Tracking system and marker device to be tracked by the tracking system

Abstract

This invention relates to a marking device and a tracking system for tracking the marking device, wherein the marking device includes a rotating, oscillating magnetic object, and the rotational oscillation is excited by an external magnetic field generated by magnetic field providing units 20, 31 located outside the marking device. The rotational oscillation of the magnetic object induces a current in a coil, wherein the position of the marking device is determined based on these induced currents, and optionally, the orientation of the marking device is also determined. This wireless tracking can be performed using a relatively small marking device, which can be placed, for example, in a guide wire, can be read over a relatively large distance, and a single marking device can be used for positioning in six degrees of freedom.

Description

Technical Field

[0001] This invention relates to a tagging device to be tracked, a medical device having the tagging device, and a tracking system, tracking method, and tracking computer program for tracking the tagging device. The invention also relates to a guidance system, guidance method, and guidance computer program for guidance during surgical procedures. Background Art

[0002] Electromagnetic tracking of medical devices is known, particularly in minimally invasive procedures. A drawback of this electromagnetic tracking is that, in order to determine not only the location but also the orientation of the medical device, it needs to be equipped with multiple electromagnetic markers, each suitable for, for example, three degrees of freedom (DoF) or five degrees of freedom positioning. Furthermore, the electromagnetic markers are significantly larger than 1 mm. For example, the tracking system disclosed in the paper "Validation of the Calypso Surface BeaconTransponder" by B. Maxwell et al. (Journal of Applied Clinical Medical Physics, Vol. 17, pp. 223-234 (2016)) uses electromagnetic markers with a size of 8 mm. Additionally, electromagnetic markers are typically not readable from relatively large distances, such as greater than 30 cm. For example, the system disclosed in the aforementioned paper by B. Maxwell et al. allows for marker readable from a distance of approximately 16 cm. Summary of the Invention

[0003] Therefore, an object of the present invention is to provide an improved marking device and an improved tracking system, method, and computer program for tracking the marking device. Another object of the present invention is to provide a medical device having an approved marking device, and a guidance system, method, and computer program for guidance during surgical procedures, which utilize the marking device and the tracking system.

[0004] In a first aspect of the invention, a tracking marking device is provided, wherein the marking device includes a) a housing, b) a magnetic object disposed within the housing such that if an external magnetic torque is applied to the magnetic object, the magnetic object can rotate away from a balance orientation, and c) a reset torque unit adapted to provide a reset torque to force the magnetic object back to a balance orientation if the external magnetic torque has caused the magnetic object to rotate away from a balance orientation, so as to allow rotational oscillation of the magnetic object excited by the external magnetic torque.

[0005] Because the magnetic object is housed within the housing, it can be rotated away from its equilibrium orientation by an external magnetic torque acting on it. Since the reset torque unit is adapted to provide a reset torque to force the magnetic object back to its equilibrium orientation after the external magnetic torque has caused it to rotate away from its equilibrium orientation, thus allowing rotational oscillations of the magnetic object excited by the external magnetic torque, an induction signal caused by the rotational oscillations of the magnetic object and dependent on the spatial position and orientation of the marking device can be generated in the excitation and induction signal unit of the tracking system. Specifically, the excitation and induction signal unit may include i) a first coil adapted to generate a magnetic field providing a magnetic torque for causing the magnetic object of the tracking device to rotate away from its equilibrium orientation and thereby exciting the rotational oscillations of the magnetic object; and ii) a second coil adapted to generate an induction signal dependent on the spatial position and orientation of the marking device. This allows the position and orientation of the marking device, i.e., six degrees of freedom, to be determined, making it possible to determine the position and orientation of a medical device equipped with the marking device using only a single marking device. Furthermore, the tracking system can read the marking device from a relatively large distance, for example, greater than 30 cm. Additionally, the marking device can be relatively small, for example, less than 1 mm. In a preferred embodiment, the housing of the marking device is cylindrical, and the outer diameter of the cylinder is less than 1 mm, more preferably less than 0.5 mm, and even more preferably less than 0.3 mm.

[0006] Note that the term "external magnetic torque" refers to the magnetic torque caused by an external magnetic field providing unit located outside the marking device. Preferably, if the marking device is disposed inside the subject's body, the magnetic field providing unit is also outside the subject.

[0007] Preferably, the magnetic object is rotatable about a virtual axis of rotation centrally passing through it, wherein the magnetic object is rotationally symmetrical with respect to the virtual axis of rotation. Specifically, the magnetic object is a magnetic sphere or a magnetic cylinder. Furthermore, the reset torque unit may include a torsion spring mechanism for providing the reset torque. Alternatively, the reset torque unit may also include another magnetic object for providing the reset torque. In one embodiment, the magnetic object is attached to one end of a filament, wherein the other end of the filament is attached to a housing, wherein the filament is adapted to prevent the magnetic object from contacting the other magnetic object due to its magnetic attraction and to allow the magnetic object to rotate and oscillate. The other magnetic object is preferably fixedly attached to the housing. However, the other magnetic object may also be arranged within the housing such that it is rotatable and oscillating relative to the housing. Specifically, the other magnetic object may be attached to one end of a filament, wherein the other end of the filament may be attached to the housing. In a preferred embodiment, the other magnetic object is rotatable about a virtual axis of rotation centrally passing through it, wherein the other magnetic object is rotationally symmetrical with respect to the virtual axis of rotation. Additionally, the other magnetic object may be a magnetic sphere or a magnetic cylinder. Furthermore, the virtual axes of the magnetic object and another magnetic object are preferably aligned with each other.

[0008] These techniques allow for the provision of a reset torque, and thus the rotational oscillation of the magnetic object, enabling the entire marking device to be relatively small, providing the resonant frequency of the marking device as needed, and keeping the construction of the marking device relatively simple.

[0009] In one embodiment, the marking device is adapted such that if an external magnetic torque is applied to another magnetic object, the other magnetic object can rotate away from the equilibrium orientation. The reset torque unit is adapted to also provide a reset torque to force the other magnetic object back to the equilibrium orientation if the external magnetic torque has already caused it to rotate away from the equilibrium orientation, thereby allowing rotational oscillations of the other magnetic object excited by the external magnetic torque, wherein the rotational oscillations of the magnetic object and the other magnetic object have the same resonant frequency and a 180-degree phase difference. This reduces, and preferably even eliminates, the torque on the housing. The reset torque unit can use the magnetic object to provide a reset force to the other magnetic object. Specifically, in one embodiment, the magnetic object forms a first magnetic dipole, the other magnetic object forms a second magnetic dipole, and the magnetic object and the other magnetic object are arranged such that, in the equilibrium orientation, the first magnetic dipole and the second magnetic dipole point in opposite directions. In one embodiment, the magnetic object and the other magnetic object are directly connected to each other via a torsion spring, such that, in this case, the reset torque unit includes a torsion spring.

[0010] Preferably, the magnetic object and / or another magnetic object is a permanent magnet. Furthermore, the housing is preferably cylindrical. If the housing is cylindrical, it can be relatively easily incorporated into tubular medical devices, such as guidewires.

[0011] Preferably, the marking device is adapted to satisfy at least one of the following conditions: i) a Q factor of at least 100, ii) at least 0.5 μm. 2 The dynamic dipole moment and (iii) a resonant frequency of at least 100 Hz. It has been found that if at least one of these conditions is met, the accuracy of determining the position of the marking device and preferably also the orientation of the marking device can be further improved.

