Gantry for a computed tomography device with an angular position measuring system

Abstract

Gantry (20) for a computer tomography device (1), - wherein the gantry (20) comprises a support structure (23), a rotating frame (24) and an angular position measuring system (5), - wherein the rotating frame (24) is arranged on the supporting structure (23) so as to be rotatable about a rotation axis (4A) relative to the supporting structure (23), - wherein the angular position measuring system (5) comprises a proximity sensor (51) and a measuring track (50), - wherein the measuring track (50) is arranged in a ring around the rotation axis (4A) and cooperates with the proximity sensor (51) for measuring angular position data of the rotating frame (24) with respect to the rotation axis (4A), - wherein the measuring track (50) is contoured and arranged relative to the proximity sensor (51) such that a distance between the measuring track (50) and the proximity sensor (51) along a measuring axis (5A) of the proximity sensor (51) follows a plateau-free waveform when the rotating frame (24) rotates relative to the support structure (23) about the rotation axis (4A).

Description

The invention relates to a gantry for a computed tomography device. The invention further relates to a computed tomography device.An angular position measurement for a rotating frame of a gantry of a computed tomography device, which rotates about an axis of rotation, is important in particular for an image reconstruction. In principle, in the case of angular position measuring systems for the axis of rotation, a distinction must be made between the accuracy classes. The background is the design and requirement of the image reconstruction of the respective system. So-called location-controlled systems require a higher absolute accuracy and location resolution than so-called time-controlled systems. In time-controlled systems, a large part of the position information is interpolated on the basis of the rotation speed assumed to be constant. The accuracy of the interpolation of the measurement of the angular position of time-controlled systems depends on the one hand on the number of interpolation points available for interpolation and actually measured, and on the stability of the rotational speed.For interpolation for measuring the angular position in time-controlled systems, supporting points, for example in the form of fixed embossings within the rotating frame, can be used and can be scanned in particular via inductive proximity switches. A data processing unit of the computed tomography device registers the occurrence of a supporting point during the rotation and adjusts the interpolation accordingly to the position of the rotating frame. The occurrence of the interpolation point can be detected in particular as binary information. In this case, it is only registered whether or not a support point is present. The embossings can be, for example, bores. The bores can be made, for example, radially or axially to the axis of rotation. This binary information is used for interpolation and / or image reconstruction.This concept is dependent in particular on the quality of the rotational speed stability, since in the case of a conventional design of the embossing within the rotating frame, due to the outlay of mechanical machining, only a relatively small number of interpolation points can be implemented for the correction of the interpolation. The stability of the rotational speed is significantly influenced by the system imbalance and the drive technology used and the regulation thereof. Both for the reductions of the system imbalance and for the regulation or drive technique used, higher outlay is necessary with increasing rotational speed.The object of the invention is to provide an alternative to conventional measurement of an angular position in computed tomography devices, in particular with a view to improving the accuracy and / or robustness with respect to rotational speed fluctuations. The independent claims relate to solutions to this task. The dependent claims relate to particular embodiments of these solutions. Regardless of the grammatical sex of a certain term, individuals with male, female or other sex identity are included.The invention relates to a gantry for a computed tomography device,wherein the gantry has a supporting structure, a rotating frame and an angular position measuring system,wherein the rotating frame is arranged on the supporting structure such that it can rotate about an axis of rotation relative to the supporting structure,wherein the angular position measuring system comprises a proximity sensor and a measuring track,wherein the measuring track is arranged annularly around the axis of rotation and interacts with the proximity sensor for a measurement of angular position data of the rotating frame with respect to the axis of rotation,wherein the measuring track is contoured and arranged relative to the proximity sensor such that a distance between the measuring track and the proximity sensor along a measurement axis of the proximity sensor follows a plateauless waveform as the rotating frame rotates about the rotational axis relative to the support structure.The gantry can have a pivot bearing, for example. The rotating frame can be connected to the supporting structure, for example, by means of the pivot bearing and / or can be rotatably mounted relative to the supporting structure. The measuring track can be closed in particular