Collimator arrangement with apertures with highly absorbent leading edge

Abstract

A collimator arrangement (4) for an X-ray emitting X-ray source (1) comprises an aperture arrangement (5) with a plurality of apertures (6) that together define an aperture opening. The apertures (6) are adjustable between a fully open position and a fully closed position, so that the size of the aperture opening varies depending on the position of the apertures (6). Each aperture (6) has a main block (7) and, in the region of an edge facing the aperture opening, an additional block (8) connected to the respective main block (7). The respective additional block (8) is made of a material that absorbs the X-rays more strongly than the material of the respective main block (7).

Description

[0001] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0002] The present invention relates to a collimator arrangement for an X-ray emitting X-ray source, - wherein the collimator arrangement comprises an aperture arrangement with a plurality of apertures which together limit an aperture opening, - wherein the apertures are adjustable between a fully open position and a fully closed position, so that the size of the aperture opening varies depending on the position of the apertures, - where each aperture has a main block.

[0003] Such collimator arrangements are generally known.

[0004] Standard X-ray machines—especially those used in the medical field—include a collimator assembly in addition to the X-ray source and detector. The collimator assembly is positioned between the X-ray source and the object being examined, and is therefore located between the X-ray source and the detector. Its purpose is to limit the area of ​​the object exposed to X-rays to the smallest possible region by adjusting the collimator aperture. Adjusting the aperture is commonly referred to as "cutting" the X-ray beam. The object being examined is often a human being.

[0005] The apertures typically consist only of the main section and an additional support element by which they are attached to the collimator assembly. The support elements themselves have no function in limiting the aperture opening. The main section is usually made of lead, and in rare cases of steel, tungsten, or other materials.

[0006] For health reasons, efforts are being made to avoid using lead wherever possible. There are also legal initiatives underway to ban the use of lead altogether. If lead is no longer permitted, an alternative, legally permissible material must be used.

[0007] One possibility is to use a different material that absorbs lead with a similar strength, such as tungsten. However, tungsten is considerably more expensive than lead and is therefore rarely used at present. Tungsten, tungsten-containing alloys, or plastic-tungsten compounds are only used in isolated cases.

[0008] Another possibility is to use a material with lower absorption but increase the thickness of the aperture. The thickness is measured in a direction orthogonal to the aperture opening. However, using a thicker aperture has the disadvantage that automated detection of the aperture edges, and thus the aperture opening, in the X-ray image captured by the X-ray detector is no longer possible or at least significantly more difficult. Furthermore, increased scatter radiation also occurs.

[0009] It has already been considered to slightly chamfer the edges of the apertures facing the aperture, so that the angular range between an X-ray beam that just touches the aperture but has not yet cut through it and an X-ray beam that penetrates the aperture across its entire thickness is kept as small as possible. However, this approach can only lead to good results with a specific aperture size, and only to acceptable results in the vicinity of this specific aperture. In areas further away from this specific aperture, chamfering the aperture edges only leads to a marginal, insufficient reduction of the angular range between an X-ray beam that just touches the aperture but has not yet cut through it and an X-ray beam that penetrates the aperture across its entire thickness.

[0010] The relevant state of the art includes the publications US 2023 / 0 110 626 A1 and CN 1 11 053 977 B.

[0011] The object of the present invention is to create possibilities by means of which a collimator arrangement of the type mentioned above can be further developed in such a way that it can be manufactured cost-effectively and yet the transition area from the aperture to a completely shielded area is kept as small as possible.

[0012] The problem is solved by a collimator arrangement with the features of claim 1. Advantageous embodiments of the collimator arrangement are the subject of dependent claims 2 to 4.

[0013] According to the invention, a collimator arrangement of the type mentioned above is designed in that, in addition to the respective main block, the apertures have a respective additional block connected to the respective main block in the area of ​​an edge facing the aperture opening, and that the respective additional block consists of a material that absorbs the X-ray radiation more strongly than the material of which the respective main block consists.