[0012] More preferably, the marking device is radiopaque. This allows the marking device to be visualized using an X-ray imaging system, such as a computed tomography system, an X-ray fluorescence examination system, an X-ray C-arm system, etc.

[0013] In another aspect of the invention, a kit comprising a plurality of marking devices is provided, wherein each marking device in the kit has a radiopaque material, wherein the radiopaque materials and resonant frequencies of at least two of the marking devices are different from each other. For example, the radiopaque materials of at least two of the marking devices may differ in shape. Thus, they may comprise the same type of radiopaque material, but the shapes of the radiopaque materials may differ. The shapes of the radiopaque materials of at least different marking devices may also be the same, but the radiopaque materials themselves may be different. For at least two of the marking devices, the shape and the radiopaque material itself (i.e., the type used as the radiopaque material) may also differ. This allows marking devices with different resonant frequencies to be distinguished in X-ray images.

[0014] The tracking system for tracking markers can be adapted to selectively excite the markers, and the tracking system can also include an allocation between the indications of different markers and their resonant frequencies, such that a user, such as a physician, can select a desired marker in an X-ray image, and thereafter, due to the known allocation, only the selected markers can be excited, and thus the position can be determined only for these markers, and preferably the orientation can also be determined.

[0015] In another aspect of the invention, a medical device having at least one marking device is provided. In one embodiment, the medical device is a catheter, guidewire, or implant. This allows the location and orientation of the medical device (such as a catheter, guidewire, or implant) to be determined over a six-DoF distance using only a single marking device, which can be relatively small and allows for relatively high sensitivity relative to the detection of the location and orientation of the medical device, i.e., the location and orientation of the medical device can be determined from a relatively large distance, such as 30 cm or 40 cm.

[0016] In another aspect of the invention, a tracking system for tracking a marking device is provided, wherein the tracking system comprises: i) an excitation and sensing signal unit adapted to a) generate a magnetic field providing a magnetic torque for rotating a magnetic object of the marking device away from its equilibrium orientation and thereby exciting rotational oscillations of the magnetic object to oscillate at the resonant frequency of the rotational oscillations of the magnetic object; and b) generate a sensing signal caused by the rotational oscillations of the magnetic object, the sensing signal depending on the spatial position and orientation of the tracking device; ii) a position determination unit adapted to determine the position of the marking device based on the generated sensing signal. Preferably, the excitation and sensing signal unit is adapted such that the sensing signal caused by the rotational oscillations of the magnetic object and depending on the spatial position and orientation of the marking device depends on the spatial position and orientation of the marking device relative to the excitation and sensing signal unit.

[0017] In one embodiment, the excitation and sensing signal unit includes a) a first coil adapted to generate a magnetic field providing a magnetic torque for rotating a magnetic object of the marking device away from its equilibrium orientation and thereby exciting rotational oscillations of the magnetic object; and b) a second coil adapted to generate a sensing signal dependent on the spatial position and orientation of the marking device, wherein the first and second coils are separate. The first and / or second coils may be arranged in a mat or in a handheld device. The coils may also be disposed in another element resembling a box.

[0018] In another embodiment, the excitation and induction signal unit includes a coil adapted to a) generate a magnetic field providing a magnetic torque for rotating a magnetic object of the marking device away from its equilibrium orientation and thereby exciting rotational oscillations of the magnetic object, and b) generate an induction signal dependent on the spatial position and orientation of the marking device. Thus, the same coil can be used to generate both the magnetic field and the induction signal. Also in this embodiment, the coil can be arranged in a pad or in a handheld device. The coil can also be housed in another element resembling a box.

[0019] Preferably, the excitation and sensing signal unit includes a plurality of coils adapted to generate sensing signals, wherein for each coil, a sensing signal is generated that depends on the position and orientation of the marking device relative to the corresponding coil. Furthermore, preferably, the position determination unit is also adapted to determine the orientation of the marking device based on the sensing signals. Specifically, the position determination unit is adapted to determine the position and orientation of the marking device at six DoF.

[0020] The tracking system may also include a magnetic field generator adapted to generate a spatially non-uniform magnetic field to produce a position-dependent resonant frequency of the rotational oscillation of the magnetic object of the marking device, wherein the position determination unit is further adapted to determine the position of the marking device based on the position-dependent resonant frequency. Specifically, the magnetic field generator is adapted to generate a magnetic field gradient as a spatially non-uniform magnetic field. The magnetic field generator may include two sets of saddle coils and discrete solenoid coils for generating the spatially non-uniform field. This allows for further refinement of the determination of the marking device's position. However, other coil configurations for generating non-uniform fields can, of course, also be used.

[0021] Preferably, the tracking system is adapted to determine the positions of multiple marking devices, wherein the magnetic objects of the multiple marking devices are capable of rotating and oscillating at different resonant frequencies, such that the inductive signals of the different marking devices have different frequencies, and the position determination unit is adapted to determine the position of the marking devices based on the generated inductive signals with different frequencies. The position determination unit is also preferably adapted to determine the orientation of the marking devices based on the generated inductive signals with different frequencies. By using different marking devices with different resonant frequencies, different marking devices can be distinguished, and for each marking device, a corresponding position is determined, and preferably, a corresponding orientation is also determined.

[0022] Multiple marking devices may be attached to an element, wherein a position determining unit may be adapted to determine the shape of the element based on the determined positions of the multiple marking devices. A shape determining unit may also be adapted to determine the shape of the element based on an orientation determined for the multiple marking devices. The element is preferably a medical device, but it may also be a body part, such as tissue.

[0023] In one embodiment, the position determining unit is adapted to determine the position of the marking device relative to another marking device. Furthermore, the orientation of the marking device can be determined relative to the orientation of the other marking device. However, the position, and optionally the orientation, can also be determined relative to another reference.

[0024] In addition, an output unit can be provided for outputting the determined position of the marking device. The output unit can also be adapted to output the orientation of the marking device.

[0025] In one embodiment, the marking device is located within the subject's body, wherein the position determination unit is adapted to determine the nearest position on the subject's surface, which is the position on the subject's surface closest to the marking device, and / or the projection of the marking device's position onto the subject's surface in a predefined direction. For example, the output unit may include a light source, such as a light-emitting diode or a laser, and the light generated by the light source can be used to generate a spot of light on the subject's surface at the determined nearest position and / or at a determined position on the surface where the determined position of the marking device has been projected. Specifically, in this example, the tracking system may be at least partially integrated into a handheld device including a light source, such that if the handheld device is held in front of the patient, the handheld device can generate a spot of light at a corresponding position on the subject's surface. In a preferred embodiment, the position determination unit is adapted to determine the distance between the determined position on the subject's surface and the position of the marking device. This distance preferably corresponds to a depth within the subject's body in the normal direction or along a predefined direction. This distance may be indicated by a corresponding number. However, alternatively, if the light source is used to indicate the determined position on the surface, the distance may also be indicated by generating a spot of light. For example, the color, shape, and / or size of the spot of light may depend on the determined distance. The predefined direction can be, for example, the X-ray projection direction of an X-ray imaging system (such as a C-arm X-ray imaging system), the normal direction of a handheld device, etc.

[0026] The tracking system and marking device are preferably adapted to cause the magnetic object of the marking device to rotate and oscillate within an angle range of at least 30 degrees.

[0027] In another aspect of the invention, a guidance system is provided for guidance during surgical procedures, wherein the guidance system includes a tracking system for tracking the position of a marking device and an output unit adapted to output the tracked position.

