Computed tomography system, detector ring, and adjusting method for diaphragm aperture of computed tomography system

Abstract

To provide a detection ring for a computed tomography system and an adjusting method for a diaphragm aperture of a computed tomography system.SOLUTION: A computed tomography system includes an examination area 2 and a static gantry 4 equipped with a detector ring 6 and an X-ray source ring 8 that surround the examination area respectively and have a substantially common axial direction. The X-ray source ring has a diameter larger than that of the detector ring. When viewed in a radial direction, the X-ray source sing is arranged on the further outside of the detector ring around the examination area. The detector ring is arranged deviated in the axial direction with respect to the X-ray source ring so that a beam outlet aperture 9 of the X-ray source ring is not covered with the detector ring at least partially when viewed in the radial direction with respect to the examination area.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a computed tomography system, a detector ring for a computed tomography system, and a method for adjusting the aperture of a computed tomography system. [Background technology]

[0002] A typical computed tomography system (CT system) typically includes an X-ray tube and a detector facing the X-ray tube. To image the patient, the X-ray tube and the detector rotate around the patient. This rotation allows a three-dimensional image of the patient to be obtained. However, rotation also entails drawbacks. Due to the rotation, the requirements for the mechanism and data transmission are relatively high. These increased requirements lead to increased efforts in manufacturing and maintenance as well as increased costs in general, and may also impair image quality. For example, rotation may cause vibrations that may cause interference frequencies in the measurement signal and thus artifacts in the CT image. Rotation in general, and accidental vibrations caused by rotation in particular, may lead to faster wear of components. Furthermore, rotation requires that components must be manufactured particularly robust, since deformations of the components may have a significant effect on image quality. This increases space requirements and hardware costs. The capacity of data transmission may also be limited, for example, because rotation makes data transmission via sliding contacts difficult. Summary of the Invention [Problem to be solved by the invention]

[0003] It is therefore an object of the present invention to provide a possibility with which the above mentioned drawbacks can be addressed and at least partially ameliorated. [Means for solving the problem]

[0004] This problem is solved by a computed tomography system according to claim 1, a detector ring according to claim 13 and a method according to claim 15. Further features and advantages emerge from the dependent claims, the description and the accompanying drawings.

[0005] According to a first aspect of the invention, there is provided a computed tomography system comprising an examination region and a static gantry. The static gantry comprises a detector ring and an X-ray source ring, each surrounding the examination region and having a substantially common axial direction. The X-ray source ring has a larger diameter than the detector ring, such that the X-ray source ring is disposed further outwardly around the examination region than the detector ring when viewed in a radial direction. The detector ring is disposed axially offset relative to the X-ray source ring such that a beam exit aperture of the X-ray source ring is at least partially uncovered by the detector ring when viewed in a radial direction relative to the examination region.

[0006] The examination area is an area in which a subject or object can be examined, in particular by means of computed tomography measurements carried out by a computed tomography system, and a computed tomography (CT) image of the subject or object can be taken. The subject or object can be, for example, a human being, an animal, or an organ or body area, for example a body part such as the chest area or the head area, or another object (for example baggage or a piece of material whose properties are to be examined).

[0007] A gantry with a detector ring and an X-ray source ring is arranged around the examination region. The gantry may be a particularly short annular tunnel. The axial direction of the annular tunnel may approximately correspond to the axial direction of the detector ring and the X-ray source ring. The axial direction may also be referred to as the z-direction. The term "approximately" in this context should be understood as meaning that there may be some deviations, for example due to the construction. However, it is preferable that the axial directions of the mentioned components, in particular the detector ring and the X-ray source ring, do not differ from each other by more than 10°. A radial direction in this context should be understood as a direction perpendicular to the axial direction and in particular extending radially outward from the center point of the respective ring. The term radial direction should therefore be understood such that there are several directions corresponding to one radial direction, i.e. according to the totality of possible radial extension directions. The radial direction is also referred to as the x-direction, the y-direction and / or the x,y-direction.