[0014] By dividing the aperture into a main block and a secondary block, a cost-effective, albeit relatively weakly absorbing, material can be used for the main block, thus requiring a relatively large main thickness. While the material of the secondary block can be considerably more expensive than that of the main block, this is acceptable because the aperture only uses this potentially expensive material in the secondary block. Due to the stronger absorption of X-rays, the transition zone from the aperture opening to a completely shielded area is kept small in the X-ray image captured by the detector. This generates, among other things, a significant absorption edge, enabling automated detection of the aperture edges.

[0015] Viewed in a thickness direction extending orthogonally to the aperture, each main block has a specific main thickness, and each additional block has a specific additional thickness. According to the invention, the respective additional thickness is smaller than the respective main thickness. This allows the amount of material in the additional block to be small, thus making the additional block cost-effective even if the material for the additional block has a high price per kilogram.

[0016] Preferably, the respective main block and the respective auxiliary block are coordinated in such a way that, regardless of the position of the respective aperture, - a first X-ray beam emanating from the X-ray source, touching but not intersecting the respective additional block, and spaced apart from the respective main block, forms a first angle with a basic X-ray beam emanating from the X-ray source and passing through the aperture at a distance from the respective aperture, and together with the basic X-ray beam defines a plane, - viewed in the defined plane, starting from the first angle and moving towards smaller angles, each X-ray ray passes through the aperture, - viewed in the defined plane, starting from the first angle and moving towards larger angles, the respective additional block is gradually penetrated further and further in the thickness direction by a respective X-ray beam, until for the first time a second X-ray beam emanating from the X-ray source penetrates the respective additional block over the full respective additional thickness at a second angle, - the second X-ray beam does not penetrate the respective main block, or at least only penetrates it minimally, and - viewed in the defined plane, only at angles larger than the second angle does the respective main block gradually penetrate further and further by a respective X-ray beam emanating from the X-ray source, until from a third angle the respective main block is penetrated by a respective X-ray beam over its full respective main thickness.

[0017] This ensures that the angular range between an X-ray beam that just touches the respective aperture but has not yet cut through it (first X-ray beam) and an X-ray beam that penetrates the additional block for the first time over its full thickness (second X-ray beam) is kept as small as possible.

[0018] The above-described situation applies regardless of the position of the respective aperture, and thus both in the fully open position and in the fully closed position as well as in every position in between.

[0019] The main block has a main half-value thickness. Likewise, the auxiliary block also has an auxiliary half-value thickness. Preferably, the respective main block and the respective auxiliary block are matched to each other such that, specifically, in the maximum open position of the respective aperture... - viewed in the defined plane, starting from the second angle towards larger angles, the respective additional block is completely penetrated in the thickness direction by a respective X-ray beam, until finally a fourth X-ray beam emanating from the X-ray source penetrates the respective additional block over its full respective additional thickness at a fourth angle, and - viewed in the defined plane, each X-ray beam emanating from the X-ray source that forms an angle with the basic X-ray beam greater than the fourth angle penetrates the respective main block in the thickness direction over a thickness that is at least as large as the difference between the respective additional thickness and the thickness of the respective additional block penetrated by the respective X-ray beam, scaled by the quotient of the main half-value thickness and the additional half-value thickness.

[0020] This ensures that from the angle at which absorption by the additional block decreases towards larger angles (fourth angle), the absorption by the main block is sufficiently high, so that from the second angle onwards, no "gap" occurs in the absorption of the X-rays when viewed across the various angles.

[0021] The apertures typically, and also within the scope of the present invention, have no moving parts. Instead, to vary the position of the apertures, they are attached to aperture holders of the collimator assembly, which in turn are movably mounted in a base body of the collimator assembly. Analogous to the prior art, it is possible for the apertures to have a support element by means of which they are attached to the aperture holders. Preferably, however, the main blocks are self-supporting, so that the apertures are attached to the aperture holders by their main blocks.

