System and Method for Computation of Coordinate System Transformations

Abstract

The present invention relates to a medical system (100) for determining a coordinate transformation between a coordinate system (INN.sub.1) of an internal structure (I.sub.1) inside a physical object (1) and a coordinate system (IMA) of a 3D image or model thereof.

Claims

1. A medical system (100), comprising: a plurality of surface fiducial markers (F.sub.i) that are configured to be attached to an outer surface (2) of a physical object (1) in arbitrary spatial configurations with respect to each other, at least one adapter (A.sub.1) that is configured to be attached to an internal structure (I.sub.1) of the physical object (1), a medical imaging unit (6) configured to generate a 3D image of said physical object (1) and the surface fiducial markers (F.sub.i) attached to said outer surface (2) within a predefined image coordinate system (IMA), a processing unit (7) configured for measuring each surface fiducial marker's pose within the 3D image and relative to the image coordinate system (IMA) and to compute a coordinate system (SUR) of the surface fiducial markers (F.sub.i) from the positions of the surface fiducial markers (F.sub.i) as well as a first coordinate transformation (.sup.SURT.sub.IMA) between the image coordinate system (IMA) and the coordinate system (SUR) of the surface fiducial markers (F.sub.i); a measuring unit (10) configured to acquire the poses of the surface fiducial markers (F.sub.i) with respect to a coordinate system (WOR) of the measuring unit (10) when the respective surface fiducial marker (F.sub.i) is attached to said outer surface (2), wherein the processing unit (7) is further configured to compute a second coordinate system transformation (.sup.IMAT.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the image coordinate system (IMA) via the coordinate system (SUR) of the surface fiducial markers (F.sub.i), thereby allowing to reference points on said outer surface (2) to points within the 3D image, wherein the medical system (100), through its pose-trackable placement of the at least one adapter (A.sub.1) is configured to measure the pose of the at least one adapter (A.sub.1) relative to the surface fiducial markers (F.sub.i) when the at least one adapter (A.sub.1) is attached to the internal structure (I.sub.1) of said physical object (1), and wherein the processing unit (7) is configured to compute a third coordinate transformation (.sup.INN1T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) and a coordinate system (INN.sub.1) of the internal structure (I.sub.1), and wherein the processing unit (7) is configured to combine the second coordinate transformation (.sup.IMAT.sub.WOR) with the first coordinate transformation (.sup.SURT.sub.IMA) and with the third coordinate transformation (.sup.INN1T.sub.SUR) to create a coordinate transformation (.sup.INN1T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the coordinate system (INN.sub.1) of the internal structure (I.sub.1), thereby allowing the medical system (100) to measure the pose of the at least one adapter (A.sub.1) in the coordinate system (WOR) of the measuring unit (10).

2. The system according to claim 1, wherein the medical system (100) is configured to establish at least one further coordinate transformation (.sup.INN2T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and a coordinate system (INN.sub.2) of a further internal structure (I.sub.2) of the physical object (1), wherein the medical system (100) is configured to at least one of: measure the pose of a further adapter (A.sub.2) relative to the surface fiducial markers (F.sub.i) when the further adapter (A.sub.2) is attached to the further internal structure (I.sub.2) of said physical object (1), and wherein the processing unit (7) is configured to compute a further third coordinate transformation (.sup.INN2T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) and the coordinate system (INN.sub.2) of the further internal structure (I.sub.2), and wherein the processing unit (7) is configured to combine the second coordinate transformation (.sup.IMAT.sub.WOR) with the first coordinate transformation (.sup.SURT.sub.IMA) and with the further third coordinate transformation (.sup.INN2T.sub.SUR) to create the further coordinate transformation (.sup.INN2T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the coordinate system (INN.sub.2) of the further internal structure (I.sub.2), thereby allowing to measure the pose of the further adapter (A.sub.2) in the coordinate system (WOR) of the measuring unit (10), or by by combining the coordinate transformation (.sup.INN1T.sub.WOR) between the coordinate (WOR) of the measuring unit (10) and the coordinate system (INN.sub.1) of the internal structure (I.sub.1) with a coordinate transformation (.sup.INN2T.sub.INN1) between the coordinate system (INN.sub.1) of the internal structure (I.sub.1) and a coordinate system (INN.sub.2) of the further internal structure (12).

3. The medical system according to claim 1 or 2, wherein the medical system (100) is configured to track said outer surface (2) using one of: c. the surface fiducial markers (F.sub.i), wherein particularly the medical system (100) is configured to track the position or the pose of each individual surface fiducial marker (F.sub.i), particularly using one of the following: an optical measurement principle, a video-optical measurement principle, an electromagnetic measurement principle, a time-of-flight measurement principle; d. tracking of the outer surface (2) by using one of: laser scanning of the outer surface (2), scanning the outer surface (2) with structured light.