[0008] The gantry is static. It should be understood that, in particular in contrast to other common gantries, the gantry does not rotate during the CT measurement. This is made possible by the provision of a detector ring and an X-ray source ring. In this way, a complete image can be generated without the need to rotate the detector and the X-ray source. In particular, the detector ring can be a 360° detector. A 360° detector is a detector that can receive signals emanating from the examination area in all radial directions without the need to rotate itself. In particular, the detector ring can be a static detector ring. In particular, the X-ray source ring can be a 360° X-ray emitter. A 360° X-ray emitter is an X-ray emitter that can send X-rays to the examination area from the entire 360° area around the examination area without the need to rotate itself. In particular, the X-ray source ring can be a static X-ray source ring. The detector ring can have, for example, a plurality of detector elements distributed around the detector ring. The X-ray source ring can have, for example, a plurality of X-ray sources distributed around the X-ray source ring. The X-ray source can preferably be based on nanotube field emission technology. X-ray sources based on field emission have the advantage that afterglow effects can be avoided as much as possible than X-ray sources based on thermally induced emission that are usually used in CT systems of the prior art, and therefore can allow faster switching. However, other X-ray sources can also generally be used. The X-ray source ring can thus be configured to activate several of its X-ray sources individually or in groups successively during a CT scan of the subject or subjects in the examination area. As a result, the advantages of the rotation or rotation can be so to speak "simulated" according to CT systems that are customary in the prior art. Advantageously, an actual rotation of the gantry can be avoided, whereby the above-mentioned disadvantages of rotating parts can likewise be largely avoided. Advantageously, therefore, typically complex and expensive interfaces between parts that move relative to each other, such as sliding contacts, are not necessary. Vibrations due to rotation and the resulting artifacts and wear of the measurement data can also be avoided. Furthermore, a more compact design is possible, since fewer stable components are required.For example, the detector or detector ring module carrier and detector mechanism can be constructed in a significantly simpler, lighter and more cost-effective manner, since the detector does not have to withstand any rotational forces. For example, the system according to the invention can be constructed for mobile applications. Furthermore, it is advantageous since it allows faster image capture and more flexibility in the selection of successive capture angles, since inertia during mechanical rotation does not have to be taken into account.

[0009] The X-ray source ring has a larger diameter than the detector ring. As a result, the X-ray source ring is arranged further outward around the examination region in the radial direction than the detector ring. In other words, the X-ray source ring is arranged further outward in the gantry than the detector ring. This is advantageous since the X-ray source ring and the detector ring can be constructed in a particularly space-efficient manner. At the same time, the detector ring is arranged axially offset relative to the X-ray source ring, so that the beam exit opening of the X-ray source ring is at least partially, i.e. not completely, covered by the detector ring when viewed radially relative to the examination region. In particular, it is possible to ensure that the center of the beam exit opening is not covered by the detector ring. The beam exit opening is understood to be wide. This generally refers to the position on the X-ray source ring at which the X-rays are emitted from the X-ray source to the outside. In many cases, for example for collimation, in particular in some of the embodiments described herein, it may be advantageous to partially limit the beam exit in a defined manner by a part of the detector ring or a part on the detector ring, in particular at the edge of the beam. The detector ring may optionally function as a collimator or part of a collimator for the beam exit aperture and may therefore cover part of the beam exit aperture, however at least part of the beam exit aperture, preferably the centre, is generally left unobstructed.

[0010] According to a preferred embodiment, the detector ring and the X-ray source ring overlap in the axial direction. This variant allows a particularly compact design of the gantry. Furthermore, the detector ring and the X-ray source ring can be assembled in an axially particularly compact manner, so that an improved image quality can be achieved. In particular, the distance of the X-ray source of the X-ray source ring and the detector center from the focal point can be reduced. As a result, for example, image errors due to axial misalignment are less likely to occur or image correction can be facilitated accordingly.

[0011] According to an embodiment, the detector ring and the X-ray source ring are attached to the gantry from different axial sides. For example, the detector ring can be attached to the gantry in the positive axial direction (or +z direction) and the X-ray source ring can be attached to the gantry in the negative axial direction (or z direction). The assembly from different sides allows, on the one hand, a particularly good spatial division and, on the other hand, a particularly good accessibility of the two components, namely the X-ray source ring and the detector ring, respectively, individually. This can be advantageous, for example, for maintenance purposes. For example, the detector ring can be removable or partially removable without making the removal of the X-ray source ring significantly more difficult. Thus, for example, the detector ring can be directly accessible and removable, for which, for example, only one cover plate needs to be removed.