[0028] The tracking system can be adapted to track the orientation of the marking device, and the output unit can also be adapted to output the tracking orientation of the marking device. For example, if the target is a tumor, the tracking system can make it relatively easy to detect the tumor in the subject's body during surgery using the marking device.

[0029] Preferably, the guidance system further includes an imaging system adapted to generate an image of the subject to be surgically examined, wherein the tracking system is registered with the imaging system, and the output unit is adapted to at least overlap the tracking position with the image of the subject. This can lead to further improved guidance for the physician, for example, during surgery to be performed on a target already attached with a marker.

[0030] In one embodiment, the marking device is located inside the subject's body, wherein the output unit is adapted to indicate the nearest location determined on the subject's surface and / or the distance between the marking device and the determined nearest location.

[0031] On the other hand, a tracking method for tracking a marking device is proposed, wherein the tracking method includes a) generating a magnetic field that provides a magnetic torque for rotating a magnetic object of the marking device away from its equilibrium orientation and thereby exciting a rotational oscillation of the magnetic object to oscillate at the resonant frequency of the rotational oscillation of the magnetic object, and generating an induction signal caused by the rotational oscillation of the magnetic object and dependent on the spatial position and orientation of the tracking device, and b) determining the position of the marking device based on the generated induction signal.

[0032] On the other hand, a guidance method for guidance during surgical procedures using a guidance system is proposed, wherein the guidance method includes tracking the position of a marking device defined by a tracking method and outputting the tracked position.

[0033] In another aspect of the invention, a tracking computer program for a tracking tagging device is provided, wherein the computer program includes a program code module that, when the computer program is run on a computer controlling the tracking system, causes the tracking system to perform steps of a tracking method.

[0034] In another aspect of the invention, a boot computer program for guiding during surgical procedures is provided, wherein the computer program includes program code modules that, when the computer program is run on a computer controlling the boot system, cause the boot system to perform steps of a boot method.

[0035] It should be understood that the marking device of claim 1, the kit formed by the marking device of claim 5, the tracking system of claim 6, the guiding system of claim 10, the tracking method of claim 12, the guiding method of claim 13, the tracking computer program of claim 14, and the guiding computer program of claim 15 have similar and / or identical preferred embodiments, especially those as defined above and / or in the dependent claims.

[0036] It should be understood that preferred embodiments of the present invention may also be any combination of dependent claims or the above embodiments with corresponding independent claims.

[0037] These and other aspects of the invention will be apparent from the embodiments described below, and will be set forth with reference to the embodiments described below. Attached Figure Description

[0038] In the following figures:

[0039] Figure 1-5 Different embodiments of the tagging device to be tracked are illustrated schematically and exemplary.

[0040] Figure 6 An embodiment of a guidance system for guiding a physician during surgical procedures is illustrated schematically and exemplary, which includes methods for tracking... Figures 1 to 5 The tracking system with a marking device is illustrated schematically and exemplary.

[0041] Figure 7 An embodiment of the medical device is illustrated schematically and exemplaryly as a guidewire having multiple marking devices.

[0042] Figure 8 An embodiment of a magnetic field generator for generating a non-uniform magnetic field in space is illustrated schematically and exemplary.

[0043] Figure 9 A flowchart illustrating an exemplary embodiment of a guidance method for guiding a physician during surgical procedures is shown.

[0044] Figure 10-12 The six-DOF positioning of the marking device is illustrated schematically and exemplary.

[0045] Figure 13 A marking device in a patient's lungs during surgery is illustrated schematically and exemplary. Detailed Implementation

[0046] Figure 1 An embodiment of a marking device for tracking using a tracking system is illustrated schematically and exemplary. The marking device 1 includes a housing 2 and a magnetic object 3 disposed within the housing 2 such that the magnetic object can rotate away from its equilibrium orientation if an external magnetic torque is applied to it. The marking device 1 also includes a reset torque unit 4 adapted to provide a reset torque to force the magnetic object 3 back to its equilibrium orientation if the external magnetic force has caused it to rotate away from its equilibrium orientation, thereby allowing rotational oscillation of the magnetic object 3 excited by the external magnetic torque. In this embodiment, the housing 2 is cylindrical, and the magnetic object 3 is rotatable about a virtual axis of rotation centrally located through it, wherein the magnetic object 3 is rotationally symmetrical with respect to the virtual axis of rotation. Specifically, in this embodiment, the magnetic object 3 is a magnetic sphere.

[0047] The reset torque unit 4 includes another magnetic object 4 for providing reset torque. Specifically, a magnetic object 3 is attached to one end of a filament 6, the other end of which is attached to the housing 2. The filament 6 is adapted to prevent the magnetic object 3 from contacting the other magnetic object 4 due to its magnetic attraction and to allow the magnetic object 3 to rotate and oscillate. In this embodiment, the other magnetic object 4 is fixedly connected to the housing 2.

[0048] Magnetic object 3 forms a first magnetic dipole, and another magnetic object 4 forms a second magnetic dipole. The magnetic object 3 and the other magnetic object 4 are arranged such that, in a balanced orientation, the first and second magnetic dipoles point in opposite directions. Preferably, the first magnetic object 3 and the second magnetic object 4 are permanent magnets, wherein, in a balanced orientation, the north pole of magnetic object 3 faces the south pole of the other magnetic object 4, and vice versa.

[0049] The shell 2 is cylindrical, wherein the cylindrical shell 2 includes two end faces 30, 31, and wherein another object 4 is fixedly attached to the first end face 30, and the end of the filament 6 opposite to the end attached to the magnetic object 3 is attached to the second end face 31 of the cylindrical shell 2.

[0050] Figure 2 Another embodiment of a tagging device 101 to be tracked by a tracking system is illustrated schematically and exemplary. The tagging device 101 is similar to... Figure 1 The marking device 1 shown in the schematic and exemplary manner differs in that another magnetic object 104 of the marking device 101 is cylindrical, while another magnetic object 4 of the marking device 1 is spherical.

[0051] Figure 3 Another embodiment of a marking device 201 that tracks using a tracking system is illustrated schematically and exemplary. Also in this embodiment, the marking device 201 includes a cylindrical housing 2 and a spherical magnetic object 3 disposed within the housing 2 such that if an external magnetic torque is applied to the magnetic object 3, it can rotate away from its equilibrium orientation. However, in this embodiment, the reset torque unit differs from the one referenced above. Figure 1 The described reset torque unit.

[0052] The reset torque unit 204 of the marking device 201 is also adapted to provide a reset torque to force the magnetic object 3 back to its equilibrium orientation if the external magnetic force has caused the magnetic object 3 to rotate away from its equilibrium orientation, so as to allow rotational oscillation of the magnetic object 3 excited by the external magnetic torque. Furthermore, also in this embodiment, the magnetic object 3 can rotate about a virtual axis of rotation centrally passing through it, wherein the magnetic object 3 is rotationally symmetrical with respect to the virtual axis of rotation. Specifically, also in this embodiment, the magnetic object 3 is a magnetic sphere. However, the reset torque unit 204 includes a torsion spring mechanism for providing the reset torque. Specifically, the torsion spring mechanism includes two torsion springs 204, wherein one of these torsion springs 204 attaches the magnetic sphere 3 to a first end face 30 of the cylindrical housing 2, and the other torsion spring 204 attaches the magnetic sphere 3 to a second end face 31 of the cylindrical housing 2.

