2D tracking marker

Abstract

The present invention relates to a medical tracking marker for location and tracking during a medical procedure, comprising a substantially planar substructure (1) having a front surface (2) and defining a plane (3), and a plurality of features (4, 5, 6) disposed on the front surface (2) and optically distinct from the front surface (2), the features (5) being aligned with a grid pattern (7) to define a unique optical appearance for the tracking marker. At least one feature (6) is aligned with the grid pattern (7) and is offset from the plane (3). The present invention also relates to a medical tracking marker set including a plurality of tracking markers having different optical appearances, and a computer-implemented medical method for identifying and tracking the location of such medical tracking markers.

Description

[Technical Field]

[0001] The present invention relates to medical tracking markers configured for location and tracking during a medical procedure, and corresponding medical tracking marker sets including a plurality of such tracking markers with different optical appearances, as well as computer-implemented methods for identifying and location tracking such medical tracking markers. [Background technology]

[0002] Marker tracking systems are commonly used in medical technology to locate and track treatment aids, devices, and / or parts of a patient's body. Device position data can be used for medical navigation to assist physicians in treating patients. This allows for image-guided surgery, since even if part of the device is obscured, a visual output can confirm the device's position relative to the treatment target (e.g., a part of the patient's body). This also makes incision planning possible and / or significantly simplified. Data about the patient's anatomy can be obtained from pre- or intraoperative detections using imaging methods, such as computed tomography, nuclear spin tomography, or X-ray images, and can be incorporated into the operating room coordinate system and / or device tracking system after a registration procedure.

[0003] Some tracking systems, such as many that rely on stereoscopic camera pairs, are configured to detect spherical tracking markers, with the centers of these markers' two-dimensional representations in the camera images defining the marker locations. Other tracking systems, such as those that rely on monocular cameras, are configured to detect complex geometric structures, such as squares, rectangles, triangles, and checkerboard patterns, and determine the spatial positions (i.e., spatial locations and spatial orientations) of the tracked markers and their associated objects by analyzing how these structures appear in two-dimensional images acquired via the monocular camera. However, tracking systems that focus on determining marker locations based on the centers of detected markers have shortcomings in determining complex geometric structures. Meanwhile, tracking systems using monocular cameras are not well-suited to detecting and tracking the spatial positions of three-dimensional arrangements of (spherical) tracking markers.

[0004] It can therefore be seen that known tracking systems only work in a satisfactory manner if they are provided with suitable tracking markers.

[0005] The present invention aims to provide a medical tracking marker that can be used appropriately with a variety of optical tracking systems, regardless of how the camera images are processed or how many cameras these tracking systems rely on.

[0006] The present invention can be used in any procedure that uses a medical tracking system, such as Curve®, Kick®, or Buzz®, all of which are products of Brainlab AG.

[0007] In the following, aspects, examples, exemplary steps and embodiments of the present invention are disclosed. Where technically appropriate and practicable, different exemplary features of the present invention can be combined in accordance with the present invention. Summary of the Invention

[0008] (Exemplary Brief Description of the Invention) The following description provides a brief description of certain features of the invention and should not be understood as limiting the invention to only those features or combinations of features described herein.

[0009] The medical tracking markers disclosed herein are generally flat and have a plurality of optically detectable features disposed on a front surface. Some of these features are arranged relative to one another to define a square grid pattern, which may be the same for multiple tracking markers. To distinguish between these tracking markers, each tracking marker exhibits a distinct optical appearance defined by the other optically detectable features, including those defining the grid pattern, and is disposed in a specific manner relative to the defined grid pattern. At least one optically detectable feature is offset from the surface containing all of the remaining features, thereby providing more reliable tracking of the tracking marker.

[0010] (Summary of the Invention) In this section, a description of the general features of the invention is given, for example, by reference to possible embodiments of the invention.

[0011] In general, the present invention achieves the foregoing objects in a first aspect by providing a medical tracking marker configured for location and tracking during a medical procedure, the medical tracking marker including a substantially planar substructure having a front surface and defining a plane, and a plurality of features disposed on the front surface and optically distinct from the front surface, the plurality of features including: - a first set of features defining dimensions and orientations of a square grid pattern having equally spaced grid spacing in a plane; - a second set of features arranged in a grid pattern and defining a unique optical appearance for the tracking marker; and - At least one feature arranged in a grid pattern and offset from a plane.

