Description

FIELD OF THE INVENTION

[0001] The present invention relates to a system for navigating surgical instruments in a patient and a method for navigating a surgical instrument in a patient. BACKGROUND OF THE INVENTION

[0002] In surgical navigation, the position of used instruments such as pointer tools, suction tubes or endoscopes is visualized in the 3-D image data of the patient (e.g. CT, MRI). Different tracking technologies are known for determining the spatial position of instruments and of the patient.

[0003] Optical tracking systems usually comprise a camera system of two or more cameras in order to determine the pose (3D position and orientation) of optical trackers. These trackers can be rigid bodies of two or more optical markers (e.g. retro-reflective spheres or active light emitting diodes), which are attached to the instrument used and to the patient. In neurosur- gery, one optical tracker is often rigidly fixed to a skull clamp, which is connected with the operating table and used to immobilize the head of the patient. Alternatively, the tracker can be fixed directly at the cranial bone with bone screws for instance.

[0004] As an alternative, electromagnetic tracking systems are known, which comprise a field generator and small sensor coils that can easily be integrated into surgical instruments. The field generator is positioned near the operating field using an articulated arm or can also be integrated into the operating table. The advantage of electromagnetic tracking is an easier handling in comparison to the optical tracking systems. [0005] Optical systems suffer from the line-of-sight problem and the navigation camera must be manually positioned and aligned toward the operating field. A disadvantage of electromagnetic tracking is the susceptibility to errors in case of ferromagnetic material in the measurement region. This leads to distortions of the electromagnetic field, which can result in inaccurate position data.

[0006] In navigated microscopic neurosurgery, operating microscopes can also be integrated by attaching a tracker to the microscope to allow the measurement of its spatial position relative to the patient. This enables the navigation of the focal point of the microscope as well as the overlay of navigation information or data from a pre-operative surgical planning in the microscopic camera image. Therefore, a calibration of the projective properties of the microscopic camera system must be performed. Due to the possible changes of zoom and focus settings of the microscope during the surgical procedure, the camera properties need to be recorded for all microscope settings. This time-consuming calibration is typically done once during system installation and requires a repeatable tracker attachment at the microscope.

[0007] Due to the materials used and the built-in electric motors in particular, the risk is given that microscopes disturb the electromagnetic measurement field. Therefore, an accurate tracking of operating microscope with electromagnetic measurement systems is not a feasible task. Thus, there is a need for a system, which is easy and quick to handle, but provides reliable data about the exact position of used instruments. [0008] Document WO 2001/034050 A2 (US 6,235,038 Bl) discloses a system for utilizing and registering at least two surgical navigation systems during stereotactic surgery. The disclosed system comprises a first surgical navigation system defining a first patient space, a second surgical navigation system defining a second patient space, and a translation device to register the coordinates of the first patient space to the coordinates of the second patient space. The translation device comprises a rigid body, at least one component for a first navigation system placed in or on the rigid body, and at least one component for a second navigation system placed in or on the rigid body, in known relation to the at least one component for the first navigation system. The translation device is positioned in a working volume of each of the at least two navigation systems. The disclosed translation device as a rigid body man- ages only the registration between the coordinate systems associated with the tracking devices (patient spaces), a further linking to optical tracked microscopes or other instruments is not described. Furthermore, the translation device is inseparable, whereby the components of the first and second navigation system of the translation device cannot be separated and used independently.

[0009] Document US 2012/0165657 Al describes a hybrid tracking system utilizing at least one combined light emitting diode (LED) and magnetoresistance sensor. The hybrid tracking system includes optical tracking technology and electromagnetic (EM) tracking technology with at least one combined LED and magnetoresistance reference sensor attached to a fixed object, at least one combined LED and magnetoresistance sensor attached to an object being tracked, and a processor coupled to the at least one combined LED and magnetoresistance reference sensor and the at least one combined LED and magnetoresistance sensor for processing signals from the at least one combined LED and magnetoresistance reference sensor and the at least one combined LED and magnetoresistance sensor. The characteristic of the described combined sensor lies in the integration of the LED and magnetoresistance sensor into one single unchangeable package. As a result of this integration, the components of the optical and electromagnetic tracking cannot be separated and used independently.

[0010] Documents US 20110054293 Al and US 8494614 B2 discloses a navigation system or combination of navigation systems, which can be used to provide two or more navigation modalities to navigate a single instrument in a volume. For example, both an Electromagnetic (EM) and Electropotential (EP) navigation system can be used to navigate an instrument within the volume. Image data can also be illustrated relative to a tracked position of the instrument in the volume for navigation. This document describes only the registration of coordinate systems, which are associated with two or more tracking systems, which tracks one instrument simultaneously. The determined simultaneous tracking data are used to compute a registration to translate positions from one tracking system coordinate system to another.

