EP0262168A1 - Compensation filter for radiography - Google Patents

Compensation filter for radiography

Info

Publication number
EP0262168A1
EP0262168A1 EP19870901465 EP87901465A EP0262168A1 EP 0262168 A1 EP0262168 A1 EP 0262168A1 EP 19870901465 EP19870901465 EP 19870901465 EP 87901465 A EP87901465 A EP 87901465A EP 0262168 A1 EP0262168 A1 EP 0262168A1
Authority
EP
European Patent Office
Prior art keywords
filtering
filter according
absorption
elements
filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19870901465
Other languages
German (de)
French (fr)
Inventor
Yves Castel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0262168A1 publication Critical patent/EP0262168A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/10—Scattering devices; Absorbing devices; Ionising radiation filters

Definitions

  • COMPENSATION FILTER FOR RADIOGRAPHY This invention relates to a compensation filter useful in radiography and. more particularly, to such a filter intended for lung radiography.
  • Filters are currently used to limit this difference artificially. Such filters, suitably located, make it possible to reduce the quantity of radiation impinging the pulmonary fields without limiting it in the mediastinum area. This results in an image having a weaker overall contrast, containing a more extensive range of information.
  • the present invention therefore, has for its object to provide a compensation filter which does not exhibit the drawbacks of the prior art filters.
  • the present invention has also for its object to provide such a filter permitting to obtain different filtering rates with a same set of filtering elements.
  • a compensation filter for radiographic use intended to reduce the contrast of a radiograph so as to take into account the differences of absorption of the various X-rayed areas, comprising a platen provided with an opening and at least two filtering elements carried by said platent according to adjustable relative positions, to filter X-rays in regions adjacent to an elongated central area separating said two elements.
  • said elements have each a transverse gradient of absorption to X-rays so that, in first and second relative positions of the filtering elements, the absorption rate of the elements in the vicinity of the central area be equal to first and second predeterminated values, respectively.
  • - Fig. 1 is an elevation view of a filtering element forming a part of the filter of the invention
  • - Fig. 2 is a cross-section view of the filtering element of Fig. 1, taken along section line 2-2 of said figure ;
  • - Fig. 3 is a cross-section view of the filtering element of Fig. 1, taken along section line 3-3 of said figure ;
  • - Fig. 4 is an elevation view of the filter according to the invention, comprising two filtering elements of the type of the one represented on Figs. 1 to 3 ;
  • Fig. 5 is a cross-section view of the filter of Fig. 4, taken along section line 5-5 of said figure ;
  • - Fig. 6. is a view similar to that of Fig. 4, showing the filtering elements in another arrangement whereby another filtering rate is obtained in the vicinity of a central area ;
  • _ Fig. 7 is a cross-section view taken along section line 7-7 of Fig. 6.
  • FIG. 8 is a view of the filter according to the invention, which illustrates the positioning flexibility of the filtering elements of the filter of the invention.
  • FIG. 1 to 3 where is represented a filtering element forming a portion of the filter according to the invention.
  • This element essentially comprises a filtering block 1 fastened with glue, for example, on a plate 2 which is highly transparent to
  • This plate can be made up in a transparent and homogeneous plastic material, e.g. a polymethacrylate such as Plexiglas from Rohm & Haas Co.
  • the filtering block 1 is made up in a material having a good absorbing power toward X-rays, such as, in particular, lead-containing polyacrylates or polymethacrylates. As it is conventional in filters used in radiology, block 1 has three bevelled faces 1', 1" and 1'". in the vicinity of three of its edges. According to a feature of the invention which appears upon examination of Fig. 2, the thickness of filtering block 2 varies progessively from an edge to the other of this block. It can be understood that block 1 thus forms a filtering gradient parallel to section line 2-2 of Fig. ⁇ . it will be explained hereafter, in connection with Figs 4 to 7, the use which is made of this feature of the present invention.
  • plate 2 has a rectilinear edge 5 whereas the opposite edge follows a broken line whose end breaks 6 and 7 are tilted according to opposite angles on the median portion of the line. The usefulness of this arrangement will be explained hereafter in connection with the description of Fig. 7.
  • Figs 4 and 5 where is represented an embodiment of the filter according to the present invention.