[0012] That is, the tracking marker is substantially flat and comprises one major surface exhibiting a plurality of optically detectable features, each of which serves one or more of the following purposes: a first subset of features defines a square grid pattern with equal grid spacing, i.e., a first set of equally spaced grid lines extending perpendicular to a second set comprising the same number of equally spaced grid lines; a second subset of features is aligned with the grid pattern and defines the individual optical appearance of a particular tracking marker so as to be able to distinguish between multiple tracking markers of the same type, i.e., features having the same square grid pattern; and a third subset of optically detected features aligned with the grid pattern and spaced apart from a plane containing all other features so as to reliably determine the spatial orientation of the tracking marker even when the camera's line of sight is oriented substantially perpendicular to that plane.

[0013] In a more specific example, the grid pattern of the tracking markers is (n+2) 2 nodes, i.e., 4, 9, 16, etc. Because the task of determining the location of features and therefrom calculating the spatial location of tracking markers increases as the number of features detected increases, it has been found that 9 nodes is the preferred quantity of nodes on which optically detectable features can be located.

[0014] In other examples, a medical tracking marker may exhibit one or more of the following characteristics: The dimensions of the grid pattern are defined by four features that define each corner node of the grid pattern. - The orientation of the grid pattern is defined by the presence or absence of a feature at each side node between the two corner nodes. The grid spacing of the grid pattern is defined by the distance between the features located at the corner nodes and the features located at the side nodes. At least one feature is offset from the plane and positioned at the center node between at least two side nodes.

[0015] In a further example, the particular optical appearance is defined by the size of the features located at the associated nodes of the grid pattern, where this size varies for each individual feature, and where the size is selected from a limited number of predefined sizes, particularly when all of the features of the tracking marker are one of two predefined sizes.

[0016] As mentioned above, the optical appearance of the tracking marker may be defined not only by the second set of features and their sizes, but also additionally by the first set of features that predefine the square grid pattern.

[0017] In another example, a particular optical appearance is defined by the spatial location of an individual feature relative to an associated node of a grid pattern, the spatial location being selected from a limited number of predefined spatial locations, particularly if all features of the tracking marker are the same size.

[0018] As is evident from the above examples, the distinguishable optical appearance of different tracking markers of the same type can be based on differences in the size of some of the features and / or differences in the position of some of the features relative to the nodes of the grid pattern. It is also possible that only the features of the second set exhibit deviations in size and / or position that define the optical appearance of the tracking marker, while at least some of the features of the first set exhibit deviations in size to give the tracking marker a particular optical appearance.

[0019] In particular, the predefined spatial locations may include: - a position on one grid line adjacent to the node, and / or - a position on one grid field adjacent to the node, In particular, the predefined spatial location may include a predefined distance from the associated node.

[0020] In other words, the features of the second set may be spaced apart from their associated nodes of the grid pattern, or may instead be located at a distance from the node on one of the grid lines that intersect at that node. Alternatively, the features may instead be located within a grid field that is spaced apart from the associated node, for example, between the grid lines that intersect at the respective node. In particular, it is contemplated that the features may be spaced apart a predefined distance from their associated nodes to establish dedicated relative positions between the features and their associated nodes. Furthermore, the distance that the features are spaced apart from their associated nodes may be the same for each feature of the tracking marker.

[0021] In another example, the features are disk-shaped and / or configured to reflect incident light, particularly - High optical contrast towards the front of the substructure, - Includes retroreflective coating.

[0022] In other words, a sufficient optical difference must be established between the feature and its surroundings, i.e., the front surface of the tracking marker substructure. This can be achieved by establishing high contrast, for example by placing a light-colored feature on a dark-colored substructure. Furthermore, the feature may be configured to have retroreflective properties, i.e., to reflect incident light in the same spatial direction. Such features may be formed in a disk shape to make their detection easier for the tracking system, which derives their location from the center of the feature image received by the tracking camera.