[0012] According to an embodiment, the gantry comprises an annular diaphragm having at least a first diaphragm part and a second diaphragm part, which is arranged or can be arranged in front of the beam exit opening of the X-ray source ring, the first diaphragm part being fixed to the detector ring or being an integral part of the detector ring. In particular, the diaphragm can be arranged in front of the beam exit opening so as to collimate the X-rays of the X-ray source ring. By fixing the diaphragm to the detector ring, the detector ring can be arranged in particular close to the beam exit opening, and an even more compact design can be achieved. The second diaphragm can be preferably attached to the X-ray source ring or to another part of the gantry, respectively, or can be an integral part thereof. The diaphragm can be a ring that is completely closed in the circumferential direction of the X-ray source ring or the detector ring. The first diaphragm part and the second diaphragm part can jointly form a channel for restricting the propagation of the X-ray radiation. The channel can extend in particular in the radial direction. This channel can have an approximately constant cross section and / or a constant channel opening relative to the beam exit opening as viewed in the circumferential direction.

[0013] According to an embodiment, the detector ring is configured to be displaceable together with the first aperture part, such that the aperture opening can be adjusted by axially displacing the detector ring. This embodiment is an efficient way to realize different aperture openings for the X-ray source. In particular, it can enable a particularly space-saving adjustable aperture. Advantageously, therefore, the position of the detector ring and the beam distribution can be adapted simultaneously. In this way, a simple and effective synchronization of the X-ray propagation and the detector position is possible.

[0014] According to one embodiment, the computed tomography system further comprises a patient couch, the detector ring being attached to the gantry in an axial direction from the side of the patient couch. The patient couch can be preferably moved in and out of the gantry in an axial direction. Particularly easy access to the detector ring, for example for maintenance purposes, is made possible by attaching the detector ring according to this embodiment. The detector ring or each element of the detector ring can be particularly easily removed from the gantry.

[0015] According to an embodiment, the detector ring comprises functional units with detector elements that can be individually removed from the gantry. Individually removable functional units are advantageous, for example, because they allow maintenance or replacement of individual detector elements without removing the entire detector ring. Thus, for example, it is easier to maintain the overall orientation and alignment of the detector ring, so that only the individual functional units need to be reinstalled, but the overall orientation of the detector ring (and possibly the aperture) remains unchanged. This can simplify maintenance and make it more cost-effective. The detector ring can include further functional units as required. The individual functional units can comprise or be modules, cables, and / or DSFs (Data Streaming Front Ends). For example, the functional units can be modules with a partially circular array of detector elements.

[0016] According to an embodiment, the detector ring comprises at least one housing piece, which is configured in such a way that at least one of the functional units can be at least partially inserted into the housing piece. At least one functional unit can be inserted into the housing piece. For example, it is possible to insert at least one functional unit into the housing piece during operation of the detector ring. The functional unit is removed or made removable from the housing for maintenance. The housing piece can preferably be annular or partially annular. The housing piece can be configured in particular so that detector elements of at least one functional unit can be inserted into the housing piece. Advantageously, therefore, the detector elements can have a position that is defined by the position of the housing piece. In this way, it is possible to replace the detector elements without having to subsequently readjust their position or it is simplified to adjust the position of the detector elements. A plurality of functional units with detector elements are or can be inserted into the housing piece. For example, one housing piece can be configured in such a way that in each case two functional units are at least partially inserted into the housing piece. In both cases the possibility of installing the two functional units is particularly advantageous since it allows both stable positioning and easy maintenance. The first throttling part described herein can preferably be fixed to the housing piece. This is advantageous since it can thus prevent fluctuations in the position of the first throttling piece from occurring during removal or replacement of the functional units.

[0017] According to an embodiment, the detector ring comprises a plurality of housing pieces that, when assembled, define the annular shape of the detector ring. The housing pieces in this sense can be segments of the detector ring, in particular circular segments. The housing pieces can be circular segments of approximately equal size to the detector ring. The detector ring can preferably comprise three or more housing parts. Particularly preferably, the detector ring can comprise three housing parts. The three housing pieces can in particular be three substantially equal-sized circular segments of the detector ring. For example, the housing pieces can each be 120° segments. The division into three housing pieces has proven to be particularly advantageous for maintenance purposes and for flexible adjustment of the orientation of the detector ring. The first diaphragm piece described herein can comprise or be assembled from a plurality of first diaphragm pieces, each of which is fixed to one of the housing pieces.