[0053] Figure 4 Another embodiment of the tagging device 301 to be tracked by the tracking system is illustrated schematically and exemplary, which is similar to the one referenced above. Figure 3 The marking device 201 described differs in that marking device 301 includes a cylindrical magnetic object 303, while marking device 201 includes a spherical magnetic object 3. Furthermore, the torsion spring 304 of marking device 301, which provides the torsion spring mechanism, is shorter than the torsion spring 204 of marking device 201.

[0054] Figure 5 Another embodiment of a marking device 401, which is tracked using a tracking system, is illustrated schematically and exemplary. The marking device 401 also includes a cylindrical housing 2 and a magnetic object 3 disposed within the housing 2 such that the magnetic object 3 can rotate away from its equilibrium orientation if an external magnetic torque is applied to it. Furthermore, also in this embodiment, the magnetic object 3 is a magnetic sphere and is attached to one of two end faces 30, 31 via filaments 7. Additionally, the marking device 401 includes reset torque units 404, 405 adapted to provide a reset torque to force the magnetic object 3 back to its equilibrium orientation if the external magnetic torque has caused it to rotate away from its equilibrium orientation, thereby allowing rotational oscillation of the magnetic object 3 excited by the external magnetic torque. Furthermore, also in this embodiment, the magnetic object 3 can rotate about a virtual axis of rotation centrally located through it, wherein the magnetic object 3, being a magnetic sphere in this embodiment, is naturally rotationally symmetrical about the virtual axis of rotation.

[0055] Also in this embodiment, the reset torque unit includes a torsion spring mechanism 404 for providing reset torque, wherein in this embodiment, the torsion spring mechanism 404 is provided by a torsion spring connecting the magnetic object 3 and another magnetic object 405 to each other. Furthermore, the reset torque unit can be considered to also include another magnetic object 405 for providing reset torque, wherein this other magnetic object 405 is also a magnetic sphere. The other magnetic object 405 is arranged within the housing such that it can oscillate relative to the housing 2, wherein the other magnetic object 405 can rotate about a virtual axis of rotation centrally passing through it. The virtual axes of the magnetic object 3 and the other magnetic object 405 are aligned with each other, and the magnetic object 3 and the other magnetic object 405 can each rotate along the virtual axis. Furthermore, the other magnetic object 405 is attached to one end of a filament 8, wherein the other end of the filament 8 is attached to the other of the two end faces 30, 31 of the cylindrical housing 2.

[0056] Figure 6 An embodiment of a guidance system 30 for guiding during surgery is illustrated schematically and exemplary. The guidance system includes an imaging system 23 adapted to generate images of a subject positioned on a support device 32 (such as a patient table) and to whom surgery is performed. In this embodiment, the imaging system 23 is a C-arm imaging system for generating two-dimensional and / or three-dimensional images of the subject. The C-arm system 23 includes an X-ray source 41 and an X-ray detector 42, which are connected to opposite ends of a C-shaped support structure 43.

[0057] The guidance system 30 also includes a tracking system for tracking the position of tagging device 1 or any other tagging device among the aforementioned tagging devices 101, 201, 301, and 401 when the tagging device is attached to an object to be tracked. For example, the object to be tracked is a lesion within the subject's body and / or a medical device moving within the subject's body. Specifically, multiple tagging devices may be attached to one or more internal parts of the subject and / or to one or more medical devices moving within the subject's body to track the position of these objects and allow, for example, guidance of the medical device to a lesion within the subject's body. However, the tracking system may also track only the position of the medical device as it moves within the subject's body, or the tracking system may track only the position of internal parts of the subject, such as lesions.

[0058] The imaging system 23 and the tracking system are registered to each other such that the output unit 36 ​​of the monitor is able to output, for example, the tracking position of lesions in the subject's body and / or medical devices, and overlay them with the image of the subject generated by using the imaging system 23.

[0059] The tracking system includes a coil 20 adapted to a) generate a magnetic field providing a magnetic torque for rotating the magnetic object 3 of the marking device 1 away from its equilibrium orientation and thereby exciting rotational oscillations of the magnetic object 3, and b) generate an induction signal dependent on the spatial position and orientation of the marking device 1. The tracking system also includes a tracking control unit 31 configured to control the coil 20 by providing and controlling current to the coil 20, thereby generating the desired magnetic field and generating a digital induction signal indicating the induced effect of the rotational oscillations of the marking device 1 on the current within the coil 20. The coil 20 and the tracking control unit 31 magnetically excite the marking device 1 and generate the induction signal, such that the coil 20 and the tracking control unit 31 can be considered as forming excitation and induction signal units 20 and 31.

[0060] In this embodiment, coil 20 is arranged in a pad 34 on a support device, which in this example is a patient table. However, coil 20 can also be arranged in a tracking system or in another part of the tracking system. For example, coil 20 can also be arranged in a handheld device so that the tracking system can be held in the hand. In this case, preferably, another tracking system is used to track the position and orientation of the handheld device relative to the imaging system 23 in order to register the tracking system with the imaging system 23. For such tracking, known tracking systems, such as optical tracking systems or other tracking systems, can be used.

[0061] Although in this embodiment the same coil 20 is used to generate a magnetic field and to generate an inductive signal, in other embodiments, it may also be a) a first coil used to generate a magnetic field that provides a magnetic torque for rotating the magnetic object 3 of the marking device 1 away from its equilibrium orientation and thereby stimulating rotational oscillation of the magnetic object 3, and b) a second coil used to generate an inductive signal that depends on the spatial position and orientation of the marking device, wherein the first and second coils are separate. The first and / or second coils may also be arranged in a mat or in a handheld device.

[0062] For each coil, an induction signal is generated, which depends on the position and orientation of the marking device 1 relative to the corresponding coil, wherein the position determination unit 33 of the tracking system is adapted to determine the position and orientation of the marking device 1 based on these induction signals. For example, during the calibration process of each position and orientation of the marking device relative to the coil 20, induction signals can be generated and stored, or at least the characteristics of these induction signals can be stored. After the calibration is completed, the position determination unit can use the stored induction signals or the characteristics of the stored induction signals to determine the position and orientation of the marking device based on the currently generated induction signals and the stored information. The position determination unit can also be adapted to determine the position and orientation of the marking device 1 based on the induction signals in another way, for example, based on an analytical model, in particular a function, which is based on physical considerations and provides the position and orientation of the marking device as an output if the induction signals are given as input. Artificial intelligence, such as neural networks, can also be used to provide the position and orientation of the marking device based on the induction signals, wherein the artificial intelligence can be trained using stored calibration information.

[0063] Although in this embodiment, the position determination unit 33 is adapted to determine not only the position of the marking device but also its orientation, in another embodiment, the position determination unit may be adapted to determine only the position of the marking device or only its orientation. However, preferably, the position determination unit 33 is adapted to determine the position and orientation of the marking device 1 using six DoF.

[0064] The position determination unit 33 can be adapted to determine the nearest position on the subject's surface, which is the position on the subject's surface closest to the position of the marking device 1. Specifically, the position determination unit 33 can be adapted to determine the distance between the nearest position on the subject's surface and the position of the marking device 1, wherein the nearest position on the subject's surface can be displayed on the monitor 36 or can be displayed directly on the subject's skin. For example, a light source such as a light-emitting diode or a laser 37 can be used to generate a light spot on the subject at the determined nearest position. The light source 37, which can be considered another output unit of the tracking system, can be arranged, for example, at the imaging system 23, in a handheld device, or in another part of the system, the handheld device may also include coils for generating a magnetic field and / or coils for generating an inductive signal. The position and orientation of the light source 37 are also registered with the tracking system.