[0023] In addition to, or as an alternative to, the optical properties of the features described above, the features may include light-emitting elements, particularly LEDs. In summary, any one of the features may be passive, i.e., reflecting light, or active, i.e., emitting light, or both.

[0024] For at least one feature arranged in a grid pattern and further offset from the surface containing the remaining features, the at least one feature may be located in a recess or protrusion on the front surface of the tracking marker substructure, in which case the at least one offset feature and all of the remaining features may be located on the smooth front surface of the substructure.

[0025] The present invention further relates to a medical tracking marker set including a plurality of tracking markers as described above, which differ in particular in the optical appearance unique to each tracking marker defined by a second feature set that is also defined by a first feature set, such that a medical tracking system can distinguish between the plurality of tracking markers used in a medical procedure based on the optical appearance unique to each tracking marker.

[0026] In a second aspect, a computer-implemented medical method is provided for identifying and tracking the location of a medical tracking marker during a medical procedure according to any of the examples described above. In one example, the method includes the steps of: a) acquiring first feature set data describing the location of a first feature set within a plane of an image acquired via an optical camera; b) determining grid data based on first feature set data describing the location of a grid pattern within the plane of the image; c) obtaining second feature set data that describes the location of the second feature set within the plane of the image, particularly relative to the first feature set; d) identification data is determined based on the second feature set data, in particular based on the first feature set data and the second feature set data, to obtain an identification of the tracking marker; e) out-of-plane data describing the position of at least one feature offset from the plane is acquired, particularly with respect to the first feature set and / or the second feature set; f) determining tracking data based on at least one of the first feature set data, the second feature set data, and the out-of-plane data describing the spatial location of the identified tracking marker;

[0027] It is important to note that any of the foregoing method steps may be performed in any order that is feasible. For example, each of the obtaining steps may be performed simultaneously if all of the determining steps are performed simultaneously.

[0028] In yet another example, the method may include the use of a monocular camera, in particular a monochrome monocular camera configured to optically detect a plurality of features disposed in front of the substructure.

[0029] In a second aspect, the present invention relates to a computer-implemented medical method for identifying and positionally tracking medical tracking markers of the type described above. The present invention also relates to a computer program comprising instructions that, when executed by at least one computer, cause the computer to implement the method according to the second aspect. Alternatively or additionally, the present invention may relate to a (physical, e.g., electrical, e.g., technologically generated) signal wave, e.g., a digital signal wave, e.g., an electromagnetic carrier wave carrying information representing the program, e.g., an electromagnetic wave transmission wave carrying information describing the program. The signal wave may be, for example, a data transmission signal transmitting the computer program. A computer program stored on a disk is a data file, and when the file is read and transmitted, it becomes a data stream, e.g., in the form of a (physical, e.g., electrical, e.g., technologically generated) signal. The signal may be embodied as a signal wave, e.g., an electromagnetic wave transmission wave as described herein. For example, the signal, e.g., the signal wave, may be configured to be transmitted over a computer network, e.g., a LAN, a WLAN, a WAN, a mobile communication network, e.g., the Internet. For example, the signal, e.g. a signal wave, is arranged to be transmitted by optical or acoustic data transmission. The invention may alternatively or additionally relate to a data stream representative of said program, i.e. a data stream constituting the program.

[0030] In yet another aspect, the present invention relates to a computer-readable storage medium having the above-mentioned program stored thereon. The program storage medium is, for example, non-transitory.

[0031] In yet another aspect, the invention is directed to at least one computer (e.g., a computer) including at least one processor (e.g., a processor) wherein a program according to the second aspect is executed by the processor, or wherein the at least one computer includes the computer-readable storage medium described above.

[0032] (definition) This section provides definitions of certain terms used in this disclosure and also constitutes a part of this disclosure.

[0033] A method according to the invention is, for example, a computer-implemented method. For example, all steps or only some steps (i.e., less than the total number of steps) of a method according to the invention can be performed on a computer (e.g., at least one computer). An embodiment of a computer-implemented method is the use of a computer for performing a data processing method. An embodiment of a computer-implemented method is a method relating to the operation of a computer, where the computer is operable to perform one, several, or all steps of the method.

