EP1517647A1

EP1517647A1 - Method and instrument for surgical navigation

Info

Publication number: EP1517647A1
Application number: EP03735605A
Authority: EP
Inventors: Martin Schmidt; Jochen Koetke; Peter Schalt; Stefan Oelckers; Rolf-Rainer Grigat; Lars Eckert; Thomas Hoell
Original assignee: Moeller Wedel GmbH
Current assignee: Moeller Wedel GmbH
Priority date: 2002-06-13
Filing date: 2003-06-11
Publication date: 2005-03-30
Also published as: WO2003105709A1; US20060122516A1; US7912532B2; AU2003237922A1

Abstract

The invention relates to a method for positional optimisation in navigation, in particular neural navigation in surgery with an operation microscope and at least one optoelectronic image detector which may be connected to the microscope and also a computer system. The data obtained from the at least one image detector which lie in the microscope field-of-view for the operator, contain information on the position of an operation instrument, in particular the instrument tip. The actual position of the instrument in the x- and y-direction as well as in the z-direction of a three-dimensional coordinate system is continuously or intermittently determined from the relevant positional data. A separation determination is carried out for the positional determination in the z-direction by means of depth of focus evaluation and/or stereoscopic image analysis. The invention further relates to a navigation instrument, using marking, close to the instrument tip, lying within the field of view of the microscope during use thereof.

Description

METHOD AND INSTRUMENT FOR SURGICAL NAVIGATION

description

The invention relates to a method for presence optimization in navigation, in particular neuronavigation, in surgery with a surgical microscope and at least one optoelectronic image receiver, which can also be connected to the microscope, and a computer system according to the preamble of claim 1, and a navigation instrument, in particular for a method for presence optimization navigation, especially neuronavigation.

Neuronavigation is concerned with the planning, but also the implementation of trajectories for interventions on the human brain, the spine and the like. To this end, the patient takes preoperative tomographic recordings, with markings attached to the patient's body, which are also recorded by the tomography. Immediately before the operation, the three-dimensional position of these markers in space is determined by navigation, thus establishing a relationship between the patient's anatomy and the preoperatively recorded data sets. A corresponding process is called registration. A basic distinction can be made between optical navigation methods and magnetically operating methods. Both methods are used to determine the three-dimensional position and orientation of a special navigation pointer instrument in space, which is used to probe relevant points. The position of the pointer tip is not determined directly in known optically operating systems, but is determined with the aid of markers, which are usually attached to the pointer in the form of balls. In known systems, reflectors for infrared light, which is generated by special infrared light radiation sources, are used as markers or marker substances. Two cameras on a traverse then take pictures and determine the position of the pointer in the room. In the methods based on magnetic fields, the pointers have sensors, which are used either for the generated spatial alternating magnetic field or for a pulsed magnetic direct field.

Optical systems have the disadvantage that there is a risk of the cameras being covered by operating personnel. Magnetic systems then fail as soon as there are objects made of soft iron nearby that disrupt or distort the magnetic fields.

The basic task of navigation systems on the market, as briefly outlined above, is the position or tip of an instrument, which is used to point to a detail in the operating area during the operation, with data from preoperative diagnostic methods, such as Correlate computed tomography or magnetic resonance imaging. After such a correlation has taken place, the surgeon can e.g. the position of a point in the site, to which it points during the operation with the instrument mentioned, is displayed in real time in the images of the preoperative images. In this way, the surgeon receives information about the current position relative to a position of a structure recognizable in the CT or MR image, e.g. a tumor.

One way of presenting this information to the surgeon is to enter the position of the instrument tip as a point in a previously selected CT or MR image. So that the navigation system can perform this task, both the position and orientation of the patient and that of the surgical instrument mentioned must be known. As explained, this information is used in current systems e.g. determined with the aid of a stereo camera pair, which is located in the vicinity of the operating table and detects the surgical instrument.

