Rotating collimator with curved slits

Abstract

The present invention relates to a collimation device (5) for an X-ray detection system (1), the collimation device comprising a carrier (51) of a substantially planar material having partial or zero X-ray transmissivity, the carrier being intended to rotate about a rotation axis (52) perpendicular to the plane of the carrier, the carrier being provided with a slit (54) that is completely transparent to X-rays and extends through the thickness of the carrier to generate an X-ray flux when the carrier is exposed to an X-ray source, wherein the shape of the slit is curved when projected onto the plane of the carrier.

Description

Technical Field

[0001] This application relates to the field of X-ray inspection systems, and more specifically to the field of spatial positioning of components in X-ray inspection systems.

[0002] This application applies to X-ray imaging, particularly so-called interventional imaging, in order to accurately determine the position of an instrument while acquiring an image, such as during surgery or an operation performed using the instrument. Background Technology

[0003] Document FR2841118A1 describes an X-ray imaging system that includes means for determining the position of a X-ray imaging instrument using a test pattern fixed to the object on which its image is acquired. In such systems, the image of the test pattern can interfere with the image taken of the object under study.

[0004] Document US6490475B1 describes a fluorescence imaging system in which the positions of the system's components are determined using markers. Digital processing is then performed to remove traces of these markers from the final image.

[0005] Document US7065393B2 discloses a method for calibrating an X-ray imaging system using inertial sensors placed on various components of the system. The use of this type of sensor often leads to low accuracy and the accumulation of a large number of errors, which can cause problems when attempting to reliably determine the position of the sensor-equipped components in the X-ray imaging system.

[0006] Document FR3042881A1 describes an X-ray imaging apparatus comprising a rotating collimator with two slits. This apparatus enables the determination of the position of elements equipped with X-ray sensors in a given reference frame, these sensors being designed to receive X-ray beams emitted from the slits of the collimator. However, this apparatus has a blind zone in which the elements are undetectable. Furthermore, this apparatus is relatively complex and has limited accuracy.

[0007] Document EP4010739A1 discloses a rotating collimation device for an X-ray detection system. This device includes a substantially planar carrier made of a material with partial or zero X-ray transmittance. The carrier is rotatable about a rotation axis passing through it and perpendicular to a first surface of the carrier. The carrier is equipped with a single linear slit that is transparent to X-rays and located at a non-zero distance from the rotation axis of the carrier. This device also has a blind zone around the rotation axis. Furthermore, this device is complex and has limited accuracy. In particular, the uncertainty in calculating the position of the element to be detected is too large when it is far from the rotation axis of the carrier. Summary of the Invention

[0008] This application is specifically intended to make the apparatus disclosed in document EP4010739A1 more precise.

[0009] More specifically, the first object of the present invention is to provide a collimation device that allows for high-precision detection of the position of an object equipped with an X-ray sensor, while limiting the object's environmental exposure to X-rays.

[0010] This invention relates to a collimating device for an X-ray detection system, comprising a substantially planar carrier made of a material having partial or zero X-ray transmittance, the carrier being designed to be driven to rotate about an axis of rotation perpendicular to the plane in which the carrier is located, the carrier being provided with a slit that is completely transparent to X-rays and extends through the thickness of the carrier to generate an X-ray flux when the carrier is exposed to an X-ray source, the slit having a shape that further satisfies the following properties:

[0011] * The shape of the slit in the projection of the carrier onto the plane is a curve.

[0012] * The slit is composed of a first semi-curve and a second semi-curve. Each semi-curve intersects only once with any virtual circle centered on the rotation axis and with radius r. The radius r is limited to the interval [Rmin, Rmax], where Rmin is the minimum radius and Rmax is the maximum radius.

[0013] * The function F defined by F(r) = α1(r)-α2(r) is a bijective function, where:

[0014] - r is the distance between a point on the first or second half-curve and the axis of rotation of the carrier, and r is limited between the minimum radius Rmin and the maximum radius Rmax.

[0015] - α1(r) is the angle of a point on the first half-curve in polar coordinates, located at a distance r from the axis of rotation, and

[0016] - α2(r) is the angle of a point on the second half-curve in polar coordinates, located at a distance r from the axis of rotation.

[0017] According to one embodiment, regardless of the value of r in the interval [Rmin, Rmax], the value of the function F(r) is strictly less than the angle π.

[0018] In one embodiment, the curve passes through the rotation axis of the carrier.

[0019] In one embodiment, the function F(r) is either strictly increasing or strictly decreasing.

[0020] In one embodiment, the curve has at least one axis of symmetry.

[0021] In one embodiment, the curve is configured such that there exists a single intersection point between the curve and an image of the curve obtained by rotating the curve by any angle about a rotation axis, the intersection point being different from the rotation axis, and if the distance between the intersection point and the rotation axis is greater than or equal to Rmax / 2, then the tangent of the curve at the intersection point forms an angle greater than or equal to 45° with the tangent of the image of the curve obtained by rotation, where Rmax is the maximum radius.

[0022] According to one embodiment, the curve is defined approximately by at least one of the following polar functions.

[0023] First polar function:

[0024] r(α) = |α|2R / π, where:

[0025] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0026] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0027] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α.