[0034] For example, a computer comprises at least one processor and, for example, at least one memory for (technical) data processing. For example, data is processed electronically and / or optically. The processor is, for example, composed of a semiconductor material or composition, for example, at least partly of n-type and / or p-type doped semiconductors, for example, at least one of type II, III, IV, V, and VI semiconductor materials, for example, (doped) silicon and / or gallium arsenide. The aforementioned calculation or determination step is, for example, performed by a computer. The determination or calculation step is, for example, a step of determining data within the framework of a technical method, for example, within the framework of a program. A computer is, for example, any kind of data processing device, for example, an electronic data processing device. A computer is a commonly envisioned device, for example, a desktop PC, a laptop, a netbook, etc., but can also be any programmable device, for example, a mobile phone or an embedded processor. A computer can, for example, be composed of a system (network) of "sub-computers," each of which represents an independent computer. The term "computer" includes cloud computers, such as cloud servers. The term "computer" includes server resources. The term "cloud computing" includes, for example, a cloud computing system that is composed of at least one cloud computing system, where multiple cloud computers, e.g., server farms, are functionally connected to one another. Such cloud computers are preferably connected to a wide area network, such as the World Wide Web (WWW), and are located within a so-called cloud of computers connected to the World Wide Web. Such an infrastructure is used for "cloud computing," which refers to computing, software, data access, and storage services that do not require end users to know the physical location and / or configuration of the computers providing a particular service. For example, the term "cloud" is used in this regard as a metaphor for the Internet (World Wide Web). For example, a cloud provides computer infrastructure as a service (IaaS).A cloud computer serves as a virtual host for an operating system and / or a data processing application, which are used to execute the method of the present invention. The cloud computer is, for example, the Elastic Computer Cloud (EC2) provided by Amazon Web Services®. The computer is equipped with an interface for receiving or outputting data and / or performing analog-to-digital conversion. The data may be, for example, data describing physical characteristics and / or data generated from technical signals. The technical signals may be, for example, data generated by (technical) detection devices (e.g., devices for detecting marker devices) and / or (technical) analysis devices (e.g., devices for performing (medical) imaging methods), and may be, for example, electrical or optical signals. The technical signals may, for example, describe data received or output by the computer. The computer is preferably operably coupled to a display device capable of displaying information output by the computer, for example, to a user. An example of a display device is a virtual reality or augmented reality device (also called virtual reality glasses or augmented reality glasses) that can be used as navigation "goggles." A specific example of such augmented reality glasses is Google Glass (a registered trademark of Google, Inc.). Augmented reality or virtual reality devices can be used both to input information into a computer through user interaction and to display information output by the computer. Another example of a display device is a standard computer monitor, e.g., with a liquid crystal display operatively coupled to the computer, receiving display control data from the computer and generating signals for displaying graphical information content on the display device. A specific form of such a computer monitor is a digital light box. An example of such a digital light box is Buzz®, a product of Brainlab AG. The monitor may also be that of a portable, e.g., handheld, device, such as a smartphone, personal digital assistant, or digital media player.

[0035] The present invention also relates to a computer program comprising instructions that, when run on a computer, cause the computer to perform the methods described herein, e.g., the method steps, and / or a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) on which the program is stored and / or a computer comprising such a program storage medium and / or a (physical, e.g., electrical, e.g., technologically generated) signal wave, e.g., an electromagnetic transmission wave carrying information describing the program, such a program comprising code means adapted to perform any or all of the method steps described herein. The signal wave is, by way of example, a data carrier signal carrying such a computer program. The present invention also relates to at least one processor and / or such a computer-readable storage medium and, e.g., a memory, on which the program is executed by the processor.

