EP3422386A1

EP3422386A1 - A rotary anode x-ray source

Info

Publication number: EP3422386A1
Application number: EP17178142.0A
Authority: EP
Inventors: Rolf Karl Otto Behling
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2017-06-27
Filing date: 2017-06-27
Publication date: 2019-01-02
Also published as: WO2019002010A1

Abstract

A trend in the design of CT and C-arm scanning systems is miniaturization, requiring system components to be accommodated in smaller spaces. This trend has begun to influence the design of X-ray system components like X-ray tubes. The present application proposes to make more space available inside an X-ray tube assembly by using asynchronous motors with stators which do not encompass the rotary anode member. The gap portion created in the stator segments can be used to house extra components. In addition, the unequal forces and momenta exerted on a rotary X-ray source by such segmented stators can be used to compensate undesirable forces, such as gyroscopic or gravitational forces, on the rotary X-ray source in operation.

Description

FIELD OF THE INVENTION

The present invention relates to a rotary anode X-ray source, an X-ray imaging system, a method of rotary anode X-ray source control, a computer program element and a computer readable medium.

BACKGROUND OF THE INVENTION

A rotating anode X-ray source is the standard device for generating a beam of X-rays useful, for example, in medical X-ray equipment such as CT scanners, and C-arm imaging systems. In a rotary anode X-ray source, a cathode and anode are arranged to face each other in a vacuum envelope at such a distance that thermionic electron emission occurs between the cathode and the anode, when a suitable potential difference is generated between them. Electrons are accelerated from the cathode through an electric field to the anode. When the electrons collide at high speed with the anode, energy is dissipated in the form of heat, and X-ray radiation. In fact, over ninety-nine percent of the energy is dissipated as heat, which has necessitated the use of a rotating anode to reduce the thermal damage to the anode in high-power applications. The small proportion of energy emitted from the anode as X-ray radiation is directed towards an X-ray window of the X-ray source for clinical use.
The need for the X-ray anode to rotate, typically at hundreds of revolutions per second, imposes constraints on the design of the rotary anode X-ray tube, and in particular on its rotary bearing system. Furthermore, the rotary anode X-ray source is typically mounted either on the gantry of a CT scanner, or on a mobile C-arm X-ray scanning system. The CT scanner gantry and the C-arm scanning system are both required to move during operation. The rotary anode of an X-ray source has a significant mass. Therefore. Significant gyroscopic forces are exerted on the rotary anode's bearing in operation, if the alignment of the X-ray source is not carefully planned. In a CT scanning system, it is usual for the axis of rotation of the rotating anode to be arranged to be in parallel with the axis of rotation of the CT scanner's gantry, enabling gyroscopic forces to be minimized. However, in the case of a C-arm imaging system, it may be difficult to avoid the application of significant gyroscopic forces to the shaft supporting the rotating anode, because C-arm X-ray scanning systems are intended to be used as part of sophisticated acquisition protocols, in which the C-arm X-ray scanning head moves through several axes. In this latter case, a significant gyroscopic force component on the rotating anode's axis cannot be avoided.
DE 10 2011 083 495 B3 describes a synchronous reluctance motor employed in an X-ray tube. However, such X-ray tubes may be further improved.

SUMMARY OF THE INVENTION

It would be advantageous to have an improved rotary anode X-ray source.
The object of the present invention is solved by the subject-matter of the independent claims wherein further embodiments are incorporated in the dependent claims.
Towards this end, a first aspect of the invention provides a rotary anode X-ray source. The X-ray source comprises:

an X-ray tube;
a rotatable anode member disposed inside the X-ray tube wherein the rotatable anode member is configured to revolve around a shaft axis; and
a rotatable anode member drive.