circumferentially around the axis of rotation. The waveform may be continuous and / or periodic, in particular. The waveform can be in particular continuous and / or smooth. The waveform may be, for example, a triangular waveform.The proximity sensor can be, for example, an inductive distance sensor and / or be configured to generate the angular position data based on the distance between the measuring track and the proximity sensor along the measurement axis. With this type of sensor system it is possible to recognize the contour or the position changes of the wave form impressed in the material. Depending on the sensor properties used (e.g. with respect to the spatial or temporal resolution) and the mechanical design of the measurement trace contour (e.g. period length over the circumference or amplitude of the mechanical contour), a significantly finer spatial resolution can be achieved with this.One embodiment provides that the plateauless waveform is periodic. One embodiment provides that the plateauless waveform is sinusoidal.The sinusoidal waveform represents, for example, a continuous signal waveform within a signal period, whereby independent position information is available at each position within a period. This additional position information can be evaluated by also appropriately adapting the sensor system used.With the generated information of the sinusoidal contour, a data processing unit of the computed tomography device is able to optimize the interpolation of the position detection, since the information is contained within the raw signal at a higher resolution compared to the current conversion with binary position information (interpolation points). Furthermore, rotational direction information can be generated by using a second inductive proximity sensor that is arranged electrically offset by 90°.One embodiment provides that the measurement axis is perpendicular, in particular radial, to the axis of rotation.One embodiment provides that the measurement axis is parallel to the rotation axis.One embodiment provides that the measuring track rests relative to the rotating frame when the rotating frame rotates relative to the supporting structure about the axis of rotation, wherein the proximity sensor rests relative to the supporting structure when the rotating frame rotates relative to the supporting structure about the axis of rotation.The invention relates to a computed tomography device, comprising the gantry according to the invention, an X-ray source for generating X-ray radiation and an X-ray detector for detecting the X-ray radiation, wherein the X-ray source and the X-ray detector are fastened to the rotating frame and cooperate for acquiring projection data, wherein the X-ray source and the X-ray detector are stationary relative to the rotating frame when the rotating frame rotates about the axis of rotation relative to the supporting structure.An embodiment provides that the gantry has an opening for receiving an examination object, for example a patient or a phantom, wherein the opening extends in a tunnel-shaped manner along the axis of rotation.One embodiment provides that the computed tomography device has an image reconstruction unit which is configured to reconstruct medical image data based on the projection data and the angular position data, wherein in particular an assignment of projection data to angular positions can take place based on the angular position data.One embodiment provides that the computed tomography device has a rotational drive for driving a rotational movement of the rotating frame relative to the supporting structure about the rotational axis, wherein the computed tomography device has a drive control unit which is configured to control the rotational movement of the rotating frame on the basis of the angular position data.A more finely resolved raw signal compared to the discrete impressed nodes can thus be provided for position detection. Based on the additional information, a higher number of interpolation nodes can be determined, which is matched to the requirement for the image reconstruction. In particular, internally used clock pulses for the image reconstruction can be varied on the basis of the raw signal.Furthermore, the position information can also be used as a signal for the drive regulation of the rotational axis. Due to the available analog sine signal and the signal processing within the data processing unit of the computed tomography device, a sufficiently resolved position signal can be provided to the converter of the drive chain. Since the position information is not interpolated but actually measured, the control performance increases and also makes it possible to use direct drive technology, for example.Within the scope of the invention, features which are described with reference to different embodiments of the invention and / or different claim categories (method, use, device, system, arrangement etc.) can be combined to form further embodiments of the invention. For example, a claim relating to a device can also be developed with features which are described or claimed in connection with a method, and vice versa. Functional features of a method can be carried out by correspondingly designed physical components. The use of the indefinite article "a" or "an" does not exclude that the feature concerned can also be present multiple times.Features of the invention are explained below on the basis of examples with reference to the attached figures. The illustration in