[0036] Within the framework of the present invention, computer program elements may be embodied in hardware and / or software (including firmware, resident software, microcode, etc.). Within the framework of the present invention, computer program elements may take the form of, e.g., computer-usable, e.g., computer-readable program instructions, "code," embodied in a computer-readable data storage medium, or a "computer program" embodied in such a data storage medium for use on or in connection with an instruction execution system. Such a system may be a computer, which may be, e.g., a data processing device comprising a digital processor (central processing unit or CPU) for executing the computer program elements and, optionally, volatile memory (e.g., random access memory or RAM) for storing data used in and / or generated by the execution of the computer program elements. Within the framework of the present invention, computer-usable, e.g., computer-readable data storage medium, may be any data storage medium capable of storing, communicating, propagating, or transmitting a program containing the program for use on or in connection with an instruction execution system, apparatus, or device. The computer-usable, e.g., computer-readable, data storage medium may be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a propagation medium, such as the Internet, but is not limited thereto. The computer-usable, e.g., computer-readable, data storage medium may be, for example, paper or other suitable medium on which a program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other suitable medium, and then compiled, interpreted, or otherwise processed in an appropriate manner. The data storage medium is preferably a non-volatile data storage medium. The computer program product and any software and / or hardware described herein constitute, in exemplary embodiments, various means for performing the functions of the present invention.The computer and / or data processing device may include, for example, a guide information device comprising means for outputting guide information. The guide information may be output, for example, optically by optical display means (e.g., a monitor and / or a lamp), acoustically by audio display means (e.g., a speaker and / or a digital audio output device), and / or tactilely by tactile display means (e.g., a vibrating element or a vibrating element integrated into a musical instrument). In this specification, a computer refers to, for example, a technical computer including technical, e.g., tangible parts, e.g., mechanical and / or electronic parts. A device described herein as a "computer" is a technical, e.g., tangible device.

[0037] For example, the expression "obtaining data" encompasses scenarios in which data are determined by a computer-implemented method or program (within the framework of a computer-implemented method). For example, "determining data" encompasses measuring physical quantities and converting measurements into data, e.g., digital data, and / or calculating (and, e.g., outputting) data by a computer, e.g., within the framework of a method according to the present invention. The "determining" step described herein may, e.g., comprise or consist of generating a command for making the decision described herein. For example, this step may comprise or consist of specifying a command to a computer, e.g., a remote computer in a cloud, e.g., a remote server, to make the decision. Alternatively, or additionally, the "determining" step described herein may, e.g., comprise or consist of receiving data resulting from the decision described herein. For example, receiving result data from a remote computer that caused the decision to be made. The expression "obtaining data" also encompasses scenarios in which data is received or obtained, e.g., by input, e.g., by a computer-implemented method or program, e.g., from another program, a previous method step, or a data storage medium, e.g., for further processing by the computer-implemented method or program. The generation of acquired data may be, but need not be, part of a method according to the present invention. Thus, the expression "acquiring data" may mean, for example, waiting to receive data and / or receiving data. Received data may be entered, for example, via an interface. The expression "acquiring data" may also mean that a computer-implemented method or program performs steps to (actively) receive or acquire data from, for example, a data source such as a data storage medium (e.g., ROM, RAM, database, hard drive, etc.) or via an interface (e.g., from another computer or a network).The data acquired by the disclosed method or device may be acquired from a database located on a data storage device operatively connected to the computer for data transfer between the database and the computer, respectively. The computer acquires the data to use as input for the data determination step. The determined data can be output again to the same or another database for storage for later use. The database or the database used to implement the disclosed method can be located on a network data storage device or network server (e.g., a cloud data storage device or cloud server) or on a local data storage device (e.g., a mass storage device operatively connected to at least one computer implementing the disclosed method). The data can be made "usable" by performing an additional step before the acquisition step. According to this additional step, the data is generated to be acquired. The data is, for example, detected or acquired (e.g., by an analytical device). Alternatively or additionally, according to the additional step, the data is input, for example, via an interface. The generated data can be, for example, input (e.g., input to a computer). According to the additional step (preceding the acquisition step), the data can also be provided by performing an additional step of storing the data on a data storage medium (e.g., ROM, RAM, CD, and / or hard drive, etc.), thereby making it usable within the framework of the method or program according to the present invention. Thus, the step of "acquiring data" also includes instructing a device to acquire and / or provide the data to be acquired. In particular, the acquiring step does not include an invasive step that results in substantial physical interference with the body, requires specialized medical expertise to perform, or involves substantial health risks even when performed with the necessary professional care and expertise. In particular, the acquiring step of data, e.g., determining data, does not include a surgical step, and in particular does not include a step of treating the human or animal body using surgery or therapy.To distinguish between the different data used in the method, the data will be referred to (i.e., referred to) as "XY data" or the like, defined based on the information they depict, and thereafter preferably referred to as "XY information" or the like.

