Information
-
Patent Grant
-
6707884
-
Patent Number
6,707,884
-
Date Filed
Monday, March 20, 200024 years ago
-
Date Issued
Tuesday, March 16, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Glick; Edward J.
- Kao; Chih-Cheng Glen
Agents
-
CPC
-
US Classifications
Field of Search
US
- 378 154
- 378 147
- 378 149
- 378 155
- 250 5051
- 250 3631
-
International Classifications
-
Abstract
A plurality of slots, which incline in directions that focus toward a source of radiation, are formed in plates constructed of a radiation-absorbing substance. Similarly, a plurality of slots, which incline in directions that focus toward the radiation source, are formed in support members constructed of a radiation-absorbing substance. If the support members and the plates are combined by the engagement between the slots, a scatter-ray removing grid in the form of a lattice is constructed such that each support member and each plate incline toward the radiation source.
Description
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 bottom plate, and the radiation-absorbing plates may be fixed to at least one among the plate-receiving means, the ceiling plate, and the bottom plate.
In the X-ray scatter reducing grid, the support members may be constructed by two first support members which support the opposite end portions of each of the radiation-absorbing plates and two second support members which connect to the two first support members so that the four support members constitute a rectangular frame. In such a case, the rigidity of the support members increases the radiation-absorbing plates are easily positioned with accuracy and the structural strength of the grid can be made greater.
The plate-receiving means can be provided so that it extends in a direction converging toward a radiation source being operated. More specifically, a focusing grid with a higher transmittance can be constructed by inserting the radiation-absorbing plates into the plate-receiving means provided so as to incline in the direction that focuses toward the radiation source. In the case where support members (plates) consisting of a radiation-absorbing substance incline in the direction which focuses toward the radiation source, the transmittance of the radiation, which is transmitted through a subject from the radiation source and travels substantially linearly, becomes high. Since cutoff in the circumferential portion of the X-ray scatter reducing grid is eliminated, a variation in the transmittance radiation in a transmitted image is eliminated and high image quality is obtainable. Similarly, in the case where the radiation-absorbing plates are inclined in the directions that focuses toward the radiation source by inserting the plates into the plate-receiving means provided so as to incline in the direction that focuses toward the radiation source, a variation in the transmitted-radiation amount is eliminated and high image quality is obtainable.
In addition to the support members, a plurality of radiation-absorbing support members, which are perpendicular to the radiation-absorbing plates and consist of a radiation-absorbing substance, may be provided over an entire area, to which radiation is exposed, in a direction parallel to the support members. In this case the radiation-absorbing plates and the radiation-absorbing support members form a cross grid as a whole. In such a case, even higher image quality is obtainable over the entire transmitted image.
Furthermore, in the case where slots are formed in both the support members and the radiation-absorbing plates, the grid has advantages in that resistance to insertion can be further reduced, fabrication becomes easy, and mutual positioning is performed with reliability.
Elastic bodies may be interposed between the two support members so that the two support members are urged in a direction in which the radiation-absorbing plates are stretched. The elastic bodies are intended to mean spring material. For example, a compression coil spring can be employed. In this case, flatness in the radiation-absorbing plates is always maintained, because the radiation-absorbing plates are kept stretched.
In accordance with the present invention, there is provided a method of fabricating an X-ray scatter reducing grid, comprising the steps of:
inserting a plurality of radiation-absorbing plates into plate-receiving means formed in at least two support members, the radiation-absorbing plates being disposed in parallel at predetermined intervals over an entire area to which radiation is exposed, and each radiation-absorbing plate consisting of a radiation-absorbing substance and having width in a direction in which the radiation travels; and
supporting the opposite end portions of each of the radiation-absorbing plates by the plate-receiving means and thereby constituting the X-ray scatter reducing grid.
In the fabrication method 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 a little possibility that the radiation-absorbing plates will bend during insertion, since the frictional resistance at the insertion is low. Thus, the X-ray scatter reducing grid can be fabricated reliably and easily with a high degree of accuracy.
In the method, it is preferable that the radiation-absorbing plates be fixed to-the plate-receiving means. Also, the X-ray scatter reducing grid may include a ceiling plate and/or a bottom plate. It is preferable that the radiation-absorbing plates be fixed to at least one among the plate-receiving means, the ceiling plate, and the bottom plate. In addition, it is preferable that the radiation-absorbing plates be fixed to the support member under the condition in which the radiation-absorbing plates are pulled in the longitudinal direction of the radiation-absorbing plates. Furthermore, the X-ray scatter reducing grid may include support members, which have the plate-receiving means, a ceiling plate, and/or a bottom plate, and the support members may be removed after the radiation-absorbing plates have been fixed to either the ceiling plate or the bottom plate, or both of them. In the case where the support members are removed after the radiation-absorbing plates have been fixed, the grid can be reduced in size and becomes easy to handle, because the number of components can be reduced.