The rotatable anode member drive is an asynchronous motor, comprising a rotor element wherein the rotor element is attached, or integral with, the rotatable anode member, and a first stator element in facing relation to the rotor element.
The first stator element is provided as a non-continuous segment having a first gap portion.
The first stator element is configured, upon the application of a driving current to the first stator element, to induce both a rotation of the rotatable anode member about the shaft axis, and a first force on the rotatable anode member away from the shaft axis in a radial direction and/or along the shaft axis.
Accordingly, a first stator element provided as a non-continuous segment having a gap portion. The gap portion (an absence of stator coil windings for a defined sector of the first stator element) causes the first stator element to induce on the rotor element a first unequal force (or momentum) component. A conventional stator element of a conventional asynchronous motor, the completely encompasses the rotor element. The magnetic repulsion on the rotor element provided by each infinitesimal slice of the stator therefore balances out with a matched infinitesimal slice on the opposite side of the rotor element. As such (and assuming a uniform and well-matched stator coil construction) there is no resultant force component acting radially on the rotor element (to push the rotor element out of alignment from its axis) or an axial component (to slide the rotor element along its axis). In the conventional case where a stator fully surrounds the rotor element, non-rotational forces and momenta exerted by the stator on the rotor element are zero.
According to the first aspect, an asynchronous motor is provided in which the first stator element is provided as a non-continuous segment having a first gap portion.
Thus, the infinitesimal force component on the rotor element contributed by respective infinitesimal portions of the first stator element do not balance each other out owing to the missing section of stator coil which is replaced by the first gap portion.
Therefore, there is a radial force acting on the rotor element to "push" the rotor element off its axial line. The direction of this resultant force component is substantially aligned through the geometrical centre of the first stator element (provided the first stator element has a symmetrical shape in the plane normal to the axis of rotation).
The axial and/or radial forces generated using such a segmented first stator element can be used, for example, to compensate gravitational, gyroscopic, or centrifugal forces in an X-ray scanning system. As one example, providing this compensation may enable an X-ray rotary anode source assembly to be angled away from an axis parallel to the axis of rotation of a gantry in a CT scanner. In a conventional X-ray source, this would imply the exertion of additional gyroscopic forces on the bearing of the rotary anode X-ray source. According to the present aspect, the first stator segment would be provided such that the first force on the rotatable anode member away from the shaft axis acted to cancel (or to reduce) the gyroscopic force.
Optionally, the rotatable anode member drive is an asynchronous motor, comprising a rotor element wherein the rotor element is disposed inside the X-ray tube, attached, or integral with, the rotatable anode member, and the first stator element is disposed outside the X-ray tube, in facing relation to the rotor element.
Optionally, there is provided a rotary anode X-ray source, wherein the rotatable anode member drive further comprises a second stator element provided as a non-continuous segment having a second gap portion, wherein the first and second stator elements together form a first stator pair arranged to partially surround the rotor element. In operation, a balanced resultant force and/or momentum on the rotatable anode member drive in a radial direction, and/or along the shaft axis is provided.
Advantageously, two stator elements provided as non-continuous segments can be provided whose resultant forces cancel each other out in operation. Therefore, a force exerted on the bearing of the rotary anode X-ray source is minimized, compared to the case of a single segmented stator element, but more space inside the X-ray source is available owing to the fact that the stator elements have gap portions which can be used to accommodate other pieces of hardware (for example, wire looms, or structural casing components) in the casing of the X-ray source.
Optionally, the rotatable anode member of the rotary anode X-ray source comprises a rotatable anode disk which in combination with the rotatable anode member substantially defines a centre of gravity of the rotatable anode member. The first stator element and the second stator element are disposed along the shaft axis on opposite sides of the centre of gravity.
Due to the relatively large mass of the anode disk, the centre of gravity of the entire rotatable arrangement is then typically located on the shaft axis close to its intersection with the centre plane of the anode disk. The first stator element and the second stator element are disposed along the shaft axis on opposite sides of the centre of gravity. This may be realized notably when the centre of gravity is located inside the volume defined by the outer envelope of the rotating anode disk by placing them on opposite faces of the rotating anode disk.
Optionally, the rotary anode X-ray source is provided so that the rotatable anode member of the rotary anode X-ray source comprises a rotatable anode disk which in combination with the rotatable anode member substantially defines a centre of gravity of the rotatable anode member. The first stator element and the second stator element are disposed on opposite faces of the rotatable anode disk.
Accordingly, the first stator element exerts a first force or momentum with respect of the centre of gravity on the rotatable shaft, and the second stator element exerts a second force or momentum on the rotatable shaft. The centre of gravity of the rotatable shaft axis is close to, or at the centre of the rotatable anode disk, because this has the dominant mass in the rotating assembly. Therefore, the first and second forces (or momenta) balance each other out around the centre of gravity of the rotating subassembly.
Optionally, the rotary anode X-ray source is provided wherein the second gap portion of the second stator element is arranged at an azimuthal offset angle to the first gap portion of the first stator element. The size of the azimuthal offset angle is in the range of between five to three hundred degrees. Optionally, the azimuthal offset angle may be smaller than ninety degrees, smaller than sixty degrees, smaller than forty-five degrees, smaller than thirty degrees, smaller than twenty degrees, smaller than ten degrees.
Offsetting the second gap portion of the second stator element with respect to the first gap portion of the first stator element implies that the force or momentum contribution from the second gap portion and the force or momentum contribution from the first gap portion can be arranged, based on the offset angle, to produce a wide variety of resultant force directions based on the azimuthal offset angle. In some arrangements, it is beneficial to arrange for an azimuthal offset or a "skew" of the stator gap portions with respect to other gap portions such that gyroscopic momenta which may appear during angulation of the entire X-ray tube (such as when a C-arm supporting the X-ray source is reconfigured during an acquisition protocol) can be counter-balanced. This provides more flexibility when determining the mounting angle of a rotary anode X-ray source in an item of moving machinery such as a CT scanner or a C-arm assembly. In certain configurations, the rotary anode X-ray source can be mounted off-parallel to the axis of rotation of a CT scanner, for example, but the gyroscopic forces resulting can be reduced or cancelled by careful design of the position of the first and second stator elements.
Optionally, a rotary anode X-ray source is provided wherein the first gap portion of the first stator element is arranged to face the rotor element at an azimuthal offset angle of ninety degrees about the shaft from the second gap portion of the second stator element. This enables gyroscopic forces on the rotatable anode member to be reduced in operation.
The component of gyroscopic force is maximized at an angle of ninety degrees from the shaft axis. Therefore, offsetting the first stator element from the second stator element at an azimuthal offset angle of ninety degrees enables an effective anti-gyroscopic force compensation to be provided, for example.
Optionally, there is a provided a rotary anode X-ray source as previously described, wherein the rotatable anode member drive further comprises:

a second stator element pair comprising a third stator element and fourth stator element.

The third stator element and the fourth stator element each have a non-continuous segment having third and fourth respective gap portions, and are provided in a facing relation to the surface of the rotor element.
The first stator element pair and the second stator element pair are arranged to provide, in operation, a balanced resultant force on the rotatable anode member drive in a radial direction, and/or along the shaft axis.
Thus, in an example, a first and second stator element pair may be provided at an azimuthal offset angle to each other, resulting in a resultant axial and/or radial force on the rotor element. In other words, the gap portions of the first and second stator elements are not aligned. In other words, a first axial and/or first radial force generated by the first stator element is not aligned with the direction and/or magnitude of a second axial and/or second radial force generated by the second stator element. However, the third and fourth stator element may be used to balance such a force.
Optionally, the rotary anode X-ray source is provided wherein the third and the fourth gap portions of the third and fourth stator elements are arranged in an azimuthally offset relationship to the first and second gap portions of the first and second stator elements, respectively.
Optionally, a rotary anode X-ray source is provided, wherein the third and fourth gap portions of the third and fourth stator elements are arranged in a facing relationship to the first and second gap portions of the first and second stator elements, respectively.
Optionally, a rotary anode X-ray source is provided as previously described, wherein the rotatable anode member drive further comprises:

a circular stator encompassing the rotatable anode member and facing the rotor element.