[0028] The second polar function:

[0029] r(α) = Rexp(|α|-π / 2), where:

[0030] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0031] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0032] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α.

[0033] The third polar function:

[0034] r(α) = (α+π / 2)R / π, the curve also includes the straight line portion between the coordinate points (0, 0) and (0, R), where:

[0035] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0036] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0037] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α.

[0038] The fourth polar function:

[0039] ,in:

[0040] - α is the angle of a point on the curve in polar coordinates, and α is limited to the interval [-π / 2, π / 2].

[0041] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α, and

[0042] - Rmin and a i It is defined as the coefficient that makes r(π / 2) = Rmax.

[0043] The fifth polar function:

[0044] When α belongs to the interval [0, π / 2], r(α) = Rsinh(α) / sinh(π / 2), and

[0045] When α belongs to the interval [-π / 2, 0], r(α) = r(-α), where:

[0046] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0047] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0048] - sinh is the hyperbolic sine function.

[0049] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α.

[0050] The sixth polar function:

[0051] When α belongs to the interval [0, α * When ], r(α) = (Rexp(α) * -π / 2))α / α * ,

[0052] When α belongs to the interval [α * ,π / 2], r(α) = Rexp(α-π / 2), and

[0053] When α belongs to the interval [-π / 2, 0], r(α) = r(-α), where:

[0054] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0055] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0056] - α * It is a strictly positive number less than or equal to π / 2, and, for example, equal to 1.

[0057] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α.

[0058] The present invention also relates to an X-ray detection system, the detection system comprising:

[0059] - An X-ray source configured to emit X-ray beams.

[0060] - As defined above, the collimating device is designed to be exposed to the X-ray beam.

[0061] - A drive device configured to drive the carrier of the collimating device to rotate about its rotation axis.

[0062] - An X-ray detection element located in the field of view opposite the carrier relative to the X-ray source, the detection element being configured to detect X-rays passing through a slit in the carrier, and

[0063] - An angle position sensor suitable for determining the angular position of the carrier of the collimation device.

[0064] The detection system can be configured to detect X-rays passing through the slit at two consecutive times as the carrier rotates about its axis of rotation. The first time corresponds to a first angular position of the slit, and the second time corresponds to a second angular position of the slit. The first and second angular positions define a single intersection point in the plane of the carrier that corresponds to the projection position of the detection element on the plane of the carrier. The detection system further includes a processing unit configured to determine the projection position of the detection element on the plane of the carrier based on the first and second angular positions.

[0065] The present invention also relates to a method for locating a detection element of an X-ray detection system as defined above, the method comprising the following steps:

[0066] - Rotate the carrier of the collimation device about its rotation axis.

[0067] - During the rotation of the carrier, the carrier is exposed to an X-ray beam generated by an X-ray source, and then

[0068] - Using the detection element, X-rays passing through the slit of the carrier are detected at two consecutive times, the first time corresponding to a first angular position of the slit, and the second time corresponding to a second angular position of the slit.

[0069] - Using the processing unit, the projection position of the detection element on the plane of the carrier is determined based on the first angular position and the second angular position. Attached Figure Description

[0070] The objects, features, and advantages of the present invention will be described in detail below with reference to the accompanying drawings, which are given in a non-limiting manner as a particular embodiment, in which:

[0071] Figure 1 This is a schematic diagram of an X-ray detection system according to an embodiment of the present invention;

[0072] Figure 2 yes Figure 1 A schematic front view of the carrier of the collimation equipment of the detection system;

[0073] Figure 3 This is a schematic diagram of one embodiment of a sensor for the angular position of the carrier of a collimation device;

[0074] Figure 4 This is a schematic front view of the second carrier of the collimation device;

[0075] Figure 5 At the initial time of the detection method according to an embodiment of the present invention Figure 2 A schematic front view of the carrier;

[0076] Figure 6 It is at the first time t1 of the detection method Figure 2 A schematic front view of the carrier;

[0077] Figure 7 It is at the second time t2 of the detection method Figure 2 A schematic front view of the carrier;

[0078] Figure 8 It is an overlay view of the carrier at time t1 and the carrier at time t2;

[0079] Figure 9 This is a schematic front view of the carrier of the collimation device according to the second embodiment of the present invention.

[0080] Figure 10 This is a schematic front view of the carrier of the collimation device according to the third embodiment of the present invention.

[0081] Figure 11 This is a schematic front view of the carrier of the collimation device according to the fourth embodiment of the present invention. Detailed Implementation

[0082] Figure 1 Schematic diagram illustrating the invention indivual An X-ray detection system 1 is provided in this embodiment. The detection system 1 is designed to locate an object 2 on which a detection element 3 is fixed. For example, the detection system 1 can be used in the context of medical interventions to locate tools, such as catheters, within a patient's body. Therefore, the detection system 1 can be integrated into an X-ray medical imaging system. The detection system 1 is designed to provide the position of the object in a projection on a plane; that is, the detection system 1 is designed to determine the position of the object in at least two spatial dimensions.

[0083] The detection system 1 includes an X-ray source 4, a collimation device 5, a device 6 for driving the collimation device 5, and an information processing unit 8.