4. The medical system according to one of the preceding claims, wherein the medical system (100) comprises different measurement modalities within one coordinate system to allow tracking of surface fiducial markers (F.sub.i) and the at least one adapter (A.sub.1) simultaneously using the different measurement modalities.

5. The medical system according to one of the preceding claims, wherein the medical system (100) comprises a pose-trackable surgical robotic device (8) configured to generate an access to the internal structure (I.sub.1) of the physical object (1) and to deliver the at least one adapter (A.sub.1) to the internal structure (3) and position the at least one adapter (A.sub.1) on the internal structure (3).

6. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to track several internal structures (I.sub.1) within the physical object (1) independently and to establish and track several coordinate transformations between those internal structures (I.sub.i) and the outer surface (2), wherein at least one adapter (A.sub.1) has been delivered to each of the several internal structures (I.sub.i) by the pose-trackable surgical robotic device (8).

7. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to track several internal structures (I.sub.i) relative to one another and absolutely against the outer surface (2) simultaneously.

8. The medical system according to one of the preceding claims, wherein the at least one adapter (A.sub.1) comprises a connecting portion (5b) that is configured to be releasably connected to a structure fiducial marker (S.sub.1), and an anchoring portion (5c) that is configured to be attached to the internal structure (I.sub.1) so that an initially registered pose of the structure fiducial marker (S.sub.1) relative to the internal structure (I.sub.1) is reproduced upon re-connection of the structure fiducial marker (S.sub.1) to the adapter (A.sub.1).

9. The medical system according to claim 8, wherein the anchoring portion (5c) comprises a thread (51) on an outside of the anchoring portion (5c) for anchoring the at least one adapter (A.sub.1) to the internal structure (I.sub.1) by screwing the anchoring portion (5c) into a bore hole of the internal structure (I.sub.1).

10. The medical system according to claim 8 or 9, wherein the connecting portion (5b) is configured to protrude from an outside of the internal structure (I.sub.1) when the anchoring portion (5c) is anchored to the internal structure (I.sub.1), wherein the connecting portion (5b) comprises a plurality of image localization features (52) that are integrated into the connecting portion (5b), wherein particularly the respective image localization feature (52) is a radiopaque marker.

11. The medical system according to claim 10, wherein the medical system (100) is configured to intraoperatively acquire at least one image (IM) of the internal structure (I.sub.1) and the image localization features (52) of the adapter (A.sub.1) and to locate the internal structure (I.sub.1) and the image localization features (52) in the at least one intraoperatively acquired image (IM) and to compute a coordinate transformation (.sup.INN′T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and a coordinate system (INN′) of the internal structure (I.sub.1).

12. The medical system according to claim 10 or 11, wherein the respective image localization feature (52) is formed by a cylindrical rod, wherein particularly the rods (52) are arranged obliquely with respect to one another.

13. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to compute the coordinate system (SUR) of the surface fiducial markers (F.sub.i) by using a position of a first surface fiducial marker (F.sub.1) as a center of the coordinate system (SUR) of the surface fiducial markers (F.sub.i), wherein the medical system is further configured to use as a first coordinate axis (x) of the coordinate system (SUR) of the surface fiducial markers (F.sub.i) a normalized vector extending from the first surface fiducial marker (F.sub.1) to a second surface fiducial marker (F.sub.2) and as a second coordinate axis (y) a normalized vector extending from the first surface fiducial marker (F.sub.1) to a third surface fiducial marker (F.sub.3) and as a third coordinate axis (z) the cross product between the first and the second coordinate axis (x, y).

14. A method for determining a coordinate transformation between a coordinate system (INN.sub.1) of an internal structure (I.sub.1) inside a physical object (1) and an image coordinate system (IMA) of a 3D image of the internal structure (I.sub.1), wherein the method comprises the steps of: (a) computing a first coordinate transformation (.sup.SURT.sub.IMA) between a coordinate system (SUR) of surface fiducial markers (F.sub.i) attached to an outer side (2) of the physical object (1) and the image coordinate system (IMA) of the 3D image; (b) computing a second coordinate transformation (.sup.INN1T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) attached to the physical object's outer side (2) and a coordinate system (INN.sub.1) of an internal structure (I.sub.1) inside the physical object (1); (c) extending the coordinate transformation (.sup.SURT.sub.IMA) computed in step (a) by the coordinate transformation (.sup.INN1T.sub.SUR) computed in step (b) to create a coordinate transformation (.sup.INN1T.sub.IMA) between the image coordinate system (IMA) of the 3D image and the coordinate system (INN.sub.1) of the internal structure (I.sub.1).