Thus, a rotary anode X-ray source can be provided in which a circular stator provides a significant proportion of the rotary momentum, and a segmented stator, or a plurality of segmented stators, are arranged to induce a force axially or radially on the rotary element, to address gyroscopic or other unbalancing forces on the rotatable anode member drive.
According to a second aspect, there is provided an X-ray imaging system comprising:

the rotary anode X-ray source as defined according to the first aspect or its embodiments:
- an X-ray imaging system state detector, and
- a stator control system.

The stator control system is configured to receive X-ray imaging system state information from the X-ray imaging system state detector, to generate a stator control signal based on the X-ray imaging system state information, and to provide the stator control signal to drive at least the first stator element of the rotary anode X-ray source.
Accordingly, information about the state (present or future) of the X-ray system can be used to compute appropriate drive signals (present or future) for at least the first stator element. A predicted CT-scanning protocol, or C-arm acquisition protocol, can be analyzed by a computer-implemented or firmware computing arrangement, and gyroscopic forces exerted on a rotating anode X-ray tube computed, or provided by a look-up table, for example. Optionally, the computing arrangement calculates compensation signals based on the gyroscopic values present in the look-up table suitable for a particular configuration of stator elements, In an embodiment, the stator element drive signals are computed during operation or provided from the lookup table to reduce the gyroscopic force and/or momentum on the rotary anode X-ray source owing to the movement of a CT gantry of the motion of a C-arm system.
Optionally, there is provided an X-ray imaging system. The X-ray imaging system state detector comprises a gantry motion indication sensor.
The stator control system is further configured to receive gantry motion indication information from the X-ray imaging system state detector, to generate a stator control setting to influence a gyroscopic moment on the rotatable anode member of the rotary anode X-ray source and to control the stator control signal to drive at least the first stator element of the rotary anode X-ray source based on the first stator control setting.
Accordingly, in an X-ray system in which the rotary anode X-ray source is moved during operation, undesirable adverse forces on the rotary anode X-ray source may be corrected based on the gantry motion indication input.
Optionally, the X-ray imaging system state detector comprises an X-ray apparatus initialization or stopping sensor.
The stator control system is configured to receive X-ray apparatus initialization or stopping information from the X-ray imaging system state detector, to generate a second stator control drive signal to influence a starting or stopping lift factor on the rotatable anode member, and to control the stator control drive signal based on the second stator control current setting to influence the starting or stopping lift factor.
Accordingly, segmented stators can be used to reduce undesired forces on a rotor element or a shaft of a rotary anode X-ray tube.
According to a third aspect, a method of rotary anode X-ray control is provided. The method comprises:

a) receiving an X-ray imaging system state signal from an X-ray imaging system state detector;
b) computing a stator drive current setting to influence a force and/or momentum on the rotatable anode member of a rotary anode X-ray source; and
c) controlling a stator drive signal based on the X-ray imaging system state signal to drive at least one stator element, to thus influence a force and/or momentum exerted on the rotatable anode member.

According to a fourth aspect, there is provided a computer program element configured, during execution, to perform the method steps of the third aspect.
According to a fifth aspect, there is provided a computer-readable medium comprising the computer program element of the fourth aspect.
In the present application, the term "X-ray tube" means a vacuum envelope in which X-ray emission from a rotating anode can occur. Typically, the X-ray tube includes a rotating anode, and a cathode arranged to emit electrons towards the rotating anode. The rotating anode is supported on a rotatable anode member attached to a rotor element which may be a part of the rotatable anode member drive.
In the present application, the statement that the stator element is "in facing relation" to the rotor element means that a stator element magnetically induces a current in the rotor element, when a current is applied to the stator element.
In the present application, the term "asynchronous motor" comprises a rotor element (sometimes referred to as a "squirrel cage") configured to rotate with respect to a stator element. The rotor element may be fabricated from a heavy copper, aluminium, or brass bar set into grooves, connected at both ends by conductive rings. The core of the rotor element may comprise stacks of electrical steel laminations. The number of rotor slots is usually a non-integral multiple of stator slots, to prevent magnetic interlocking of the two components during operation.
In the present application, the term "stator element" refers to the stationary part of the asynchronous motor, sometimes also referred to as the "armature". The stator comprises stator windings which are connected to a driving current, usually an AC supply. When a current flows in the windings of the stator, a magnetic field is induced in the rotor. The interaction of the stator magnetic field and the rotor magnetic field causes the rotor element to rotate.
In the present application, the first stator element is provided as a "non-continuous segment having a first gap portion". This means that the first stator element does not completely encompass the rotor element, but rather that an angular portion of the stator element does not contain field windings and the first gap portion will optionally be an air gap. Optionally, the first gap portion contains a section of an X-ray source housing, or electrical components. As will be discussed, the first gap portion may subtend an angle in the ranges of, for example, less than five degrees, less than ten degrees, less than fifteen degrees, less than twenty degrees, less than thirty degrees, less than forty-five degrees, less than sixty degrees, less than ninety degrees, and less than one hundred and twenty degrees.
Accordingly, it is a basic idea of the present application that a non-circular stator segment, or multiple non-circular stator segments, may be arranged such that the momentum (or force) generated with respect to the centre of the rotor (centre of gravity in a centre plane of the motor) by repelling stationary axial or radial forces compensate each other in the rotary anode X-ray source. The resulting momenta and/or forces may be controlled by design of the stator element to be substantially reduced, or to have a resultant value which can provide an advantage such as the cancellation of gyroscopic forces.
Additionally, the space which is provided inside the rotary anode X-ray source in the gap portions may be used to accommodate extra hardware in the X-ray source, thus enabling further reduction in size of rotary anode X-ray sources.
These, and other aspects, of the present invention will become apparent from, and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described with reference to the following drawings:

Fig 1 shows a schematic central cut-through view along the shaft axis of a conventional rotary anode X-ray source.
Fig. 2 shows a schematic central cut-through view of a rotary anode X-ray source in accordance with a first aspect.
Fig. 3 shows a schematic central cut-through schematic view of a rotary anode X-ray source configured to correct gyroscopic forces, for example.
Fig. 4 shows a schematic central cut-through view of a rotary anode X-ray source in accordance with an embodiment.
Fig. 5 shows a schematic central cut-through view of a rotary anode X-ray source in accordance with an embodiment.
Figs. 6a) to d) show as schematic side-views some options for the provision of the segmented stator.
Figs. 7a) and b) shows schematically end-on views of two stator segments as two examples of skew between first and second stator segments.
Fig. 8 shows a method in accordance with the third aspect.
Fig. 9 shows an X-ray imaging system in accordance with the second aspect.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In a CT or C-arm X-ray system, a rotary anode X-ray tube rotates about a region of interest configured to accommodate a patient. The rotary anode X-ray tube generates a beam of X-rays. Opposite to the rotary anode X-ray tube, held on a gantry rotor assembly of a CT scanner or a C-arm assembly, is a detector subsystem which converts attenuated X-rays into electrical signals. A computer system reconstructs an image of the anatomy of a patient.
Fig. 1 illustrates a schematic central cut-through view of a conventional rotary anode X-ray tube assembly. Housing 10 provides a mounting point for the X-ray source assembly, and typically also holds an insulating oil 14 used to provide more effective thermal management by conducting heat away from a rotary anode X-ray tube in operation. Rotary anode X-ray tube 12 is arranged inside the housing 10. Rotary anode X-ray tube 12 is typically formed from glass, and encloses a vacuum 16.
A prior- art stator 18a, 18b would be mounted to the housing and typically entirely encompasses X-ray tube 12. The prior-art stator is denoted in Fig. 1 as portions 18a and 18b, but these are section views of the same, unitary circular stator. In Fig. 1, a single circular stator 18a, 18b is shown in cross-section. An anode support shaft 20 supports a rotor body 22, a bearing system 24, and a rotatable anode disk 26. Rotor body 22, bearing system 24 and anode disk 26 are all arranged to be rotatable around the anode support shaft 20 (aligned with the centre axis 28) inside the rotary X-ray tube 12. Rotor body 22 is, typically, made from copper. The stator 18a, 18b and rotor body 22 are arranged in a facing relationship such that when a driving current is applied to stator 18a, 18b, a magnetic field induces a current in rotor body 22. The current circulating in the rotor body 22 itself opposes the stator magnetic field causing the rotor to exert a rotational force on the bearing system, thus rotating the anode disk 26. Typically, anode disk 26 rotates between one hundred and two hundred revolutions per second.
The bearing system 24 typically comprises a spiral groove bearing (hydrodynamic bearing) having a thrust bearing portion and a radial bearing portion. This ensures a relatively low maintenance and temperature resistant support of the rotational components of the X-ray tube. The bearing system is typically lubricated with a liquid metal lubricant to enable an electrical connection between the anode disk and the outside of the X-ray tube envelope. Cathode 30 is provided at the opposite end of the tube to the rotor, and comprises an electrode 32 configured, when energized with a high negative voltage relative to the voltage of the rotary anode, to emit electrons across the gap between the cathode and the anode disk 26. Electrons are accelerated across the anode disk 32 and, upon colliding with the anode disk, the energy of the emitted electrons is substantially converted to heat, which must be dissipated from the anode disk 26, into the bearing system and then into the insulating oil 14. Less than one percent of the electron energy is converted into X-rays emitted from the focal spot 34 on the anode disk 26 outside of the X-ray tube. The X-rays emitted from the focal spot 34 may then be collimated, focused, and applied to a patient.
The asynchronous motor used in the rotary anode X-ray source 10 described in Fig. 1 typically uses a "squirrel cage" rotor to drive the rotating anode in the X-ray tube. In conventional designs, the centre of the stator magnet 18a, 18b entirely encompasses the rotor body 22 by surrounding three hundred and sixty degrees of the anode support shaft 20. The stator magnet 18a, 18b of a conventional rotary anode asynchronous motor is arranged to coincide with the centre of the rotor body 22 to avoid the generation of unbalanced axial and radial forces in the rotor body 22. For the purposes of Fig. 1, bold arrow 36 illustrates a force applied to the anode support shaft in the axial direction, and bold arrow 38 indicates a force applied to the anode support shaft in the radial direction. In other words, in this arrangement, the stator 18a, 18b and rotor body 22 arrangements generate a tangential driving torque in the rotor body.
With the continual trend towards making medical systems more compact, a greater number of components need to be fitted into a smaller X-ray tube body. It is an observation of the present application that a stator of an asynchronous motor may be shaped so that it does not entirely encompass the rotor body 22, enabling more space for additional components to be provided. In the proposed arrangement, the unbalanced force acting on a rotor body can be arranged to compensate partially or totally unbalanced forces acting on the rotor body owing to gyroscopic effects, for example.
Fig. 2 shows a schematic central cut-through view of a rotary anode X-ray source in accordance with a first aspect.
Fig. 2 illustrates a section of rotary anode X-ray source 40a comprising:

an X-ray tube 42;
a rotatable anode member 50 disposed inside the X-ray tube wherein the rotatable anode member is configured to revolve around a shaft axis 46; and
a rotatable anode member drive 48.