  • This filter comprises two filtering elements 9 and 10 fixed in a removable manner on square platen 11 provided with window 11'. The whole is intended to be interposed on the X-ray beam emitted in an examination X-ray device and or X-ray camera, between the radiation source and the plane wherein is the patient to be X-rayed.
  • the filter according to the present invention can be fixed on the exit of the X-ray tube.
  • Element 9 is quite identical to the one represented in Figs 1 and 3.
  • Element 10 differs from the latter in the fact that the thickness of filtering block 1 a. varies, along section line 5-5 of Fig. 4.
  • the filter according to the present invention does not absorb X-rays going through region 12 separating both filtering elements.
  • the filter is placed in such a way that this region corresponds to the mediastinum, which has a natural strong absorption. On both parts of this region, the filters cover the lung fields, having a lower absorption, which is compensated by filtering.
  • the filtering elements are arranged as represented in Figs. 4 and 5. In the vicinity of central area 12, the filtering elements exhibit their greater thickness, which decreases gradually from the central area.
  • the filtering elements are arranged as represented in Figs. 6 and 7. This arrangement is simply obtained by reversing the positions of filtering elements 9 and 10 on platen 11.
  • the filtering gradient obtained in this arrangement is such that the filtering increases from the central area, on both sides.
  • the filtering level set up in the vicinity of region 12 is quite weaker than in the arrangement of Fig. 4, because of the lesser thickness of the filtering elements in their parts close to region 12.
  • two different absorption rates can be set up in the vicinity of central region 12, which separates the filtering elements and corresponds to the mediastinum in lung radiography, by means of the same set of filtering elements, only by changing their relative arrangement.
  • Such a result is of interest as it makes it possible to simply adjust the absorption rate in relation to the desired contrast. With conventional filters, this result can be only obtained by using different sets of filters.
  • the present invention is also advantageous from the economical point of view.
  • the filtering gradient sought after could be obtained by other means than linear and continuous variation in the thickness of filtering blocks.
  • the gradient can also be obtained by continuous or discontinuous variation in the composition of the material which constitutes the filtering block, preferably to a variation in thickness, as it will be apparent for those skilled in the Art.
  • the relative positions of the filtering elements on platen 11 can vary continuously to adapt these positions to the anatomic peculiarities of the patients.
  • the width of central area 12 can vary in relation to the particular dimensions of certain organs such as the heart or the lungs.
  • the filtering elements are fixed, in a removable manner, on platen 11 by fastening means allowing variations in their positioning, for example strips marketed under the trademark Velcro.
  • magnets 3,4 (Fig. 3) are fastened on the back of plate 2 and platen 11 is made up by means of a metallic plate acting with the magnets to fasten each filtering element in a position chosen by the operator.
  • FIG. 8 This flexibility in the choice of the positioning of the filtering elements is also shown in Fig. 8, wherein central area 12 separating these elements exhibits a width increasing gradually form the top to the bottom, in this figure. In this manner, it is easy to adapt the device to patients exhibiting hearts of varying sizes, whose fields are incribed in the widest part of region 12.
  • the necessary tilt of filtering element 10 on filtering element 9 is made possible by break 7 of the left outline of element 10. This break prevents both elements from interfering, even if they are together very close. It will be noted in addition in Fig.
  • filtering block 1 of filtering element has cutt-off corners or dissymetrical truncations 13, 14 in its lower part (in this figure), cutt-off corner 13 being larger than cutt-off corner 14.
  • Figs 4. 6 and 8 Reference is made to Figs 4. 6 and 8 to understand the reason for this arrangement.
  • the filter according to the present invention used in lung radiography, clears the central part corresponding to the mediastinum, having at its base in particular the heart, strongly absorbing X-rays. Cutt-off corners 13, 14' (Fig. 4) or 13'. 14 (Fig. 6 and 8) and part 12 which separates them, correspond to the position of the heart in the lung image, approximately.
  • cutt-off corners make it possible to reduce the absorption of the filtering elements if placed on a strongly absorbent organ.
  • the dissymetry in cutt-off corners allows to take into account the incline of the axis of the heart in the mediastinum. This incline leads to delimit a cutt-off corner having a larger surface on the left edge of each filtering element (in Figs 4,6 and 8).