[0084] X-ray source 4 is configured to emit an X-ray beam F. X-ray source 4 can be considered a point source, while X-ray beam F can be a diverging beam. The X-ray beam produced by X-ray source 4 is, for example, a cone beam. X-ray beam F is centered on the emission axis. The X-axis is defined as an axis parallel to the emission axis. X-ray source 4 includes, for example, an X-ray tube operating at an inter-electrode voltage between 40 and 125 kV.

[0085] The collimating device 5 (or collimator) is designed to be exposed to the X-ray beam generated by the X-ray source 4. The collimating device 5 is configured to spatially confine the incident X-ray beam. The collimating device 5 is inserted between the X-ray source 4 and the detection element 3.

[0086] The collimating device 5 includes a carrier 51 that is substantially planar and made of a material with partial or zero X-ray transmittance. "Partial X-ray transmittance" refers to a percentage attenuation of the monoenergetic photon flux that is not zero, for example, between 1% and 99%, preferably greater than or equal to 10%, even greater than or equal to 50%, or even greater than or equal to 80%. This percentage depends on the material used for the carrier 51 and the thickness of the carrier. The material of the carrier 51 can be, for example, selected from materials such as NaI, CsI, CdWO4, BGO, LSO, PreLude®, or any other equivalent material. The thickness of the carrier 51 can be, for example, between 0.5 mm and 5 mm (inclusive). For example, a carrier made of CdWO4 with a thickness of 0.9 mm can attenuate 95% of the flux of a monoenergetic photon beam with an energy of 100 keV. "Zero X-ray transmittance" refers to complete X-ray impermeability. More precisely, "zero X-ray transmittance" refers to a percentage attenuation of the monoenergetic photon flux exceeding 99%.

[0087] The carrier 51 is located in a plane perpendicular to the X-axis. The carrier 51 is intended to be driven to rotate about a rotation axis 52 parallel to the X-axis. For this purpose, the carrier 51 is mounted to be able to rotate about an axis 53 aligned with the rotation axis 52.

[0088] The Y-axis and Z-axis are defined as two axes that are perpendicular to each other and to the X-axis. The Y-axis and Z-axis are fixed in the ground reference frame. Therefore, the carrier lies in a plane parallel to the Y-axis and Z-axis. The Y'-axis and Z'-axis are also defined as two axes that are perpendicular to each other and to the X-axis in the reference frame of carrier 51. Therefore, for a given orientation of carrier 51 about the rotation axis 52, the Y'-axis and Z'-axis coincide with the Y-axis and Z-axis, respectively. Angle β is defined as the angle formed between the Y-axis and Y'-axis (this angle is equal to the angle formed between the Z-axis and Z'-axis). Angle β is the orientation angle. The origin O is defined as the intersection of the Y-axis and Z-axis, which also corresponds to the intersection of the Y'-axis and Z'-axis. The origin O also corresponds to the intersection of the rotation axis 52 and the surface of carrier 51.

[0089] Preferably, the carrier 51 has a circular outer profile, and the rotation axis 52 passes through the center of the circle. Therefore, the carrier has good balance and can rotate at relatively high speeds without vibration. Alternatively, the carrier can be any other two-dimensional shape.

[0090] Figure 2 The illustration shows a front view of the carrier 51 according to the first embodiment. The carrier 51 is provided with a slit 54, which is completely transparent to X-rays and extends throughout the entire carrier, thereby generating an X-ray flux when the carrier is exposed to the X-ray source 4. "Completely transparent to X-rays" means that the slit 54 does not absorb or significantly absorbs the X-ray beam. For example, the thickness or material of the slit defined in the carrier 51, or a combination of both, can be selected to obtain a slit 54 that is completely transparent to X-rays. This is, for example, if the slit corresponds to an opening in the carrier (i.e., if it is filled with air). In all cases, the percentage attenuation of the monoenergetic photon flux by the slit 54 is strictly less than the percentage attenuation of the monoenergetic photon flux by the carrier 51.

[0091] When the slit 54 is observed in a section parallel to the rotation axis 52 on the thickness of the carrier 51, the slit 54 may have a rectangular shape or a trapezoidal shape tailored to the divergence of the incident X-ray beam. The width of the slit 54, i.e., the dimension of the slit 54 between its two opposite edges perpendicular to its extension direction, may be a constant width along the entire length of the slit 54. As a variant, the slit 54 may also have a variable width. The width of the slit 54 may optionally be optimized to improve the signal-to-noise ratio and / or increase the uniformity of the X-ray distribution during the implementation of the detection method.

[0092] Therefore, the X-ray beam downstream of the collimating device 5 extends in a planar or sheet-like shape, the shape of which is determined by the shape of the slit 54. As the carrier 51 rotates about its axis of rotation 52, the collimated beam emitted from the collimating device 5 sweeps across a portion of a space called the field of view. As shown below, this scanning allows the position of the detection element 3 within this field of view to be determined.

[0093] Therefore, the detection element 3 is located in the field of view opposite the carrier 51 relative to the X-ray source 4. The detection element 3 is configured to detect X-rays passing through the slit 54 of the carrier 51. The detection element 3 is configured to send a signal to the information processing unit 8 when it is irradiated by X-rays. For this purpose, the detection element 3 can be based on gallium nitride (GaN).