The rotatable anode member drive 48 is an asynchronous motor, comprising a rotor element 50a, wherein the rotor element 50a is attached to the rotatable anode member, and a first stator element 52 in facing relation to the rotor element 50a.
The first stator element 52 is provided as a non-continuous segment having a first gap portion.
The first stator element is configured, upon the application of a driving current to the first stator element, to induce both a rotation of the rotatable anode member about the shaft axis, and a first force 54 on the rotatable anode member away from the shaft axis in a radial direction and/or along the shaft axis. In the example of fig. 2, the rotatable anode member is supported on, and rotatable around, a stationary shaft 44 aligned with the shaft axis 46.
The X-ray tube is not depicted in fig. 2 to aid clarity. It will be appreciated
by the skilled reader that the envelope of the X-ray tube surrounds, and seals in a vacuum, all of the elements shown in fig. 2 apart from first stator element 52. The first stator element 52 is positioned outside the X-ray tube envelope. Figs. 3 to 5 have been drawn similarly. As shown in fig. 2, the rotatable anode member 50 comprises a rotatable anode disk 56. The rotatable anode member 50 of the rotary anode X-ray source comprises a rotatable anode disk 56 which in combination with the rotatable anode member substantially defines a centre of gravity 58 of the rotatable anode member. If the rotatable anode disk 56 is arranged at the centre of the rotatable anode member 50, then the centre of gravity 58 of the rotatable anode member 50 and the rotatable anode disk 56 is substantially central to the rotatable anode member 50. The axial and/or radial force is illustrated by the right-angled arrows 54. In fig. 2, a schematic cut-through view through the centre of the rotary anode X-ray source is shown, and thus the first stator element 52 is seen in section. However, dotted lines illustrate the non-continuous segment extending around a portion of the rotatable anode member 50.
In operation, the first stator element 52 configured to face the rotor element 50a provides a radial component 54 acting to repel the rotor element 50a away from the first stator element 52. The force may also have a component along the shaft axis 46. In this embodiment, the force on the rotatable anode member 50 due to the presence of the first stator element 52 would be unbalanced. Such an arrangement is beneficial under circumstances where a balancing external force is exerted on the rotatable anode member 50.
For example, an external force could be a gravitational force, a gyroscopic force, or a centrifugal force in a CT system may at least be partly compensated using a first stator element 52 positioned to act in a substantially opposite direction on the rotatable anode member 50.
Optionally, the first stator element encloses the rotor element 50a by an angle of three hundred and fifty degrees, three hundred and forty degrees, three hundred and thirty degrees, three hundred and twenty degrees, three hundred degrees, two hundred and ninety degrees, two hundred and eighty degrees, two hundred and seventy degrees, down to one hundred and eighty degrees.
Fig. 3 shows a schematic central cut-through schematic view of a rotary anode X-ray source configured to correct gyroscopic forces, for example.
The X-ray tube 42 is not depicted in fig. 3 to aid clarity.
In fig. 3, common reference numerals of features common between embodiments are provided, with new elements being introduced additively with new reference numerals.
Fig. 3 shows an asynchronous motor section of rotary anode X-ray source 40b. The rotary anode X-ray source illustrated in the embodiment of fig. 3 comprises a rotatable anode member 50 configured to revolve around a shaft axis 46 disposed inside an X-ray tube 42. A rotatable anode member drive is provided as an asynchronous motor having a first stator element 52 and a second stator element 62. The second stator element 62 is provided as a non-continuous segment having a second gap portion. The first and second stator elements 52, 62 together form a first stator pair 60. They are arranged to partially surround the rotor element 50a and a second rotor element 50b. The rotor element 50a and the second rotor element 50b may be attached to, or integral with, the rotatable anode member 50.
In operation, a balanced resultant force on the rotatable anode member drive in a radial direction, and/or along the shaft axis is provided by first stator pair 60. Force arrow 54 illustrates the pair of axial and/or radial forces exerted on the rotatable anode member 50 by the first stator element 42. Force arrows 64 illustrate the forces exerted on the rotatable anode member 50 by the second stator element 52.
Optionally, the first stator element and second stator element of the first stator pair 60 are aligned with respect to the rotatable shaft axis 46. Therefore, their non-continuous segments and gap portions are in alignment.
Optionally, the first stator element 52 may be driven with a signal of the opposite polarity compared to the signal that drives the second stator element 62. In that case, the axial components of forces 54 and 64 would cancel each other out. However, because the non-continuous segments are in alignment, the radial component of the force on the rotatable anode member 50 acts radially outwards, away from the first stator pair 60. Therefore, in this embodiment, the stator segments are arranged such that the forces and/or momenta generated with respect to the centre of gravity 58 of the rotor y repelling stationary axial forces compensate each other. The resulting axial forces would be substantially zero.
In the two-stator embodiment illustrated in fig. 3, the area opposite the first stator pair 60 is unoccupied, and may be used to shrink the size of the X-ray tube 42, to enable more electrical equipment to be housed in the gap portions, or to shrink the overall size of the rotary anode X-ray source 40b.
Fig. 4 shows a schematic cut-through view of another embodiment of a rotary anode X-ray source 40c.
In fig. 4, the same reference numerals are used for elements in common with previous embodiments, and new elements are introduced with new reference numerals. The X-ray tube 42 is not depicted, to aid clarity.
As in the embodiment of fig. 3, the X-ray source 40c comprises a first stator pair 60 comprising a first stator 52 and a second stator 62. The rotatable anode X-ray source's shaft drive 50 further comprises a second stator element pair 66 comprising a third stator element 68 and a second stator element 70 facing the rotatable anode member drive 50.
The third stator element 68 and the fourth stator element 70 each have a non-continuous segment having third and fourth respective gap portions, and are provided in a facing relation to the surfaces third and fourth rotor elements 50c and 50d.
The first stator element pair 60 and the second stator element pair 66 are arranged to provide, in operation, a balanced resultant force 72, 74 on the rotatable anode member 50 in a radial direction, and/or along the shaft axis 46.