Abstract

Le filtre décrit comprend une plaque métallique (11), sur laquelle des éléments de filtrage (9, 10) sont fixés de façon amovible à l'aide d'aimants. Une région médiane (12) sans fonction de filtrage est délimitée par lesdits éléments. Les éléments de filtrage, placés transversalement à ladite région, présente un gradient d'absorption qui varie graduellement ou pas à pas d'un bord à l'autre de chaque élément de filtrage. Dans les éléments représentés dans la figure, l'absorption est maximum à proximité de la région (12). En permutant les positions des éléments (9) et (10), on obtient une absorption minimum à proximité de ladite région. Ledit filtre sert à réduire les contrastes dans les radiographies pulmonaires.The filter described comprises a metal plate (11), on which filter elements (9, 10) are removably attached using magnets. A middle region (12) without filtering function is delimited by said elements. The filter elements, placed transversely to said region, have an absorption gradient which varies gradually or step by step from one edge to the other of each filter element. In the elements shown in the figure, the absorption is maximum near the region (12). By swapping the positions of elements (9) and (10), a minimum absorption is obtained near said region. Said filter is used to reduce the contrasts in chest x-rays.

Description

COMPENSATION FILTER FOR RADIOGRAPHY This invention relates to a compensation filter useful in radiography and. more particularly, to such a filter intended for lung radiography.
In lung radiography, a substantial difference of absorption of the X-rays is observed between the pulmonary fields and the median portion of the thorax . that contains in particular the heart.
Filters are currently used to limit this difference artificially. Such filters, suitably located, make it possible to reduce the quantity of radiation impinging the pulmonary fields without limiting it in the mediastinum area. This results in an image having a weaker overall contrast, containing a more extensive range of information.
The filters known to this effect nevertheless exhibit various drawbacks. Some of them are formed so as to be adapted to the shape of the fields to be filtered, by suitably cut out outlines. Unfortunately, the rigid character of said outlines is such that they are suitable only to the anatomy of a limited selection of patients. In French Patent 2.530,857. is also disclosed a system of filters for radiography, which comprises two filtering elements movable with respect to each other on a common supporting member, so as to define between them an opening having a variable width. This arrangement makes it possible, to some extent, to adapt the filter to the physiology of the different patients to be examined. However, the filtering rate of the filtering elements used cannot be varied from an examination to the other while using the same elements.
The present invention, therefore, has for its object to provide a compensation filter which does not exhibit the drawbacks of the prior art filters.
The present invention has also for its object to provide such a filter permitting to obtain different filtering rates with a same set of filtering elements.
These objects of the invention are reached with a compensation filter for radiographic use, intended to reduce the contrast of a radiograph so as to take into account the differences of absorption of the various X-rayed areas, comprising a platen provided with an opening and at least two filtering elements carried by said platent according to adjustable relative positions, to filter X-rays in regions adjacent to an elongated central area separating said two elements. According to the invention, said elements have each a transverse gradient of absorption to X-rays so that, in first and second relative positions of the filtering elements, the absorption rate of the elements in the vicinity of the central area be equal to first and second predeterminated values, respectively.
On the attached drawing, given only as an example :
- Fig. 1 is an elevation view of a filtering element forming a part of the filter of the invention ; - Fig. 2 is a cross-section view of the filtering element of Fig. 1, taken along section line 2-2 of said figure ;
- Fig. 3 is a cross-section view of the filtering element of Fig. 1, taken along section line 3-3 of said figure ; - Fig. 4 is an elevation view of the filter according to the invention, comprising two filtering elements of the type of the one represented on Figs. 1 to 3 ;
- Fig. 5 is a cross-section view of the filter of Fig. 4, taken along section line 5-5 of said figure ;
- Fig. 6. is a view similar to that of Fig. 4, showing the filtering elements in another arrangement whereby another filtering rate is obtained in the vicinity of a central area ; _ Fig. 7 is a cross-section view taken along section line 7-7 of Fig. 6. and
- Fig. 8 is a view of the filter according to the invention, which illustrates the positioning flexibility of the filtering elements of the filter of the invention.
Reference is made to Figs. 1 to 3 where is represented a filtering element forming a portion of the filter according to the invention. This element essentially comprises a filtering block 1 fastened with glue, for exemple, on a plate 2 which is highly transparent to
X-rays. This plate can be made up in a transparent and homogeneous plastic material, e.g. a polymethacrylate such as Plexiglas from Rohm & Haas Co.
The filtering block 1 is made up in a material having a good absorbing power toward X-rays, such as, in particular, lead-containing polyacrylates or polymethacrylates. As it is conventional in filters used in radiology, block 1 has three bevelled faces 1', 1" and 1'". in the vicinity of three of its edges. According to a feature of the invention which appears upon examination of Fig. 2, the thickness of filtering block 2 varies progessively from an edge to the other of this block. It can be understood that block 1 thus forms a filtering gradient parallel to section line 2-2 of Fig. ι. it will be explained hereafter, in connection with Figs 4 to 7, the use which is made of this feature of the present invention.
It will be noted that plate 2 has a rectilinear edge 5 whereas the opposite edge follows a broken line whose end breaks 6 and 7 are tilted according to opposite angles on the median portion of the line. The usefulness of this arrangement will be explained hereafter in connection with the description of Fig. 7.