the figures is schematic, greatly simplified and not necessarily true to scale.FIG. 1 shows a rotating frame of a gantry.FIG. 2 shows the measuring track and the proximity sensor in a first view.FIG. 3 shows the measuring track and the proximity sensor in a second view.FIG. 4 shows examples of waveforms.FIG. 5 shows a computed tomography device.FIG. 1 shows the rotating frame 24 of the gantry 20. The basic structure 240 has the recording region 244 for the X-ray source 44 and the recording region 248 for the X-ray detector 48. The measuring track 50 rests relative to the rotating frame 24 when the rotating frame 24 rotates relative to the supporting structure 23 about the axis of rotation 4A, wherein the proximity sensor 51 rests relative to the supporting structure 23 when the rotating frame 24 rotates relative to the supporting structure 23 about the axis of rotation 4A.FIG. 2 shows the measuring track 50 and the proximity sensor 51 in a first view. FIG. 3 shows the measuring track 50 and the proximity sensor 51 in a second view. The measurement trace contour produces a sinusoidal periodic waveform with the period length 5L, which corresponds to an electrical angle of 360°. The measurement axis 5A is perpendicular, namely radial, to the rotation axis 4A.FIG. 4 shows examples of the plateauless sinusoidal waveforms SINand COS, and the plateaued square waveforms AP0and AP90, respectively, for the clockwise rotational motion ROT1and the counterclockwise rotational motion ROT2. 90N stands for negative 90° electrical. 90P stands for positive 90° electrical. 360SC represents a period of the sine waveform. 360SW represents a period of the rectangular waveform. By using a further proximity sensor that is arranged electrically offset by 90°, rotational direction information can be generated based on the angular position data of the two proximity sensors.FIG. 5 shows the computed tomography apparatus 1 with the gantry 20,wherein the gantry 20 has a supporting structure 23, a rotating frame 24 and an angular position measuring system 5,wherein the rotating frame 24 is arranged on the supporting structure 23 such that it can rotate about an axis of rotation 4A relative to the supporting structure 23,wherein the angular position measuring system 5 comprises a proximity sensor 51 and a measuring track 50,wherein the measuring track 50 is arranged annularly around the rotational axis 4A and interacts with the proximity sensor 51 for a measurement of angular position data of the rotating frame 24 with respect to the rotational axis 4A,wherein the measuring track 50 is contoured and arranged relative to the proximity sensor 51 such that a distance between the measuring track 50 and the proximity sensor 51 along a measurement axis 5A of the proximity sensor 51 follows a plateauless waveform when the rotating frame 24 rotates about the rotation axis 4A relative to the support structure 23.The support structure 23 has the support frame 21, the tilting frame 22 and the tilting bearing arrangement 2B, wherein the tilting frame 22 is arranged on the support frame 21 such that it can be tilted about a tilting axis 2B relative to the support frame 21 by means of the tilting bearing arrangement 2B in such a way that a tilting angle of the tilting frame 22 relative to the support frame 21 can be changed about the tilting axis 2A by a tilting movement of the tilting frame 22 relative to the support frame 21. For a reference angle of the tilting frame 22 relative to the supporting frame 21 about the tilting axis 2A, the axis of rotation 4A and the system axis 1A are congruent. The rotating frame 24 is arranged on the tilting frame 22 such that it can rotate about the axis of rotation 4A relative to the tilting frame 22.The computed tomography device 1 has the patient couch 10 with the couch base 11 and the couch board 12. The examination object 13 is mounted on the bed board 12. The bed board 12 is displaceable relative to the bed base 11 along the system axis 1A. The computed tomography device 1 has the data processing unit 30 with a processor 3, a memory 32, the manual input unit 38 and the visual output unit 39 for a graphical user interface GUI. The data processing unit 30 can be configured in particular for interpolating the angular position data.The computed tomography device 1 comprises the gantry 20, an X-ray source 44 for generating X-ray radiation 47 and an X-ray detector 48 for detecting the X-ray radiation 47, wherein the X-ray source 44 and the X-ray detector 48 are fastened to the rotating frame 24 and cooperate for acquiring projection data, wherein the X-ray source 44 and the X-ray detector 48 are stationary relative to the rotating frame 24 when the rotating frame 24 rotates about the axis of rotation 4A relative to the supporting structure 23.The gantry 20 has an opening 9 for receiving an examination object 13, wherein the opening 9 extends in a tunnel-shaped manner along the axis of rotation 4A. The computed tomography device 1 has an image reconstruction unit 31 which is configured to reconstruct medical image data based on the projection data and the angular position data. The computed tomography device 1 has a rotation drive 4 for driving a rotational movement of the rotation frame 24 relative to the supporting structure 23 about the rotation axis 4A, wherein the computed tomography device 1 has a drive control unit 33 which is configured to control the rotational movement of the rotation frame 24 on the basis of the angular position data.