[0065] The tracking system and marking device 1 are preferably adapted to cause the magnetic object 3 to rotate and oscillate within an angular range of at least 30 degrees. The tracking system may be adapted to determine the position and orientation of a plurality of marking devices 1, wherein the magnetic objects 3 of the plurality of marking devices 1 may rotate and oscillate at different resonant frequencies, such that the sensing signals of different marking devices 1 have different frequencies, and wherein these different frequencies are used by the position determination unit 33 to determine the position and orientation of the marking devices 1 based on the generated sensing signals having these different frequencies.

[0066] In one embodiment, multiple marking devices 1 are attached to a medical device 51, such as a guidewire or catheter, to provide a medical device 50 that can be tracked by a tracking system. Figure 7 The medical device 50 is illustrated schematically and exemplary. The position determination unit 33 can be adapted to determine the position and orientation of a plurality of marking devices 1 arranged along the length of the elongated medical device 50, and to determine the shape of the medical device 50 based on these determined positions and orientations.

[0067] In one embodiment, the tracking system may further include a magnetic field generator 21, which may be attached to the support device 32 or otherwise positioned close to the subject to be treated. The magnetic field generator 21 is adapted to generate a spatially non-uniform magnetic field to produce a position-dependent resonant frequency of the rotational oscillation of the magnetic object 3 of the marking device 1, wherein the position determination unit 33 may also be adapted to determine the position of the marking device 1 based on the position-dependent resonant frequency. Specifically, the magnetic field generator 21 is adapted to generate a magnetic field gradient as a spatially non-uniform magnetic field. In this example, the magnetic field generator 21 includes two sets of saddle-shaped coils and discrete solenoid coils for generating the spatially non-uniform magnetic field. These coils may also be controlled by the tracking control unit 31.

[0068] The following will refer to Figure 9 The flowchart shown exemplarily describes an embodiment of a guidance method that uses a guidance system for guidance during surgical procedures.

[0069] In step 501, a magnetic field is generated, providing a magnetic torque that causes the magnetic object 3 of the marking device 1 within the subject's body to rotate away from its equilibrium orientation, thereby exciting the rotational oscillation of the magnetic object 3 at its resonant frequency. Furthermore, in step 501, an induction signal is generated, caused by the rotational oscillation of the magnetic object 3, and depends on the spatial position and orientation of the tracking device relative to the coil 20. In step 502, the position of the marking device 1 is determined based on the generated induction signal, and in step 503, the determined position is output.

[0070] Steps 501 to 503 are executed cyclically, allowing the position of the marking device to be tracked substantially continuously and output to, for example, a surgeon performing a procedure, until, for example, the surgeon ceases position tracking. Specifically, the surgeon can indicate that tracking should be stopped via input unit 35, such as a keyboard, touchpad, or a specific button on the system. Steps 501 and 502, which only involve tracking, can also be considered steps in a tracking method for tracking the marking device. The tracking method and system can also be adapted to determine the position of the marking device at a point in time and optionally also determine the orientation of the marking device at a point in time; that is, they can be adapted not to determine the position over time and optionally not to determine the orientation over time. However, preferably, the tracking method and system are adapted to determine the position over time and optionally determine the orientation over time.

[0071] Electromagnetic (EM) positioning is known to be used in the three-dimensional tracking of medical devices during minimally invasive medical procedures or for detecting target motion during external beam radiation therapy (EBRT). To obtain not only the position of the tracked medical device but also its orientation—that is, to track the medical device at six DoF—the medical device is typically equipped with multiple 3DoF or 5DoF EM markers. In contrast, the above specifically refers to… Figures 1 to 5 The described tagging device and the tracking system described above achieve wireless 6DoF detection, i.e., detection of three-dimensional position and three azimuth angles, using a single tagging device. The tagging devices can be sub-millimeter in size and can be read from distances of, for example, 30 to 40 cm. As mentioned above, especially the reference... Figure 8 Additional spatial coding schemes can provide independent location information to further improve positioning accuracy. Furthermore, multiple marker devices can be detected in parallel; that is, the positions and orientations of multiple marker devices can be detected in parallel.

[0072] A single device in the aforementioned marking apparatus is sufficient to obtain complete position and orientation information in space, while conventional EM positioning requires at least two marking devices, i.e., at least two coils, located within or attached to the medical device, to obtain complete orientation information in addition to complete position information. Furthermore, for example, refer to... Figure 6 The aforementioned tracking system allows for the combination of two independent positioning methods, namely, positioning using coil 20 and positioning using coil 21. Furthermore, as disclosed in the aforementioned article by B. Maxwell et al., conventional wireless EM tagging devices are generally larger than 1 mm, i.e., for example, they have a diameter of approximately 8 mm, while the aforementioned, especially referenced... Figures 1 to 5 The described marking device has a sub-millimeter size.

[0073] Furthermore, since the tagging device preferably uses permanent magnets, it is more sensitive than conventional EM tagging devices and can therefore be read from a greater distance, i.e., from a distance greater than 30 cm. Conventional EM tracking systems with wireless EM tagging devices have a smaller workspace; for example, the wireless EM tagging device disclosed in the aforementioned article by B. Maxwell et al. can only be read from a distance of approximately 16 cm.

[0074] The tagging device can be considered as a magnetic micro-tag, which can be adapted to operate at different frequencies to make them distinguishable. The tracking system includes a coil array, namely coil 20, for wireless tag excitation, signal reception, and positioning. This is achieved by using elements such as a coil array (i.e.,...) Figure 6 The known spatial coil sensitivity map of coil 20 shown indicates that six-DoF positioning is feasible. To increase spatial accuracy, the tracking system and method can also utilize the aforementioned independent spatial encoding, which is based on the use of, for example, the reference above. Figure 8 The field gradient generator generates position-related frequency changes by superimposing a low-frequency non-uniform field.

[0075] The marking device may include a permanent magnet, which may be spherical, attached to a filament, and capable of freely rotating and oscillating about a balanced orientation determined by the magnetic field of a fixed magnet, as described above. Figure 1 and 2 Furthermore, the permanent magnet can be multiple magnets. The marking device may also include a permanent magnet connected to a torsion spring mechanism that provides a restoring force for resonant torsional oscillation, as described above. Figures 3 to 5 Furthermore, cylindrical magnets can be used to maximize the magnetic moment within the cylindrical container, i.e., within the cylindrical shell, as described above. Figure 4 Furthermore, to decouple the oscillation from the outer cylinder and the environment, the marking device can also use spring-based counter-oscillations utilizing filaments connected to the outer shell, i.e., the two spheres of the shell, for example, as described above. Figure 5 As mentioned above. (Refer to the above reference.) Figures 1 to 4 Compared to the aforementioned marking device, by using the counter-current spring-based oscillation of two spheres, little or no torque is applied to the housing, thus creating vibration decoupling from the surrounding environment. This is in contrast to the case without such a central torsion spring. Figure 5 The central torsion spring 404 shown increases the resonant frequency. However, if the low frequency is sufficient, the torsion spring 404 can also be removed.