At the positions where the radiation-absorbing plates are supported by the support members, the radiation-absorbing plates may be provided with a second set of slots (plate-receiving means) which engage a first set of slots (plate-receiving means) provided in the support members, and an X-ray scatter reducing grid may be constructed by the engagement between the first and second sets of slots. In this case, if the height of the support members is made the same as that of the radiation-absorbing plates, and if each slot is formed by approximately half of the height of the support members or the radiation-absorbing plates, the upper and lower ends of the plates become substantially coplanar with those of the support members when they are assembled. As a result, the grid is capable of having a well-ordered configuration as a whole.
The opposite end portions of the radiation-absorbing plate may be formed with holes and stretched in the opposite directions by metal wires, or rods, passed through the holes. Also, the opposite end portions of the radiation-absorbing plate may be provided with cutouts and stretched in the opposite directions by metal wires or the like wound around the cutouts. In these cases, the other end of the metal wire or the rod may be fixed to a jig disposed to surround the circumference of the X-ray scatter reducing grid, and a stretch in the radiation-absorbing plate may be temporarily maintained until the radiation-absorbing plate is fixed to the support members and/or the ceiling plate (or the bottom plate). Furthermore, the opposite end portions of the radiation-absorbing plate may be clamped by a tool such as cutting pliers and stretched in the opposite directions.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A
is a plan view showing an X-ray scatter reducing grid constructed according to a first embodiment of the present invention;
FIG. 1B
is a front view of the support member used in the grid of
FIG. 1A
;
FIG. 1C
is aside view of the radiation-absorbing plate used in the grid of
FIG. 1A
;
FIG. 2A
is a plan view showing an X-ray scatter reducing grid constructed according to a second embodiment of the present invention;
FIG. 2B
is a front view of the support member used in the grid of
FIG. 2A
;
FIG. 2C
is a side view of the radiation-absorbing plate used in the grid of
FIG. 2A
;
FIG. 3
is a perspective view of the X-ray scatter reducing grid constructed according to the second embodiment of the present invention;
FIG. 4A
is a plan view showing an X-ray scatter reducing grid constructed according to a third embodiment of the present invention;
FIG. 4B
is a front view of the support member used in the grid of
FIG. 4A
;
FIG. 4C
is a side view of the radiation-absorbing plate used in the grid of
FIG. 4A
;
FIG. 5
is a perspective view of the X-ray scatter reducing grid constructed according to the third embodiment of the present invention;
FIG. 6
is a perspective view of an X-ray scatter reducing grid constructed according to a fourth embodiment of the present invention;
FIG. 7A
is a front view of the support member used in the grid of
FIG. 6
;
FIG. 7B
is a side view of the radiation-absorbing plate used in the grid of
FIG. 6
;
FIG. 8A
is a plan view showing an X-ray scatter reducing grid constructed according to a fifth embodiment of the present invention;
FIG. 8B
is a front view of the support member used in the grid of
FIG. 8A
;
FIG. 8C
is a front view of another thin support member used in the grid of
FIG. 8A
;
FIG. 8D
is a side view of the radiation-absorbing plate used in the grid of
FIG. 8A
;
FIG. 9
is a perspective view of an X-ray scatter reducing grid constructed according to a sixth embodiment of the present invention;
FIG. 10
shows front and side views of the support member and radiation-absorbing plate used in the grid of
FIG. 9
, along with a radiation source;
FIG. 11A
is a plan view showing an X-ray scatter reducing grid constructed according to a seventh embodiment of the present invention;
FIG. 11B
is a front view of the support member used in the grid of
FIG. 11A
;
FIG. 11C
is a side view of the radiation-absorbing plate used in the grid of
FIG. 11A
;
FIG. 12A
is a diagram showing an embodiment of the method of stretching the radiation-absorbing plate shown in
FIG. 11C
;
FIG. 12B
is a diagram showing another embodiment of the stretching method;
FIG. 12C
is a diagram showing still another embodiment of the stretching method;
FIG. 13A
a plan view showing a grid that is capable of keeping radiation-absorbing plates stretched;
FIG. 13B
a plan view showing another grid that is capable of keeping radiation-absorbing plates stretched;
FIG. 14
is a perspective view showing a grid constructed according to an eighth embodiment of the present invention;
FIG. 15
is a schematic view showing another embodiment of the grid shown in
FIG. 14
;
FIG. 16
is a schematic view showing still another embodiment of the grid shown in
FIG. 14
;
FIG. 17A
is a perspective view showing a conventional X-ray scatter reducing grid; and
FIG. 17B
is an enlarged plan view of the part enclosed by a two-dotted line in FIG.
