Abstract
The invention relates to a target apparatus for use in a surgical navigation system, comprising at least one marker, for pose determination both by way of a device for marker reference point-based pose determination using at least two image capturing devices for imaging the marker and by way of a device for marker shape-based pose determination using at least one further image capturing device for imaging the marker , the marker having a detection surface, the detection surface having at least one first region and at least one further region, wherein the first region is designed to be more reflective than the further region, at least one portion of the first region and at least one portion of the at least one further region forming a pattern for identifying the marker, and to a surgical navigation system and a method for producing the target apparatus.
Claims
1. A target apparatus for use in a surgical navigation system, comprising at least one marker, for pose determination both by way of a device for marker reference point-based pose determination using at least two image capturing devices for imaging the marker and by way of a device for marker shape-based pose determination using at least one further image capturing device for imaging the marker, the marker having a detection surface, the detection surface having at least one first region and at least one further region, wherein the first region is designed to be more reflective than the further region, at least one portion of the first region and at least one portion of the at least one further region forming a pattern for identifying the marker.
2. The target apparatus as claimed in claim 1, wherein the first region is designed to be retroreflective and the further region is designed to scatter diffusely or absorb radiation.
3. The target apparatus as claimed in claim 1, wherein the first and/or further region have/has a symmetric, more particularly point symmetric design.
4. The target apparatus as claimed in claim 1, wherein the further region is completely or partially surrounded by the first region, or vice versa.
5. The target apparatus as claimed in claim 1, wherein the device for marker reference point-based pose determination is designed as, or comprises, a stereo camera system and/or the device for marker shape-based pose determination is designed as, or comprises, a monoscopic tracking system.
6. The target apparatus as claimed in claim 1, wherein the first and the further region are arranged centered with respect to one another.
7. The target apparatus as claimed in claim 1, wherein the first and/or further region have/has a circular, ellipsoid or ring-shaped design.
8. The target apparatus as claimed in claim 1, wherein the first region has smaller dimensions and/or covers a smaller partial area of the detection surface than the further region.
9. The target apparatus as claimed in claim 1, wherein the further region or portions of the further region is/are not resolvable by the first image capturing device, in particular if the marker is arranged spaced apart from the first image capturing device at a predetermined working distance.
10. The target apparatus as claimed in claim 1, wherein the target apparatus comprises at least two markers, with each detection surface of the markers spanning a respective plane, with the at least two planes being arranged so as not to be parallel to one another or so as to be parallel and spaced apart from one another.
11. The target apparatus as claimed in claim 1, wherein the first and/or further region of the detection surface encode information.
12. The target apparatus as claimed in claim 1, wherein the target apparatus comprises at least three markers.
13. The target apparatus as claimed in claim 12, wherein the at least three markers are arranged with respect to one another, in particular spaced apart from one another, such that no ambiguity arises during the pose determination in space.
14. A surgical navigation system comprising a target apparatus as claimed in claim 1, the navigation system comprising at least two first and at least one further image capturing device.
15. A method for producing a target apparatus as claimed in claim 1 , wherein a less reflective medium is applied to a more reflective detection surface or wherein a more reflective medium is applied to a less reflective detection surface or wherein a more reflective ink is applied to a first region of the detection surface and a less reflective ink is applied to a further region of the detection surface or wherein a detection surface is reflective, with a region of the detection surface being irradiated in thermally sensitive and/or photosensitive fashion using a radiation source, with the reflective property of this region changing and this region being less reflective following the irradiation.
Description
[0039] The invention is explained in more detail on the basis of exemplary embodiments. In the figures:
[0040] FIG. 1: shows a target apparatus according to the invention in the captured region of a first image capturing device,
[0041] FIG. 2: shows a target apparatus according to the invention in the captured region of a further image capturing device,
[0042] FIG. 3: shows a target apparatus according to the invention comprising three markers,
[0043] FIG. 4: shows a target apparatus according to the invention comprising two markers,
[0044] FIG. 5: shows a surgical navigation system according to the invention,
[0045] FIG. 6: shows a schematic flowchart for a method for pose determination,
[0046] FIG. 7: shows a schematic flowchart for a production method according to the invention, and
[0047] FIG. 8: shows a target apparatus comprising a marker.