[0022] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These drawings show, in schematic representation: Fig. 1 an X-ray setup, Fig. 2 a top view of an aperture arrangement in a maximally open position, Fig. 3 the aperture arrangement of Fig. 2 in a maximally closed position, Fig. 4 a section through an aperture, Fig. 5 an X-ray source and a diaphragm, Fig. 6 a perspective view of an aperture and Fig. 7 a part of a collimator arrangement.

[0023] According to Fig. The X-ray arrangement comprises an X-ray source 1. During operation, the X-ray source 1 emits X-rays, which are detected by an X-ray detector 2. The X-rays pass through a test object 3 (for example, a human). A collimator arrangement 4 is positioned between the X-ray source 1 and the test object 3. The collimator arrangement 4 includes (at least) one aperture arrangement 5.

[0024] The aperture arrangement 5 has several apertures 6, for example according to the illustration in the Fig. 2 to 4 are four f-stops of 6. The f-stops of 6 together define one aperture opening. The f-stops of 6 are, as in the Fig. 1 to 3 are indicated by double arrows or arrows, between a maximally open position ( Fig. 2) and a maximally closed position ( Fig. 3) Adjustable. The size of the aperture varies according to the position of the aperture 6. In the fully open position, the aperture 6 form a large aperture, and in the fully closed position, a small aperture. Often, the adjustment of opposing aperture 6 is achieved in pairs by a common drive mechanism.

[0025] The f / 6 aperture lenses are generally constructed in the same way. According to Fig. Each of the apertures 6 has a main block 7. The main block 7 is made of a material that absorbs X-rays, but not very strongly. For example, the main block 7 could be made of copper, brass, or tungsten-alloyed steel. Furthermore, each aperture 6 has an additional block 8. The additional block 8 is connected to the main block 7 at one edge facing the aperture opening. The additional block 8 is made of a material that strongly absorbs X-rays, in any case more strongly than the material of the main block 7. For example, the additional block 8 could be made of lead or tungsten. The connection between the additional block 8 and the main block 7 can be as required. For example, the additional block 8 could be screwed or glued to the main block 7.It is also possible that the respective main block 7 has a recess into which the respective additional block 8 is pressed.

[0026] To achieve a uniform attenuation or shielding of the X-rays, the thicknesses d1 and d2 of the respective main block 7 and the respective auxiliary block 8 are different. Specifically, each main block 7 has a thickness d1 perpendicular to the aperture, while each auxiliary block 8 has an auxiliary thickness d2. The auxiliary thickness d2 is smaller than the main thickness d1.

[0027] Fig. Figure 5 shows an X-ray source and an aperture (Figure 6). In conjunction with Fig. 5 below explains a preferred coordination of the respective main block 7 and the respective additional block 8 towards each other.

[0028] According to Fig. In step 5, X-ray source 1 emits different types of X-rays. All X-rays originate from X-ray source 1. Some of these X-rays are specified in more detail below.

[0029] For example, the X-ray source 1 emits a basic X-ray beam 9. In principle, the basic X-ray beam 9 can be chosen arbitrarily, as long as it fulfills the condition that it passes through the aperture of the respective aperture 6 at a certain distance. The in Fig. The case shown in Figure 5, in which the basic X-ray beam 9 passes centrally through the aperture, is preferred, but not mandatory.

[0030] Furthermore, the X-ray source 1 emits a first X-ray beam 10. The first X-ray beam 10 can also be chosen arbitrarily in principle, as long as it fulfills the condition that it touches, but does not cut into, the respective additional block 8, and is spaced away from the respective main block 7.

[0031] The basic X-ray beam 9 and the first X-ray beam 10 share a common origin (namely, the X-ray source 1) and propagate from there in different directions. The basic X-ray beam 9 and the first X-ray beam 10 therefore form a first angle α1 and together define a plane. All subsequent X-ray beams lie within this plane.

[0032] Starting from the first angle α1, each X-ray beam passes through the aperture at smaller angles – this follows automatically from the definition of the basic X-ray beam 9 and the first X-ray beam 10. Also starting from the first angle α1, the respective additional block 8 is gradually penetrated further and further in the thickness direction by each X-ray beam as the angle increases. The angle at which an X-ray beam first penetrates the respective additional block 8 across its full thickness d2 is referred to below as the second angle α2, and the corresponding X-ray beam as the second X-ray beam 11.