[0011] US 7,702,379 B2 discloses a system and method for hybrid tracking in surgical navigation. The system according to the disclosure comprises the use of a plurality of tracking technologies in a medical procedure where a reconciler determines an active tracking technol- ogy. The reconciler determines the active tracking technology during the medical procedure. A switch may then activate one or more tracking technologies. The determination of which technology or technologies are to be activated may be based, for example, on metrics measured by each of the technologies, such as an accuracy measurement. In addition, a display may present representations based on at least data obtained by one or more of the tracking technologies. The switch may employ weighted switching to gradually switch the display of a first representation corresponding to a first tracking technology to the display of a second representation corresponding to a second tracking technology, where the first technology is deac- tivated and the second technology is activated. This document describes only a method for selecting the active tracking system which is used for navigation from a plurality of available tracking systems based on metrics which are associated with each tracking system. The disclosed method does not combine the tracking data of different tracking systems. [0012] The International application WO 2000039576 Al discloses a system that tracks the 3-dimensional position and orientation of one or more bodies in a volume by a light based, as well as at least one non-light based mensuration sub-system. Such a system overcomes the limitation of light based mensuration systems to the necessity of the bodies to be in constant line-of-sight of its light based position sensors. According to the disclosure, the system pos- sesses most of the accuracy and stability of its light based position measurement sub-system, but can also work without direct line of sight either for short periods of time or within certain parts of the volume. The system incorporates other sensors, such as inertial or magnetic sensors, which are frequently recalibrated against the light based sub-system while the bodies are visible by the light based sub-system. The disclosure is limited to a system that is only a tool equipped with localizers for two tracking systems (optical and EM).

[0013] In US 5831260 A hybrid motion tracker is disclosed, which captures the motion of a person. Magnetic field sensors and optical sources are placed on a person, each located on different limbs. A fixed transmitter emits electromagnetic energy and infrared light is trans- mitted from the optical light sources to the fixed optical sensors. The magnetic field sensors sense the magnetic field and a computer calculates each sensor's position and orientation relative to the fixed transmitter. The optical system's Position Sensing Detectors measure the transmitted infrared light and the computer calculates the position and orientation of each optical light source. The position and orientation of each sensor is used to reconstruct the per- son's motion in real time, which is sent to a host computer. The computer utilizes the optical system which is more precise than the magnetic field system to compensate for the magnetic field system and thereby achieve higher accuracies. The system is a hybrid system using both magnetic fields and infrared light. By combining the two different technologies into one sys- tern, accuracy and dynamic performance are enhanced over results obtained through sole use of a magnetically based system. The system refers only to a hybrid tracker for motion tracking of human persons. There is neither an application for surgical navigation with microscopy nor the registration to preoperative image data disclosed or proposed.

[0014] In summary, the existing systems and methods from the state of the art combine at least two different tracking systems in order to improve the availability or accuracy of the tracking data for single instruments. BRIEF SUMMARY OF THE INVENTION

[0015] The present invention provides a system for navigating surgical instruments relative to a patient, comprising the following components:

- a first tracking system for measuring the position of at least one of a first type of tracker;

- a second tracking system for measuring the position of at least one of a second type of tracker;

- at least one patient tracker belonging to the first type of tracker measuring the position of the patient;

- a surgical instrument comprising a tracker belonging to the second type of tracker and at least one geometric primitive of interest; and

- a connector for rigidly, but removably connecting the at least one of a first type of tracker with at least one of a second type of tracker for registration and/or transformation of the coordinates of the surgical instrument to the coordinates of the image data of the patient and vice versa wherein the connector allows that the separate trackers can be removably connected by the user during preparation of system and even during surgery.

[0016] The first tracking system can be an electromagnetic tracking system and the second tracking system can be an optical tracking system.

[0017] The system can further comprise a hybrid navigation unit comprising at least a computer system for providing simultaneous support for the first and second tracking system. [0018] It is intended that the at least one of a first type of tracker or the at least one of a second type of tracker may be connected to the hybrid navigation unit.

[0019] The connector of a system of the present invention can be a hybrid tracker compris- ing stored information of pre-operatively known transformation between the trackers.