[0094] The drive device 6 is configured to drive the carrier 51 of the collimating device 5 to rotate about its rotation axis 52. The drive device 6 may include, for example, an electric motor. The output shaft 61 of the electric motor may be mechanically connected to the shaft 53 of the carrier, for example, via a belt 62 and / or gears. As a variant, the drive device 6 may also interact with the outer periphery of the carrier to drive the carrier to rotate. Preferably, the drive device 6 is configured to drive the carrier 51 to rotate at a fixed angular velocity (e.g., an angular velocity greater than or equal to 1000 rpm).

[0095] The detection system 1 also includes at least one angle position sensor 7 configured to determine the angular position of the carrier 51 of the collimating device about the rotation axis 52. The angle position sensor 7 may, for example, be configured to calculate the value of the angle β as defined above. The angle position sensor 7 may, for example, be integrated into the collimating device 5, or as a variant, integrated into the drive device 6.

[0096] according to Figure 3 and Figure 4In one embodiment illustrated in the diagram, the angular position sensor 7 may include a through-beam fork-shaped sensor 71 that interacts with a second carrier 51b extending parallel to the carrier 51. The second carrier 51b may be securely attached to the carrier 51 or form part of the carrier 51. The second carrier 51b may include a series of N openings 55 or windows 55, which are transparent in the visible or near-infrared domain and are angularly uniformly distributed on a circular periphery centered at a point corresponding to the intersection of the second carrier 51b and the rotation axis 52. These N windows are indexed relative to a reference window 56, which may correspond to a window that is wider (or narrower) than the others. The through-beam fork-shaped sensor 71 is equipped with a transmitter 72 and a receiver 73 positioned facing each other. The transmitter 72 emits light waves that are picked up by the receiver 73 as they pass through one of the windows 55, 56. The receiver 73 generates an electrical pulse when the window allows a signal from the transmitter 72 to pass through. If the reference window 56 is wider (or narrower), the electrical pulse received for that reference window 56 will be wider (or correspondingly narrower) than the electrical pulses received for other windows 55. The electrical pulses emitted by the angle position sensor 7 can be processed by the information processing unit 8 to determine the angular position of the carrier 51 at any given time.

[0097] The information processing unit 8 (e.g., a computer) includes a memory 81, a microprocessor 82, and a communication interface 83 capable of receiving signals transmitted by the detection element 3 and the angle position sensor 7. The memory 81 is a data recording medium storing a computer program thereon, the computer program containing program code instructions for implementing the detection method according to embodiments of the present invention. The microprocessor 82 is capable of executing the computer program. Thus, the information processing unit 8 is configured to implement a method for positioning the detection element 3.

[0098] Now refer to Figure 2 The shape of the slit 54 of the collimating device 5 is described in more detail. The shape of the slit in its projection onto the plane of the carrier is described by curve Cx. Since the slit 54 has a given width, it is conventionally defined that curve Cx corresponds to the midline equidistant between two opposite edges of the slit 54. A “curved” shape refers to a non-linear shape. Thus, curve Cx has a radius of curvature less than or equal to a predefined value, at least locally. Furthermore, at least two points on curve Cx whose tangents are not parallel to each other can be found. However, curve Cx may contain one or more straight segments. Curve Cx can be described in particular by a function expressed in polar coordinates. This function is advantageously continuous and differentiable. The derivative of this function can itself be a continuous function.

[0099] Curve Cx can be decomposed into a first half-curve C1 and a second half-curve C2. Each half-curve C1 and C2 is defined between a minimum radius Rmin and a maximum radius Rmax. Radius Rmax corresponds to the maximum radius of slit 54. The maximum radius Rmax can correspond to the radius of the functional surface of carrier 51. The minimum radius Rmin corresponds to the minimum radius of slit 54. The minimum radius Rmin can be equal to 0, in which case each half-curve C1, C2 is in contact with the origin O. Figure 2 In the example shown in the diagram, the two semi-curves C1 and C2 are symmetrical about the Y' axis. These two semi-curves intersect only at the origin O. Neither semi-curve has an inflection point.

[0100] The curve Cx also has certain geometric properties that can be described as follows. According to the first property of the curve Cx, each semi-curve C1 and C2 intersects only one point with any virtual circle centered at the origin O (i.e., centered at the rotation axis 52, since the rotation axis 52 passes through the origin O) with a radius r, and the radius r of the virtual circle is confined within the interval [Rmin, Rmax]. Figure 2 The virtual circle CV is drawn with a dashed line. In other words, the distance from each point on the semi-curve to the origin O is singular. This first property allows substantial ambiguity to be avoided in the implementation of the method for positioning the detection element 3 by means of the collimating device 5.

[0101] Next, the mathematical function F can be defined as follows: F(r) = α1(r) - α2(r), where:

[0102] - r is the distance between a point on the first or second half-curve and the axis of rotation of the carrier, and r is limited between the minimum radius Rmin and the maximum radius Rmax.