[0018] According to an embodiment, at least one of the functional units comprises a guide, which allows for a positionally accurate insertion of the functional unit into the housing piece. Alternatively or additionally, the guide is provided as part of the housing piece. The guide can be, for example, a guide rail or a guide rod. The housing piece can comprise, for example, an inner edge or a guide tunnel, which is configured to interact with the guide of the functional unit. The guide can be used to allow a particularly accurate positioning of the functional unit in the housing piece. Furthermore, the guide can contribute to preventing damage to the functional unit, in particular the detector element, for example due to impacts during use.

[0019] According to one embodiment, the detector ring and / or the housing pieces comprise a scattered beam collimator oriented to shield the detector elements of the detector ring from the scattered beam of the X-ray source ring, and the housing pieces are configured such that when the at least one functional unit is inserted into the housing piece, the detector elements of the at least one functional unit are inserted with a precise fit relative to the scattered beam collimator, thus advantageously allowing the positioning of the scattered beam collimator to be maintained, for example while exchanging functional units.

[0020] According to an embodiment, the X-ray source ring comprises a plurality of X-ray source segments. All advantages and features regarding the maintenance of the detector ring can be transferred to the X-ray source ring as well. Thus, individual segments of the X-ray source ring can be advantageously removed. For example, corresponding functional units and / or housing pieces of the X-ray source ring can also be provided.

[0021] A further aspect of the invention is directed to a detector ring for a computed tomography system, the detector ring comprising at least one annular or partially annular housing piece and one or more functional units with detector elements, the housing piece being configured such that at least one functional unit can be at least partially inserted into the housing piece. The detector ring can be a detector ring as described herein, in particular with respect to the computed tomography system. All advantages and features of the computed tomography system can be transferred to the detector ring as well, and vice versa. The detector ring can comprise a plurality of housing pieces as described herein, which, when assembled, define the annular shape of the detector ring.

[0022] According to one embodiment, at least one of the functional units comprises a guide oriented so that the functional unit can be inserted in a positionally accurate manner into the housing piece. Alternatively or additionally, the guide is used as part of the housing piece. The guide can be, for example, a guide rail or a guide rod. The housing piece can comprise, for example, an inner edge or a guide tunnel configured to interact with the guide of the functional unit.

[0023] According to one embodiment, the detector ring comprises a first iris portion fixed to or part of the detector ring, which first iris portion is configured together with the second iris portion to form an iris for an X-ray emission ring having a larger diameter than the detector ring. In particular, the iris is provided for an X-ray ring as described herein. The first iris portion can be fixed to, for example, a housing piece.

[0024] According to one embodiment, the detector ring and / or the housing piece comprises a scattered beam collimator, and the housing piece is adapted to be inserted such that when the at least one functional unit is inserted into the housing section, the detector elements of the at least one functional unit fit precisely relative to the scattered beam collimator.

[0025] A further aspect of the invention is a method for adjusting an aperture of a computed tomography system with a static gantry, where the gantry comprises a detector ring, an X-ray source ring with a beam exit aperture, and an annular aperture with at least a first aperture portion and a second aperture portion, the aperture being arranged in front of the beam exit aperture of the X-ray source ring, the first aperture portion being fixed to the detector ring or being an integral part of the detector ring. The computed tomography system may in particular be a computed tomography system as described herein. The method comprises the following steps: - By displacing the detector ring and thus the first aperture part in the axial direction, the spacing between the first aperture part and the second aperture part is changed and adjusted. The process includes:

[0026] All advantages and features of the computed tomography system and the detector ring can be applied to this method and vice versa.

[0027] All embodiments described herein can be combined with each other unless otherwise stated. [Brief description of the drawings]

[0028] Hereinafter, embodiments will be described with reference to the accompanying drawings.