[0020] It is further envisaged that the at least one patient tracker which belongs to the at least one of a first type of tracker and at least one patient tracker which belongs to the at least one of a second type of tracker can be rigidly, but removably fixed to each other via the con- nector at the beginning or during surgery. The poses of the trackers relative to each other may be known from construction data.

[0021] It is further envisaged that the at least one patient tracker which belongs to the at least one of a first type of tracker and at least one patient tracker which belongs to the at least one of a second type of tracker can be rigidly fixed to the patient.

[0022] The connector may further consist of a solid, hard tissue of the patient for connecting the two or more patient trackers of both types of trackers, being rigidly fixed relative to each other and to the operating region of interest.

[0023] The surgical instrument of a system of the present invention can be an electrically powered and its geometric primitive of interest is the tip of the surgical instrument.

[0024] The surgical instrument can also be an operating microscope and the geometric prim- itives of interest are at least one of the image rectangle in the focal plane, the focus point or the camera origin of the operating microscope.

[0025] The system of the present invention may further comprise a monitor for displaying the real microscopic image superimposed with a virtual microscopic image or an image injec- tion module in the microscope for displaying a virtual microscopic image for visual perception of the surgeon when looking through the oculars. [0026] Another object of the present invention is a method for navigating a surgical instrument relative to a patient, the method comprising the steps of

connecting at least one of a first type of tracker with at least one of a second type of tracker by using a connector;

- measuring the position of at least one of a first type of tracker with a first tracking system;

- measuring the position of a surgical instrument by using at least one of a second type of tracker with a second tracking system;

- measuring the position of the patient with at least one patient tracker belonging to the at least one of a first type of tracker;

- registering and/or transforming the coordinates of the surgical instrument and its geometric primitive of interest to the coordinates of the image data of the patient and vice versa. [0027] The method may further comprise the step of using an electromagnetic tracking system as first tracking system and an optical tracking system as second tracking system.

[0028] It is further intended that the method may comprise the step of using a device comprising stored information of pre-operatively known transformation between the trackers for registering and/or transforming the coordinates of a surgical instrument and its geometric primitive of interest to the coordinates of the image data of the patient and vice versa.

[0029] Furthermore it is intended that the step of connecting at least one of a first type of tracker with at least one of a second type of tracker by using a connector may be conducted pre- or intra-operatively by the user so that the trackers are then rigidly fixed relative to each other in a known or approximately known spatial relation. Furthermore the method may comprise the step of verifying and/or optimizing a previously known or approximately known transformation between these trackers. The trackers may be rigidly, but removably fixed to the connector.

[0030] It is further intended that the step of connecting at least one of a first type of tracker with at least one of a second type of tracker by using a connector is conducted with two patient trackers, which are then rigidly, but removably fixed relative to each other in a known or approximately known spatial relation. Furthermore the method may comprise the step of verifying and/or optimizing a previously known or approximately known transformation between these patient trackers. [0031] Furthermore the method may comprise the step of connecting intra-operatively two or more patient trackers of both types of trackers, which are rigidly fixed relative to each other, and the step of intra-operatively determining the transformation between these trackers.

[0032] The transformation between the patient trackers may be determined, optimized or verified by performing two patient image registration procedures, one for the patient trackers of the at least one of a first type of tracker und one for the patient trackers of the at least one of a second type of tracker.

[0033] Alternatively or in addition the transformation between the patient trackers may be determined, optimized or verified by performing one patient image registration procedures using a navigated instrument equipped with trackers of both types of tracker.

[0034] It is further intended that the transformation between the trackers or patient trackers may be determined, optimized or verified by sampling features whose spatial positions are known relative to a tracker or patient tracker of one type of tracker using a navigated instrument equipped with a tracker of the other type of tracker. These features can include touch points, plane surfaces or faces of geometric primitives which may be a part of a rigid body of the patient tracker of at least one type of tracker. [0035] An electrically powered tool may be used as surgical instrument or an operating microscope can be as surgical instrument.

[0036] The coordinates of the image data of the patient may be transformed into the reference coordinate system of the microscopic camera enabling the generation of a virtual micro- scopic image.