17
A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will hereinafter be described in detail with reference to the drawings. Note that in
FIGS. 1
to
16
, the thickness of each component, the width of each slot, the number of radiation-absorbing plates, the ratio of the dimensions of each component, etc., do not always agree with reality.
Referring to
FIG. 1
, there is shown an x-ray scatter reducing grid (hereinafter referred simply to as a grid)
1
in accordance with a first embodiment of the present invention. The grid
1
has support members (first support members)
2
,
2
consisting of radiation-transmitting material (radiation non-absorbing material) such as wood, aluminum and the like. The support members
2
are formed thick and connected at the opposite ends of each member to two connecting members (second support members)
6
. That is, the support members
2
and the connecting members
6
as a whole constitute a rectangular frame
8
,thereby giving rigidity to the grid
1
. The connecting members
6
and the support members
2
may be coupled by means of adhesion, or they may be formed integrally with one another. While this first embodiment is provided with the connecting members
6
, structure without the connecting members
6
is also possible. Similarly, in other embodiments to be described later, structure without the connecting members
6
is possible. The grid
1
further has radiation-absorbing plates
4
. Each radiation-absorbing plate
4
consists of a plate containing a substance, which absorbs radiation relatively well, such as lead, tantalum, tungsten and the like. Note that in other embodiments to be described later, radiation-absorbing plates also consist of the same material.
In the support members
2
of the first embodiment, from the upper edge
2
a
thereof toward the lower edge
2
b
a plurality of plate-receiving means (in this embodiment, slots
14
) are formed in parallel at predetermined intervals at approximately half (½ h) of the height h of the support member
2
, as shown in FIG.
1
B. The slots
14
extend in a direction going substantially toward the side of a radiation source (not shown), i.e., in a direction perpendicular to the paper surface of FIG.
1
A. On the other hand, the radiation-absorbing plate
4
is formed with two parallel slots
16
(which extend in the direction opposite from the slots
14
of the support member
2
), at positions corresponding to the two opposite support members
2
, i.e., positions crossing the opposite support members
2
perpendicularly. That is, each slot
16
of the radiation-absorbing plate
4
is formed from the lower edge
4
b
thereof toward the upper edge
4
a
at approximately half (½ h) of the height h of the radiation-absorbing plate
4
.
If the slots
16
of the radiation-absorbing plates
4
are positioned with respect to the slots
14
of the support members
2
and engage with the slots
14
, a linear grid, i.e., a grid with the radiation-absorbing plates
4
disposed in parallel at predetermined intervals, is constructed as shown in FIG.
1
A. In this construction, the radiation-absorbing plates
4
are disposed in parallel to one another and form a parallel grid and are also disposed at right angles to the support members
2
. In this way, the support members
2
are capable of supporting and holding the radiation-absorbing plates
4
at predetermined positions.
Since the slots
14
and
16
each have a dimension of half the height h of the respective members, the upper edge
4
a
of the radiation-absorbing plate
4
becomes substantially coplanar with the upper edge
2
a
of the support member
2
after fabrication. The height dimension h of the radiation-absorbing plate
4
is, for example, 1 to 3 cm, while the thickness is 0.1 mm. In addition, the spacing between adjacent slots
14
of the support member
2
, i.e., the intervals at which the radiation-absorbing plates
4
are disposed, is approximately 1 mm.
In fabricating the radiation-absorbing plates
4
and the support members
2
, the radiation-absorbing plates
4
are inserted in the support members
2
through the respective lower edges
16
and upper edges
14
. In this case, the height h of the support member
2
is short compared with the longitudinal direction thereof, and consequently, the resistance during the insertion becomes low. Furthermore, the insertion up to half of the height h is very easy because the resistance between the slot
16
of the radiation-absorbing plate
4
and the slot
14
of the support member
2
is much lower. The same may be said of the following embodiments in which the slot length is approximately half of the height h. Of course, the same is also true of the case where the length of one slot is one-third of h and the other slot length is two-thirds of h. After fabrication, the radiation-absorbing plates
4
and the support members
2
support one another without having solid matter as a member intervening between adjacent radiation-absorbing plates
4
, and consequently, the radiation-absorbing plates
4
and the support members
2
, as they are, can hold the fabricated form and result in a so-called self-supporting grid. The fixation between the radiation-absorbing plates
4
and the support members
2
may remain inserted, or the fixation may be reinforced by an adhesive agent, fusing, etc. Reinforcing the structure by an adhesive agent, fusing or the like is likewise possible for other embodiments that are to be described later.
FIGS. 2 and 3
show a grid
20
similar to the grid
1
of the first embodiment, constructed according to a second embodiment of the present invention. Notice that in
FIG. 3
, the thickness of each component and the connecting members
26
shown in
FIG. 2
are omitted for a clear understanding of the present invention.