[0103] - α1(r) is the angle of point P1 on the first half-curve in polar coordinates, located at a distance r from the axis of rotation, and

[0104] - α2(r) is the angle of point P2 on the second half-curve in polar coordinates, which is located at a distance r from the axis of rotation.

[0105] According to the second property of curve Cx, function F is a bijective function, meaning that each element in the graph of function F has a single preimage in the domain of function F. Specifically, this bijective function can be, for example, a strictly increasing function or a strictly decreasing function. For example, according to... Figure 2 In the embodiment illustrated in the diagram, the function F increases from 0 to π over the interval [0; Rmax]. This second property allows the distance between the projection of the detection element 3 onto the plane of the carrier and the axis of rotation to be determined.

[0106] It has been observed that choosing a curved shape possessing the first and second properties described above enables a method for detecting the position of the detection element 3 that is highly accurate compared to using a carrier equipped with a straight slit. Various curves with these properties can be envisioned, and examples are given below. Mathematically, it can be determined that the position error obtained using a carrier equipped with a straight slit increases linearly with the distance between the projection of the detection element onto the plane of the carrier and the origin O, provided that this distance is less than or equal to √2xD. Then, once this distance is greater than or equal to A / 2xD, the error increases with the square of this distance, where D is the distance between the straight slit and the origin O. Furthermore, this error increases as the area of ​​the central blind zone decreases. Therefore, for carriers according to the prior art, a trade-off must be made between the area of ​​the central blind zone (desirably as small as possible) and the position error (also desired to be as small as possible). Conversely, when using a curved slit as defined above, this trade-off is no longer necessary. In particular, a carrier without a central blind zone can be obtained, and its position error is minimized near the origin O, increasing only proportionally to the distance between the projection of the detection element on the plane of the carrier and the origin O, which corresponds to the minimum possible position error.

[0107] Furthermore, when the curve crosses the rotation axis 52, that is, when it crosses the origin O, the detection system has no blind spots around the rotation axis of the carrier. Therefore, the position of the detection element can be determined regardless of the position of the observation element in the field of view.

[0108] According to another aspect of the invention, a third mathematical condition can be defined for the curve Cx, which requires that the function F(r) is strictly less than the angle π, regardless of the value of r in the interval [Rmin, Rmax]. In other words, the curve Cx is contained within a semi-disc, that is, within half of the carrier 51 defined by the diameter of the carrier. This condition ensures that when the curve Cx(t1) is superimposed on the curve Cx(t2) obtained by arbitrarily rotating the curve Cx(t1) about the rotation axis 52 (e.g., as...), the curve Cx(t1) is more stable than the curve Cx(t2) obtained by arbitrarily rotating the curve Cx(t1) about the rotation axis 52. Figure 8 As shown in the diagram, a single intersection point Px is still obtained between curves Cx(t1) and Cx(t2). Therefore, this property of curve Cx ensures that a unique position of detection element 3 can be obtained regardless of its position within the field of view. Alternatively, assuming that the function F is greater than or equal to π for a radius r within the interval [R1;R2], then if the projection of the detection element onto the plane of carrier 51 is located at a distance r from the origin O within the interval [R1;R2], the implementation of this detection method will result in the identification of two potential positions of detection element 3. In such a possible case, one of these two positions can be ruled out, for example, based on previously detected positions of detection element 3 and / or based on reasonableness criteria.

[0109] According to another aspect of the invention, a fourth mathematical condition can be defined for the curve Cx, which requires that the curve Cx has an axis of symmetry. The use of a curve Cx with an axis of symmetry facilitates calculations performed during the execution of the detection method.

[0110] Now for reference Figures 5-8 An embodiment of a method for detecting the position of a detection element 3 by means of a detection system 1 is described. During the implementation of this detection method, the detection element 3 is considered to remain stationary in a ground reference frame, or to move at a speed negligible considering the execution rate of the detection method according to the invention.

[0111] Figure 5 The collimation device 5 is shown at the initial time t0. It is assumed that the detection element 3 is located at an arbitrary point in the field of view. This point forms a projection 3' on the plane of the carrier 51 parallel to the direction of X-ray propagation. This projection... Figure 5 A cross is used for identification. X-ray source 4 is activated and emits X-rays in the direction of collimating device 5. Only X-rays incident on slit 54 can propagate into the field of view. Other X-rays are generally blocked by the material of carrier 51, which has partial or zero X-ray transmittance. Projection 3' does not pass through slit 54. Therefore, detection element 3 does not receive any X-rays, and thus no signal is sent to information processing unit 8.

[0112] Then, the carrier 51 is rotated about its axis of rotation 52. At the end of time t1, the carrier 51 has rotated by an angle β1 and reached... Figure 6 The position is shown in the diagram. The first half-slit corresponding to the first half-curve C1 intersects with the projection 3' of the detection element. Therefore, the detection element 3 receives X-rays and sends a first signal to the information processing unit 8. The value of the angle β1 when the information processing unit 8 receives the first signal from the detection element 3 can be determined or approximated by means of the angle position sensor 7. Thus, the information processing unit can determine the orientation of the slit 54 at time t1 when the detection element receives the X-rays. At time t1, it can then be determined that the projection 3' is located at a point on the curve Cx(t1), just as the curve is oriented at time t1.