Optionally, and as illustrated, the first and second stator elements of the first stator element pair 66 are arranged one hundred and eighty degrees around the shaft axis 46. Optionally, the non-continuous segment arc length (or gap portion arc length) of the first to fourth stator elements 52, 62, 68, 70 is the same. Therefore, the radial force illustrated by arrow 72 due to first stator element 52 and third stator element 68 has a resultant of zero, if the driving current of the first and third stator elements is the same. Likewise, the radial force illustrated by arrow 74 has a resultant of zero if the second stator element 62 and the fourth stator element 70 are driven with an equal driving current. In the arrangement of fig. 4, the radial force on the rotatable anode member 50 balances to zero. Through similar analysis, the axial forces 73 and 75 on the rotatable anode member 50 balance to zero.
Hence, fig. 4 illustrates a schematic cut-through view of a balanced rotary anode X-ray source 40c in which the four stator elements are provided as segments, to improve space utilisation inside the X-ray tube housing 42, whilst still providing a balanced force on the rotatable anode member 50.
Optionally, the rotary anode X-ray source 40a, 40b, 40c, 40d is provided as previously described, wherein the rotatable anode member 50 of the rotary anode X-ray source comprises a rotatable anode disk 56. The first stator element 52 and the second stator element 62 are disposed on opposite faces of the rotatable anode disk 56.
Accordingly, if the stator elements are disposed in a balanced configuration around the rotatable anode disk 56, the force balance on the rotatable anode member 50 can be further improved.
Fig. 5 illustrates a schematic view of a centre cut-through of a rotary anode X-ray source 40d arranged in an example configuration suitable for enhanced gyroscopic moment cancellation. To aid clarity, the X-ray tube 42 is not depicted. Rotary anode X-ray source 40d is enclosed in an X-ray housing 42, and comprises a first stator segment 52 having a gap portion arranged to face the rotor element 50 at an azimuthal offset angle of ninety degrees about the shaft axis 46 from the second stator element 62. In this case, first stator element 76 exerts a first radial force 76 on the rotor element 50. Second stator element 62 exerts a second radial force 78 (shown in fig. 5 as a cross travelling out of the page) against the rotor element 50. Assuming that axis 80 illustrates the axis of, for example, a CT gantry rotation, the angle enclosed between the shaft axis 46 and the CT gantry axis 80 represents a tilt angle of the rotor element 50 of the rotary X-ray source in relation the CT axis. In an uncompensated condition, any rotation of the rotatable anode 56 at an angle offset from that of the CT gantry axis upon which the assembly is supported, would result in a gyroscopic force to be exerted on the rotary anode X-ray source 40d. The second stator element 62 arranged at an azimuthal offset angle of ninety degrees clockwise compared to the first stator element compensates the gyroscopic moment. This enables gyroscopic forces on the rotatable anode member 50 and connected bearing arrangement to be reduced during operation.
Optionally, a third stator element 68 and a fourth stator element 70 may be arranged on an opposite side of the rotatable anode disk 56, with the angle between the fourth stator element 70 and the second stator element 62 around the rotatable anode member 50 and shaft axis 46 being one hundred and eighty degrees. This enables a gyroscopic force resulting from clockwise and counter clockwise movement to be compensated.
Figs. 6a)-d) show schematic cut-through side views of typical stator elements (stator segments). It will be appreciated that these drawings are shown in cross-section, and represent rectangular sectioned "ring-shaped" stators. However, the skilled person will realize that the stators may have a round cross-section, a flat cross-section, or many other cross-sections, and that an important aspect is the size of the gap portion, G. A small gap portion implies a more efficient driving of the rotor element 50a by the magnetic coupling generated by the stator element. A larger gap G implies a weaker magnetic coupling to the rotor element 50a, however, a greater space saving inside the rotary anode X-ray source.
Accordingly, fig. 6a) shows a rotor gap G₁ partially encompassing shaft axis 46 with a first gap portion G₁ of thirty degrees.
Fig. 6b) shows a first stator segment partially encompassing shaft axis 46 in which the gap portion G₂ subtends sixty degrees.
Fig. 6c) shows a first stator segment encompassing a shaft axis 46 in which the gap portion G₃ is ninety degrees.
Fig. 6d) shows a first stator element encompassing a shaft axis 46 in which the gap portion G₄ subtends one hundred and twenty degrees.
Accordingly, a rotary anode X-ray source 40 may optionally be provided according to any of the foregoing embodiments, wherein the second gap portion of the second stator element 62 is arranged at an azimuthal offset angle G to the first gap portion 52 of the first stator element, wherein the actual offset angle is in the range of five to three hundred and fifty-five degrees.
Fig. 7a) illustrates an exemplary side view of a first stator element 52 (shown in bold) next to a second stator element 62 (shown as a dotted line). The first stator element 52 and the second stator element 62 both have a gap portion subtending thirty degrees around the shaft axis 46. The first stator element 52 is aligned ninety degrees counter clockwise compared to the gap portion of the second stator element 62. In practice, this arrangement will exert a resultant radial force in the direction of the arrows in Fig. 7a.
Fig. 7b) shows a first stator element 52 and a second stator element 62 each with gap portions subtending sixty degrees around the shaft axis 46. The first stator element 52 is positioned at a ninety degree clockwise skew angle compared to the second stator element 62, with a resultant radial force exerted on the rotary anode member 50 in the direction of arrow 65.
The skilled person will appreciate that a wide variety of gap portion angles and stator element combinations are possible, dependent upon the forces which are required to be compensated.
Optionally, a rotary anode X-ray source 40 is provided, wherein the rotatable anode member drive 48 further comprises a circular stator encompassing the rotatable anode member 50 and facing the rotor element 50a.
Accordingly, it may be possible to benefit from the higher power efficiency of a fully circular stator encompassing the entire face of rotatable anode member 50, whilst compensating for certain force imbalances (for example, due to gyroscopic forces) using a segmented stator element, applied to another part of the rotatable anode member 50.
According to a second aspect, an X-ray imaging system 87 is provided. The system comprises:

