Patent Number: 
Section: description

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 2a thereof toward the lower edge 2b a plurality of plate-receiving means (in this embodiment, slots 14) are formed in parallel at predetermined intervals at approximately half (xc2xd h) of the height h of the support member 2, as shown in FIG. 1B. 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. 1A. 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 4b thereof toward the upper edge 4a at approximately half (xc2xd 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. 1A. 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 4a of the radiation-absorbing plate 4 becomes substantially coplanar with the upper edge 2a 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 22a to the vicinity of its lower edge 22b.  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 42a of the support member 42 to the lower edge 42b. Therefore, the opposite edges 44c of each radiation-absorbing plate 44 are inserted and supported in the corresponding grooves 54 of the support members 42 through the upper edges 42a 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 44c 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 42a of the support member 42 to the lower edge 42b, 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 74d 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 74d gradually sequentially approach a right angle with respect to the upper edge 62a of the support member 62, and only the central slot 74c crosses the upper edge 62a 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 104b of the radiation-absorbing plate 104 toward the other edge 104a 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. 7A. 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 124a and are tied in loop form. Then, the radiation-absorbing plate 124a 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 124a have been inserted into the support members 122, and the same applies to radiation-absorbing plates 124b, 124c 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 124a is wound and fixed to this jig 133. Next, the radiation-absorbing plates 124a 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 124b shown in FIG. 12B, cutouts 128 are formed in the opposite end portions 125 of the radiation-absorbing plate 124b, 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. 12A. 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 124c may be clamped by a tool 135 such as cutting pliers and pulled in the opposite directions, as shown in FIG. 12C. 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 180a 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 112a 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 122a is shown. Thereafter, if the support members 122a are removed, the grid 180a 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 122a may be removed. In the case where the support members 122a are finally made unnecessary in this manner, the grid 180a 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 122a becomes much greater because the support members 122a 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.