Further known navigation systems furthermore offer the possibility of displaying images of preoperative diagnostic methods in the correct position, orientation and scale with the optical image of a surgical microscope overlap. To achieve this, the position and orientation of the surgical microscope as well as the currently selected magnification and focal plane must also be recorded. In the known navigation systems, the position and orientation of the surgical microscope are usually recorded by attaching reflective markings to the microscope, which, like the markings mentioned on the pointer, are recorded by the two cameras on the crossmember mentioned. There is also a known system in which the relative position and orientation of the microscope is determined with the aid of rotary angle sensors in the microscope carrier system. A disadvantage of the latter systems is that the carrier systems used had to be stiffened to ensure sufficient accuracy and are therefore disproportionately heavy and expensive. The superimposition itself can then take place, for example, by reflecting the CT or MR image into the optical observation beam path of the microscope using a projector.

The navigation systems according to the prior art have some significant disadvantages. This includes the fact that the markings on the surgical instrument or on the pointer must be seen at all times by the stereo camera pair arranged on the camera arm. Hiding the markings affects the functionality and leads to errors in the data acquisition. Experience has shown that the so-called presence times of optical as well as magnetic navigation systems are around 2/3. Furthermore, the large distance between the markings of known optical instruments and the camera pair in the case of optical measurement causes large measurement inaccuracies and relatively large-volume markings are necessary.

Another problem with current navigation systems in neurosurgery is the movement of the brain tissue after opening the skull and during the operation. This situation, known as the brain shift, means that the tissue geometry during the operation no longer fully corresponds to the tissue geometry during the preoperative diagnostic procedures. This leads to Errors, for example, in the aforementioned position indication of a pointer instrument relative to the tissue structures in a preoperative diagnostic MR or CT image. The described error can be corrected by, for example, following the change in the position of the tissue surface in the vicinity of the operating area during the operation. For this purpose, however, the surgeon must repeatedly tap and mark several points on the tissue surface mentioned with a marking instrument of the navigation system in order to make the necessary data for this correction available to the system. However, this is disadvantageous given the already high load of a neurosurgical operation.

Taking into account the aforementioned disadvantages of the prior art, the aim in new navigation systems is to enable a three-dimensional measurement of the operating field and trajectory tracking of the tip of the surgical set and to increase the presence, particularly in the case of optical navigation. Furthermore, the large, expensive and occlusion-sensitive camera traverses should be avoided. The operation of the systems is simple and clear in order to exclude sources of error from the outset.

From the foregoing, it is therefore an object of the invention to provide a method for presence optimization in navigation, in particular neuronavigation, in surgery which is based on an operating microscope known per se and at least one optoelectronic image receiver coupled directly or indirectly to the observation beam path of the microscope ,

Furthermore, a subordinate task of the invention is to create a new type of navigation instrument, in particular for use in operations with the aid of an operating microscope.

The object of the invention is achieved with a method for presence optimization in navigation as defined in claim 1 and with regard to the navigation instrument with the feature Combination according to claim 12 and with a view to the surgical microscope through the teaching of claims 18 ff.

Accordingly, the basic idea of the invention lies in the fact that the inclusion of the images from or parallel to the observation channels of the surgical microscope in the actual image evaluation of a navigation system improves both the presence time of the navigation system and further advantageous effects, in particular with a view to improving the accuracy of the position determination to reach.

The data obtained from the at least one image receiver, each of which lies in the microscope field of view of the surgeon, contains information about the position of the surgical instrument or pointer used, in particular the tip thereof, the specific position of the instrument in x and. From the respective position data being continuous or discontinuous y direction and in the z direction of a three-dimensional coordinate system is determined. For the determination of the position in the z direction, either a distance determination is carried out by means of depth of field evaluation or a stereoscopic image evaluation takes place. Instead of two cameras with stereoscopic image evaluation, a new type of optoelectronic image receiver called PMD array (PMD: Photonic Mixer Device) can also be used. The measuring method of these sensors is related to the “time of flight” distance measuring method, but achieves a better result by means of novel principles with less equipment expenditure and much smaller size

Accuracy of measurement and can also be implemented as a sensor array, so that when mapping an area to be topographed onto a PMD array it is possible to obtain a complete topography with just one measurement. Since the pointer and its suitably shaped markings can be easily separated from the topography of a pointer against the background of the operation field, such a PMD array can also be used to track said pointer. If a PMD sensor is used, the object field of the sensor must be illuminated with a suitably modulated and preferably narrow-band light source the background light as well as the unmodulated white light of the surgical microscope are discriminated by suitable filters before hitting the PMD array.