Reference is made now to Figs 4 and 5 where is represented an embodiment of the filter according to the present invention. This filter comprises two filtering elements 9 and 10 fixed in a removable manner on square platen 11 provided with window 11'. The whole is intended to be interposed on the X-ray beam emitted in an examination X-ray device and or X-ray camera, between the radiation source and the plane wherein is the patient to be X-rayed. For example the filter according to the present invention can be fixed on the exit of the X-ray tube. Element 9 is quite identical to the one represented in Figs 1 and 3. Element 10 differs from the latter in the fact that the thickness of filtering block 1 a. varies, along section line 5-5 of Fig. 4. inversely as the one of filtering block 1 of element 9. (See Fig. 5). In the arrangement represented in Figs 4 and 5. it appears that the filter according to the present invention does not absorb X-rays going through region 12 separating both filtering elements. In lung radiology, the filter is placed in such a way that this region corresponds to the mediastinum, which has a natural strong absorption. On both parts of this region, the filters cover the lung fields, having a lower absorption, which is compensated by filtering.
According to the invention, if it is desired to set up a strong filtering on the fields close to the mediastinum, the filtering elements are arranged as represented in Figs. 4 and 5. In the vicinity of central area 12, the filtering elements exhibit their greater thickness, which decreases gradually from the central area.
If it is desired to set up a weaker filtering in the vicinity of the mediastinum, to take into account, for example the characteristics of the radiant source or of the X-rayed patient, according to the invention, the filtering elements are arranged as represented in Figs. 6 and 7. This arrangement is simply obtained by reversing the positions of filtering elements 9 and 10 on platen 11.
It appears on Fig. 7 that the filtering gradient obtained in this arrangement is such that the filtering increases from the central area, on both sides. The filtering level set up in the vicinity of region 12 is quite weaker than in the arrangement of Fig. 4, because of the lesser thickness of the filtering elements in their parts close to region 12. In this manner, by means of the filter according to the present invention, two different absorption rates can be set up in the vicinity of central region 12, which separates the filtering elements and corresponds to the mediastinum in lung radiography, by means of the same set of filtering elements, only by changing their relative arrangement. Such a result is of interest as it makes it possible to simply adjust the absorption rate in relation to the desired contrast. With conventional filters, this result can be only obtained by using different sets of filters. The present invention is also advantageous from the economical point of view.
Of course the filtering gradient sought after could be obtained by other means than linear and continuous variation in the thickness of filtering blocks. One can decide upon a variation in steps or any other non-linear variation in the thickness. The gradient can also be obtained by continuous or discontinuous variation in the composition of the material which constitutes the filtering block, preferably to a variation in thickness, as it will be apparent for those skilled in the Art.
To make the use of the filter according to the present invention as flexible as possible, it is essential that the relative positions of the filtering elements on platen 11 can vary continuously to adapt these positions to the anatomic peculiarities of the patients. For example the width of central area 12 can vary in relation to the particular dimensions of certain organs such as the heart or the lungs.
For this purpose, the filtering elements are fixed, in a removable manner, on platen 11 by fastening means allowing variations in their positioning, for example strips marketed under the trademark Velcro. According to a preferred embodiment of the present invention, magnets 3,4 (Fig. 3) are fastened on the back of plate 2 and platen 11 is made up by means of a metallic plate acting with the magnets to fasten each filtering element in a position chosen by the operator.
This flexibility in the choice of the positioning of the filtering elements is also shown in Fig. 8, wherein central area 12 separating these elements exhibits a width increasing gradually form the top to the bottom, in this figure. In this manner, it is easy to adapt the device to patients exhibiting hearts of varying sizes, whose fields are incribed in the widest part of region 12. The necessary tilt of filtering element 10 on filtering element 9 is made possible by break 7 of the left outline of element 10. This break prevents both elements from interfering, even if they are together very close. It will be noted in addition in Fig. 1 that filtering block 1 of filtering element has cutt-off corners or dissymetrical truncations 13, 14 in its lower part (in this figure), cutt-off corner 13 being larger than cutt-off corner 14. Reference is made to Figs 4. 6 and 8 to understand the reason for this arrangement. The filter according to the present invention, used in lung radiography, clears the central part corresponding to the mediastinum, having at its base in particular the heart, strongly absorbing X-rays. Cutt-off corners 13, 14' (Fig. 4) or 13'. 14 (Fig. 6 and 8) and part 12 which separates them, correspond to the position of the heart in the lung image, approximately. The cutt-off corners make it possible to reduce the absorption of the filtering elements if placed on a strongly absorbent organ. The dissymetry in cutt-off corners allows to take into account the incline of the axis of the heart in the mediastinum. This incline leads to delimit a cutt-off corner having a larger surface on the left edge of each filtering element (in Figs 4,6 and 8).
The invention has been disclosed above in practicing frontal lung radiography. It will be apparent for those skilled in the Art that the filter according to the present invention could be readily adapted for reducing contrasts in radiographs of other parts of human or animal bodies, and even in industrial radiographs of mechanical parts.

