An x-ray beam collimator and a method of collimating x-ray beams from a plurality of x-ray emitters

Abstract

In chest imaging it is important to only image the lungs without exposing the thyroid gland or the abdominal organs, so the width of the X-ray beam is restricted so that the projection area matches the size of the lungs of each individual patient. For 2D X-ray systems and traditional computed tomography systems there is only one X-ray emission point so it is easy to use a conventional collimator box. However, when using stationary multi-emitter arrays, using lots of conventional collimator boxes would get in the way of neighbouring X-ray beams. The present invention uses a pair of sliding plates 41, 43 with matching holes 45 therein, such that apertures 47 of variable size are formed for each X-ray emitter.

Description

AN X-RAY BEAM COLLIMATOR AND A METHOD OF COLLIMATING X-RAY BEAMS FROM A PLURALITY OF X-RAY EMITTERS

[0001] The present invention relates generally to an X-ray beam collimator for use with a plurality of X-ray emitters and a method of collimating X-ray beams from a plurality of X-ray emitters and finds particular, although not exclusive, utility in X-ray tomosynthesis.

[0002] It is well established that reducing exposure to unnecessary X-rays is desirable. In particular, it is well known to attempt to limit X-ray exposure to a region of interest, which may appear on only a relatively small portion of an X-ray detector, as opposed to directing X-rays over the entire detector. For example, in chest imaging it is important to only image the lungs without exposing the thyroid gland or the abdominal organs, so the width of the X-ray beam is restricted so that the projection area matches the size of the lungs of each individual patient.

[0003] For 2D X-ray systems there is only one X-ray emission point so it is easy to use a conventional collimator box, as illustrated in figures 1 and 2. Computed tomography systems (and other 3D systems) that move a single X-ray source through multiple positions can also use a conventional collimator box.

[0004] However, when using stationary multi-emitter arrays, a conventional collimator box is ineffective because X-ray beams from different emitters will be collimated by different amounts and, in particular, beams from emitters one side of the array can pass under the frame of the collimator on an opposing side of the array, while beams on that opposing side of the array may be blocked entirely, as shown in.

[0005] Collimating each X-ray beam individually would address this problem; however, a conventional collimator box (typically at least several centimetres wide) would get in the way of neighbouring X-ray beams (typically produced by X-ray sources that are at most only a few centimetres apart).

[0006] According to a first aspect of the present invention, there is provided an X-ray beam collimator for use with a plurality of X-ray emitters, the X-ray beam collimator comprising: a first plate comprising: a first hole; and a second hole, spaced from the first hole; a second plate disposed adjacent to, and in a plane parallel to, the first plate, the second plate movable relative to the first plate within the plane between a first position and a second position, the second plate comprising: a third hole located to at least partially overlap the first hole by a first amount when the second plate is in the first position, and by a second amount when the second plate is in the second position, thereby forming a first composite aperture of variable size; and a fourth hole spaced from the third hole, the fourth hole located to at least partially overlap the second hole by a third amount when the second plate is in the first position, and by a fourth amount when the second plate is in the second position, thereby forming a second composite aperture of variable size.

[0007] In this way, each X-ray beam of an array of X-ray emitters may be adjusted at the same time to illuminate a respective varying area on the detector. That is, the present invention uses a pair of sliding plates with matching holes therein, such that apertures of variable size are formed for each X-ray emitter.

[0008] An X-ray beam may be termed a cone or conelet, and may comprise a plurality of parallel rays, but preferably comprises a plurality of diverging rays originating from the emitter and modelled as originating from an idealised point source. The plurality of diverging rays may project over a limited solid angle; that is, significantly less than 4 pi steradians. For example, a beam may diverge around a normal line by 30 degrees (i.e. having a total aperture angle of 60 degrees) thereby projecting over approximately 0.86 steradians.

[0009] According to the present disclosure, an X-ray beam prior to and / or after collimation may project over a solid angle of less than 1 sr, in particular less than 0.8 sr, more particularly less than 0.5 sr. Despite the term cone or conelet being used, such an X-ray beam may not be limited to having only a circular cross-section; rather, such X-ray beams may comprise square and or rectangular cross-sections, thereby having a substantially pyramid shape. In fact, various cross-sections, such as triangular and / or irregular, may be employed.