The one or more optoelectronic image receivers can be connected directly to the observation beam path, in particular by means of a beam splitter, although there is also the possibility of providing at least one separate image receiver beam path which is independent of the observation beam path and which is likewise directed towards the microscope field of view of the operator ,

The position of the surgical microscope in the room is determined and this surgical microscope position data is supplied to a computer system known per se in order to place the instrument position data in a higher-level spatial coordinate system, including existing data about the current position of the patient and preoperatively obtained three-dimensional data from the inside of the patient Transform patient.

In one embodiment of the invention, in addition to data acquisition for intraoperative position and position determination of a navigation instrument by means of known optical and / or magnetic methods, it is possible to carry out a supplementary three-dimensional position determination by means of the data provided by the image receiver of the surgical microscope.

The use of these two independent redundant systems results in the advantageous possibilities mentioned below. If one of the systems does not deliver valid measured values, for example due to the masking being covered, the measured values of the other system can be used and it is possible in this way to increase the presence time. In the case of redundant valid measured values, the accuracy of the measurement can be increased, for example by averaging. In the case of redundant valid measured values, the uncertainty of the measured values, for example due to the Difference of the redundant measured values are quantified and in this way a navigation system is created for the first time, which can quasi control itself. The latter is standard for the majority of the medical devices critical for patient safety, but has not yet been implemented in known navigation systems.

As an alternative to the known methods, a module is provided for detecting the position of the surgical microscope in the room, which module is integrated in the microscope or at least connected to the microscope in a fixed and invariant manner, which is used next to the operating table without the use of the known systems space-filling trusses to be positioned can use cameras. This module enables the microscope to determine its relative position in space or relative to the patient. The components and measuring methods mentioned in claims 19 to 24 are used individually or in combination. To minimize the size of the module mentioned, the required infrastructure (power supplies, computers, etc.) can e.g. can be integrated into the base of the carrier system.

If the microscope can itself determine its position in the room or relative to the patient and if the pointer is also tracked without the stereo camera pair of the conventional navigation system, the stereo camera pair of the conventional navigation system can be omitted. In this case, space in the operating room is significantly saved; Furthermore, commissioning is simplified, since fewer devices have to be moved and put into operation with fewer cables before the operation begins, and the risk of occlusions during the operation is eliminated or at least considerably reduced.

With regard to the problem of so-called brain shifting, the invention provides for marking points to be arranged on or on the tissue surface of the patient, the change in position of which is detected by the image receiver and determined by means of the computer system, in order to to correct data obtained preoperatively based on the current status.

As is known, a stereo light microscope can either consist of two convergent monocular mono-objective microscopes or comprise two decentered optical channels behind a common front lens. Surgical microscopes are built almost exclusively as so-called Common Main Objectives (CMO) microscopes due to their design-specific advantages. The modeling of a CMO microscope from an optical point of view is extremely difficult, however, since the treatment of so-called skewed light beams is required here. This is due to the lateral offset of the two optical channels behind the common front lens mentioned.

If a stereoscopic evaluation for neuronavigation is required, the person skilled in the art will first exclude the use of CMO microscopes, taking into account the problems mentioned. According to the invention, this prejudice was overcome in that an exclusive analytical formulation of the microscope model was found, which in the end corresponds to two rectified pinhole cameras, in which corresponding points in both views theoretically lie on the corresponding parts of the image. With this knowledge, the further image processing steps can be greatly simplified and image processing techniques known per se can be used.

According to the invention, the data obtained from the image receiver provided for each channel are corrected with regard to the distortion errors present in the x and y directions and the disparity errors given in the z direction. This correction depends on the respective settings of the microscope, i.e. Zoom and focus.