[0037] Further, the virtual microscopic image can be superimposed on the real microscopic image on a monitor of the navigation system. [0038] The virtual microscopic image may further be injected into the microscope beam path for visual perception of the surgeon when looking through oculars. [0039] A further object of the present invention is the use of a system for navigating surgical instruments relative to a patient, comprising a first tracking system for measuring the position of at least one of a first type of tracker, a second tracking system for measuring the position of at least one of a second type of tracker, at least one patient tracker belonging to the first type of tracker measuring the position of the patient, a surgical instrument with comprising a track- er belonging to the second type of tracker; and a connector for rigidly connecting the at least one of a first type of tracker with at least one of a second type of tracker for registration and/or transformation of the coordinates of the surgical instrument to coordinates of the image data of the patient and vice versa in surgical interventions BRIEF DESCRIPTION OF THE FIGURES

[0040] The present invention will be described by figures and examples. It is obvious for a person ordinary skilled in the art that the scope of the invention is not limited to the disclosed embodiments. It shows:

[0041] Figure 1 Hybrid navigation system for microscopic neurosurgery using a hybrid tracker

[0042] Figure 2 Reference coordinate systems of the first embodiment

[0043] Figure 3 Second embodiment of the invention using an optical and an electromagnetic patient tracker for patient tracking

[0044] Figure 4 Reference coordinate systems of the second embodiment when using a direct registration of the patient trackers after the fixation to the patient

DETAILLED DESCRIPTION OF THE INVENTION

[0045] The objective of the invention is the integration of microscopic imaging into an electromagnetic navigation system. The advantages of the electromagnetic tracking with the simplified handling of instruments, the unrestricted visibility and easier mounting of the patient tracker are retained and expanded to include a uncomplicated integration of microscopy. [0046] The present invention provides a hybrid navigation system that combines two or more tracking systems and may comprise the following functional groups:

• Hybrid navigation unit with simultaneous support for two or more tracking systems

• First tracking system for measuring the pose of trackers of a first tracker type

• Second tracking system for measuring the pose of trackers of a second tracker type

• Tracker of the first tracker type for spatial position measurement of the patient

• Rigid assembly of two or more trackers of either the first or the second tracker type using a connector

• Navigated pointer instrument with an attached or integrated tracker of the first tracker type for patient image registration

• Surgical instrument with attached or integrated tracker of the second tracker type with a geometric primitive of interest (e.g. operating microscope or active instruments like drills or shavers)

[0047] The basic part of the system is the hybrid navigation unit, which may comprise a computer system and electronic parts of the two tracking systems. Other components of the tracking systems can be hooked up to the navigation unit in order to establish a communication for reporting measurement results or for direct connecting of tracking components to integrated parts of the tracking systems. In case of using an optical tracking system, a navigation camera can be connected. In case of using an electromagnetic tracking system, the field generator and the wires of the sensor coils may be connected to the hybrid navigation unit.

[0048] The computer system of the hybrid navigation unit processes the position and orientation data of the tracking systems and calculates 2-D and 3-D visualisations of the current position of used navigated instruments in the 3-D image data of the patient. These image data are imported from CD-ROM, USB storage device or PACS before surgery.

[0049] The further system components and their functions within the hybrid navigation systems are explained in the following descriptions of possible embodiments of this invention. It is obvious for a person ordinary skilled in the art that the scope of the invention is not limited to the disclosed embodiments.

[0050] This first embodiment of the invention is a hybrid navigation system, which combines electromagnetic pointer navigation with optical tracking of an operating microscope using a hybrid tracker.

[0051] In this embodiment, the first tracking system is an electromagnetic tracking system which comprises of a field generator which is a set of coils which generate an electromagnetic field in the operating area. The pose measurement of the electromagnetic tracking system is performed with the help of small sensor coils which are incorporated into electromagnetic trackers and the navigated electromagnetic instruments (e.g. pointer instruments, suctions). The electromagnetic tracking system measures the spatial position at least of the patient and of one instrument (e.g. a pointer instrument) which can be used for performing the registration procedure of the image data of the patient. The position of the patient is measured using a patient tracker which is rigidly attached to the operating field at the patient. [0052] To enable the calculation of the position of instruments in the 3-D image data, a registration of the 3-D image data must be performed at the beginning of the navigated surgery. In this case, a transformation between the reference coordinate system of the 3-D image data and the reference coordinate system of the patient tracker is determined. In the literature several methods for registration of the patient image data are known like the landmark registration and the surface registration (Eggers et al, 2006, Int. J. Oral and Max. Surg., 35(12), 1081- 1095; Maintz and Viergever, 1998, Med. Int. Ana. 2(1), 1-36.). Here, anatomical or artificial landmarks or surfaces marked in or derived from 3-D image data of the patient and are touched or captured with the navigated instruments (e.g. pointer instruments) at the patient.