As illustrated in
FIGS. 2 and 3
, the essential difference between the grid
20
of the second embodiment and the grid
1
of the first embodiment is that a radiation-absorbing plate
24
has no slot and the slots
34
of a support member
22
extend from its upper edge
22
a
to the vicinity of its lower edge
22
b.
The manufacture of the radiation-absorbing plate
24
is easy because it has no slot. When fabricating the grid
20
, all that is required is to insert the radiation-absorbing plates
24
into the slots
34
of the support members
22
. As the slots
34
of the two support members
22
are aligned with one another and formed in parallel, the radiation-absorbing plates
24
are disposed in parallel and constitute a parallel grid, as with the first embodiment. In
FIGS. 2 and 3
, although the number of radiation-absorbing plates
24
is omitted for convenience, a large number of radiation-absorbing plates
24
are actually disposed in the slots
34
of the support members
22
. It is preferable that the radiation-absorbing plates
24
be bonded to the slots
34
of the support members
22
so that the plates
24
do not to move within the slots
34
. Alternatively, protrusions (
FIG. 3
) may be formed on the radiation-absorbing plate
24
to interpose the support member
22
therebetween in order to prevent positional misalignment. In this case, the fixation between the protrusions
25
and the support member
22
can also be reinforced by adhesion.
FIGS. 4 and 5
show a grid
40
constructed according to a third embodiment of the present invention. In the third embodiment, the plate-receiving means for receiving and supporting radiation-absorbing plates is constructed by grooves
54
formed in support members
42
. Note that in
FIG. 5
, the connecting members
46
shown in
FIG. 4
are omitted for a clear understanding of the present invention.
As illustrated in
FIGS. 4 and 5
, the grid
40
of the third embodiment, as with the aforementioned two embodiments, is a linear grid, but differs in that the plate-receiving means is constructed by the grooves
54
of the support members
42
. Radiation-absorbing plates
44
have no slot, as in the second embodiment. In the inner surfaces of the opposite support members
42
, a plurality of grooves
54
are formed in parallel from the upper edge
42
a
of the support member
42
to the lower edge
42
b
. Therefore, the opposite edges
44
c
of each radiation-absorbing plate
44
are inserted and supported in the corresponding grooves
54
of the support members
42
through the upper edges
42
a
of the support members
42
, and the parallel grid
40
is formed.
The width of the groove
54
of the support member
42
is of such a dimension that the edge
44
c
of the radiation-absorbing plate
44
is press-fitted and supported. However, since the insertion is performed over a short distance, the frictional resistance at the time of insertion is low even if the groove
54
is not formed wide, and there is only a slight possibility that the radiation-absorbing plate
44
will bend. Because the structure of the radiation-absorbing plate
44
in the third embodiment is also simple, it can be easily manufactured and is inexpensive. In addition, as the groove
54
is formed over the overall length from the upper edge
42
a
of the support member
42
to the lower edge
42
b
, the two support members
42
can be made the same. In the third embodiment, the support member
42
is very strong because the groove
54
is not an opening penetrating the plate thickness of the support member
42
. Therefore, the rigidity of the grid
40
is significantly increased and positioning accuracy of the radiation-absorbing plate
44
is enhanced.
FIGS. 6 and 7
show a grid
60
constructed according to a fourth embodiment of the present invention. This fourth embodiment, as with the aforementioned embodiments, is a linear grid, but is different in that a focusing grid in which radiation-absorbing plates
64
incline toward a radiation source X (
FIG. 7
) is located at a predetermined position. As illustrated in
FIGS. 6 and 7A
, the plate-receiving means in the fourth embodiment is constructed by a plurality of slots
74
, which extend by approximately half of the height h of a support member
62
in the directions that focus toward the radiation source X. Note that some of the slots
74
shown in
FIGS. 6 and 7
are omitted in order to make understanding of the present invention easy, but there are actually a large number of slots
74
. Since the radiation source X is usually positioned above the central portion of the grid
60
, the opposite slots
74
d
of the support member
62
incline most so that they are directed toward the radiation source X. As shown in
FIG. 7A
, the slots
74
inside the opposite slots
74
d
gradually sequentially approach a right angle with respect to the upper edge
62
a
of the support member
62
, and only the central slot
74
c
crosses the upper edge
62
a
at a right angle.
The radiation-absorbing plate
64
has two slots
76
similar to those of the radiation-absorbing plate
4
of the first embodiment shown in FIG.
1
. If the support members
62
and the radiation-absorbing plates
64
are assembled, the grid
60
is obtained as shown in FIG.
6
. Since the radiation-absorbing plates
64
are disposed in the directions that focus at the radiation source X, some of the rays, transmitted through a subject (not shown) positioned between the radiation source X and the grid
60
, are linearly incident on the grid
60
without being intercepted by the radiation-absorbing plates
64
. These rays then reach a radiation detector (not shown) positioned under the grid
60
, and form a transmitted image. As a result, so-called cutoff, which is normally caused by interception of the transmitted radiation performed by the radiation-absorbing plates
64
, will not occur, and a variation in the transmittance is eliminated and an image of high image quality is obtained. As with the aforementioned embodiments, the two support members
62
can be made the same.