For error correction, calibration is first carried out, the surgical microscope being described as a two-pinhole camera on the imaging side, as mentioned. The calibration is carried out for all zoom and focus levels. The calibration data received are saved, to allow later online or offline error correction. Of course, there is the possibility of storing microscope-specific error correction data in a look-up table, so that the actual correction process can be simplified from a computational point of view and thus shortened.

All physical quantities required for the calculation of the nominal pinhole camera parameters for a CMO microscope are easily accessible and can usually be found in the manufacturer's data sheet. Starting values for an iterative calibration can be measured easily on the microscope. The necessary information on the image receivers, for example CCD sensors, is also available as manufacturer information. Knowledge of internal lens data is not necessary. The CMO microscope-adapted stereoscopic image processing is carried out using a method in which the image from both two-dimensional camera planes is formulated into the three-dimensional space by means of the least possible degree of polynomial approximation. A necessary set of control points acts as a set of nodes for the polynomials and is selected in the entire volume.

For the practical use of microscopes with stepless zoom and / or focus, it is proposed to calibrate the individual system parameters at several zoom and focus positions and to interpolate the corresponding system parameters from the calibrated support points when intermediate values are set. The current settings of zoom and focus are expediently made available to the evaluation unit during the calibration procedure, but also during the measurement procedure, by the microscope via a data line.

In the novel navigation instrument according to the invention, in particular for use in a method which uses image information from the beam path of a surgical microscope for neuronavigation, markings, in particular micro-markings, are applied close to the tip of the instrument, specifically when in use lying in the field of view of the microscope. A certain minimum distance to the instrument tip results from the fact that the markings should not be contaminated by blood or other body fluids and that the use of the pointer instrument must not be impeded in the case of raised markings.

The markings are e.g. can be formed as at least three coplanar, colored spheres which lie in a plane which runs parallel to the instrument's longitudinal axis but does not contain it. Other forms of training are colored or reflective ring markings. If the microscope is to be operated over a particularly large zoom and focus range, it may happen that the markings are no longer completely in the field of view of the microscope at particularly high magnifications and short focus lengths, or that the markings are too small at particularly weak magnifications and large focus lengths are. In this case, it is expedient to attach several sets of markings of different sizes, the smallest set of markings being closest to or attached to the instrument tip.

The navigation instrument according to the invention can be sterilized and can be easily recognized by the microscope. One end shape is designed as a distinctive tip and can be used as a pointer. In the case where the tip is not directly visible for operational reasons, it can be detected via the above-mentioned markings and the remaining shape information of the instrument.

The increase in presence achieved according to the invention in the case of optical systems is achieved by taking the image directly through the microscope and thereby ensuring that the navigation instrument is not covered by the fingers or other surgical instruments. A risk of concealment by operating room personnel, as with conventional optical navigation systems, is excluded from the outset. Due to the measurability of relative distances from points in the coordinate system of the microscope, there is still the possibility of differential navigation given, ie distances from points to a reference point can be measured.

In contrast to navigation instruments previously available on the market, markings according to the invention are positioned close to the top. Since navigation takes place through the microscope, much smaller markings can also be used. This in turn offers the possibility of making the navigation instrument itself smaller and cheaper and, above all, of using it more flexibly and ergonomically.

An exemplary navigation instrument is designed as a bayonet-shaped round steel of essentially 4 mm, which tapers conically at the tip over a region of essentially 30 mm. Bayoneting or cranking is expedient from the point of view, since it can thereby rule out that the instrument for the area covered by cameras is covered by fingers or the like.

In one embodiment, the coplanar spheres mentioned are used as markers, which have a diameter of approximately 1.5 mm, for example. In order to make the segmentation of the balls from the background as simple as possible, they are painted in different colors. In view of the special properties of the situs, blue, green and violet and / or brilliant yellow are preferred. The use of infrared reflecting spheres is also possible.