[0038] The markers have the ability to be detected by a marker detection device (e.g., a camera, an ultrasound receiver, or an analysis device such as a CT or MRI device) and their spatial location (i.e., spatial position and / or arrangement) can be ascertained. The detection device is, for example, part of a navigation system. The markers may be active markers. Active markers can emit electromagnetic radiation and / or waves, for example in the infrared, visible, and / or ultraviolet spectral ranges. However, the markers can also be passive, for example, reflecting electromagnetic radiation in the infrared, visible, and / or ultraviolet spectral ranges or blocking X-ray radiation. For this purpose, the markers can be provided with a surface with corresponding reflection properties or made of metal to block X-ray radiation. The markers can also reflect and / or emit electromagnetic radiation and / or waves in the radio frequency range or ultrasonic wavelengths. The markers are preferably spherical and / or spheroidal and can therefore be referred to as marker spheres. However, the markers can also exhibit angular shapes, for example, cubes.

[0039] The marker device may be, for example, a reference star, a pointer, a single marker, or multiple (individual) markers, preferably in a predetermined spatial relationship. The marker device may consist of one, two, three, or more markers, where the two or more markers are in a predetermined spatial relationship. This predetermined spatial relationship is known to, for example, a navigation system and is stored, for example, in a computer of the navigation system.

[0040] In another embodiment, the marker device comprises an optical pattern, for example, on a two-dimensional surface. The optical pattern may comprise multiple geometric shapes, such as circles, rectangles, and / or triangles. The optical pattern can be identified in an image captured by a camera, and the position of the marker device relative to the camera can be determined from the size of the pattern in the image, the orientation of the pattern in the image, and the distortion of the pattern in the image. This allows the determination of relative positions in up to three rotational dimensions and up to three translational dimensions from a single two-dimensional image.

[0041] The location of a marker device can be determined, for example, by a medical navigation system. When a marker device is attached to an object, such as a bone or a medical instrument, the object's location can be determined from the location of the marker device and the relative position of the marker device to the object. Determining this relative position is also called registering the marker device and the object. It is also possible to track a marker device or object, which means determining the location of the marker device or object more than once over time.

[0042] Marker holder refers to a mounting device for attaching an individual marker to a device, a body part, and / or a holding element of a reference star, and can be fixedly mounted or, advantageously, removably mounted. The marker holder can be, for example, rod-shaped and / or cylindrical. A fixing device (e.g., a latch mechanism) for the marker device can be provided at the end of the marker holder facing the marker to aid in placement by press-fitting and / or snap-fitting the marker device into the marker holder.

[0043] The present invention can also be applied to a navigation system for computer-assisted surgery. The navigation system preferably includes the aforementioned computer for processing data provided by the computer-implemented method according to any one of the embodiments described herein. The navigation system preferably includes a detection device for detecting the positions of detection points representing principal and auxiliary points, generating detection signals, and transmitting the generated detection signals to a computer, allowing the computer to determine absolute principal and auxiliary point data based on the received detection signals. The detection points are points on the surface of an anatomical structure detected, for example, by a pointer. In this way, absolute point data can be provided to the computer. The navigation system preferably further includes a user interface for receiving calculation results from the computer (e.g., the positions of the principal plane, the auxiliary plane, and / or the reference plane). The user interface provides the received data as information to the user. Examples of the user interface include a display device such as a monitor and a speaker. The user interface can use any type of display signal (e.g., optical, audio, and / or vibration signals). One example of a display device is an augmented reality device (also called augmented reality glasses) that can be used as so-called "goggles" for navigation. A specific example of such augmented reality glasses is Google Glass (a registered trademark of Google, Inc.) Augmented reality devices can be used both to input information into a navigation system computer through user interaction and to display information output by the computer.