[0113] Next, the carrier 51 continues its rotation, and the projection 3' leaves the slit 54. Therefore, the detection element 3 no longer receives any X-rays and thus no longer sends any signals to the information processing unit 8.

[0114] Next, at the end of time t2, the carrier 51 rotated by an angle β2 and reached... Figure 7The position is shown in the diagram. The second half-slit, corresponding to the first half-curve C2, intersects with the projection 3' of the detection element. The detection element 3 receives X-rays again and sends a second signal to the information processing unit 8. The value of the angle β2 when the information processing unit 8 receives the second signal from the detection element 3 can be determined or approximated by means of the angle position sensor 7. Thus, the information processing unit can determine the orientation of the slit at time t2. At time t2, it can be determined that the projection 3' is located at a point on the curve Cx(t2), just as the curve is oriented at time t2.

[0115] Figure 8 The diagram illustrates the superposition of two curves C at times t1 and t2. These two curves, labeled Cx(t1) and Cx(t2), only touch at two points: the origin O and the intersection Px. Therefore, it can be inferred that projection 3' is either located at the origin O or the intersection Px. The case where projection 3' is exactly at the origin O is easily identifiable because, in this case, the detection element 3 is continuously exposed to X-rays, thus generating a continuous signal. If the information processing unit 8 does not observe such a continuous signal, it can be inferred that the projection 3' of the detection element is located at the intersection Px. Therefore, it can be determined that the detection element 3 is located on the axis passing through the X-ray source 4 and the intersection Px.

[0116] The intersection point Px of the two curves Cx(t1) and Cx(t2) at times t1 and t2, respectively, can be calculated by the information processing unit 8 using methods such as graphical methods, empirical methods, or even analytical methods. For empirical methods, a lookup table can be provided, indicating the coordinates of the previously observed intersection point Px as a function of the values ​​of angles β1 and β2. Assuming an analytical solution, the coordinates of the intersection point Px can be calculated by solving the equations. In this case, the presence of the axis of symmetry in curve Cx reduces the complexity of the calculations.

[0117] An analytical solution method is provided below. Estimation of the intersection point Px. The following formula can be used to calculate

[0118]

[0119] in

[0120]

[0121]

[0122] and These are the measured values ​​of angles β1 and β2 transmitted by the angle position sensor 7.

[0123] r(α) is the polar function describing the curve Cx.

[0124] from Figure 8 As can be seen, the tangents Ta1 and Ta2 of curves Cx(t1) and Cx(t2) at the intersection point Px form an angle Ax close to 90°. Curve Cx can be advantageously defined such that angle Ax is greater than or equal to a given value regardless of the position of projection 3' on carrier 51. Therefore, regardless of the position of projection 3' on carrier 51, or at least when the distance between projection 3' and the origin O is greater than or equal to a given threshold, for example, equal to the threshold of Rmax / 2, this angle Ax is preferably greater than or equal to 45°, or even greater than or equal to 60°. Therefore, even if there is inaccuracy in the measurement of angles β1 and / or β2, this inaccuracy will only cause a slight shift in the intersection point Px. Thus, despite some inaccuracy in the measurement of angles β1 and / or β2, high accuracy is maintained in calculating the position of the detection element 3.

[0125] It should be noted that, Figure 2 and Figures 5-8 The Cx curve shown in the diagram can be approximately defined by the polar function r(α) = |α|²Rmax / π, where:

[0126] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0127] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0128] "Approximately" means that the definition covers any curve inscribed within the region defined by r(α) plus or minus 10%, or even plus or minus 20%.

[0129] Finally, the detection element 3 is positioned while limiting the environment of the detection element to be exposed to X-rays, because only X-rays incident on the slit 54 can irradiate the environment.

[0130] More generally, the polar function of curve Cx, as defined according to this invention, can be defined as an nth-degree polynomial function. In this case, the polar function can be written in the following form:

[0131] , in

[0132] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0133] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0134] - Rmin and ai are coefficients defined to make r(π / 2) = Rmax.

[0135] Furthermore, in one or more embodiments, the X-ray source 4 may be a pulsed source configured to emit X-rays in an alternating emission cycle consisting of two modes: an X-ray emission mode and an X-ray non-emission mode. The detection element 3 is then configured to detect X-rays passing through the slit 54 in synchronization with the X-ray emission cycle. In this case, the rotational speed of the carrier 51 can be selected such that the carrier completes one revolution within the duration of the pulsed source's emission (i.e., the duration of the X-ray emission mode). This emission duration can range from a few milliseconds to tens of milliseconds. This can further reduce environmental exposure to X-rays.

[0136] Furthermore, the information processing unit 8 can also be configured to determine the distance L1 between the detection element 3 and the X-ray source 4. Specifically, assuming the X-ray source 4 is divergent, it can be demonstrated that the farther the detection element 3 is from the X-ray source 4, the longer the irradiation duration of the detection element 3. The distance L1 can be calculated using the formula L1 = Ti · r · V · L2 / L3, where:

[0137] - Ti is the irradiation duration of the detection element 3 (which can be estimated by measuring the duration of the first signal or the second signal).