a rotary anode X-ray source 40, 40a, 40b, 40c, 40d as defined according to the first aspect, or one of the embodiments of the first aspect,
an X-ray imaging system state detector and
a stator control system 96.

The stator control system 96 is configured to receive X-ray imaging system state information from the X-ray imaging system state detector, to generate a stator control signal based on the X-ray imaging system state information, and to provide the stator control signal to drive at least the first stator element of the rotary anode X-ray source 40, 40a, 40b, 40c.
Fig. 8 shows an X-ray imaging system 87 according to the second aspect in a C-arm X-ray imaging suite.
The C-arm imaging system 87 has a support arrangement 90 which may translate through azimuth and elevation axes around the object of interest 82. For example, the C-arm X-ray imaging system 80 may be supported from the ceiling of an X-ray facility. The support arrangement holds a rotary anode X-ray source 86 according to the first aspect, or one of its embodiments, and an X-ray detector 84.
The C-arm imaging system (or CT imaging system) is optionally provided with motion sensors (for example, rotary encoders in the C-arm or CT gantry axes). This enables the feedback of motion information to the X-ray imaging system state detector.
Alternatively, or in combination, the X-ray imaging system state detector is configured to receive a list of motion commands representing a pre-planned imaging protocol.
The C-arm X-ray imaging system is controlled, for example, from a control console 92, comprising, for example, display screens 94, computer apparatus 96 optionally functioning as a stator control system, controllable via a keyboard 98 and a mouse 100.
The C-arm 88 is configured to translate around the object of interest 82, not simply in a flat rotational sense (in the sense of a CT scanner), but also by tilting. For an X-ray tube source 86 located in the C-arm imaging system, this implies that extra gyroscopic forces will be applied to the bearing system of the rotary anode X-ray source. Accordingly, an X-ray imaging system state detector may be provided to monitor the movement of the C-arm system. A stator control system may be provided to compensate for the effects of a gyroscopic force, for example, during an imaging run using the C-arm. The stator control system generates a stator control current, and provides the stator control current to at least the first stator element.
Optionally, the stator control system is a computer-implemented or firmware processing system configured to use a list of motion commands representing a pre-planned imaging protocol, or configured to receive X-ray system motion signals during an acquisition. The stator control system calculates, using a mechanical simulation model, or a look-up table, a stator control signal based on the current and predicted position and motion of the X-ray imaging system. The stator control signals may be calculated to minimize or dampen gyroscopic forces from a pre-planned imaging protocol.
In operation, an object of interest 82 is placed in between the detector 84 and the X-ray source 86 of a C-arm imaging system 88. An X-ray imaging system scanning protocol is initiated using the control console 92. The X-ray imaging system state detector obtains information about the current or predicted motion of the X ray system (C-arm or CT), and calculates a stator control signal by calculating excess forces on the bearing of a rotary anode X-ray tube, and driving first, second, third and/or fourth stator elements to compensate or influence such excess forces. The stator control signal may be applied to the first, second, third and/or fourth stator elements using power electronics circuitry.
Optionally, the system is a C-arm imaging system.
Optionally, the system is a CT imaging system.
Optionally, the system is a fluoroscopy system.
Optionally, an X-ray imaging system 80 is provided, wherein the X-ray imaging system state detector comprises:

a gantry motion indication input.

The stator control system is configured to receive gantry motion indication information from the gantry motion indication input, to generate a first stator control setting to influence a gyroscopic moment on the rotatable anode member, and to control the stator control current to at least the first stator element based on the first stator control setting.
Optionally, the gantry motion indication input may, be a live indication of the gantry motion movement from a motion sensor provided at least at the joints of the C-arm imaging system. An example of a motion sensor is a rotary encoder, or accelerometers.
Optionally, the gantry motion indication input can be received from the X-ray imaging system control system 92 based on a patient scanning plan. A scanning plan will hold the motion commands to be provided to the C-arm in advance, and as such these commands can be used to calculate the signal to be applied to the first stator element to compensate unwanted forces. The stator control system calculates points at which the gyroscopic moment caused by the movement of the C-arm 88 is unacceptable, and generates a stator control current to compensate for the gyroscopic moment at these points.
Optionally, the stator control system uses a lookup table to calculate the stator control current based on a gantry motion indication input.
Alternatively, or in addition, the stator control system is configured to receive information about the initialization or stopping of the C-arm system, and to generate a second stator control current setting to influence the starting or stopping lift factor of a rotary anode X-ray source.
Optionally, an X-ray apparatus initialization or stopping sensor is provided as a voltage or current sensor operably connected to the control electronics of the stator elements. Alternatively, the X-ray apparatus initialization or stopping sensor is a software module operating in the control system 92 configured to detect the approach of a start or stop command.
The stator control system may compensate starting or stopping forces on the X-ray tube by adjusting the current delivered to the first, second, third, or fourth stator elements as the rotary anode X-ray tube spins from zero revolutions per second to its operating speed. Optionally, gantry or C-arm position information from rotary encoders or accelerometers may be used to compensate for starting and stopping forces based on the resting direction of the C-arm or CT system gantry.
According to a third aspect, there is provided a method of rotary anode X-ray source control. The method comprises:

According to a fourth aspect, a computer program element is configured, during execution, to perform the method steps of the third aspect.
According to a fifth aspect, a computer readable medium is provided comprising the computer program element of the fourth aspect.
A computer program element might be stored on a computer unit, which might also be part of an embodiment of the present invention. This computer unit may be adapted to perform or induce performance of the steps of the method described above.
Moreover, the computer unit may be adapted to operate the components of the above-described apparatus. The computer unit can be adapted to operate automatically and/or execute the orders of a user. A computer program may be loaded into a working memory of a computer unit. The computer unit may, thus, be equipped to carry out the method of the invention.
This exemplary embodiment covers both the computer program that has the invention installed from the beginning, and a computer program that, by means of an update, turns an existing program into a program that uses the invention. The computer program may be stored and/or distributed on a suitable medium, such as optical storage media, or a solid state medium supplied together with, or as part of, a hardware. It may also be distributed in other forms, such as via the internet, or the wired or wireless telecommunication systems.
However, the computer program may also be presented over a network, such as the worldwide web, and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.
It should be noted that embodiments of the invention are described with reference to different subject matter. In particular, some embodiments are described with reference to method-type claims. Other embodiments are described with reference to the device-type claims.
However, a person skilled in the art will gather from the above, and following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter, also any other combination between features relating to different subject matter is considered to be disclosed with this application.
All features can be combined to provide a synergetic effect that is more than a simple summation of the features.
Whilst the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary, and not restrictive. The invention is not limited to the disclosed embodiments.
Other variations to the disclosed embodiments can be understood, and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the dependent claims.
In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor, or a unit, may fulfil the functions of several items recited in the claims. The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