[0044] A navigation system, such as a surgical navigation system, is understood to mean a system comprising at least one marker device, a transmitter emitting electromagnetic waves and / or radiation and / or ultrasound, a receiver receiving electromagnetic waves and / or radiation and / or ultrasound, and an electronic data processing device connected to the receiver and / or transmitter, the data processing device (e.g. a computer) comprising, for example, a processor (CPU), a working memory, and preferably a display device for displaying instruction signals (e.g. an optical display device such as a monitor and / or an audio display device such as a speaker and / or a tactile display device such as a vibrator), and a permanent data memory, the data processing device being able to process navigation data transferred from the receiver and to output guidance information to the user, preferably via the display device. The navigation data can be stored in the permanent data memory and, for example, compared with data previously stored in said memory. [Brief explanation of the drawings]

[0045] The following background description and specific embodiments of the invention are provided with reference to the accompanying figures, without limiting the scope of the invention to the specific features disclosed in connection with the figures.

[0046] [Figure 1a] 1 illustrates a first embodiment of a medical tracking marker. [Figure 1b] 1b shows a perspective view of the tracking marker of FIG. 1a. [Figure 2a] 1 shows a second embodiment of a medical tracking marker. [Figure 2b] 2b shows a perspective view of the tracking marker of FIG. 2a. [Figure 3] The basic steps of the method according to the second aspect are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0047] 1a shows a first embodiment of a medical tracking marker in a first perspective. The top view on the left shows the arrangement of features 4, 5, and 6 disposed on a front surface 2 of a substantially planar substructure 1 of the tracking marker. All of the features 4 and 5, except for the central feature 6, are disposed within the same plane 3 defined by the front surface 2, i.e., the surface of the substructure 1.

[0048] As shown in the side view and cross section on the right side of Figure 1a, the central feature 6 is located in a recess 10 formed in the center of the substructure 1 and is therefore offset from the plane 3 containing all the remaining features 4, 5.

[0049] A square grid pattern 7 is defined by four features 4 at each corner of the substructure 1, and a further feature 4 located at the top centre of the substructure 1 not only defines the distance or grid spacing d, but also the "up" direction of the tracking marker.

[0050] The grid pattern has a total of nine nodes 8 where the grid lines of the grid pattern 7 intersect, and also defines four square grid fields 9 .

[0051] To establish a distinct optical appearance for a particular tracking marker, additional features 5 are placed at side nodes 8 between the corner nodes 8. Each feature 5 has a total of three possible placements, i.e., on one of three total grid lines that intersect at the respective side node 8. In the illustrated example, the features 5 are spaced from their associated side node 8 by a predetermined distance s that is equal for all features 5. A total of three features 5 can be placed in three different locations, providing 27 distinct tracking markers that the tracking system can distinguish from one another in the illustrated example.

[0052] FIG. 2a illustrates another example of a medical tracking marker that differs from the one illustrated in FIG. 1a. Rather than establishing a particular optical appearance by spacing some of the features 5 away from their associated nodes 8 in a particular orientation, the particular optical appearance is established by providing features 5 that have different sizes compared to the remaining features 4, 6. While all features 4, 5, and 6 are centered within their respective nodes 8, the features 5 at the lower left and upper right corners of the substructure 1 exhibit larger sizes than the remaining features 4, 6. In this regard, the features 5, among other features 4, define the dimensions and orientation of the grid pattern 7 (see FIG. 1a), while simultaneously providing a unique optical appearance for one of the tracking markers.

[0053] Furthermore, instead of placing one of the features 4 at the center of the associated node 8 to define the "up" direction, as described in connection with the example of Figure 1a, in the example of Figure 2a the "down" direction is defined by the absence of a feature at the bottom center of the substructure 1.

[0054] Figures 1b and 2b show perspective views of the examples shown in Figures 1a and 2a, respectively.

Claims

1. A medical tracking marker for location detection and tracking during a medical procedure, comprising: a substantially planar substructure (1) having a front surface (2) and defining a plane (3); and a plurality of features (4, 5, 6) disposed on the front surface (2) and optically distinct from the front surface (2), the plurality of features (4, 5, 6) comprising: a first set of features (4) defining dimensions and orientations of a square grid pattern (7) in a plane (3) with equally spaced grid spacing; a second set of features (5) arranged in a grid pattern (7) and defining a unique optical appearance for the tracking marker; and at least one feature (6) arranged in accordance with a grid pattern (7) and offset from the plane (3).