[0053] The second tracking system in this embodiment is an optical tracking system, which measures the pose of optical trackers which are attached at rigid instruments. Optical trackers are rigid bodies equipped with usually three or more optical markers in a known spatial configuration which allows the measurement of the pose the tracker with six degrees of freedom. For measuring the pose of the microscope during surgery, the microscope is also equipped with an optical tracker which is rigidly and possibly reproducibly attached to the microscope. [0054] The rigid, but removable assembly of two trackers of the two tracking systems may be realized in form of a hybrid tracker comprising a connector to removably connect a rigid body with at least three attached markers for optical tracking and sensor coils for electromagnetic tracking. [0055] The hybrid tracker is used to provide a link between the reference coordinate systems associated with the electromagnetic and optical tracking system, respectively. The spatial relationship of the optical and the electromagnetic trackers and their defined reference coordinate systems has to be known. A possible embodiment of implementation may comprise the onetime calibration of the hybrid trackers during the manufacturing process. The transformation between the reference coordinate systems of the optical and electromagnetic tracker can be stored on a memory module of the electromagnetic tracker. During the intraoperative use, the hybrid navigation unit can read out and utilize the stored transformation data.

[0056] For the management and calculation of the spatial relationships between the various system components, reference coordinate systems are associated with these components. The following reference coordinate systems are defined:

• img for the image data of the patient

• cam for the navigation camera

• fg for the field generator

• pt_em for the electromagnetic patient tracker · hybrid_opt for the optical tracker of the hybrid tracker

• hybrid_em for the electromagnetic tracker of the hybrid tracker

• tool_opt for the tracker of the optically tracked intrument

• tool_em for the electromagnetic tracked instrument

[0057] A transformation matrix for converting coordinates between one reference coordinate system refl and a second reference coordinate system ref2 is suitable to describe the relative pose of two reference coordinate systems. This transformation matrix ^rejr2 T _re fi can be used in the mapping rule = ^ref2 T _re fi * ^ , which describes the computation of the homogeneous coordinates ^re ^ in the reference coordinate system ref2 based on homogeneous coordinates fl^ _{m me re} f _erence coordinate system re/2.

[0058] The relevant transformations between the reference coordinate systems of the first embodiment are:

[0059] ^cam Ttooi opt: Rigid transformation between the reference coordinate system of the optical tracking system and the reference coordinate system of the optical tracker of the microscope. This transformation is continuously reported by the optical tracking system.

[0060] ^cam Thybrid opt: Rigid transformation between the reference coordinate system of the optical tracking system and the reference coordinate system of the optical tracker of the hybrid tracker. This transformation is continuously reported by the optical tracking system.

[0061] ^vldeo Ttooi opt: Rigid transformation between the reference coordinate system of the optical tracker of the microscope and the reference coordinate system origin of the camera of the microscope according to the pin-hole camera model. This transformation is determined during a microscope calibration procedure for different microscope zoom und focus settings.

[0062] ^hybnd - ^em Thybrid opt: Rigid transformation between the reference coordinate system of the electromagnetic tracker of the hybrid tracker and the reference coordinate system of the optical tracker of the hybrid tracker. This transformation is usually determined during manufacturing process and can be stored on a memory module in the electromagnetic tracker. [0063] ^fg Thybrid _em : Rigid transformation between the reference coordinate system of the electromagnetic tracking system and the reference coordinate system of the electromagnetic tracker of the hybrid tracker. This transformation is continuously reported by the electromagnetic tracking system.

[0064] ^fg Ttooi _em : Rigid transformation between the reference coordinate system of the electromagnetic tracking system and the reference coordinate system of the electromagnetic tracker of the pointer instrument. This transformation is continuously reported by the electromagnetic tracking system. [0065] ^fg T _p t _em : Rigid transformation between the reference coordinate system of the electromagnetic tracking system and the reference coordinate system of the electromagnetic patient tracker. This transformation is continuously reported by the electromagnetic tracking system. [0066] ^pt - ^em Ti _mg : Rigid transformation between the reference coordinate system of the electromagnetic patient tracker and the reference coordinate system of the image data of the patient. This transformation is determined during the patient image registration procedure at the beginning of the navigated surgery.