FIG. 8
shows a cross grid
80
constructed according to a fifth embodiment of the present invention The difference between the grid
80
of the fifth embodiment and the linear grids
1
,
20
,
40
and
60
of the aforementioned four embodiments is that radiation-absorbing plates
84
are each provided with a plurality of slots
96
disposed in parallel at predetermined intervals. Also, a plurality of thin support members (plates)
82
, which are composed of the same material as the radiation-absorbing plate
84
, i.e., a radiation-absorbing substance such as lead, tantalum and the like, are disposed in parallel in the slots
96
of the radiation-absorbing plates
84
. With this disposition, the radiation-absorbing support members
82
and the radiation-absorbing plates
84
as a whole constitute the cross grid
80
. The opposite ends of each radiation-absorbing support member
82
are connected to the opposite connecting members
86
through the opposite slots
96
of the radiation-absorbing support member
84
. In addition, since the radiation-absorbing support members
82
and the radiation-absorbing plates
84
engage with one another, the self-supporting grid
80
with great structural strength is obtained.
In cooperation with the radiation-absorbing plates
84
, the radiation-absorbing support members
82
in the cross grid
80
absorb more scattered radiation than the linear grid, and consequently, the cross grid
80
achieves high image quality. However, cutoff will occur in the circumferential portion of the grid
80
, because the radiation-absorbing support members
82
and the radiation-absorbing plates
84
in the fifth embodiment of
FIG. 8
do not incline in the directions that focus at the radiation source X (FIG.
7
). For this reason, radiation, transmitted through the subject and traveling linearly, is absorbed to some degree in the circumferential portion of the grid
80
, so there is a possibility that the image quality will degrade.
A grid
100
of a sixth embodiment improving the above disadvantage is shown in
FIGS. 9 and 10
.
FIG. 10
shows a support member
102
and a radiation-absorbing plate
104
used in the grid
100
. In the grid
100
of the sixth embodiment, slots
114
and
116
, inclining in the directions that focus at a radiation source X (FIG.
10
), are formed in the support member
102
and the radiation-absorbing plate
104
, respectively. The slot
116
of the radiation-absorbing plate
104
is formed from one edge
104
b
of the radiation-absorbing plate
104
toward the other edge
104
a
by approximately half of the height h of the radiation-absorbing plate
104
. With this construction, the support members
102
and the radiation-absorbing plates
104
engage with one another, whereby the cross grid
100
is formed as shown in FIG.
9
. As with the fifth embodiment, it is desirable that the support members
102
intervening between the opposite support members
102
be thin.
The height of the slot
114
of the support member
102
is approximately half of the height h of the support member
102
, as in FIG.
7
A. Since the intervening support members
102
, as with the fifth embodiment, consist of a radiation-absorbing substance, rays scattered at the subject (not shown) are absorbed by the cross grid
100
. In addition, the rays, transmitted through the subject and traveling linearly, arrive at a detector (not shown) without being intercepted by the cross grid
100
, i.e., without giving rise to cutoff. Therefore, in the cross grid
100
of this sixth embodiment, the transmittance is enhanced and the scattered radiation are effectively reduced. Thus, a high quality transmitted image is obtained over the entire surface of the grid
100
.
FIG. 11
shows a grid
120
of a seventh embodiment of the present invention. The seventh embodiment differs from the aforementioned embodiments in that the plate-receiving means provided in the support members
122
are constructed by elongated holes
134
. The support members
122
are connected at the opposite ends to the connecting members
126
and are formed into the shape of a frame as a whole, as with the first embodiment. In each support member
122
, a plurality of vertical elongated holes
134
(i.e., plate-receiving means) are formed at predetermined intervals along the longitudinal direction of the support member
122
. Rectangular radiation-absorbing plates
124
are inserted into these elongated holes
134
, and the end portions
125
of each radiation-absorbing plate
124
penetrate the elongated holes
134
and project from the holes
134
. After the radiation-absorbing plates
124
have been inserted into the elongated holes
134
, movement of the radiation-absorbing plates
124
in the vertical direction perpendicular to the longitudinal direction is regulated and therefore there is no possibility that the radiation-absorbing plates
124
will slide in the vertical direction. In this way, the radiation-absorbing plates
124
are supported in parallel by the support members
122
, whereby the grid
120
is constructed. In this condition the radiation-absorbing plates
124
may be fixed to the support members
122
by adhesion or the like. However, in the case where there is deformation, such as deflection, wrinkles and the like, in the radiation-absorbing plates
124
, there is a need to correct the plate deformation before fixation and make the radiation-absorbing plates
124
flat.