[0010] Within the meaning of the present disclosure, the terms collimator and / or collimation are not limited to only the case in which an X-ray beam is adjusted such that all its component rays are parallel. Rather, the terms collimator and / or collimation are used to refer to limiting the opening angle of the beam; that is, limiting the solid angle over which the rays project.

[0011] The X-ray emitters may form part of an emitter array and / or emitter panel. Such an array / panel may comprise a plurality of regularly spaced emitters, for example in a square, triangular and / or hexagonal arrangement; however, in some arrangements the plurality of emitters may be irregularly spaced. The array or panel may be planar / flat, or may be curved. The X-ray emitters may form part of a plurality of (e.g. a pair of) emitter arrays and / or emitter panels. Such a plurality of emitter arrays may be orientated in the same plane, in parallel (and / or spaced) planes, or may be orientated in respective planes oblique to one another.

[0012] The plates may be planar and / or flat. The plates may comprise an X-ray impermeable / attenuating material such that X-rays cannot pass through the plate other than through the holes. In particular, the holes may be through-holes and may be substantially empty voids; however, in some arrangements the holes may comprise windows containing X-ray permeable material such as glass.

[0013] The second hole may be spaced from the first hole by a first distance in a first orientation. The collimator may comprise a plurality of holes in each plate, which may be two holes, but also may be more than two. The holes may be regularly spaced, for example in a square, triangular and / or hexagonal arrangement; however, in some arrangements the plurality of holes may be irregularly spaced. In particular, each hole in each plate may correspond to a respective one of the emitters, and may have corresponding spacing from each adjacent hole in said plate.

[0014] The second plate may be disposed touching or spaced from the first plate. For instance, the second plate may be spaced from the first plate by at most 5mm, in particular 3mm, more particularly 1mm. The second plate may be slidably movable relative to the first plate. For example, the first (or second) plate may be held fixed relative to the emitters, and the second (or first) plate may be movable with respect thereto. Alternatively, both the first and second plates may be movable (for instance by equal amounts) relative to the emitters.

[0015] The holes overlapping mean that there exists at least one ray that can pass from a respective emitter through both respective holes, which may then impinge on a detector. The size of the composite aperture thus formed is variable in the sense that more such rays may pass through the aperture in one of the first and second positions than in the other.

[0016] Between the first and second positions, there may be one or more additional positions whereby the holes at least partially overlap by additional respective amounts.

[0017] The collimator may further comprise an actuator configured to move the second plate relative to first plate between the first and second positions. The actuator may comprise a motor and / or may be motorised. Alternatively or additionally, the actuator may be manually controllable (for example with a rotating dial). The actuator may be configured to move the second plate continuously and / or by discrete amounts.

[0018] The or each hole may be of any shape, but are preferably rectangular or square to suit common detector shapes; however, triangular holes are also considered. The or each hole may be parallelogram and or trapezoid shape, for instance in arrangements in which pairs of emitter arrays are angled with respect to each other, and / or in which an emitter array is angled with respect to a detector. The or each hole may have a quadrilateral shape.

[0019] The or each hole may be regular in shape (e.g. equilateral triangle, square, etc.) or may be irregular in shape (e.g. right-triangle, rectangle, rhombus, etc.). The or each hole may be provided with a respective corner. The or each hole may be provided with a respective corner that is orientated in a first direction. Movement of the second plate relative to the first plate (e.g. between the first position and the second position) may be in the first direction; that is, the movement direction may be parallel to an angle that bisects the corner.

[0020] In this way, all shapes of the first and / or second composite apertures formed by corresponding pairs of holes may be similar; that is, they may change in size but remain the same shape.

[0021] Alternatively or additionally, the movement of the second plate relative to the first plate may be in a second direction different to the first direction. In this way, the shapes of the first and / or second composite apertures formed by corresponding pairs of holes may change shape and size, thereby not being similar. For example, by moving the plates in a different direction, the aspect of the hole can be changed, for instance changing from a square to a rectangle.