Claims

Gantry (20) for a computed tomography device (1), - wherein the gantry (20) has a supporting structure (23), a rotating frame (24) and an angular position measuring system (5), - wherein the rotating frame (24) is arranged on the supporting structure (23) such that it can rotate about an axis of rotation (4A) relative to the supporting structure (23), - wherein the angular position measuring system (5) has a proximity sensor (51) and a measuring track (50), - wherein the measuring track (50) is arranged annularly around the axis of rotation (4A) and interacts with the proximity sensor (51) for measuring angular position data of the rotating frame (24) with respect to the axis of rotation (4A), - wherein the measuring track (50) is contoured in this way and arranged relative to the proximity sensor (51), a distance between the measuring track (50) and the proximity sensor (51) along a measuring axis (5A) of the proximity sensor (51) follows a plateauless waveform when the rotating frame (24) rotates about the axis of rotation (4A) relative to the supporting structure (23).The gantry (20) of claim 1, - wherein the plateauless waveform is periodic.The gantry (20) of claim 1 or 2, - wherein the plateauless waveform is sinusoidal.Gantry (20) according to one of Claims 1 to 3, - wherein the measurement axis (5A) is perpendicular, in particular radial, to the axis of rotation (4A).Gantry (20) according to one of claims 1 to 3, - wherein the measurement axis (5A) is parallel to the rotation axis (4A).Gantry (20) according to one of claims 1 to 5, - wherein the measuring track (50) rests relative to the rotating frame (24) when the rotating frame (24) rotates relative to the supporting structure (23) about the axis of rotation (4A), - wherein the proximity sensor (51) rests relative to the supporting structure (23) when the rotating frame (24) rotates relative to the supporting structure (23) about the axis of rotation (4A).Computed tomography apparatus (1) comprising the gantry (20) according to one of claims 1 to 6, an X-ray source (44) for generating X-ray radiation (47) and an X-ray detector (48) for detecting the X-ray radiation (47), - wherein the X-ray source (44) and the X-ray detector (48) are fastened to the rotating frame (24) and cooperate for acquiring projection data, - wherein the X-ray source (44) and the X-ray detector (48) are stationary relative to the rotating frame (24) when the rotating frame (24) rotates about the axis of rotation (4A) relative to the supporting structure (23).Computed tomography device (1) according to Claim 7, - wherein the gantry (20) has an opening (9) for receiving an examination object (13), - wherein the opening (9) extends in a tunnel-shaped manner along the axis of rotation (4A).Computed tomography device (1) according to claim 7 or 8, - wherein the computed tomography device (1) comprises an image reconstruction unit (31), which is configured to reconstruct medical image data based on the projection data and the angular position data.Computed tomography device (1) according to one of claims 7 to 9, - wherein the computed tomography device (1) comprises a rotation drive (4) for driving a rotational movement of the rotating frame (24) relative to the supporting structure (23) about the axis of rotation (4A), - wherein the computed tomography device (1) comprises a drive control unit (33) which is configured to control the rotational movement of the rotating frame (24) based on the angular position data.

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