The method of correcting plate deformation will be described with reference to FIG.
12
. As shown in
FIG. 12A
, the end portions of two metal wires
131
are passed through holes
126
formed in the end portions
125
of a radiation-absorbing plate
124
a
and are tied in loop form. Then, the radiation-absorbing plate
124
a
is pulled in the opposite directions by the two metal wires
131
, whereby deformation, such as wrinkles and the like, is corrected. This correcting operation is performed after the radiation-absorbing plates
124
a
have been inserted into the support members
122
, and the same applies to radiation-absorbing plates
124
b
,
124
c
to be described later. A frame-shaped jig
133
(only the part of which is shown in
FIG. 12A
) is disposed to surround the circumference of the grid
120
, and the other end of the metal wire
131
which stretches each radiation-absorbing plate
124
a
is wound and fixed to this jig
133
. Next, the radiation-absorbing plates
124
a
thus stretched are fixed to the support members
122
by adhesion or the like. In addition, instead of the metal wire
131
, a rod (not shown) may be inserted into the hole
125
and the other end of this rod fixed to the jig
133
by an appropriate method.
In the case of the radiation-absorbing plate
124
b
shown in
FIG. 12B
, cutouts
128
are formed in the opposite end portions
125
of the radiation-absorbing plate
124
b
, respectively. The end portions of the aforementioned wires
131
are wound around these cutouts
128
and tied in the form of a loop. The operation thereafter is the same as the case of FIG.
12
A.
In the case where the metal wires
131
are not used, irregularities
130
on the surfaces of both end portions
125
of the radiation-absorbing plate
124
c
may be clamped by a tool
135
such as cutting pliers and pulled in the opposite directions, as shown in FIG.
12
C. The irregularities
130
are formed by embossing and prevent the tool
135
from slipping when clamped by the tool
135
. When the tool
135
is not used, the aforementioned jig
133
is not used. In addition, the irregularities
130
may be formed by notching.
Note that while the method of correcting plate deformation has been described in the case of the elongated holes
134
, plate deformation can also be corrected for the slots
14
,
34
(
FIGS. 1 and 2
) and the grooves
54
(
FIG. 4
) in the same manner. For instance, for the slots
14
shown in
FIG. 1
, the radiation-absorbing plates
4
are inserted into the support members
2
, as in the elongated holes
134
. After insertion, the end portions of each radiation-absorbing plate
4
protruding from
64
the slots
14
are pulled, and after deformation in each radiation-absorbing plate
4
has been corrected, the radiation-absorbing plates
4
are glued to the support members
2
. This method can also be used in the cross grid
80
(
FIG. 8
) in which the radiation-absorbing support members
82
and the radiation-absorbing plates
84
are disposed in the form of a lattice. In this case, deformation in all the radiation-absorbing support members
82
and radiation-absorbing plates
84
can be corrected by pulling them vertically and horizontally, i.e., in 4 directions. Thereafter, they may likewise be fixed by adhesion.
In the grooves
54
shown in
FIG. 4
, each radiation-absorbing plate
44
is pulled to a length equal to the space between the support members
42
plus two groove depths, and then the radiation-absorbing plates
44
are connected to the grooves
54
by adhesion. When the radiation-absorbing plate
44
is longer than the aforementioned length, it may be cut to coincide with that length. Thereafter, the radiation-absorbing plates
44
are likewise glued to the support members
42
.
FIG. 13
shows a grid
140
that is capable of keeping radiation-absorbing plates
124
stretched, after the grid has been constructed. Note that a description is made by applying the same reference numerals to the same components. As illustrated in
FIG. 13A
, two compression coil springs (hereinafter referred to simply as springs) (elastic bodies)
144
are interposed between both end portions of two support members
142
supporting a large number of radiation-absorbing plates
124
in parallel. As the springs
144
pull support members
142
in the opposite directions, the radiation-absorbing plates
124
fixed to the support members
142
are stretched and their flatness is ensured. The springs
144
are inserted onto shafts (not shown) or into a cylindrical member (not shown), whereby the shape is maintained. Instead of the springs
144
, other elastic bodies, for example, synthetic resin material with elasticity, such as polyurethane, may be employed.
In a grid
160
shown in
FIG. 13B
, springs
164
for urging support members
162
are provided on both sides of a pair of fixed or unmovable portions
166
. The fixed portions
166
are disposed at the opposite end portions of the support members
162
and are coupled with a base
168
, which is part of the grid
160
, or are formed integrally with the base
168
. The fixed portions
166
are disposed approximately midway between the two support members
162
. This can make the length of the springs
164
shorter and prevent the springs
164
from being deflected horizontally.
