the two support members
202
a
and
202
b
, the support grooves
204
,
206
are first formed at predetermined intervals in the two support members
202
a
,
202
b
. Then, the two support members
202
a
,
202
b
are fixed with a constant space to form the frame of the X-ray scatter reducing grid
200
. Next, the collimator plates
210
are inserted in the grooves
204
,
206
through the end of the grid frame.
However, because of deflection in the support members
202
a
,
202
b
, deflection in the collimator plate
200
, friction between the collimator plate
210
and the grooves
204
,
206
developed in inserting the collimator plate
210
, etc., the aforementioned method has the disadvantage that the collimator plates
210
are easily bent when they are being inserted over a long distance and the number of fabrication steps is increased. If the width of the grooves
204
,
206
is widened to make insertion easy, play will occur between the collimator plate
210
and the groove
204
(or
206
) and therefore accurate positioning will become difficult. As a result, focusing accuracy of the collimator plates
210
is reduced. Also, if another set of collimator plates extending in a direction perpendicular to the collimator plates
210
are used to make a cross grid, as shown at
12
in
FIG. 1
of the aforementioned Publication No. 10(1998)-5207, the collimator plates
210
have to curved. As a result, the step of inserting the collimator plates
210
along the grooves curved over an even longer length becomes necessary and the fabrication becomes even more difficult.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned disadvantages found in the prior art. Accordingly, the primary object of the invention is to provide an X-ray scatter reducing grid which can be reliably and easily fabricated with a high degree of accuracy.
To achieve this end, there is provided a self-supporting grid comprising:
a plurality of radiation-absorbing plates disposed in parallel at predetermined intervals over an entire area to which radiation is exposed, each radiation-absorbing plate consisting of a radiation-absorbing substance and having width in a direction in which the radiation travels; and
at least two support members for supporting the opposite end portions of each of the radiation-absorbing plates;
wherein the support members are provided with plate-receiving means which receives the plurality of radiation-absorbing plates, the radiation-absorbing plates being inserted in the plate-receiving means and being supported by the support members.
The expression “the radiation-absorbing plates are inserted in the plate-receiving means and are supported by the support members” includes fixing the radiation-absorbing plates by firm attaching means, such as adhesion, fusing and the like, as well as supporting the radiation-absorbing plates by friction.
In the X-ray scatter reducing grid according to the present invention, the radiation-absorbing plates do not need to be inserted over a long distance, because the radiation-absorbing plates are inserted and supported at the opposite ends thereof with respect to the two support members. In addition, there is only a slight possibility that the radiation-absorbing plates will bend during insertion, since the frictional resistance at the time of insertion is low. Thus, the X-ray scatter reducing grid can be fabricated reliably and easily with a high degree of accuracy.
The plate-receiving means provided in the support member can be constructed by a plurality of grooves which receive and support the opposite edges of the radiation-absorbing plate, or by a plurality of slots which receive and support the opposite end portions of the radiation-absorbing plate, or by a plurality of elongated holes which receive and support the opposite end portions of the radiation-absorbing plate. In the case where the plate-receiving means is constructed by the grooves, the structural strength of the support members can be kept because there is no slot in the support members. In the case where the plate-receiving means is constructed by the slots, the structural strength of the grid after fabrication can be increased because the radiation-absorbing plates are firmly supported by the support members. In the case where the plate-receiving means is constructed by the elongated holes, vertical positioning can be performed even more accurately, because there is no possibility that the radiation-absorbing plates will shift vertically, i.e., in the direction perpendicular to the longitudinal direction of the support members, after the insertion of the radiation-absorbing plates into the elongated holes.
The radiation-absorbing plates may be pulled so that they are stretched in the longitudinal direction of the radiation-absorbing plates and may be fixed to the support members under the pulled condition. Even if deflection occurs in the radiation-absorbing plates, in the case where the radiation-absorbing plates are stretched in the longitudinal direction and fixed to the support members and/or the ceiling plate (or the bottom plate), focusing accuracy is enhanced because the deflection can be reduced.
The X-ray scatter reducing grid may further include a ceiling plate and/or a bo
Fuji Photo Film Co. , Ltd.
Glick Edward J.
Kao Chih-Cheng Glen
Sughrue & Mion, PLLC
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