[0029] [Figure 1] 1 shows a schematic cross-sectional side view of a computed tomography system according to an embodiment of the present invention; [Diagram 2] 1 shows a perspective view of a gantry of a computed tomography system according to one embodiment of the present invention; [Diagram 3] 1 shows a housing piece and two functional units of a detector ring according to an embodiment of the present invention. [Figure 4] FIG. 2 shows a schematic illustration for adjusting the aperture of a computed tomography system having a static gantry according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] FIG. 1 shows a schematic cross-sectional side view of a computed tomography system according to an embodiment of the invention. The computed tomography system comprises a static gantry 4 arranged as a short annular tunnel around an examination region 2. The gantry 4 comprises a detector ring 6 and an X-ray source ring 8, one upper and one lower of which are shown, each surrounding the examination region 2. The detector ring 6 and the X-ray source ring 8 have a common axial direction, which corresponds to the illustrated z direction. The detector ring 6 is attached to the gantry 4 from the right side with respect to this figure, and the X-ray source ring 8 is attached to the gantry 4 from the left side. This means that the detector ring 6 and the X-ray source ring 8 are attached to the gantry 4 from different sides. In this case, the detector ring 6 is attached to the gantry 4 from the side on which the patient couch 3 is also provided. The detector ring 6 and the X-ray source ring 8 partially overlap in the axial direction, i.e. part of the X-ray source ring 8 is at the same z position as part of the detector ring 6. The X-ray source ring 8 has a larger diameter than the detector ring 6, so that the X-ray source ring 8 is arranged further outward around the examination area 2 than the detector ring 6 in the radial direction, in other words in the x- and y-directions. Furthermore, the detector ring 6 is arranged axially offset relative to the X-ray source ring 8, so that the beam exit opening 9 of the X-ray source ring 8 is not completely covered by the detector ring 6 in the radial direction relative to the examination area 2. A first diaphragm part 11, which is part of an annular diaphragm 10 arranged in front of the beam exit opening 9, is fixed to the detector ring 6. A second diaphragm part 12 of the diaphragm 10 is attached to the X-ray source ring 8 itself. In this embodiment, and preferably also in the other embodiments, the diaphragm part 11 and the diaphragm part 12 are in particular separate components, but functionally interact with each other. The detector ring 6 is configured to be displaceable in the axial direction (in other words in the z-direction) together with the first diaphragm part 11, so that the aperture of the diaphragm 10 can be adjusted by displacing the detector ring 6 in the axial direction.

[0031] FIG. 2 shows a perspective view of a gantry 4 of a computed tomography system according to an embodiment of the invention. In this case, the gantry 4 is shown without an outer cover. A detector ring 6 is attached to the gantry 4. An X-ray source ring 8 (not shown here) is provided on the opposite side (rear side from this point of view) of the gantry 4. The detector ring 6 comprises three partly annular housing pieces 61 and two functional units 62 for each housing piece 61, each with a detector element 63 which is inserted into the housing piece 61. The housing pieces 61 together result in the annular shape of the detector ring 6. Each functional unit 62 can be removed individually from the gantry 4. The X-ray source ring 8, which is not shown here, can also optionally include several X-ray source pieces, as well as the functional units 62 or housing pieces 61 of the detector ring 6.

[0032] 3 shows a housing piece 61 and two functional units 62 of a detector ring 6 according to an embodiment of the present invention. The detector elements 63 of the two functional units 62 can be inserted into the housing piece 61. The functional units 62 each comprise a guide 64 in the form of a guide bar, which allows the functional units 62 to be guided along the inner edge of the housing piece 61 and thus inserted into the housing piece 61 positionally accurately by orienting the respective functional units 62. The housing piece 61 further comprises a scattered beam collimator 65 oriented to shield the detector elements 63 from the scattered beam of the X-ray source ring 8. The guide 64 further ensures that the detector elements 63 are inserted with an accurate fit relative to the scattered beam collimator 65 when the functional units 62 are inserted into the housing piece 61.

[0033] 4 shows a schematic diagram of a method for adjusting the aperture of a computed tomography system with a static gantry 4 according to an embodiment of the present invention. The gantry 4 comprises a detector ring 6, an X-ray source ring 8 with a beam exit aperture 9, and an annular aperture 10 with a first aperture section 11 and a second aperture section 12 arranged in front of the beam exit aperture 9 of the X-ray source ring 8. The first aperture section 11 is fixed to the detector ring 6. As shown here, in this method, the detector ring 6 and thus the first aperture section 11 are displaced in the axial direction (z direction), so that the distance between the first aperture section 11 and the second aperture section 12 is changed (in this case enlarged) and the aperture opening of the aperture 10 is adjusted.