[0033] It is possible that the respective main block 7 is not yet penetrated by X-rays at the second angle α2. However, it is also possible that the respective main block 7 is penetrated by X-rays over part of its main thickness d1 at the second angle α2, viewed in the thickness direction. In any case, however, the respective main block 7 is not yet penetrated by X-rays over its full main thickness d1 at the second angle α2. At angles larger than the second angle α2, the respective main block 7 is thus gradually penetrated further and further by a respective X-ray beam until the respective main block 7 is penetrated by a respective X-ray beam over its full main thickness d1. The angle at which an X-ray beam first penetrates the respective main block 7 over its full main thickness d1 is referred to below as the third angle α3, and the corresponding X-ray beam as the third X-ray beam 12.

[0034] Aperture 6 is located in the representation of Fig. 5 in its fully open position. The foregoing statements also apply if the aperture 6 is in any other position, including its fully closed position. However, the following statements specifically assume that the aperture 6 is in its fully open position.

[0035] According to Fig. 5. Starting from the second angle α2, the respective additional block 8 is completely penetrated by a respective X-ray beam towards larger angles, until the respective additional block is penetrated for the last time in the thickness direction over the full respective additional thickness d2. The angle at which an X-ray beam last penetrates the respective additional block 8 over the full respective additional thickness d2 is hereinafter referred to as the fourth angle α4, and the corresponding X-ray beam as the fourth X-ray beam 13. At angles larger than the fourth angle α4, the respective X-ray beam thus penetrates the respective additional block 8 progressively less and less, until an X-ray beam touches the respective additional block 8 but does not cut through it.

[0036] The angle at which this occurs is referred to below as the fifth angle α5, and the corresponding X-ray beam as the fifth X-ray beam 14. The difference between the fifth X-ray beam 14 and the first X-ray beam 10 is that the fifth X-ray beam 14 does not travel at a distance from the respective main block 7, but rather penetrates the respective main block 7 in the thickness direction over its full main thickness d1. In the region between the fourth angle α4 and the fifth angle α5, each X-ray beam penetrates the respective main block 7 in the thickness direction over a thickness that is at least as large as the difference, scaled by the quotient of a main half-value thickness d10 and an additional half-value thickness d20, between the respective additional thickness d2 and the thickness of the respective additional block 8 penetrated by the respective X-ray beam.The principal half-value thickness d10 is the thickness of the principal block 7 at which the intensity of the X-ray radiation exiting the principal block 7 is reduced by half. Similarly, the supplementary half-value thickness d20 is the thickness of the supplementary block 8 at which the intensity of the X-ray radiation exiting the supplementary block is reduced by half.

[0037] If, for example, the additional thickness d2 is 3 mm, the additional block 8 is penetrated by an X-ray beam by only 1 mm in the thickness direction, and the principal half-value thickness d10 is 4 mm and the additional half-value thickness d20 is 1.2 mm, then the principal block 7 will be penetrated by this X-ray beam by a thickness of at least (3 mm - 1 mm) · 4 mm / 1.2 mm = 6.66 mm. Therefore, given these numerical ratios, the principal thickness d1 must be at least 10 mm.

[0038] The fifth X-ray beam 14 can be shown in the illustration in Fig. The fifth angle α5 is identical to the third X-ray beam 12. This is preferred, but not strictly necessary. In the general case, the fifth angle α5 is larger than the third angle α3.

[0039] As far as the arrangement of the apertures 6 in the collimator arrangement 4 is concerned, the apertures 6 are arranged according to the illustration in Fig. 6 no moving parts. Rather, the apertures 6 are according to Fig. 7 - this is shown in Fig. 7 for a single aperture 6 - attached to aperture holders 15 of the collimator assembly 4. To vary the position of the apertures 6, the aperture holders 15 are movably mounted in a base body 16 of the collimator assembly 4. Preferably, the main blocks 7 are self-supporting, so that the apertures 6 with their main blocks 7 themselves can be attached to the aperture holders 15.