Since, according to the invention, it is possible to work with the light source that is already present on the microscope side, special spherical coatings, which reflect infrared radiation, for example, in a pronounced directional pattern, are omitted in the embodiment with colored markings.

A further development of the invention is that the marker configuration does not rest on the navigation instrument and is fastened there, but only consists of imprints. In case of necessary Detection of the rotation of the navigation instrument about its own axis is conceivable, for example, an angular coding running in the azimuthal direction.

The balls are preferably detected in the camera views using color image processing methods. Depending on the strength of a color cast that may be present, this is compensated for by a white balance directly with the image acquisition. For this purpose, the intensities of the red and blue channels of each image receiver or camera are scaled.

The feature extraction or pattern recognition of the markings in the form of coplanar, colored spheres takes place via the fact that a spherical object is imaged differently. If the center of the sphere is not on the perpendicular of the camera plane, the outline of the sphere is projected as an ellipse. The shape shown allows conclusions to be drawn about the position or location of the individual balls.

If the instrument tip is not directly visible in the camera images, the three-dimensional position of the pointer tip is determined from the three-dimensional positions of the ball centers. Of course, the navigation instrument can also be formed from a conventional surgical set, in order not to have to interrupt the operation unnecessarily for navigation purposes.

The underlying geometry is calibrated to calculate the three-dimensional coordinates of the tip position from the three-dimensional spherical centers. For this, a local instrument coordinate system originating in a central sphere is defined, of which two axes run through the remaining two spheres and the third axis is orthogonal to the plane spanned in this way. In this affine coordinate system, the position of the pointer tip has three unique coordinates, so that it can be reconstructed indirectly via the reconstruction of the axes of the local instrument coordinate system. The affine coordinates are independent of the intrinsic or extrinsic parameters of the camera arrangement and can be calibrated for a number of given tip and ball coordinates.

In the present description, the terms position and location are used essentially as synonyms. It is within the knowledge of the person skilled in the art that to determine the position of a three-dimensional body in space, six coordinates, e.g. Point of focus / center of gravity or the like in x, y and z orientation and with the three so-called Euler angles are to be specified. The only exception is the tip of the instrument, which only needs three coordinates to describe the position.

The invention will be explained in more detail below using exemplary embodiments.

In a first exemplary embodiment, the operating area is located in the head of a patient and a surgical instrument with a corresponding marking is located in the visual field of the surgical microscope.

The images of both observation channels are transferred to two image receivers, e.g. CCD cameras directed. The camera images are then evaluated by a computer and the position of the surgical instrument in the coordinate system of the microscope is calculated from the stereoscopic image evaluation and the device parameters, such as zoom and focus position, which are additionally output by the microscope via a data connection.

At the same time, the position of the microscope and the patient in the coordinate system of the stereo camera arm is determined by a stereo camera pair with corresponding cameras, which is positioned near the operating table, by means of stereoscopic image evaluation with the aid of the patient markings and the microscope markings.

This enables the coordinate systems of the microscope and the patient to be calculated and, for example, the position of the surgical instrument can be specified in the patient's coordinates. Optionally, the camera pair can additionally detect and evaluate markings on the surgical instrument, with the result of a redundant measurement of the determination of the position of the surgical instrument.

In a further exemplary embodiment, visible light or radiation in the near infrared region can be used to generate marking points, lines or a grating into the field of view of the microscope. These marking points, lines or grids can then be recorded with a corresponding camera, which is coupled to one of the observation channels. The position of the marking points in coordinates relative to the microscope can be determined by evaluating the camera image. Technically, the aforementioned teaching can be implemented in that light is directed via a diaphragm into the observation channel of the surgical microscope and is imaged on a point in the focal plane of the microscope. This point of light is then captured by a camera, in particular a CCD camera. With known coordinates in the x- and y-direction of the aperture hole in a Cartesian coordinate system perpendicular to the optical axis, together with the coordinates of the light point on the camera chip, there is a possibility of working analogously to the usual stereoscopic image evaluation. The location of the point at which the light that passes through the diaphragm can be determined in coordinates of the microscope. As mentioned, light projection systems can be used instead of the illuminated diaphragm, each of which projects a number of points, lines or grids into the operating area.