[0022] In some embodiments, the first direction is in a direction diagonally across a square hole such that the composite aperture remains square in shape as it changes size.

[0023] Corresponding pairs of holes (i.e. overlapping holes) may have the same size and / or shape as one another.

[0024] The first hole may be larger than the second hole. The first hole may be larger than the third hole.

[0025] The first plate may comprise at least sixteen distinct holes, including the first hole and the second hole. The second plate may comprises at least sixteen distinct further holes, including the third hole and the fourth hole, wherein each one of the at least sixteen distinct further holes is located to at least partially overlap with a respective one of the at least sixteen distinct holes by a respective first amount when the second plate is in the first position, and by a respective second amount when the second plate is in the second position, thereby forming sixteen respective composite apertures, each of variable size.

[0026] In this way, an array of composite apertures may be formed.

[0027] Holes and / or composite apertures around a periphery of an array may be smaller than holes and / or composite apertures in a centre of an array. In this way, beams at a periphery of an array may be collimated more than those in the middle. This enables broad beams to still be used in the centre of a region of interest in order to optimise overlap for tomosynthesis. However, collimating around the periphery may be performed to limit the overall tissue exposed to X-rays, so as to avoid exposure of regions outside the region of interest. This may be achieved by off-setting the spacing of corresponding pairs of holes, or by changing the size of one or both of the holes in a corresponding pair of holes.

[0028] According to a second aspect of the present invention, there is provided an X-ray system for collimating X-ray beams from a plurality of X-ray emitters, the X-ray system comprising: an X-ray beam collimator of the first aspect; a first X-ray emitter arranged to emit a first beam of X-rays over the entire first composite aperture; and a second X-ray emitter arranged to emit a second beam of X-rays over the entire second composite aperture.

[0029] The system may further comprise a detector arranged to receive the first beam of X-rays through the first composite aperture, and to receive the second beam of X-rays through the second composite aperture.

[0030] According to a third aspect of the present invention, there is provided a method of collimating X-ray beams from a plurality of X-ray emitters, the method comprising the steps of: providing the X-ray beam collimator of the first aspect having the second plate in the first position; providing a first X-ray emitter arranged to emit a first beam of X-rays over the entire first composite aperture; providing a second X-ray emitter arranged to emit a second beam of X-rays over the entire second composite aperture; and moving the second plate relative to the first plate within the plane between the first position and the second position.

[0031] The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

[0032] is a schematic representation of a prior art collimator being used with a single X-ray source.

[0033] is shows they key elements of a prior art collimator box.

[0034] is a schematic representation of how a prior art collimator box would operate if used in conjunction with a one-dimensional array of five X-ray emitters.

[0035] is a schematic representation of an X-ray beam collimator for use with a one-dimensional array of five X-ray emitters.

[0036] shows the relative positions of two plates for use in an X-ray beam collimator for use with a two-dimensional array of nine X-ray emitters.

[0037] is a plan view of an X-ray beam collimator for use with a two-dimensional array of twenty-five X-ray emitters.

[0038] The present invention will be described with respect to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. Each drawing may not include all of the features of the invention and therefore should not necessarily be considered to be an embodiment of the invention. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0039] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other sequences than described or illustrated herein. Likewise, method steps described or claimed in a particular sequence may be understood to operate in a different sequence.

[0040] Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that operation is capable in other orientations than described or illustrated herein.

[0041] It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

[0042] Reference throughout this specification to “an embodiment” or “an aspect” means that a particular feature, structure or characteristic described in connection with the embodiment or aspect is included in at least one embodiment or aspect of the present invention. Thus, appearances of the phrases “in one embodiment”, “in an embodiment”, or “in an aspect” in various places throughout this specification are not necessarily all referring to the same embodiment or aspect, but may refer to different embodiments or aspects. Furthermore, the particular features, structures or characteristics of any one embodiment or aspect of the invention may be combined in any suitable manner with any other particular feature, structure or characteristic of another embodiment or aspect of the invention, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments or aspects.