[0076] The above reference Figure 6 The described coil array 20 provides 6DoF positioning information through the spatial sensitivity distribution of its individual coil elements. (See above reference.) Figure 8The described additional coil system 21 can be used to generate a spatially non-uniform positioning field that provides independent positioning information, which can be used to improve positioning accuracy if needed. This active spatial encoding can be provided by two sets of saddle coils and discrete solenoid coils.

[0077] Figures 10 to 12 Six-DoF positioning is shown, achieved by using a rotating permanent magnet 3 similar to a marking device 1. Figure 10 The rotationally symmetric dipole field characteristics are shown, as illustrated in isoplanar plot 60 of the field strength. Therefore, by measuring the dipole field, the position and orientation x″ of the marking device can be determined (5DoF: three-dimensional position plus two angles describing the orientation of x″ in the local coordinate system (x', y', z'). Figure 10 In the diagram, arrow 61, orthogonal to x", indicates the unknown orientation of the y" and z" axes. This is typical when the dipole field of the coil is used for positioning. Although the suspended permanent magnet 3 of the marking device 1 also has dipole field characteristics, the plane traversed by the dipole vector motion when the magnet 3 oscillates allows for the allocation of missing axes. The direction z" is the direction in which the field strength does not change during oscillation, while the direction y" is derived from x" and z" (see [link to diagram]). Figure 11 and 12 A convenient way to achieve six-DoF is to separate the measurements of the dipole fields in frequency space. The dynamic dipole moment of the fundamental frequency has an orientation orthogonal to the dipole moment of the rotating permanent magnet and to the oscillation axis. The dynamic dipole moment of the second harmonic (twice the fundamental frequency) has an orientation parallel to the dipole moment of the rotating magnet and perpendicular to the oscillation axis. Using two distinguishable orthogonal dipoles, six-DoF can be reconstructed.

[0078] The above reference Figures 1 to 5 The described marking device is based on the magnetomechanical resonance of a permanent magnet. Modern permanent magnet materials have very high remanence (NdFeB, MR≈1.45T), thus enabling efficient coupling to an externally applied magnetic field. As a result, energy can be efficiently coupled into the resonant mechanical rotational oscillation of the permanent magnet, which is either connected to, for example, the referenced above. Figures 3 to 5 The aforementioned torsion spring mechanism, and / or exposed to, for example, as referenced above Figure 1 , Figure 2 and Figure 5 The magnetic field of the second permanent magnet is used to form a high-Q oscillating system. If decoupling from the environment is desired, it can be achieved, for example, as described in the reference above. Figure 5 The aforementioned reverse-oscillating sphere. The oscillation frequency is preferably in the range from 100Hz or several hundred Hz to 1kHz or several kHz. The oscillation of the permanent magnet of the marking device generates a time-varying magnetic field, which can be referenced as above. Figure 6 Electromagnetic induction is used to detect electromagnetic induction in a coil system such as the described coil array 20.

[0079] For the design of the marking device, the above reference can be used. Figures 1 to 5 Exemplary combinations of mechanisms are described, such as using the magnetic field of another permanent magnet and / or using a torsion spring to generate a restoring force, which is here a restoring torque. The aim of the marking device is to maximize sensitivity with a minimal size. For this purpose, a high-volume magnetic material and a high oscillation frequency are desired. While purely magnetic markers can be constructed most simply, as referenced above... Figure 4 The combination of the cylindrical oscillating magnet and the spring mechanism can provide optimal sensitivity.

[0080] The length of the marker capsule, i.e., the length of the corresponding marking device housing, can be less than one millimeter, while still providing sufficient signal to detect the marker at distances up to, for example, 40 cm. In a preferred embodiment, the diameter of the marking device housing is less than 0.3 mm, because the marking device can then be integrated into a conventional guidewire typically having a diameter of 0.355 mm. The marking device can also be attached to small implants such as stents or placed directly in tissue. Multiple marking devices operating at different frequencies can be tracked in parallel to determine the shape deformation of objects or tissues in the subject's body.

[0081] To excite the oscillations in the marking device, at least one excitation coil is required to generate the excitation field. For 6DoF positioning based on the marking device response signal, it is necessary to refer to the above. Figure 6 The coil array is described above. Each coil transmits an induced signal, which depends on the spatial position and orientation of the coil relative to an oscillating magnet within a corresponding marking device. Based on the known sensitivity of the coils, the position and orientation of the dipoles can be reconstructed, where the fact that the dipoles oscillate in a plane allows for the extraction of 6DoF information, as referenced above. Figures 10 to 12 As illustrated in the example. Depending on the desired application, the coil can be integrated into, for example... Figure 6 The non-planar coils can be placed in a box in the mattress on the patient table illustrated in the illustration, or if a flat shape factor is not required.

[0082] For example, if only the mutual distance and orientation between the labeled medical device and the labeled tissue are required, this can be done relative to the coil array (as referenced above). Figure 6 The known position and orientation of the described coil array 20 absolutely determine the position and orientation of the corresponding marking device, or absolutely determine the position and orientation of the corresponding marking device relative to one or more reference marking devices. The marking device may also be made radiopaque to directly link the position information to X-ray or computed tomography data.

[0083] Using references similar to those above Figure 8An additional set of coils, or other means such as a set of permanent magnets similar to mechanical actuation, can apply a dynamic field gradient to modify the frequency response of the marking device based on its spatial location. This positioning method is independent of coil sensitivity-based positioning methods and can be used to improve positioning accuracy. The additional set of coils can include at least six coils, enabling the generation of local fields and field gradients with different orientations. By applying several different field configurations, the position and orientation information of the marker can be obtained.

[0084] To distinguish multiple marking devices, their resonant frequencies must be adjusted to achieve sufficient spectral separation. If the marking device includes a spring, this adjustment can be performed, for example, by adjusting the spring constant accordingly, and / or, if a second magnet is present in the respective marking device, by modifying the distance from the oscillating magnet to the second magnet. The spectral separation of the resonant frequencies of the different marking devices is preferably greater than 20 Hz, especially if a positioning update rate of 10 Hz is desired. The excitation pulse can be, for example, a short “delta” pulse timed for in-phase excitation of all oscillating spheres. However, the excitation pulse can also have a considerably long frequency-selective pulse shape, which can excite multiple marking devices with sufficient spectral selectivity.

[0085] The marking device can also be used as a sensing device to detect physical parameters that change the resonant frequency of the marking device. For example, similar to... Figure 1 The end face 31 of the marking device 1 shown can be flexible, allowing changes in external pressure. Figure 1 The distance between the two magnets 3 and 4 in the system allows the position determination unit to not only determine the position of the marking device and optionally its orientation, but also to determine the pressure at a specific location of the marking device based on the frequency of the rotational oscillations of the magnets within the respective marking device. For example, during calibration, multiple frequencies can be assigned to multiple pressure values, and these assignments can be used during actual pressure measurements to determine the pressure at a specific location of the marking device based on the actual measured frequency of the rotational oscillations within the marking device. The marking device can also be adapted to sense another physical parameter, such as radiation, that affects the resonant frequency of the marking device.

[0086] This marking device can be used for three-dimensional radiation-free continuous tissue localization in surgical procedures or radiotherapy. Figure 13 Two marking devices 1 inside the contracted lung of patient 22 are illustrated schematically and exemplary.

[0087] However, tagging devices can also be used to locate untethered devices inside or outside the body. Multiple tagging devices can be used for wireless shape sensing, such as determining the shape of catheters and / or guidewires.