In the case of a light grid, intersection points can be detected by the cameras. The coordinates of the crossing points of the light grid on the surface of the operation area can then be determined in the coordinate system of the microscope by means of stereoscopic image evaluation. The information derived from this can then be displayed on a display as a three-dimensional, perspective grid in the form of contour lines or the like are shown and used for the allocation of positions, based on preoperative images.

As part of quality assurance, video recordings and photos are mostly made in today's operating rooms. These video recordings and photos do not contain quantitative three-dimensional information, nor are they generally to be extracted from the video recordings and photos.

If topographies of the area of operation can be acquired with reasonable effort during the operation, the lack of quantitative 3D information in today's documentation would be eliminated. Such topographies can be saved without any problems and, as part of quality assurance measures, e.g. the actual resection profile can be compared with the findings from preoperative diagnostic data such as magnetic resonance imaging and computed tomography. Appropriate topographies can e.g. can also be visualized as relief diagrams during the operation. This makes it possible - in addition to postoperative quality assurance - to offer the surgeon decision aids during the operation to optimize the resection limits.

In principle, a topography of the microscope object field can already be obtained with the microscope described above with stereo cameras using standard methods of stereoscopic image evaluation. Correspondence analysis, in particular, is computationally time-consuming and prone to errors in areas that are naturally weakly structured.

An improvement can be achieved by the following description of the methods and devices, among other things, for the projection of light markings. The corresponding points required for stereoscopic image evaluation can be determined quickly, clearly and with an extremely low error rate using light markings.

A possible first embodiment uses stereo cameras permanently connected to the microscope and a projection system which does not necessarily have to be permanently connected to the microscope.

A second embodiment is based on the light projection device at the location of one of the two stereo cameras and using the optical channels / paths which were used by this camera in the first-mentioned embodiment. In this case, the methods of stereoscopic image evaluation can already be used with only one camera, which is known as the inverse camera.

In a further embodiment, the topography is obtained directly from the data of a PMD array (PMD: Photonic Mixer Device) and an assigned personal computer.

In the first exemplary embodiment, it is possible to produce marking points, lines or a grating into the field of view of the microscope with visible light or with radiation in the region of the near infrared. The tissue in the visual field of the surgical microscope can then be recorded together with the marking points, lines or grids projected onto this tissue with two cameras, which are coupled, for example, to the observation channels of the microscope. The position of the marking points in coordinates relative to the microscope can be determined by evaluating the camera images with stereoscopic image evaluation. The main source of error in stereoscopic image evaluation - correspondence analysis - is drastically simplified and failsafe, since only the marked points of both camera images are included in the evaluation, for which the uncertainty of the correspondence assignment is significantly less than for unmarked points. In order to obtain a topography of the marked points in the coordinates of the patient instead of in the coordinates of the microscope, the relative position and orientation of the patient and the microscope must be determined, which can be done in the manner shown.

According to the second embodiment, the procedure is largely analogous to that of the first embodiment. Instead of the two cameras coupled to the observation channel of the microscope, one of the two cameras is replaced by an aperture. The same optics, which previously mapped the object field on this camera, are now used to image the aperture on the object field. If an aperture structured with dots, lines or grids is used and light is directed through these aperture structures and the assigned optical channel onto the object field and if the correspondingly illuminated area is recorded with the remaining camera, the principle of the inverse camera and the methods can be used the stereoscopic image evaluation can be used despite the use of only one camera. With regard to error security, the advantages of the first exemplary embodiment are also given here. If invisible light is used, visible light can also be added to make the support points of the topography visible in the image of the microscope.

In a third exemplary embodiment, a PMD sensor array is used instead of the conventional cameras. In order to be able to use this, in addition to the visible light of the microscope, it must be illuminated with modulated light. The PMD sensor is protected with suitable optical filters against excessive lighting by the white non-modulated light. With this new technology, the topography of the area mapped onto the PMD sensor array can be obtained directly from the PMD chip with an associated computer with a suitable interface.