[0048] Identical reference signs hereinafter denote elements having identical or similar technical features. FIGS. 1 and 2 show a target apparatus 1 according to the invention comprising a marker 2. In the embodiment of the target apparatus 1 shown, the latter has a detection surface which is divided into a first region 4 and a further region 3. The further region 3 has a circular design and is labeled by a dotted surface, with this surface being a diffusely scattering or light-absorbing surface. The first region 4 is labeled by a hatched surface which is a retroreflective surface and designed in annular fashion. The first and the further region 4, 3 form a pattern, with the first region 4 completely surrounding the further region 3. In FIG. 1, the target apparatus 1 is arranged in a captured region 25 of a first image capturing device 20. The captured region 25 is depicted by a dash-dotted line. A light source 21 of the first image capturing device 20, which emits light coaxially with a capturing direction 24 of the image capturing device 20, is also depicted. This light source may be an infrared light source. The light is radiated into the entire captured region 25. If a light beam emitted by the light source 21 strikes the first region 4, it is cast directly back to the image capturing device 20 on account of the retroreflective coloration. Thus, a small amount of luminous energy is already sufficient for imaging the first region 4 of the marker 2 since the light beams emitted by the light source 21 are not diffusely scattered but retroreflected by the first region 4. In particular, the image capturing device 20 can be configured such that light beams diffusely scattered in the captured region 25 are captured to a much lesser extent than the retroreflected light beams. This facilitates the detection of the first region 4 by the first image capturing device 20 since only retroreflected light beams are captured. The first image capturing device 20 has an internal coordinate system 22, which may serve as a reference coordinate system for pose determination. In this case, a longitudinal axis 23 may be oriented parallel to the capturing direction 24 of the coordinate system 22, with the capturing direction corresponding to a direction of the optical axis of the first image capturing device 20. Further, the first image capturing device 20 is part of a device for marker reference point-based pose determination (not depicted here). This device for pose determination uses the coordinate system 22 in order to determine a pose, that is to say a position and/or orientation, of the target apparatus 1 relative to the reference coordinate system. Also imaged here is a further image capturing device 30 which is different from the first image capturing device 20 and which is also suitable for pose determination; see FIG. 2. The first region 4 is assigned an annulus as a shape. A center of the image region in which the annulus is imaged by the first image capturing device 20 may form a reference point for marker reference point-based pose determination, with the pose of the marker being determined on the basis of the image coordinates of the reference point. Thus, in particular, the pose of the reference point can be determined as pose of the marker. It is also possible that the first image capturing device 20 is one of two image capturing devices for stereoscopic imaging of the target apparatus 1 and consequently the device for marker reference point-based pose determination comprises a further first image capturing device, not depicted here, in addition to the first image capturing device 20. In this case, the center of the first region 4 imaged by the two image capturing devices of the device for marker reference point-based pose determination can be determined in each corresponding image representation, with a spatial pose of the target apparatus 1 being determined on the basis of the pose of the centers in the image representations by way of known triangulation methods.
[0049] In FIG. 2, the target apparatus 1 is arranged in a captured region 35 of the further image capturing device 30, with the captured region 35 likewise being delimited by a dash-dotted line. The captured region 35 and the captured region 25 may differ from one another. The further image capturing device 30 has an internal coordinate system 32 with a longitudinal axis 33, with the longitudinal axis 33 specifying a capturing direction of the further image capturing device 30. The internal coordinate system 32 may likewise serve as a reference coordinate system. Shown further is a further light source 31, which emits light non-directionally into the captured region 35. In this case, the emission direction 34 of the further light source 31 is non-parallel, in particular, to the longitudinal axis 33. The further image capturing device 30 is different from the first image capturing device 20 and part of a device for marker shape-based pose determination. The image capturing device 30 produces an image representation of the first and the further region 3, 4, which is analyzed by means of the device for shape-based pose determination. Capturing the first and the further region 3, 4 by the further image capturing device 30 is schematically depicted by four dashed lines. By way of known methods of image processing and image analysis, the device for shape-based pose determination, in particular the evaluation device 40 thereof, is able to identify, for example, a pattern comprising an ellipse or a circle and an elliptical ring or annulus in the image representation generated, with then an identity assigned to this pattern and hence marker 2, in particular in biunique fashion, being determined. Further, the lengths of the major and minor axes of the ellipse and the elliptical ring or the radii of the inner circle and annulus can be determined in image-based fashion. Depending on the identity, it is then possible to determine, more particularly retrieve, reference properties of the marker 2 known in advance, for example a radius of the outer circle and/or of the inner circle known in advance. The properties with which the first region 4 and/or the further region 3 are imaged in various possible poses, that is to say positions and/or orientations, by means of the further image capturing device 30 may also be known in advance, for example be determined by way of a calibration, and/or be retrievable, in particular the radii or lengths of the major and minor axes with which the inner circle, imaged in circular or elliptical form, and/or the outer circle, imaged in circular or elliptical form, of the annulus are imaged. As a result, the current pose of the marker 2 can be determined by comparing the properties determined in image-based fashion with the pose-specific properties known in advance, which were determined on the basis of the identity.