Claims

1. An inspection area (2); a static gantry (4) including a detector ring (6) and an X-ray source ring (8), each of which surrounds the examination region (2) and has a generally common axial direction; Equipped with the X-ray source ring (8) has a larger diameter than the detector ring (6), such that the X-ray source ring (8) is positioned radially further outwardly around the examination region (2) than the detector ring (6); the detector ring (6) is arranged axially offset with respect to the X-ray source ring (8) such that a beam exit aperture (9) of the X-ray source ring (8) is at least partially not covered by the detector ring (6) in a radial direction with respect to the examination region (2); Computed tomography system.

2. the detector ring (6) and the X-ray source ring (8) are attached to the gantry (4) from different axial sides; The computed tomography system of claim 1 .

3. the gantry (4) comprises an annular diaphragm (10) having at least a first diaphragm portion (11) and a second diaphragm portion (12); a diaphragm is arranged in front of the beam exit aperture (9) of the X-ray source ring (8); The first iris portion (11) is attached to the detector ring (6) or is integrated into the detector ring (6).

2. The computed tomography system of claim 1.

4. the detector ring (6) is configured to be axially displaceable together with the first iris portion (11), such that the aperture of the iris (10) can be adjusted by the axial displacement of the detector ring (6); 4. The computed tomography system of claim 3.

5. the second iris portion (12) is attached to or integral with the X-ray source ring (8) or another portion of the gantry (4); 5. A computed tomography system according to claim 3 or 4.

6. The detector ring (6) and the X-ray source ring (8) partially overlap each other in the axial direction. A computed tomography system according to any one of claims 1 to 5.

7. the computed tomography system further comprises a patient couch (3) which is detachably attached to said gantry (4), in particular in the axial direction, The detector ring (6) is attached to the gantry (4) in an axial direction from the side of the patient couch (3); A computed tomography system according to any one of claims 1 to 6.

8. the detector ring (6) includes a functional unit (62) having detector elements (63) that can be individually removed from the gantry (4); A computed tomography system according to any one of claims 1 to 7.

9. The detector ring (6) comprises at least one annular or partially annular housing piece (61), The housing piece (61) is arranged such that at least one of the functional units (62) is at least partially inserted into the housing piece (61).

9. A computed tomography system according to claim 7 or 8.

10. At least one of the functional units (62) is provided with a guide (64) oriented so that the functional unit (62) is inserted into the housing piece (61) with positioning accuracy.

10. The computed tomography system of claim 9.

11. the housing piece (61) comprises a scattered beam collimator (65) oriented to shield the detector elements (63) of the detector ring (6) from a scattered beam of the X-ray source ring (8); The housing piece (61) is inserted such that when the at least one functional unit (62) is inserted into the housing piece (61), the detector elements (63) of the at least one functional unit (62) fit precisely with the scattered beam collimator.

11. A computed tomography system according to claim 9 or 10.

12. the detector ring (6) includes a plurality of housing pieces (61) that, when assembled, define an annular shape of the detector ring (6); A computed tomography system according to any one of claims 9 to 11.

13. A detector ring (6) for a computed tomography system, in particular a detector ring (6) according to any one of claims 1 to 12, The detector ring (6) comprises at least one annular or partially annular housing piece (61) and one or more functional units (62) having detector elements (63), the housing piece (61) is configured such that at least one of the functional units (62) is at least partially inserted within the housing piece (61); Detector ring for a computed tomography system.

14. the detector ring (6) comprises a first iris piece (11) fixed to or being an integral part of the detector ring (6), said first diaphragm piece (11) together with a second diaphragm piece (12) forms an aperture (10) for an X-ray radiation ring having a diameter larger than said detector ring (6); Detector ring (6) according to claim 13.

15. 13. A method for adjusting an aperture of a computed tomography system having a static gantry (4), in particular of a computed tomography system according to any one of claims 1 to 12, comprising: the gantry (4) comprises the detector ring (6), an X-ray source ring (8) having the beam exit aperture (9), and an annular aperture (10) having at least a first aperture piece (11) and a second aperture piece (12); the aperture (10) is arranged in front of the beam exit aperture (9) of the X-ray source ring (8), The first throttle piece (11) is attached to or integral with the detector ring (6), A step of axially displacing the detector ring (6) and thus the first iris piece (11), thereby changing the distance between the first iris piece (11) and the second iris piece (12) and adjusting the aperture of the iris (10); 23. A method for adjusting an aperture of a computed tomography system, comprising:

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