[0067] Using the presented transformations based on the defined reference coordinate sys- terns, a transformation chain can be formed in order to easily transfer coordinates of a preoperative planning within the image data of the patient ^img p into the microscope camera reference coordinate system "video":

[0068] ^Vlde °p = ^Vlde °TtooLopt * * ^Cam T _h ybnd_opt * * brid emr yl * fgy \-l * fgy * pt em . img„

l ybrid opt ybrid em pt em img * [0069] If the intrinsic camera properties (e.g. focal length f, image center C _x , C _y , aspect ratio Sx) of the microscope are also known from a previous calibration, the coordinates in the "video" reference coordinate system can be projected onto the image plane of the microscope according to the pin-hole camera model and used to generate virtual microscopic images containing preoperative planning data. An augmented reality visualization can then be realized by superimposing the real with the virtual microscopic image data. One way of implementation is the monitor-based augmented reality, in which the real image and the virtual image are superimposed on the screen. Alternatively, the option of injecting external image data into the optical channel of some microscopes allows a display of the virtual microscope image data directly in the field of view of the surgeon. [0070] Furthermore, coordinates given in the reference coordinate system of the microscope tracker "tool opt" (e.g. the position of the focal point of the microscope or the position of the microscope camera origin) have to be transformed into the reference coordinate system of the image data of the patient in order to visualize this position in the 3D or slice views of the image data. The computation of a coordinate in the reference coordinate system of the image data ^img p can also be done using the defined transformations: [0071 ] ^lmg _P = * ^fg Thybnd_em * ^hybnd - ^em Thybnd_opt * * ^Cam Ttoo _L opt * ^t00L0pt

[0072] The geometric primitive of interest of the microscope can be the focal point of the microscope, the position of the microscope camera origin according to the pin-hole camera model or the image rectangle in the focal plane of the microscope. For surgical instruments like drills or shavers, the position and shape of the instrument tip is the geometric primitive of interest. The shape of the geometric primitive of interest is usually modelled as a point, a sphere, a cylinder or a capsule.

[0073] The second embodiment of the invention is a hybrid navigation system, which com- bines electromagnetic pointer navigation with optical tracking of an operating microscope using an electromagnetic patient tracker and an optical patient tracker simultaneously.

[0074] The second embodiment also uses electromagnetic pointer tracking with an integration of an optical tracked operating microscope. The following system components are similar to the first embodiment: the hybrid navigation unit, the electromagnetic tracking system with the field generator, the optical tracking system with the navigation camera, the electromagnetic tracked pointer instrument for patient image registration and the operating microscope with an optical tracker.

[0075] The difference in comparison to the first embodiment is the usage of two patient trackers, where both are tracked with the corresponding tracking system, instead of using one pa- tient tracker and a hybrid tracker. This means that the implementation of the rigid assembly of tracker elements of the first and the second tracking system is realized by a rigid attachment of the two patients tracker relative to the operating field. In analogy to the hybrid tracker, this results in a temporary rigid connection between one tracker of the electromagnetic and one tracker of the optical tracking system. [0076] The spatial relationship between these two patient trackers is initially not know after the tracker fixation at the patient. Several methods are conceivable to determine the rigid transformation between the reference coordinate systems associated with these two trackers:

• pt_em for the electromagnetic patient tracker

• pt_opt for the optical patient tracker [0077] One option is to perform two patient image registrations, one using electromagnetic and one using optical tracking. As a result, the transformations between the reference coordinate system of the image data of the patient and the reference coordinate system of the optical tracker ^pt - ^opt Ti _mg and of the electromagnetic tracker ^pt - ^em Ti _mg are known. This allows the computation of the rigid transform between the reference coordinate systems of the two patient trackers:

[0078] ^pt - ^em Tpt_o _P t = ^pt - ^em T _img *

[0079] A second option is the use of a pointer tool equipped with an optical as well as an electromagnetic tracker. That allows the computation of the two patient image registrations for the optical and the electromagnetic patient tracker in one stage of registration procedure. The computation of the transformation ^pt - ^em T _p t_ ₀ pt is performed as shown in the description of the first option.

[0080] A third option is to perform only one patient image registration, for example using the electromagnetic pointer instrument in order to determine the transformation between the image data of the patient and the electromagnetic patient tracker. Then, given features of the other (optical) patient tracker (e.g. 3D points or planes) are sampled with the electromagnetic pointer and thus recorded in the reference coordinate system of the electromagnetic patients tracker. By knowing the location of these features in the reference coordinate system of the optical tracker, the rigid transformation between the reference coordinate systems of the optical and electromagnetic patient tracker ^pt - ^em T _p t_ ₀ pt can be calculated.

[0081] In addition to the described transformations of the first embodiment, in this second embodiment the following transformations are relevant:

[0082] ^cam Tpt opt: Rigid transformation between the reference coordinate system of the optical tracking system and the reference coordinate system of the optical patient tracker. This transformation is continuously reported by the optical tracking system.