[0088] One or more marking devices can be used in minimally invasive lung surgeries, such as video-assisted thoracoscopic surgery (VATS) for breast tumor resection. Minimally invasive lung surgery is a treatment used to remove lung tumors as well as lung segments or lobes. While the location of lung tumors in preoperative medical images, such as computed tomography images, is straightforward, during surgery, the target becomes more difficult to locate due to the contraction of the relevant lung portion. For this location, one or more of the aforementioned magnetic marking devices can be used, which allows the tumor to be located without the use of X-ray fluorescence examination. These marking devices, also considered “microbots,” can be inserted into the tumor by using needle-based placement or, more advantageously, by injecting them into the blood vessels supplying blood to the tumor using a catheter-based method. Thus, an entire tumor region can be identified based on one or more marking devices, where the marking devices can be placed in a relatively conservative manner. During thoracoscopic surgery, the marking devices can be located in real time in three dimensions. As mentioned above, the marking devices can have a diameter of less than, for example, 0.5 mm, and they comprise a magnetic resonator based on one or more permanent magnets excited by an external magnetic field. This oscillation generates a magnetic field, which is detected by induction in, for example, a set of coils identical to those used to generate the excitation field, i.e., in the reference above. Figure 6 The location of the marker device is detected by induction in the described coil 20 and can be superimposed on video images acquired during thoracoscopic surgery to provide guidance during the procedure.

[0089] The marking device includes at least one permanent magnet capable of performing rotational oscillations, preferably at least 30 degrees. In one embodiment, the magnet is attached to a thread and is attracted by a second magnet, for example, as referenced above. Figure 1 As described above, in this application, the labeling device is placed or injected into the tumor region, so it is not firmly attached to a large mass, and the oscillating magnet thus causes torque to be generated on the housing of the labeling device, and therefore torque to be generated on the tissue. In semi-rigid tissue, the energy of the oscillator may therefore be rapidly depleted. Therefore, in similar situations to the above reference... Figure 5 In the embodiments described, at least one second mass block exhibits rotational oscillations at the same frequency. This second mass block counteracts the torque on the housing. Preferably, this second mass block is also a magnet to increase the overall magnetization variation.

[0090] The coil used to excite oscillation and generate induced signals can be referenced as above. Figure 6The marking devices are arranged in a pad as described, wherein the pad may have a size of approximately 50 × 50 square centimeters. The pad may contain, for example, a 4 × 4 array of coils. The coils may be made of aluminum or other metals. This pad with coils can simultaneously position all marking devices in the lung region. However, at least during open surgery, such a pad may not be suitable for the operating room. In one embodiment, a smaller handheld version can therefore be used. The handheld version may include coils for exciting oscillations and for generating inductive signals, wherein control of the coils and tracking is similar to that using coils in the pad, but in the handheld device, the number and size of the coils can be reduced. The handheld device may also include a display unit. It may also include a microprojector or laser projector system under which markings are placed on the tissue surface to locate the corresponding marking device. Color codes or shapes may indicate depth; for example, a larger circle may indicate a deeper location.

[0091] During surgical procedures in the operating room, the coordinate system of the tracking system is spatially related to the imaging system, such as imaging system 23 used during thoracoscopic surgery. This can be accomplished through a direct calibration process. For example, the position and optional orientation of a set of sample markers can be tracked using a tracking system visible to the imaging system, which can also be considered a camera system. The markers can also be attached to the imaging system itself so that the tracking system tracks the imaging system. Registration can also be accomplished in another way, for example, via the imaging space of a hybrid operating room system, i.e., by using the relationship between the tracked surgical instruments and the marker coil array and, for example, the image space of a C-arm system 23. For co-registration in computed tomography planning or C-arm imaging, the markers can be made radiopaque.

[0092] The location of the marker can be presented to the surgeon as an overlay on images produced by an imaging system (such as an X-ray CT system used during thoracoscopic surgery).

[0093] Because of the selective sensing signal generated by the use of the marking device—that is, because the marking devices can have different resonant frequencies, allowing only specific marking devices to be excited—in the case of injection / insertion of marking devices at incorrect locations within the subject's body, these marking devices at incorrect locations may not be excited during surgery to allow for accurate surgical guidance. For example, in the preoperative calibration step, the different resonant frequencies of different marking devices can each be associated with the corresponding positioning of the marking devices in the X-ray image, where the positioning of the marking devices in the X-ray image can be used to determine which marking devices have been placed in the correct locations within the subject's body and which marking devices have been positioned in incorrect locations within the subject's body. The tracking control unit 31 can be adapted to control the excitation of the marking devices such that only marking devices at the correct locations are excited by using the coil 20, where the frequency to be used to excite the marking devices at the correct locations can only be obtained from the preoperative calibration.

[0094] The tracking system can be adapted to determine the position of one or more surgical devices to which a marking device has been attached, relative to the marking device located at the tumor site, and preferably also to determine the orientation of the one or more surgical devices relative to the marking device located at the tumor site. Thus, the position of one or more surgical devices and preferably the orientation of one or more surgical devices, as well as the position of the marking device at the tumor region and optionally the orientation of the marking device, can be provided in the same frame of reference. The marking device may include a radiopaque marker having a frequency-dependent shape or attenuation pattern to simplify position / type identification and to avoid the need for a positioning system during preoperative examination. In other words, marking devices with different resonant frequencies will appear differently in X-ray images showing the marking devices, and the relationship between appearance and resonant frequency is known. Therefore, after the surgeon has identified the marking devices that have been placed in the correct position, the exact frequencies from which these marking devices are located are immediately known due to their appearance in the X-ray image, and the marking devices can be excited accordingly.

[0095] Although the marking device has been used to mark lung tumors in the above embodiments, the marking device can of course also be used to mark other objects, such as other types of tumors, medical devices as described above, or any other objects that need to be tracked.

[0096] Although some embodiments of the marking device have been described above, other marking devices may also be used, which have a housing, a magnetic object, and a reset torque unit adapted to provide a reset torque to force the magnetic object back to its equilibrium orientation if an external magnetic torque has caused the magnetic object to rotate away from its equilibrium orientation, thereby allowing rotational oscillation of the magnetic object excited by the external magnetic torque. For example, the above-referenced... Figure 5 The marking device described herein does not have a spring 404, wherein in this case, a reset torque is generated by another magnetic object 405.

[0097] Although the imaging system is preferably an X-ray C-arm system in the above embodiments, other imaging systems may also be used, such as a C-arm system with an optical camera system, an ultrasound imaging system, such as a transesophageal echocardiography (TEE) ultrasound imaging system or an intravascular ultrasound imaging system.

[0098] The marking device may also include means for reducing the potential temperature dependence of the resonant frequency. For example, the marking device may include a magnetic material whose magnetization varies with temperature, thereby altering the magnetic field at the location of the magnetic object, and thus changing the temperature-dependent resonant frequency. The magnetic material may be arranged such that the temperature-dependent change in the resonant frequency caused by the magnetic material compensates for the overall possible change in the resonant frequency due to temperature variations caused by one or more other elements of the marking device. The magnetic material may be located on or adjacent to another magnetic object. Alternatively or additionally, the magnetic material may be applied to the magnetic object to change its magnetic dipole moment with temperature, such that this change in the magnetic dipole moment compensates for the overall possible change in the resonant frequency due to temperature variations caused by one or more other elements of the marking device.