FIG. 14
shows a grid
180
that is an eighth embodiment of the present invention, in which stretched radiation-absorbing plates
184
are fixed by use of surface plates consisting of carbon, i.e., a ceiling plate
186
and a bottom plate
188
. First, the radiation-absorbing plates
184
are fixed to the support members
182
by an adhesive agent
185
, or protrusions
187
, etc. Then, the ceiling plate
186
and the bottom plate
188
are disposed to interpose the radiation-absorbing plates
184
therebetween and are glued to the radiation-absorbing plates
184
by adhesion or the like. The ceiling plate
186
and the bottom plate
188
are slightly smaller in outside dimensions than a frame
192
, constructed by the support members
182
and connecting members
190
. The ceiling plate
186
and the bottom plate
188
, therefore, can easily be inserted into the frame
192
and glued to the radiation-absorbing plates
184
. In this way, fixing of the radiation-absorbing plates
184
can be performed even more reliably and therefore the rigidity of the entire grid and the structural strength of the frame
192
are enhanced. In this case, the support members
182
with slots are removable, since the ceiling plate
186
, the bottom plate
188
, and the radiation-absorbing plates
184
are fixed. In addition, in the case where the ceiling plate
186
and the bottom plate
188
are glued and fixed to the circumferential edges
194
of the frame
192
instead of being inserted into the frame
192
, the radiation-absorbing plates
184
are not glued to the ceiling plate
186
and the bottom plate
188
, but can maintain the entire rigidity. Furthermore, the radiation-absorbing plates
184
can be held in position, as they are protected from external influence.
In the case of using the ceiling plate
186
and the bottom plate
188
in this manner, the radiation-absorbing plates
184
can be fixed by various methods. For instance, another embodiment of the grid
180
is illustrated in FIG.
15
. In the case of this grid
180
, the bottom plate
188
is glued to the radiation-absorbing plates
184
, while the ceiling plate
186
is glued to the support members
182
, i.e., the upper edge of the frame
192
. In this case, the bottom plate
188
can also be glued to the frame
192
, because it is located inside the frame
192
. With this construction, straightness in the radiation-absorbing plates
184
is ensured and the rigidity of the frame
192
can be maintained.
Conversely, the ceiling plate
186
may be inserted into the frame
192
and glued to the radiation-absorbing plates
184
, and the bottom plate
188
may be glued to the lower edge
194
of the frame
192
, away from the radiation-absorbing plates
184
. Similarly, the same effect is obtainable.
In the former case, i.e., in the case where the ceiling plate
186
and the bottom plate
188
are glued to the radiation-absorbing plates
184
, grooves may be formed at positions on the inner surfaces of the ceiling plate and bottom plate
186
and
188
which correspond to the radiation-absorbing plates
184
. In this case, adhesion and positioning of the radiation-absorbing plates
184
can be performed reliably by inserting the radiation-absorbing plates
184
into the grooves. In addition, in the latter case, i.e., in the case where the ceiling plate
186
and the bottom plate
188
are not glued to the radiation-absorbing plates
184
, grooves or stepped portions may likewise be formed at positions on the ceiling plate and bottom plate
186
and
188
which correspond to the support members
182
and the connecting members
190
. In this case, positioning of the frame
192
can be formed reliably and these components become difficult to deform.
Illustrated in
FIG. 16
is a grid
180
a
of still another embodiment. Although the radiation-absorbing plates used in this embodiment are the same as the aforementioned radiation-absorbing plates
184
, they are mounted on the bottom plate
188
so that they incline toward a source of radiation (not shown). For example, the radiation-absorbing plates
184
are inclined by use of support members
112
a
in which the elongated holes
134
shown in
FIG. 11
are arranged to incline toward the radiation source. Then, the inclined radiation-absorbing plates
184
are glued and fixed to the bottom plate
188
. Notice that in
FIG. 16
, only one of the two support members
122
a
is shown. Thereafter, if the support members
122
a
are removed, the grid
180
a
is obtained as shown. In this case, the radiation-absorbing plates
184
are kept inclined by the bottom plate
188
alone, because they are not glued to the ceiling plate
186
.
conversely, as another variation, the radiation-absorbing plates
184
may be glued and fixed to the ceiling plate
184
, and the bottom plate
188
and the support members
122
a
may be removed.
In the case where the support members
122
a
are finally made unnecessary in this manner, the grid
180
a
can be reduced in size and becomes easy to handle. When the radiation-absorbing plates
184
are great in width, i.e., height, the effect of removing the support member
122
a
becomes much greater because the support members
122
a
becomes greater in height and weight.
While the present invention has been described with reference to the preferred embodiments thereof, the invention is not limited to the details given herein, but may be modified within the scope of the appended claims.