[0083] ^{pt em} Tpt opt: Rigid transformation between the reference coordinate system of the electromagnetic patient tracker and the reference coordinate system of the optical patient tracker. This transformation can be determined at the beginning of the surgery for example using one of the three options which are described above. [0084] With the transformation chain based on the defined reference coordinate systems, coordinates of a preoperative planning given in the reference coordinate system of the image data of the patient ^img p can easily transformed into the reference coordinate system of microscope camera "video": [0085] ^vldeo p = ^vldeo TtooLopt * ( ^cam TtooLo _P t)- ¹ * ^cam T _P t_o _P t * * ^pt - ^em T _img * ^img p

[0086] If the intrinsic camera properties (e.g. focal length f, image center C _x , C _y , aspect ratio Sx) of the microscope are also known from a previous calibration, the coordinates in the "video" reference coordinate system can be projected onto the image plane of the microscope according to the pin-hole camera model and used to generate virtual microscopic images con- taining preoperative planning data. An augmented reality visualization can then be realized by superimposing the real with the virtual microscopic image data.

[0087] Furthermore, coordinates given in the reference coordinate system of the microscope tracker "tool opt" (e.g. the position of the focal point or the position of the microscope camera origin) have be transformed into the reference coordinate system of the image data of the patient in order to visualize this position in the 3D or slice views of the image data. The computation of a coordinate in the reference coordinate system of the image data ^img p can also be done using the defined transformations:

ΓΠΠΟ ΟΙ im ~ spt emT \-l * pt em * /camT vl * camT * videcrr -l * video„

LUUOOJ T> ^{- "} l img I pt opt I pt opt 1 tool opt 1 tool opt) P

[0089] In addition, the computation and visualisation of navigation information may be bene- ficial, for example the visualisation of the expected position of the tip of the electromagnetic pointer instrument in the microscopic camera image in order to allow the surgeon to estimate the overlay error of navigation or planning data in the microscopic camera image:

[0090] ^Vlde °p = ^Vlde °TtooLopt * ( ^Cam TtooLopt)- ^{l !i: Cam} Tpt_opt * * ^fg Ttoo _L em * (0

0 0 1) ^T [0091] As a simplification of this system concept, a use of a hybrid patient tracker is also conceivable. In this case, the hybrid tracker, a fixed spatial arrangement of an electromagnetic tracker and an optical tracker, is rigidly attached directly to the patient. Thereby, the positional relationship between the optical and electromagnetic trackers ^pt - ^em T _p t_ ₀ pt is known. [0092] The invention is new, because the combination of two or more tracking systems to combine electromagnetic navigation with microscopy has not been disclosed in the relevant state of the art. By using a rigid assembly of trackers of the two or more tracking systems, a registration of these tracking systems is realized in order to enable the tracking of the microscope with a second tracking device and combine the tracking information with the electromagnetic navigation data. Different intra-operative realisations of the rigid assembly of trackers are disclosed in order to enable the transformation of coordinates between the reference coordinate systems of the microscope, the image data and electromagnetic tracked instruments. This allows for the first time a feasible integration of microscopy to electromagnetic navigation.

[0093] The major advantage of the invention is the integration of electromagnetic navigation into surgical microscopes. The advantages of the realisation with a so-called hybrid tracker in form of a rigid but removable connection of at least two trackers of at least two types of trackers are:

• Easy placement of the hybrid tracker in the operating environment within the measurement fields of the used tracking systems. There is no need for a special fixation relative to the patient or a tracking device.

• Removably connected tracker components may also be used separately for pose measurement of the patient or of surgical instruments if they are not connected.

• There are no additional requirements to the fixation of the electromagnetic patient tracker at the patient. In particular, the electromagnetic tracker can be tucked under the sterile covering of the patient.

• In addition to the registration of the patient image registration, no further intraoperative calibration is needed.

• The patient may be located outside the measurement field of the second tracking system. Only the hybrid tracker must be positioned measurement fields of the used tracking systems. In case of an optical tracking system, this can significantly reduce line-of-sight problems during surgery. [0094] The advantages of the second embodiment disclosed in the instant disclosure is an increased system accuracy, because less trackers are used so that the influence of the inaccuracies of the pose measurement might be lower.