[0043] Similarly, it should be appreciated that in the description various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Moreover, the description of any individual drawing or aspect should not necessarily be considered to be an embodiment of the invention. Rather, as the following claims reflect, inventive aspects lie in fewer than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

[0044] Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0045] In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[0046] In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

[0047] The use of the term “at least one” may mean only one in certain circumstances. The use of the term “any” may mean “all” and / or “each” in certain circumstances.

[0048] The principles of the invention will now be described by a detailed description of at least one drawing relating to exemplary features. It is clear that other arrangements can be configured according to the knowledge of persons skilled in the art without departing from the underlying concept or technical teaching, the invention being limited only by the terms of the appended claims.

[0049] is a schematic representation of a prior art collimator 1 being used with a single X-ray source 3. An uncollimated beam 5 can be seen emanating from the source 3, and being intercepted by the collimator 1. The path of the uncollimated beam 5, had it not been so intercepted, is projected toward a detector panel 7, and is shown in dashed lines 9. The collimated beam 11 continues past the collimator 1 to impinge on a smaller region of the detector panel 7 than the uncollimated beam projection 9.

[0050] is shows they key elements of a prior art collimator box that includes two upper plates 13 and two lower plates 15. The upper plates 13 can move toward and away from each other in the figure (left and right) to narrow the aperture 17 in a lateral direction. In contrast lower plates 15 (the corners that are hidden behind the upper plates 13 shown dashed for clarity) can move toward and away from each other in the figure (up and down) to narrow the aperture 17 in a longitudinal direction.

[0051] Typically, such plates 13, 15 are formed of lead, and are located 8 to 18 cm below an X-ray tube. These plates 13, 15 form shutters having longitudinal and lateral leaves or blades, each of which may have its own control. This design makes the collimator adjustable in terms of its ability to produce projected fields of varying sizes and shapes.

[0052] is a schematic representation of how a prior art collimator 19, such as the one shown in, would operate if used in conjunction with a one-dimensional array of five X-ray emitters 21. Uncollimated beams 23 can be seen emanating from the emitters 21. The outermost two uncollimated beams 23 are entirely intercepted by the collimator 19. The central uncollimated beam 23 is unaffected by the collimator. The remaining two uncollimated beams 23 are partially intercepted by the collimator. The path of the uncollimated beams 23, had they not been so intercepted, is projected toward a detector panel 7, and is shown in dashed lines 27. The collimated beams 29 continue past the collimator 19 to impinge on a smaller region of the detector panel 25 than the uncollimated beam projection 23.

[0053] is a schematic representation of an X-ray beam collimator 31 for use with a one-dimensional array of five X-ray emitters 21. Each uncollimated beam 23 can be seen emanating from a respective emitter 21, and being intercepted by the collimator 31. The paths of the uncollimated beams 23, had they not been so intercepted, is projected toward a detector panel 7, and is shown in dashed lines 33. The collimated beams 35 continue past the collimator 31 to impinge on a smaller region of the detector panel 7 than the uncollimated beam projection 33.

[0054] shows the relative positions of two plates (upper plate 41 and lower plate 43) for use in an X-ray beam collimator for use with a two-dimensional array of nine X-ray emitters. Each plate 41, 43 is provided with an array of nine equally-sized square holes 45 therein.

[0055] In (A) the two plates 41, 43 are aligned one above the other such that the nine holes in the upper plate 41 completely align with the nine holes in the lower plate 43 (not shown) to form nine combined apertures 47 of maximal size.

[0056] In (B) the two plates have been offset diagonally by a first distance such that the nine combined apertures 47 formed by the overlapping holes 45 in the upper 41 and lower 43 plates are of intermediate size.

[0057] In (C) the two plates have been offset diagonally by a second distance such that the nine combined apertures 47 formed by the overlapping holes 45 in the upper 41 and lower 43 plates are of a smaller size.