Claims
- 1. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and at least two support members for supporting opposite end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein at least some of said radiation-absorbing plates are pulled so as to be stretched in a longitudinal direction of said radiation-absorbing plates, and said radiation-absorbing plates are fixed to said support members.
- 2. The X-ray scatter reducing grid as set forth in claim 1, wherein said support members are constructed by two first support members which support the opposite end portions of each of said radiation-absorbing plates and two second support members which connect to said two first support members so that said four support members constitute a rectangular frame.
- 3. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed in parallel at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and at least two support members for supporting opposite lengthwise end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein said plate-receiving means are constructed by a plurality of slots which receive and support the opposite lengthwise end portions of each of said radiation-absorbing plates, and wherein at least some of said radiation-absorbing plates are pulled so as to be stretched in a longitudinal direction of said radiation-absorbing plates, and said radiation-absorbing plates are fixed to said support members.
- 4. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed in parallel at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and at least two support members for supporting opposite lengthwise end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein said plate-receiving means are constructed by a plurality of elongated holes which receive and support the opposite lengthwise end portions of each of said radiation-absorbing plates, and wherein at least some of said radiation-absorbing plates are pulled so as to be stretched in a longitudinal direction of said radiation-absorbing plates, and said radiation-absorbing plates are fixed to said support members.
- 5. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and at least two support members for supporting opposite lengthwise end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein said plate-receiving means is constructed by a plurality of elongated holes which receive and support the opposite end portions of each of said radiation-absorbing plates, and wherein at least some of said radiation-absorbing plates are pulled so as to be stretched in a longitudinal direction of said radiation-absorbing plates, and said radiation-absorbing plates are fixed to said support members.
- 6. A method of fabricating an X-ray scatter reducing grid, comprising:inserting lengthwise opposite end portions of each of a plurality of radiation-absorbing plates into plate-receiving means formed in at least two support members, said radiation-absorbing plates being disposed in parallel at predetermined intervals over an entire area to be exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; supporting the lengthwise opposite end portions of each of said radiation-absorbing plates by said plate-receiving means; fixing said radiation-absorbing plates to said plate-receiving means by at least one of adhering, fusing, and press-fitting, pulling at least some of said radiation-absorbing plates so as to stretch pulled ones of said radiation-absorbing plates in a longitudinal direction of said radiation-absorbing plates; and fixing said pulled ones of said radiation-absorbing plates to said support members.
- 7. A method of fabrication an X-ray scatter reducing grid, comprising:inserting lengthwise opposite end portions of each of a plurality of radiation-absorbing plates into plate-receiving means formed in at least two support members, said radiation-absorbing plates being disposed in parallel at predetermined intervals over an entire area to be exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; supporting the lengthwise opposite end portions of each of said radiation-absorbing plates by said plate-receiving means; wherein said X-ray scatter reducing grid includes at least one of a ceiling plate and a bottom plate, the method further comprising fixing said radiation-absorbing plates to at least one of said ceiling plate and said bottom plate, pulling at least some of said radiation-absorbing plates so as to stretch pulled ones of said radiation-absorbing plates in a longitudinal direction of said radiation-absorbing plates; and fixing said pulled ones of said radiation-absorbing plates to said support members.
- 8. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed in parallel at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and two support members for supporting opposite end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein said radiation-absorbing plates are fixed to said two support member, elastic bodies being interposed between said two support members so that said two support members are urged in a direction in which said radiation-absorbing plates are stretched.
- 9. The X-ray scatter reducing grid as set forth in claim 8, wherein said support members are constructed by two first support members which support the opposite end portions of each of said radiation-absorbing plates and two second support members which connect to said two first support member so that said four support members constitute a rectangular frame.
- 10. An X-ray scatter reducing grid comprising:a plurality of radiation-absorbing plates disposed at predetermined intervals over an entire area exposed to radiation, each radiation-absorbing plate comprising a radiation-absorbing substance and having width in a direction in which said radiation travels; and at least two support members for supporting opposite lengthwise end portions of each of said radiation-absorbing plates, said support members being provided with plate-receiving means which receive said plurality of radiation-absorbing plates, said radiation-absorbing plates being inserted in said plate-receiving means and being supported by said support members, wherein said plate-receiving means is constructed by a plurality of elongated holes which receive and support the opposite end portions of each of said radiation-absorbing plates, and wherein said radiation-absorbing plates are fixed to said two support members, elastic bodies being interposed between said two support members so that said two support members are urged in a direction in which said radiation-absorbing plates are stretched.
Priority Claims (2)
Number |
Date |
Country |
Kind |
11/076038 |
Mar 1999 |
JP |
|
2000/024048 |
Feb 2000 |
JP |
|
US Referenced Citations (8)
Foreign Referenced Citations (2)
Number |
Date |
Country |
10-5207 |
Jan 1998 |
JP |
10-005207 |
Jan 1998 |
JP |