[0050] FIG. 3 shows a target apparatus 1 according to the invention comprising three markers 2. In terms of their configuration, the markers 2 correspond to the markers described in FIGS. 1 and 2. The markers 2 are arranged on a carrier 6, for example by adhesive bonding on a surface of the carrier 6. The carrier 6 is part of the target apparatus 1 and may be attached to a surgical instrument such that a pose of the surgical instrument is determinable by determining a pose of the target apparatus 1. The markers 2 are arranged at a predetermined spacing 7 from one another. The spacing can be chosen so that the markers 2 do not conceal one another in the captured region of an image capturing device and an accuracy during pose determination is increased. In this case, the spacing 7 is defined as a distance between the centers of the areas of the respective detection surfaces. In the centroids of the areas, a marker coordinate system 5 is arranged per marker 2.
[0051] This can ensure that it is possible to determine the pose of each marker 2 arranged on the carrier 6. Further, ambiguities when determining the pose of the target apparatus 1 can be resolved by determining the poses of the markers 2.
[0052] FIG. 4 shows a target apparatus 1 according to the invention comprising two markers 2. The markers 2 are arranged on a carrier 6, with the carrier 6 being subdivided into a first carrier part 8 and a second carrier part 9. The two carrier parts 8, 9 of the carrier 6 are arranged at an angle W with respect to one another, with the angle W differing from 0° or 180°. One marker 2 is attached to a surface of the first part 8 and another marker 2 is attached to a surface of the second part 9. If the markers 2 are detected by means of a device for pose determination, a marker coordinate system 5 can be assigned to each marker 2, as described above. By assigning the marker coordinate system 5, a plane lying in the detection surface of the marker 2 is spanned by the longitudinal and transverse axes 13, 14. On account of the non-parallel arrangement of the parts 8, 9 of the carrier 6, the planes spanned thus intersect at the angle W, the planes are consequently non-parallel. It is mentioned that the perspective views of the target apparatus 1 chosen in FIGS. 1 to 4 should be understood to be schematic examples of image representations of the target apparatus 1 capturable by the first and/or the further image capturing device 20, 30 and therefore may naturally also be configured differently.
[0053] FIG. 5 shows a surgical navigation system according to the invention. A target apparatus 1 comprising a marker 2 is located in a captured region 25, 35 (see FIGS. 1 and 2) of the first and/or the further image capturing device 20, 30, the marker 2 having a detection surface with a first and a further region 4, 3. Shown further is a further first image capturing device 50, with the two first image capturing devices 20, 50 forming the two image capturing devices of a stereo camera system which - as explained above -enables a stereoscopic, marker reference point-based determination of the pose of the target apparatus 1 or of the marker 2 by evaluating the image representations produced by the two first image capturing devices 20, 50. To this end, the target apparatus 1 is likewise located in the captured region (not depicted here) of the further first image capturing device 50. The image capturing devices 20, 30, 50 are data-connected to an evaluation device 40. The evaluation device 40 can be part of the first and/or the further device for pose determination. If an image representation of the marker 2 is generated by the first image capturing devices 20, 50 and/or further image capturing device 30, such an image representation can be evaluated by the evaluation device 40 for the purposes of determining a pose of the target apparatus 1.