[0058] is a plan view of an X-ray beam collimator for use with a two-dimensional array of twenty-five X-ray emitters. The beam collimator comprises a first plate 51 having an array of twenty-five square holes 53 therethrough. The first plate 51 is movably mounted on a support structure 55. A second plate 57 is disposed between the first plate 51 and the support structure 55, and is provided with an additional twenty-five square holes therethrough, identical in size to the twenty-five square holes 53 in the first plate 51. The holes 53 of the first plate 51 and the holes of the second plate 57 are shown aligned to form composite apertures 59.

[0059] The support structure 55 is provided with two rotating toothed pinions 60 thereon. Each of the pinions 60 engages with a respective toothed rack 61 on the first plate 51, and with a respective toothed rack 63 on the second plate 57.

[0060] An armature 65 for moving the second plate 57 is provided, such that linear movement of the armature to the upper left of the figure causes the second plate 57 to move to the upper left of the figure. In addition, this causes rotation of the pinions 59, thereby causing movement of the first plate 51 to the bottom right of the figure. Such movement causes the size of the composite apertures 59 to reduce.

Claims

An X-ray beam collimator for use with a plurality of X-ray emitters, the X-ray beam collimator comprising:a first plate comprising:a first hole; anda second hole, spaced from the first hole;a second plate disposed adjacent to, and in a plane parallel to, the first plate, the second plate movable relative to the first plate within the plane between a first position and a second position, the second plate comprising:a third hole located to at least partially overlap the first hole by a first amount when the second plate is in the first position, and by a second amount when the second plate is in the second position, thereby forming a first composite aperture of variable size; anda fourth hole spaced from the third hole, the fourth hole located to at least partially overlap the second hole by a third amount when the second plate is in the first position, and by a fourth amount when the second plate is in the second position, thereby forming a second composite aperture of variable size.

2. The X-ray beam collimator of claim 1, further comprising an actuator configured to move the second plate relative to first plate between the first and second positions.

3. The X-ray beam collimator of claim 2, wherein the actuator comprises a motor.

4. The X-ray bean collimator of claim 2 or claim 3, wherein the actuator is manually controllable.

5. The X-ray beam collimator of any preceding claim, wherein any one of the first, second, third and fourth holes has a quadrilateral shape.

6. The X-ray beam collimator of any preceding claim, wherein any one of the first, second, third and fourth holes is provided with a respective corner that is orientated in a first direction, and wherein movement of the second plate between the first position and the second position is in the first direction.

7. The X-ray beam collimator of any preceding claim, in which any one of the first, second, third and fourth holes is provided with a respective corner that is orientated in a first direction, and wherein movement of the second plate between the first position and the second position is in a second direction different to the first direction.

8. The X-ray beam collimator of any preceding claim, wherein the first hole is larger than the second hole.

9. The X-ray beam collimator of any preceding claim, wherein the first hole is larger than the third hole.

10. The X-ray beam collimator of any preceding claim, wherein:the first plate comprises at least sixteen distinct holes, including the first hole and the second hole; andthe second plate comprises at least sixteen distinct further holes, including the third hole and the fourth hole, wherein each one of the at least sixteen distinct further holes is located to at least partially overlap with a respective one of the at least sixteen distinct holes by a respective first amount when the second plate is in the first position, and by a respective second amount when the second plate is in the second position, thereby forming sixteen respective composite apertures, each of variable size.

11. An X-ray system for collimating X-ray beams from a plurality of X-ray emitters, the X-ray system comprising:an X-ray beam collimator of any preceding claim;a first X-ray emitter arranged to emit a first beam of X-rays over the entire first composite aperture; anda second X-ray emitter arranged to emit a second beam of X-rays over the entire second composite aperture.

12. A method of collimating X-ray beams from a plurality of X-ray emitters, the method comprising the steps of:providing the X-ray beam collimator of any one of claims 1 to 10 having the second plate in the first position;providing a first X-ray emitter arranged to emit a first beam of X-rays over the entire first composite aperture;providing a second X-ray emitter arranged to emit a second beam of X-rays over the entire second composite aperture; andmoving the second plate relative to the first plate within the plane between the first position and the second position.

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