[0138] - r is the distance between the projected position 3' on the carrier plane P and the origin O.

[0139] - V is the angular rotational speed of the carrier (which can be calculated based on the data provided by the angle position sensor 7).

[0140] - L2 is the distance between the X-ray source and the carrier 51 (given by the structure), and

[0141] - L3 is the width of slit 54 (given by the structure).

[0142] Determining the distance L1 allows the detection element 3 to be positioned in three dimensions in space.

[0143] Figure 9 The diagram illustrates a second embodiment of the collimation device, wherein the slit describes the curve Cx2. According to this second embodiment, the curve Cx2 is at least approximately defined by the polar function r(α) = Rmax exp(|α|-π / 2), where:

[0144] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0145] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, which is located at angle α.

[0146] Therefore, curve Cx2 is defined for each value of r between Rmin and Rmax, where Rmin is strictly greater than 0. Thus, the collimating device 54 defined by this function contains a blind zone ZA bounded by a dashed circle of radius Rmin.

[0147] Figure 10 The diagram illustrates a third embodiment of the collimation device, wherein the slit describes the curve Cx3. According to this third embodiment, the curve Cx3 is at least approximately defined by the polar function r(α) = (α+π / 2) Rmax / π, and the curve also includes a straight line portion PR between the coordinate points (0, 0) and (0, R), where:

[0148] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0149] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, which is located at angle α.

[0150] Figure 11 The diagram illustrates a fourth embodiment of the collimation device, wherein the slit describes a curve Cx4 having the properties of the present invention. Of course, other examples of curves having the aforementioned properties may also be provided.

[0151] Typically, it is advantageous to choose a curve Cx whose polar function satisfies the following first and second conditions, the first condition being expressed by the following formula:

[0152]

[0153] The second condition is expressed by the following formula:

[0154]

[0155] in:

[0156] r(α) is the polar function describing the curve Cx.

[0157] r'(α) is the derivative of the polar function r(α), Rmin is the minimum radius of the slit, and

[0158] Rmax is the maximum radius of the slit.

[0159] The curve Cx that satisfies these two conditions allows for particularly low errors in the position of the detection element 3.

[0160] Figure 12The fifth embodiment of the collimation device is illustrated in the figure, wherein the slit is described by curve Cx5 defined by the following equation:

[0161] When α belongs to the interval [0, π / 2], r(α) = Rsinh(α) / sinh(π / 2), and

[0162] When α belongs to the interval [-π / 2, 0], r(α) = r(-α), where:

[0163] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0164] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0165] - sinh is the hyperbolic sine function.

[0166] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α. In the current case, Rmax = 25.

[0167] The fifth curve has the advantage of minimizing the energy factor defined by the integral of r(α)² + r'(α)² over α in the interval [0, π / 2], where r'(α) is the derivative of r(α).

[0168] Figure 13 The sixth embodiment of the collimation device is illustrated in the figure, wherein the slit is described by curve Cx6 defined by the following equation:

[0169] When α belongs to the interval [0, α * When r(α) = Rexp(α) * -π / 2)α / α * ,

[0170] When α belongs to the interval [α * ,π / 2], r(α) = Rexp(α-π / 2), and

[0171] When α belongs to the interval [-π / 2, 0], r(α) = r(-α), where:

[0172] - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2].

[0173] - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α.

[0174] - α * It is a strictly positive constant, less than π / 2, which is equal to 1 in the current case.

[0175] - R is defined as a constant that makes the maximum value of r(α) equal to Rmax within the defined interval of α. In the current case, Rmax = 25.

[0176] This sixth curve allows for a continuous connection at α* between a linear spiral in [0, α*] and an exponential function in [α*, π / 2]. Specifically, the derivative r'(α) is also continuous when α* = 1. This curve has the advantage of minimizing the integral of max(r(α), r'(α)) where α belongs to the interval [0, π / 2]. It also minimizes the maximum value of max(r(α), r'(α)) for α belonging to the interval [0, π / 2].

[0177] The curves according to the fifth embodiment and the sixth embodiment have the advantage of enabling extremely low errors in the position of the detection element 3.

Claims

1. A collimating device (5) for an X-ray detection system (1), the collimating device comprising a carrier (51) that is substantially planar and made of a material having partial or zero X-ray transmissivity, the carrier being intended to be driven to rotate about a rotation axis (52) perpendicular to the plane in which the carrier is located, the carrier being provided with a slit (54) that is completely transparent to X-rays and passes through the thickness of the carrier to generate an X-ray flux when the carrier is exposed to an X-ray source, characterized in that: The shape of the slit in the projection of the carrier onto the plane is a curve (Cx). The slit is composed of a first semi-curve (C1) and a second semi-curve (C2). Each semi-curve intersects only one point with any virtual circle (CV) centered on the rotation axis and with radius r. The radius r is limited to the interval [Rmin, Rmax], where Rmin is the minimum radius and Rmax is the maximum radius. • The function F defined by F(r) = α1(r) - α2(r) is a bijective function, where: - r is the distance between a point on the first or second half-curve and the axis of rotation of the carrier, and r is limited between the minimum radius Rmin and the maximum radius Rmax. - α1(r) is the angle of a point (P1) on the first half-curve in polar coordinates, located at a distance r from the axis of rotation, and - α2(r) is the angle of a point (P2) on the second half-curve in polar coordinates, which is located at a distance r from the axis of rotation.