Claims

8 CLAIMS
1 - A compensation filter for radiographic use, intended to reduce the contrast of a radiograph to take into account the differences of absorption of the various X-rayed areas, comprising a platen provided with an opening and at least two filtering elements carried by said platen according to adjustable relative positions, to filter X-rays in regions adjacent to an elongated central area separating said two elements, characterized in that said elements have each a transverse gradient of absorption to X-rays so that, in first and second relative positions of the filtering element's, the absorption rate of the elements in the vicinity of the central area be equal to first and second predetermined values, respectively.
2 - A filter according to claim 1. characterized in that the transversal variation of absorption of each filtering element is gradual. 3 - A filter according to claim 1, characterized in that the absorption of each filtering element varies transversely by steps.
4 - A filter according to any of claims 1 to 3 characterized in that the absorption gradient is obtained by transversal variation of the thickness of filtering block (1) which is part of the filtering element.
5 - A filter according to any of claims 1 to 3 characterized in that the absorption gradient is obtained by transversal variation of the chemical composition of filtering block (1) which *s part of the filtering element.
6 - A filter according to any claims 1 to 5. characterized in that in their first and second relative positions, the filtering elements respectively occupy reversed positions on the platen. - A filter according to any of claims 4 to 6. characterized in that each filtering block exhibits cutt-off corners (13, 14, 13', 14') intended to reduce the absorption of the filters locally. - A filter according to claim 7, characterized in that said cutt-off corners are dissymetrical. - A filter according to any claims 4 to 8 characterized in that each filtering block exhibits bevelled edges (1. 1'. 1"'). - A filter according to any of claims 1 to 9. characterized in that each filtering element is carried by the platen in a removable manner according to adjustable position, by means of quick fastening means. - A filter according to claim 10. characterized in that fastening means are of "Velcro" type. - A filter according to claim 10. characterized in that fastening means are made of magnets (3,4)/metal joints between each filtering element and platen - A filter according to any of claims 1 to 12. characterized in that each filtering element comprises breaks (3,4) on one of its edges, for being easily tilted over the other filtering element, - An application of the filter according to any of the previous claims, to frontal lung radiography.
EP19870901465 1986-03-17 1987-02-26 Compensation filter for radiography Withdrawn EP0262168A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8603758A FR2595860A1 (en) 1986-03-17 1986-03-17 COMPENSATION FILTER FOR RADIOGRAPHY
FR8603758 1986-03-17

Publications (1)

Publication Number Publication Date
EP0262168A1 true EP0262168A1 (en) 1988-04-06

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19870901465 Withdrawn EP0262168A1 (en) 1986-03-17 1987-02-26 Compensation filter for radiography

Country Status (3)

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EP (1) EP0262168A1 (en)
FR (1) FR2595860A1 (en)
WO (1) WO1987005739A1 (en)

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Also Published As

Publication number Publication date
WO1987005739A1 (en) 1987-09-24
FR2595860A1 (en) 1987-09-18

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