A rotary anode X-ray source (40a, 40b, 40c, 40d), comprising:
an X-ray tube (42);

a rotatable anode member (50) disposed inside the X-ray tube wherein the rotatable anode member is configured to revolve around a shaft axis (46); and

a rotatable anode drive (48);

wherein the rotatable anode drive is an asynchronous motor, comprising a rotor element (50a) wherein the rotor element is attached to, or integral with, the rotatable anode member 50, and a first stator element (52) in facing relation to the rotor element;

wherein the first stator element is provided as a non-continuous segment having a first gap portion; and

wherein the first stator element is configured, upon the application of a driving current to the first stator element, to induce both a rotation of the rotatable anode member about the shaft axis, and a first force (54) on the rotatable anode member away from the shaft axis in a radial direction and/or along the shaft axis.
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to claim 1,
wherein the rotatable anode member drive (48) further comprises a second stator element (62) provided as a non-continuous segment having a second gap portion, and wherein the first and second stator elements together form a first stator pair (60) arranged to partially surround the rotor element (50a), to thus provide, in operation, a balanced resultant force on the rotatable anode member drive (48) in a radial direction, and/or along the shaft axis.
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to one of the preceding claims,
wherein the rotatable anode member (50) of the rotary anode X-ray source comprises a rotatable anode disk (56) which in combination with the rotatable anode member substantially defines a centre of gravity (58) of the rotatable anode member; and
wherein the first stator element (52) and the second stator element (62) are disposed along the shaft axis (46) on opposite sides of the centre of gravity.
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to one of claims 1 or 2,
wherein the rotatable anode member (50) of the rotary anode X-ray source comprises a rotatable anode disk (56) which in combination with the rotatable anode member substantially define centre of gravity (58); and
wherein the first stator element (52) and the second stator element (62) are disposed on opposite faces of the rotatable anode disk.
The rotary anode X-ray source (40d) according to one of the preceding claims,
wherein the second gap portion of the second stator element (62) is arranged at an azimuthal offset angle in relation to the shaft axis (46) to the first gap portion of the first stator element (52), wherein the azimuthal offset angle is in the range of 5 to 355 degrees.
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to claim 5,
wherein the first gap portion of the first stator element (52) is arranged to face the rotor element (50a) at an azimuthal offset angle in relation to the shaft axis (46) of substantially ninety degrees about the shaft axis (46) from the second gap portion of the second stator element (62), to enable gyroscopic forces on the rotatable anode member (50) to be reduced in operation.
The rotary anode X-ray source (40d) according to one of the preceding claims,
wherein the rotatable anode member drive (48) further comprises:
a second stator element pair (66) comprising a third stator element (68) and a fourth stator element (70),

wherein the third stator element (68) and the fourth stator element (70) each have a non-continuous segment having third and fourth respective gap portions, and are provided in a facing relation to the surface of the rotor element; and

wherein the first stator element pair (60) and the second stator element pair (66) are arranged to provide, in operation, a balanced resultant force on the rotatable anode member drive (48) in a radial direction, and/or along the shaft axis (46).
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to one of claims 1 to 6,
wherein the third and fourth gap portions of the third (68) and fourth (70) stator elements are arranged in an azimuthal offset relationship to the first and second gap portions of the first (52) and second stator elements (62), respectively.
The rotary anode X-ray source (40c, 40d) according to one of claims 1 to 7,
wherein the third and fourth gap portions of the third (68) and fourth stator elements (70) are arranged in a facing relationship to the first and second gap portions of the first (52) and second (62) stator elements, respectively.
The rotary anode X-ray source (40a, 40b, 40c, 40d) according to one of the preceding claims,
wherein the rotatable anode member (48) further comprises:
a circular stator encompassing the rotatable anode member and facing the rotor element (50a).
An X-ray imaging system (80) comprising:
the rotary anode X-ray source (40a, 40b, 40c, 40d) as defined according to one of claims 1 to 10;

an X-ray imaging system state detector; and

a stator control system (96);

wherein the stator control system (96) is configured to receive X-ray imaging system state information from the X-ray imaging system state detector, to generate a stator control signal based on the X-ray imaging system state information, and to provide the stator control signal to drive at least the first stator element of the rotary anode X-ray source (40, 40a, 40b, 40c).
The X-ray imaging system (80) of claim 11,
wherein the X-ray imaging system state detector comprises a gantry motion indication sensor;
wherein the stator control system is configured to receive gantry motion indication information from the X-ray imaging system state detector, to generate a stator control setting to influence a gyroscopic moment on the rotatable anode member (50) of the rotary anode X-ray source (40, 40a, 40b, 40c), and to control the stator control signal to drive at least the first stator element of the rotary anode X-ray source (40, 40a, 40b, 40c) based on the first stator control setting.
The X-ray imaging system (80) of claim 11 or 12,
wherein the X-ray imaging system state detector comprises an X-ray apparatus initialization or stopping sensor;
wherein the stator control system is configured to receive X-ray apparatus initialization or stopping information from the X-ray imaging system state detector, to generate a second stator control drive signal to influence a starting or stopping lift factor on the rotatable anode member, and to control the stator control drive signal based on the second stator control current setting to influence the starting or stopping lift factor.
A method of rotary anode X-ray source control, comprising:
a) receiving an X-ray imaging system state signal from an X-ray imaging system state detector;

b) computing a stator drive current setting to influence a force and/or momentum on the rotatable anode member of a rotary anode X-ray source; and

c) controlling a stator drive signal based on the an X-ray imaging system state signal to drive at least one stator element, to thus influence a force and/or momentum exerted on the rotatable anode member.
A computer program element configured, during execution, to perform the method steps of claim 14.
A computer readable medium comprising the computer program element of claim 15.