[0040] The present invention has many advantages. In particular, the design of the apertures 6 remains essentially cost-effective even when the additional blocks 8 are made of a relatively expensive material. Furthermore, reliable and robust automated detection of the aperture edges in an X-ray image is still possible.

Claims

[1] Collimator arrangement for an X-ray emitting X-ray source (1), - wherein the collimator arrangement comprises an aperture arrangement (5) with a plurality of apertures (6) which together define an aperture opening, - wherein the apertures (6) are adjustable between a maximally open position and a maximally closed position, so that the size of the aperture opening varies depending on the position of the apertures (6), - wherein the apertures (6) each have a main block (7) and in the area of ​​one edge facing the aperture opening have a respective additional block (8) connected to the respective main block (7), - wherein the respective additional block (8) consists of a material that absorbs the X-ray radiation more strongly than the material of which the respective main block (7) consists characterized by, that, viewed in a thickness direction extending orthogonally to the aperture opening, the respective main block (7) has a respective main thickness (d1) and the respective additional block (8) has a respective additional thickness (d2) and that the respective additional thickness (d2) is smaller than the respective main thickness (d1). [2] Collimator arrangement according to claim 1, characterized by , that the respective main block (7) and the respective auxiliary block (8) are coordinated in such a way that, regardless of the position of the respective aperture (6) - a first X-ray beam (10) emanating from the X-ray source (1), touching but not intersecting the respective auxiliary block (8) and spaced apart from the respective main block (7), forms a first angle (α1) with a basic X-ray beam (9) emanating from the X-ray source (1) and passing through the aperture at a distance from the respective aperture (6), and together with the basic X-ray beam (9) defines a plane, - viewed in the defined plane, starting from the first angle (α1) towards smaller angles, each X-ray ray passes through the aperture, - viewed in the defined plane, starting from the first angle (α1) towards larger angles, the respective additional block (8) is gradually penetrated further and further in the thickness direction by a respective X-ray beam until, for the first time, a second X-ray beam (11) emanating from the X-ray source (1) at a second angle (α2) penetrates the respective additional block (8) over the full respective additional thickness (d2), - the second X-ray beam (11) does not penetrate the respective main block (7) or at least only penetrates it to an insignificant extent and - viewed in the defined plane, only at angles larger than the second angle (α2) does the respective main block (7) gradually penetrate further and further by a respective X-ray beam emanating from the X-ray source (1), until from a third angle (α3) the respective main block (7) is penetrated by a respective X-ray beam over the full respective main thickness (d1). [3] Collimator arrangement according to claim 2, characterized by , that the main block (7) has a main half-value thickness and the additional block (8) has an additional half-value thickness and that the respective main block (7) and the respective additional block (8) are matched to each other such that in the maximum open position of the respective aperture (6) - viewed in the defined plane, starting from the second angle (α2) towards larger angles, the respective additional block (8) is completely penetrated in the thickness direction by a respective X-ray beam, until finally a fourth X-ray beam (13) emanating from the X-ray source (1) penetrates the respective additional block (8) over the full respective additional thickness (d2) at a fourth angle (α4), and - viewed in the defined plane, each X-ray beam emanating from the X-ray source (1) which forms an angle with the basic X-ray beam (9) that is greater than the fourth angle (α4) penetrates the respective main block (7) in the thickness direction over a thickness that is at least as large as the difference between the respective additional thickness (d2) and the thickness of the respective additional block (8) penetrated by the respective X-ray beam, scaled by the quotient of the main half-value thickness and the additional half-value thickness. [4] Collimator arrangement according to one of the above claims, characterized by , that the apertures (6) have no moving parts, that the main blocks (7) are self-supporting, that the apertures (6) with their main blocks (7) are attached to aperture holders (15) of the collimator arrangement and that the aperture holders (15) are movably mounted in a base body (16) of the collimator arrangement to vary the position of the apertures (6).

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