The topographical data obtained in the above exemplary embodiments can then, for example, as a three-dimensional, perspective grid or in Form of contour lines or the like can be shown on a display. Furthermore, these topographical data can be displayed in a location-correlated manner with data from preoperative diagnostic data (magnetic resonance imaging data, computed tomography data, etc.).

Claims

claims

1. A method for presence optimization in navigation, in particular neuronavigation in surgery, with an operating microscope and at least one optoelectronic image receiver, which can also be connected to the microscope, and a computer system, characterized in that the data obtained from the at least one image receiver, each in the microscope The surgeon's field of vision includes information about the position of a surgical instrument, in particular the tip of this instrument, the specific position of the instrument in the x- and y-direction and in the z-direction of a three-dimensional coordinate system being determined continuously or discontinuously from the respective position data and in particular for determining the position in the z direction, a distance determination by means of depth of field evaluation and / or stereoscopic image evaluation and / or evaluation of the modulated document using a PMD sensor (photonic mixer device) together with the associated modulated document signals obtained.

2. The method according to claim 1, characterized in that the or the optoelectronic image receiver directly to the

Observation beam path, in particular connected by means of beam splitters.

3. The method according to claim 1, characterized in that at least one separate, independent of the observation beam path image receiver beam path is provided, which is directed to the microscope field of view of the surgeon.

4. The method according to any one of the preceding claims, characterized in that the position of the surgical microscope in the room is detected and this surgical microscope position data is fed to the computer system in order to transform the instrument position data into a superordinate spatial coordinate system including existing data about the current position of the patient and preoperatively obtained three-dimensional data from the inside of the patient.

5. The method according to any one of the preceding claims, characterized in that in addition to the data acquisition for intraoperative position and position determination of a navigation instrument by means of known optical and / or magnetic methods, an additional three-dimensional position determination is carried out by means of the data provided by the image receiver of the surgical microscope.

6. The method according to claim 5, characterized in that in the presence of valid data records in only one of the two systems, the data determined to be valid are used to determine the position and position of the instrument or for instrument tracking.

7. The method according to claim 5, characterized in that in the presence of redundant data records defined as valid, these are used to increase the measuring accuracy and / or to quantify the measuring accuracy.

8. The method according to claim 4, characterized in that a stereo camera pair is provided for detecting the position of the surgical microscope in the room on or on the microscope, which enables movement tracking based on fixed, attached to the patient and / or in the room markings.

9. The method according to any one of the preceding claims, characterized in that marking points are provided on or on the tissue surface of the patient, whose change in position detected via the image receiver and determined by means of the computer system is used to determine brain shifting on the open skull in order to correct it to perform data obtained preoperatively.

10. The method according to claim 1 and 2 or 4 to 9, characterized in that the surgical microscope has two decentered optical channels behind a common front lens with a common object plane and the same magnification for both optical channels, with a correction function for the distortion in the stereoscopic image evaluation - Incoming error, which depends on the zoom and focus settings currently used.

11. The method according to claim 10, characterized in that a calibration is carried out for error correction, the parameters of said correction function being empirically determined by calibration measurements at different positions of zoom and focus and different object distances, and the parameter set obtained is thus stored.

12. Navigational instrument with markings, in particular for a method according to one of claims 1 to 11, characterized in that the markings are arranged in the vicinity of the instrument tip, the maximum distance from the instrument tip being chosen such that the markings are in use in Field of view of the microscope and the minimum distance to the instrument tip is substantially greater than 2mm.

13. Navigation instrument according to claim 12, characterized in that the markings are designed as micro-markings or micro-bodies.

14. Navigation instrument according to claim 13, characterized in that the markings are designed as at least three microspheres or elevations spanning a triangle, colored or infrared light reflecting microbeads or elevations on the navigation instrument.

15. Navigation instrument according to claim 13, characterized in that the markings are designed as ring-like hatching and / or coloring and / or reflectors on the navigation instrument.