[0099] The generation of a magnetic field can be achieved in many different ways. This magnetic field provides a magnetic torque that causes the magnetic object of the measuring device to rotate away from its equilibrium orientation, thereby exciting the rotational oscillation of the magnetic object to oscillate at a resonant frequency. For example, the excitation can use a single pulse of the magnetic field, where the frequency and phase of the induced signal can be measured between pulses. The timing of the next short pulse can then be calculated to increase the oscillation amplitude of the magnetic object. Alternatively, the single pulse can be replaced by a pulse train consisting of several pulses with positive and negative amplitudes. This short pulse train still covers a relatively wide potential excitation spectrum, with its center designed to be approximately located at the desired resonant frequency. The timing of the pulse train is then adjusted again to increase the oscillation amplitude of the magnetic object. The resulting optimized frequency of the induced signal can be considered the resonant frequency.

[0100] Those skilled in the art, when practicing the claimed invention, can understand and implement other variations of the disclosed embodiments by studying the accompanying drawings, the disclosure, and the appended claims.

[0101] 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.

[0102] A single unit or device can perform the functions of several items recited in the claims. The fact that certain measures are recited in different dependent claims does not mean that combinations of these measures cannot be used advantageously.

[0103] Processes performed by one or more units or devices, such as determining the position of the marking device based on the generated inductive signal and preferably its orientation, and controlling the excitation of the marking device by controlling the current in the control coil, can be performed by any other number of units or devices. These processes and / or the control of the tracking system according to the tracking method and / or the control of the guidance system according to the guidance method can be implemented as program code modules of a computer program and / or dedicated hardware.

[0104] Computer programs can be stored / distributed on suitable media provided with or as part of other hardware, such as optical storage media or solid-state media, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0105] Any reference numerals in the claims should not be construed as limiting the scope.

[0106] This invention relates to a marking device and a tracking system for tracking the marking device, wherein the marking device includes a rotationally oscillating magnetic object, and the rotational oscillation can be excited by an external magnetic field, namely a magnetic field generated by a magnetic field providing unit located outside the marking device. The rotational oscillation of the magnetic object induces a current in a coil, wherein the position of the marking device is determined based on these induced currents, and optionally, the orientation of the marking device is also determined. This wireless tracking can be performed using a relatively small marking device, which can be placed, for example, in a guide wire, can be read over a relatively large distance, and a single marking device can be used for positioning in six degrees of freedom.

Claims

1. A tagging device to be tracked, wherein, The marking device (1; 101； 201； 301; 401) include: -Shell (2) - A magnetic object (3; 303), said magnetic object being arranged within the housing (2) such that if an external magnetic torque is applied to said magnetic object (3; 303), said magnetic object is able to rotate away from its equilibrium orientation. - A reset torque unit, adapted to provide a reset torque to force the magnetic object (3; 303) back to the equilibrium orientation if an external magnetic torque has caused the magnetic object (3; 303) to rotate away from the equilibrium orientation, so as to allow rotational oscillation of the magnetic object (3; 303) excited by the external magnetic torque. The reset torque unit includes another magnetic object (4; 104; 405) for providing the reset torque, wherein the magnetic object (3; 303) and the other magnetic object (4; 104; 405) are permanent magnets each having their own magnetic dipoles, wherein the magnetic object (3; 303) and the other magnetic object (4; 104; 405) are arranged such that, in the balanced orientation, the magnetic dipoles of the magnetic object (3; 303) and the magnetic dipoles of the other magnetic object (4; 104; 405) point in opposite directions, wherein the north pole of the magnetic object (3; 303) faces the south pole of the other magnetic object (4; 104; 405), and the south pole of the magnetic object (3; 303) faces the north pole of the other magnetic object (4; 104; 405).

2. The marking device according to claim 1, wherein, The reset torque unit also includes a torsion spring mechanism for providing the reset torque.

3. The marking device according to claim 2, wherein, The marking device is adapted such that if an external magnetic torque is applied to the other magnetic object, the other magnetic object can rotate away from the equilibrium orientation, wherein the reset torque unit further includes the magnetic object and is adapted to provide a reset torque to force the other magnetic object back to the equilibrium orientation if the external magnetic torque has already caused the other magnetic object to rotate away from the equilibrium orientation, so as to allow rotational oscillation of the other magnetic object excited by the external magnetic torque, wherein the rotational oscillation of the magnetic object and the other magnetic object have the same resonant frequency and a phase difference of 180 degrees.

4. The marking device according to any one of claims 1 to 3, wherein, The marking device (1; 101; 201; 301; 401) is adapted to satisfy at least one of the following conditions: i) a Q factor of at least 100, ii) at least 0.5 μAm 2 The dynamic dipole moment and (iii) a resonant frequency of at least 100 Hz.

5. A kit comprising a plurality of marking devices according to any one of claims 1 to 4, wherein each marking device in the kit has a radiopaque material and a resonant frequency, wherein the radiopaque material and the resonant frequency of at least two of the marking devices are different from each other.

6. A tracking system for tracking a tagging device (1) according to any one of claims 1 to 4; 101； 201； 301； 401), wherein the tracking system includes: - An excitation and induction signal unit (20, 31) adapted to a) generate a magnetic field providing a magnetic torque for causing the magnetic object (3; 303) of the marking device (1; 101; 201; 301; 401) to rotate away from its equilibrium orientation and thereby excite rotational oscillations of the magnetic object (3; 303) and b) generate an induction signal caused by the rotational oscillations of the magnetic object (3; 303). - A position determination unit (33) adapted to determine the position and orientation of the marking device (1; 101; 201; 301; 401) relative to the tracking system based on the generated sensing signals. The excitation and sensing signal unit includes at least two coils adapted to generate the sensing signal, wherein for the at least two coils, a corresponding sensing signal is generated depending on the position and orientation of the marking device relative to the respective coil.

7. The tracking system according to claim 6, wherein, The tracking system is adapted to determine the position of a plurality of marking devices (1; 101; 201; 301; 401) according to any one of claims 1 to 4, wherein the magnetic objects (3; 303) of the plurality of marking devices (1; 101; 201; 301; 401) are capable of rotating and oscillating at different resonant frequencies, such that the sensing signals of the different marking devices (1; 101; 201; 301; 401) have different frequencies, and the position determination unit (33) is adapted to determine the position of the marking devices (1; 101; 201; 301; 401) based on the generated sensing signals with different frequencies.

8. The tracking system according to any one of claims 6 to 7, wherein, The marking device (1; 101; 201; 301; 401) is adapted to be located within the subject (22), wherein the position determining unit (33) is adapted to determine the nearest position on the surface of the subject (22), the nearest position being the position on the surface of the subject (22) closest to the marking device (1; 101; 201; 301; 401) and / or the projection of the position of the marking device on the surface of the subject in a predefined direction.

9. A guidance system for guiding during surgical procedures, the guidance system (30) comprising: - A tracking system according to any one of claims 6 to 8, wherein the system is used to track a tagging device (1); 101；201； The position and orientation of the marking device (1; 101; 201; 301; 401), wherein the marking device (1; 101; 201; 301; 401) is attached to the object to be tracked and is the marking device (1; 101; 201; 301; 401) according to any one of claims 1 to 4. - Output unit (36, 37), the output unit is adapted to output the tracked position.

10. The boot system according to claim 9, wherein, The guidance system further includes an imaging system (23) adapted to generate an image of the subject (22) to which the surgery is performed, wherein the tracking system is registered with the imaging system (23), and the output unit is adapted to at least overlap the tracked position with the image of the subject (22).

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