2. 2. The medical tracking marker of claim 1, wherein the grid pattern (7) is (n+2) ２ A medical tracking marker comprising eight nodes, particularly nine nodes.

3. 3. The medical tracking marker according to claim 1 or 2, The dimensions of the grid pattern (7) are defined by four features (4) that define each corner node (8) of the grid pattern (7); The orientation of the grid pattern (7) is defined by the presence or absence of a feature (4) at each side node (8) between two corner nodes (8); the grid spacing of the grid pattern (7) is defined by the distance (d) between the features (4) located at the corner nodes (8) and the features (4) located at the side nodes (8); and / or A medical tracking marker, wherein at least one feature (6) offset from the plane (3) is located at a center node (8) between at least two side nodes (8).

4. 4. A medical tracking marker according to claim 1, wherein the particular optical appearance is defined by the size of the features (4, 5, 6) arranged at the associated nodes (8) of the grid pattern (7), the size being different for each individual feature (4, 5, 6), the size being selected from a limited number of pre-defined sizes, and in particular all features (4, 5, 6) of the tracking marker being one of two pre-defined sizes.

5. 5. The medical tracking marker of claim 4, wherein the optical appearance is defined by the size of the features of the first feature set (4) and the size of the features of the second feature set (5).

6. 4. A medical tracking marker according to any one of claims 1 to 3, wherein the particular optical appearance is defined by the spatial position of the individual features (5) relative to the associated nodes (8) of the grid pattern (7), the spatial positions being selected from a limited number of predefined spatial positions, in particular when all features (4, 5, 6) of the tracking marker are the same size.

7. 7. The medical tracking marker of claim 6, wherein the predetermined spatial position is: a position on one grid line (7) adjacent to the node (8), and / or a location on one grid field (9) adjacent to the node (8); In particular, the predetermined spatial location of the medical tracking marker comprises a predetermined distance from an associated node (8).

8. A medical tracking marker according to any one of claims 1 to 7, wherein the features (4, 5, 6) are disc-shaped and configured to reflect incident light, in particular: exhibiting high optical contrast with the front surface (2) of the substructure (1); A medical tracking marker including a retroreflective coating.

9. A medical tracking marker according to any one of claims 1 to 8, wherein each of the plurality of features (4, 5, 6) comprises a light emitting element, in particular an LED.

10. A medical tracking marker according to any one of claims 1 to 9, wherein at least one feature (6) offset from the face (3) is arranged in a recess (10) or on a protrusion in the front face (2) of the substructure (1).

11. 11. A medical tracking marker set comprising a plurality of tracking markers according to any one of claims 1 to 10, wherein the tracking markers have different optical appearances defined by a second feature set (5), in particular by the first feature set (4) and the second feature set (5), which are unique to each tracking marker.

12. 11. A computer-implemented medical method for identifying and tracking the location of a medical tracking marker according to any one of claims 1 to 10, comprising: a) acquiring (S11) first feature set data describing the position of a first feature set (4) in the plane of an image acquired by an optical camera; b) determining grid data (S12) based on first feature set data describing the position of the grid pattern (7) in the plane of the image; c) obtaining (S13) second feature set data describing the position of the second feature set (5) in the plane of the image, particularly relative to the first feature set (4); d) determining identification data describing the identification of the tracking marker based on the second feature set data, in particular the first feature set data and the second feature set data (S14); e) acquiring (S15) out-of-plane data describing the position of at least one feature (6) offset from the plane (3), in particular with respect to the first set of features (4) and / or the second set of features (5); f) determining tracking data based on at least one of the first feature set data, the second feature set data, and the out-of-plane data, the first feature set data describing a spatial position of the identified tracking marker (S16).

13. 13. The method according to claim 12, comprising the use of a monocular camera, in particular a monochrome monocular camera, configured to optically detect and identify a plurality of features (4, 5, 6) from the front side (2) of the substructure (1).

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