DETAILLED DESCRIPTION OF THE FIGURES [0095] Figure 1 discloses a first embodiment of the hybrid navigation system, which combines electromagnetic pointer navigation with optical tracking of an operating microscope 1 using a hybrid tracker 15. The figure 1 shows the system components and their tracking connections. The field generator 50 of the electromagnetic is attached to the operating table 90 and is connected to the hybrid navigation unit 20. Additionally, the electromagnetic trackers and electromagnetic tracked instruments as well as the navigation camera 10 as a part of the optical tracking system are connected to the hybrid navigation unit 20. The patient tracker is rigidly fixed to the operating field of the patient 100. In neurosurgery, the patient tracker is possibly attached to the skull bone of the patient 100. The electromagnetic tracked pointer instrument 31 is used for patient registration of the 3D image data of the patient 100 and for usual pointer navigation. The hybrid tracker 15 must be positioned within the measurement field of the electromagnetic and the optical tracking system so that the pose of the optical and electromagnetic tracker of the hybrid tracker 15 are simultaneously measured by the two tracking systems. In addition, the navigation camera 10 tracks the pose of the microscope with the help of the microscope tracker 5, which is rigidly attached to the operating microscope 1. The visual position measurement is illustrated by the lines of sight between the navigation camera 10 and the markers of the optical trackers.

[0096] Figure 2 illustrates the reference coordinate systems associated with the system components of the first embodiment. Additionally, relevant transformations between the reference coordinate systems are visualised using dashed arrows. The visualised transformations are either measured with one of the tracking systems or determined during a registration or calibration process. The measurement results of the electromagnetic tracking system are continuously made available in form of the transformations ^fg Th _y brid em, ^fg T _t0 oi em and ^fg T _{pt em} . The measurement results of the optical tracking system are continuously made available in form of the transformations ^cam Th _y brid opt and ^cam T _t0 oi _ _op t. The transformation ^vldeo Ttooi opt is usually de- termined in a calibration procedure during system installation and is depending on the current zoom und focus settings of the microscope. The transformation ^hybrid - ^em Th _y brid opt describes the spatial relationship between the electromagnetic and optical trackers of the hybrid tracker 15. The transformation ^pt - ^em Ti _mg stores the result of the image data registration which is determined at the beginning of the navigated surgery.

[0097] Figure 3 discloses a second embodiment of the hybrid navigation system which com- bines electromagnetic pointer navigation with optical tracking of an operating microscope 1 using an optical and an electromagnetic patient tracker 40. These both patient trackers 40 are rigidly attached to the operating field of the patient 100 at the beginning of the surgery. As the trackers are attached rigidly to the patient 100, they result in a rigid assembly of two trackers of the two different tracking systems. The spatial relationship between the two patient trackers 40 must be determined intra-operatively. For that, the registrations of the trackers to a common reference coordinate system (e.g. of the patient 3D image data) can be used. Alternatively the reference coordinate systems of the two trackers are registered directly by sampling feature elements, which are known in the reference coordinate system of one tracker with a tracked instrument associated with the other tracking system. [0098] The illustrated system components hybrid navigation unit 20, the navigation camera 10, the field generator 50, the electromagnetic tracked pointer instrument 31 and the operating microscope 1 with its optical tracker are similar to the first embodiment.

[0099] The shown optical tracked pointer instrument 16 can be used for registration of the patient image data relative to the optical patient tracker 40. If direct registration of the patient trackers 40 using feature elements at the optical tracker is performed, the optical tracked pointer instrument 16 is not necessary.

[00100] Figure 4 illustrates the reference coordinate systems associated with the system components of the second embodiment using direct registration of the two patient trackers 40. Additionally, relevant transformations between the reference coordinate systems are visual- ised using dashed arrows. The visualised transformations are either measured with one of the tracking systems or determined during a registration or calibration process. The measurement results of the electromagnetic tracking system are continuously made available in form of the transformations ^fg T _{pt em} and ^fg T _t0 oi em. The measurement results of the optical tracking system are continuously made available in form of the transformations ^cam T _p t _ _op t and ^cam Tt ₀₀ i opt. The transformation ^vldeo Ttooi opt is usually determined in a calibration procedure during system in- stallation and is depending on the current zoom und focus settings of the microscope. The transformation ^pt - ^em T _p t ₀ pt describes the spatial relationship between the electromagnetic and optical trackers, which is determined intra-operatively by sampling feature points on the optical patient tracker 40 using the electromagnetic pointer instrument 31. The transformation ^pt - ^em Timg stores the result of the image data registration which is determined at the beginning of the navigated surgery.

REFERENCE NUMBER LIST

1 Operating Microscope

5 Microscope Tracker

10 Navigation Camera

15 Hybrid Tracker

16 Optical Pointer Instrument

20 Hybrid Navigation Unit

30 Pointer Instrument

31 EM Pointer Instrument

40 Patient Tracker

50 Field Generator

90 Operating Table

100 Patient