2. Collimation device (5) according to the preceding claim, characterized in that Regardless of the value of r in the interval [Rmin, Rmax], the value of the function F(r) is strictly less than the angle π.

3. The collimation device (5) according to any one of the preceding claims, characterized in that The curve (Cx) passes through the rotation axis (52) of the carrier (51).

4. The collimation device (5) according to any one of the preceding claims, characterized in that The function F(r) is either strictly increasing or strictly decreasing.

5. The collimation device (5) according to any one of the preceding claims, characterized in that The curve (Cx) has at least one axis of symmetry.

6. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is configured such that there exists a single intersection point (Px) between the curve (Cx) and the image of the curve obtained by rotating the curve by any angle about the rotation axis (52), the intersection point being different from the rotation axis (52), and if the distance between the intersection point (Px) and the rotation axis (52) is greater than or equal to Rmax / 2, then the tangent (Ta1) of the curve at the intersection point (Px) forms an angle greater than or equal to 45° with the tangent (Ta2) of the image of the curve obtained by rotation, where Rmax is the maximum radius.

7. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: · r(α) = |α|2R / π, where: - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α. - R is defined as a constant that makes the maximum value of r(α) equal to Rmax on the defined interval of α.

8. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: · r(α) = Rexp(|α| - π / 2), where: - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α. - R is defined as a constant that makes the maximum value of r(α) equal to Rmax on the defined interval of α.

9. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: · r(α) = (α + π / 2)R / π, the curve also includes the straight line portion between the coordinate points (0,0) and (0,R), where: - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α. - R is defined as a constant that makes the maximum value of r(α) equal to Rmax on the defined interval of α.

10. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: · ,in: - α is the angle of a point on the curve in polar coordinates, and α is limited to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α, and - Rmin and ai are coefficients defined to make r(π / 2) = Rmax.

11. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: For α belonging to the interval [0, π / 2], r(α) = Rsinh(α) / sinh(π / 2), and For α belonging to the interval [-π / 2, 0], r(α) = r(-α), where: - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α. - sinh is the hyperbolic sine function. - R is defined as a constant that makes the maximum value of r(α) equal to Rmax on the defined interval of α.

12. The collimation device (5) according to any one of the preceding claims, characterized in that... The curve (Cx) is defined at least approximately by the following polar functions: • for a belonging to the interval [0, a * ], r(a) = (Rexp(a * - π / 2))α / α * , • for a belonging to the interval [a * , π / 2], r(a) = R exp(a - π / 2), and • for a belonging to the interval [π / 2, π], r(a) = R exp(a - π / 2). For α belonging to the interval [-π / 2, 0], r(α) = r(-α), where: - α is the angle of a point on the curve in polar coordinates, and α is confined to the interval [-π / 2, π / 2]. - r(α) is the distance between a point on the curve and the axis of rotation of the carrier, located at angle α. - a * is a strict positive number smaller than π / 2 and for example equal to 1, - R is defined as a constant that makes the maximum value of r(α) equal to Rmax on the defined interval of α.

13. An X-ray detection system (1), the detection system comprising: - An X-ray source (4) configured to emit an X-ray beam (F), - The collimating device (5) according to any of the preceding claims, the collimating device being designed to be exposed to an X-ray beam, - A drive device (6) configured to drive the carrier (51) of the collimating device to rotate about its rotation axis (52), - An X-ray detection element (3) located in the field of view opposite the carrier (51) relative to the X-ray source, the detection element being configured to detect X-rays passing through a slit (54) of the carrier, and - An angle position sensor (7) suitable for determining the angular position of the carrier of the collimation device.

14. The detection system (1) according to the preceding claim, wherein the detection element (3) is configured to detect X-rays passing through the slit (54) at two consecutive times as the carrier (51) rotates about its rotation axis (52), the first time (t1) corresponding to a first angular position (β1) of the slit and the second time (t2) corresponding to a second angular position (β2) of the slit, the first angular position and the second angular position defining a single intersection point (Px) in the plane of the carrier corresponding to the projection position (3') of the detection element (3) on the plane of the carrier, the detection system (1) further comprising a processing unit (8) configured to determine the projection position (3') of the detection element on the plane of the carrier based on the first angular position and the second angular position.

15. A method for locating a detection element (3) of an X-ray detection system (1) according to the preceding claim, the method comprising the steps of: - Rotate the carrier (51) of the collimation device (5) about its rotation axis (52). - During the rotation of the carrier, the carrier is exposed to an X-ray beam generated by the X-ray source (4), and then - Using the detection element (3), X-rays passing through the slit (54) of the carrier are detected at two consecutive times, the first time (t1) corresponding to the first angular position (β1) of the slit, and the second time (t2) corresponding to the second angular position (β2) of the slit. - Using the processing unit (8), the projection position (3') of the detection element (3) on the plane of the carrier (51) is determined based on the first angular position and the second angular position.

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