[0054] FIG. 6 shows a flowchart of a method for pose determination by means of a target apparatus 1 according to the invention, wherein, in a step S1, an image representation of the target apparatus 1 or at least of a first region 4 of a marker 2 is generated using the first image capturing devices 20, 50 of a stereo camera system (see FIG. 5) and/or an image representation of the first and a further region 4, 3 is generated using a further image capturing device 30. In a step S2, the image representations of at least the first region 4, which are generated by the first image capturing devices 20, 50, are evaluated by means of an evaluation device 40 and a marker reference point-based determination of the pose of the marker 2 is carried out in a reference coordinate system. In a step S3, an identity of the marker 2 is determined by evaluating the pattern formed by the first and the further region 4, 3 and a marker shape-based determination of the pose of the marker 2 in the reference coordinate system is subsequently carried out on the basis of the identity. Consequently, marker reference point-based pose determination is implemented independently of marker shape-based pose determination; in particular, these two types of pose determination are based on image representations produced by different image capturing devices 20, 30, 50. Thus, the two types of pose determination form alternatives for pose determination. In particular, the pose determined in marker reference point-based fashion can be verified by means of the pose determined in marker shape-based fashion, or vice versa, without this requiring the use of another marker. It is also conceivable that a resultant pose is determined from the pose determined in marker reference point-based fashion and the pose determined in marker shape-based fashion, for example using a method of data fusion.
[0055] In this context, the depicted sequence of the second and the third step S2, S3 is not mandatory; position determinations implemented in these steps S2, S3 may also be carried out simultaneously or in reversed order.
[0056] FIG. 7 shows a flowchart of a production method according to the invention for producing a target apparatus 1. A blank of a marker 2 or a target apparatus 1 is provided in a first step H1. This blank may have a detection surface which is retroreflective or diffusely scattering at least in part. The blank, in particular the detection surface thereof, may be produced from a film or a laminate. In one form of a production step H2, a diffusely scattering medium is applied to a retroreflective detection surface of the blank. Alternatively, a reflective medium is applied to a diffusely scattering detection surface of the blank. It is also conceivable that, within the scope of production step H2, a retroreflective ink is applied to a first region 3 of the detection surface of the blank and a diffusely scattering ink is applied to a further region 4 of the detection surface. The respective inks are printed onto the blank of the target apparatus 1 such that the first and/or the further region 4, 3 form as a result of printing. It is further possible that a further region 3 of the detection surface is irradiated in thermally sensitive and/or photosensitive fashion using a radiation source, with a retroreflective property of the further region 3 changing and the further region 3 diffusely scattering after the irradiation. To this end, the detection surface of the blank may be coated with a photoresist in particular, the latter reacting in a thermally sensitive and/or photosensitive fashion. An advantage arising is that no additional materials are required to produce the target apparatus 1. The irradiation and production of the target apparatus can be implemented directly on the sterile blank, directly in the operating theater in particular, for example by means of a laser.
[0057] FIG. 8 shows a target apparatus 1 with a marker 2, which has a first region 4 which is depicted by hatching and which is composed of portions 4-A, 4-B. A first portion 4-A has an annular design and encompasses a further region 3, with three further portions 4-B of the first region 4 being arranged in the further region 3, that is to say the further region 3 encompasses the three further portions 4-B of the first region 4. In this case, what is depicted is that the further portions 4-B of the first region 4 have a triangular design. Alternatively, these can be formed like a circular sector.
List of Reference Signs
[0058] TABLE-US-00001 1 Target apparatus 2 Marker 3 Further region 4 First region 5 Marker coordinate system 6 Carrier 7 Spacing between markers 8 First part of a carrier 9 Second part of a carrier 10 Vertical axis of a marker coordinate system 13 Longitudinal axis of a marker coordinate system 14 Transverse axis of a marker coordinate system 20 First image capturing device 21 Light source for the first image capturing device 22 Coordinate system of the first image capturing device 23 Longitudinal axis of the coordinate system of the first image capturing device 24 Capturing direction of the first image capturing device 25 Captured region of the first image capturing device 30 Further image capturing device 31 Light source for the further image capturing device 32 Coordinate system of the further image capturing device 33 Longitudinal axis of the coordinate system of the further image capturing device 34 Emission direction 35 Captured region of the further image capturing device 40 Evaluation device H1 First production step H2 Second production step S1 First method step S2 Second method step S3 Third method step W Angle