16. Navigation instrument according to claim 13, characterized in that several of said marker sets of different sizes are attached to the instrument and the smaller of the marker sets are located closer to the tip of the instrument with respect to the larger marker sets.

17. Navigation instrument according to one of claims 12 to 16, characterized in that in addition on the side facing away from the instrument tip further, with known navigation systems markings of a non-microscopic type are arranged or the body of the instrument is designed for detection with magnetic navigation systems.

18. Surgical microscope, in particular for use in a method according to one of the preceding claims, characterized in that the microscope comprises a module for determining the spatial coordinates relative to the operating room or to the patient.

19. Surgical microscope according to claim 18, characterized in that the module contains a stereo camera pair, to which a computer for stereo-scopic image evaluation is assigned, the stereo camera pair being aligned with marking points on the patient or in space and thus the position and orientation of the microscope relative to Patient or to the room is determinable.

20. Surgical microscope according to claim 18, characterized in that the module contains a PMD sensor array, to which a computer is assigned for evaluating the sensor data, the PMD sensor array with associated optics and modulated lighting being aligned with marking points on the patient or in space and thus the position and orientation of the microscope relative to the patient or to the room can be determined.

21. Surgical microscope according to claim 18, characterized in that the module has a magnetic navigation system or components of such a system, in particular Hall sensors.

22. Surgical microscope according to claim 18, characterized in that the module has one or more transmitters of a transit time measuring system based on sound, ultrasound or electromagnetic radiation, which operates in the time or frequency domain.

23. Surgical microscope according to claim 18 or 22, characterized in that the module contains one or more receivers of a transit time measuring system based on sound or ultrasound or on electromagnetic radiation, which operates in the time or frequency domain.

24. Surgical microscope according to claim 18, characterized in that the module comprises gyroscopes and / or inclination sensors.

25. Surgical microscope according to claim 18, characterized in that the module comprises arrangements or devices for combining different measuring methods of claims 19 to 24.

26. Surgical microscope, in particular for use in a method according to one of the preceding claims, characterized in that the distance measurement value of a PMD sensor from a predetermined area of the microscope image field, e.g. the center of the picture, which is handed over to the navigation system.

27. Surgical microscope, in particular for use in a method according to one of the preceding claims, characterized in that the distance measurement value of a PMD sensor from a predetermined area of the microscope image field, e.g. the center of the image is provided and used as a manipulated variable for the focusing unit of the microscope.

28. Surgical microscope, in particular for use in a method according to one of claims 1 to 11, characterized in that a device for projecting light markings is provided, the areas of the operation field marked with this light being stereo by means of two cameras connected to the microscope - subject to scopic image evaluation.

29. Surgical microscope, in particular for use in a method according to one of claims 1 to 11, characterized in that this contains a device for the projection of light markings connected to the microscope and the areas of the operating field marked with this light are evaluated by means of a camera connected to the microscope and stereoscopic image evaluation using the principle of the inverse camera.

30. Surgical microscope, in particular for use in a method according to one of claims 1 to 11, characterized in that the microscope has a PMD sensor module connected thereto, on which the image of the site is imaged and an associated modulated illumination device is provided.

31. Surgical microscope according to one of claims 28 to 30, characterized in that the currently received topography data are transferred to a navigation system and are used by the latter as output data for the correction of a brain shift.

32. Surgical microscope according to one of claims 28 to 31, characterized in that the distance measurement value from a predetermined area of the microscope field of view, e.g. the middle of the picture is transferred to a navigation system.

33. Surgical microscope according to one of claims 28 to 32, characterized in that the distance measurement value from a predetermined area of the microscope field of view, e.g. the center of the image is fed as a manipulated variable to the focusing unit of the microscope.

34. Surgical microscope according to one of claims 28 to 33, characterized in that one or more support points of determined topograms are marked by the projection of visible light onto these points.

35. Surgical microscope according to one of claims 28 to 34, characterized in that for the cameras, the device for the projection of light markings and / or the PMD sensor, either the optical observation channels of the

Microscope used or additional, optical channels are provided and used.