15. The method according to claim 14, wherein the outer surface (2) is tracked by one of: a. individually tracking the pose or position of the surface fiducial markers (F.sub.i), particularly by means of one of optical tracking, video-optical tracking, electromagnetic tracking, time-of-flight tracking; b. tracking of the outer surface (2) by means of laser scanning or scanning with structured light.

16. The method according to claim 14, wherein additionally at least one adapter (A.sub.1) is attached to the internal structure (I.sub.i) by a pose-trackable surgical robotic device (8) and wherein the at least one adapter (A.sub.1) can be tracked relative to the surface fiducial markers (F.sub.i) by the processing unit (7) computing the coordinate transformations (.sup.SURT.sub.IMA and .sup.INN1T.sub.SUR and .sup.INN1T.sub.IMA).

17. A medical system (100), comprising: a plurality of surface fiducial markers (F.sub.i) that are configured to be attached to an outer surface (2) of a physical object (1) in arbitrary spatial configurations with respect to each other, at least one adapter (A.sub.1) that is configured to be attached to an internal structure (I.sub.1) of the physical object (1), a medical imaging unit (6) configured to generate a 3D image of said physical object (1) and the surface fiducial markers (F.sub.i) attached to said outer surface (2) within a predefined image coordinate system (IMA), a processing unit (7) configured for measuring each surface fiducial marker's pose within the 3D image and relative to the image coordinate system (IMA) and to compute a coordinate system (SUR) of the surface fiducial markers (F.sub.i) from the positions of the surface fiducial markers (F.sub.i) as well as a first coordinate transformation (.sup.SURT.sub.IMA) between the image coordinate system (IMA) and the coordinate system (SUR) of the surface fiducial markers (F.sub.i); a measuring unit (10) configured to acquire the poses of the surface fiducial markers (F.sub.i) with respect to a coordinate system (WOR) of the measuring unit (10) when the respective surface fiducial marker (F.sub.i) is attached to said outer surface (2), wherein the processing unit (7) is further configured to compute a second coordinate system transformation (.sup.IMAT.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the image coordinate system (IMA) via the coordinate system (SUR) of the surface fiducial markers (F.sub.i), thereby allowing to reference points on said outer surface (2) to points within the 3D image, according to .sup.IMAT.sub.WOR=(.sup.SURT.sub.IMA).sup.−1,SURT.sub.WOR, wherein the medical system (100), through its pose-trackable placement of the at least one adapter (A.sub.1) is configured to measure the pose of the at least one adapter (A.sub.1) relative to the surface fiducial markers (F.sub.i) when the at least one adapter (A.sub.1) is attached to the internal structure (I.sub.1) of said physical object (1), and wherein the processing unit (7) is configured to compute a third coordinate transformation (.sup.INN1T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) and a coordinate system (INN.sub.1) of the internal structure (I.sub.1), and wherein the processing unit (7) is configured to combine the second coordinate transformation (.sup.IMAT.sub.WOR) with the first coordinate transformation (.sup.SURT.sub.IMA) and with the third coordinate transformation (.sup.INN1T.sub.SUR) to create a coordinate transformation (.sup.INN1T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the coordinate system (INN.sub.1) of the internal structure (I.sub.1), according to .sup.INN1T.sub.SUR*.sup.SURT.sub.IMA*.sup.IMAT.sub.WOR=.sup.INN1T.sub.WOR, thereby allowing the medical system (100) to measure the pose of the at least one adapter (A.sub.1) in the coordinate system (WOR) of the measuring unit (10).

18. The system according to claim 17, wherein the medical system (100) is configured to establish at least one further coordinate transformation (.sup.INN2T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and a coordinate system (INN.sub.2) of a further internal structure (12) of the physical object (1), wherein the medical system (100) is configured to at least one of: measure the pose of a further adapter (A.sub.2) relative to the surface fiducial markers (F.sub.i) when the further adapter (A.sub.2) is attached to the further internal structure (I.sub.2) of said physical object (1), and wherein the processing unit (7) is configured to compute a further third coordinate transformation (.sup.INN2T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) and the coordinate system (INN.sub.2) of the further internal structure (I.sub.2), and wherein the processing unit (7) is configured to combine the second coordinate transformation (.sup.IMAT.sub.WOR) with the first coordinate transformation (.sup.SURT.sub.IMA) and with the further third coordinate transformation (.sup.INN2T.sub.SUR) to create the further coordinate transformation (.sup.INN2T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and the coordinate system (INN.sub.2) of the further internal structure (I.sub.2), thereby allowing to measure the pose of the further adapter (A.sub.2) in the coordinate system (WOR) of the measuring unit (10), or by by combining the coordinate transformation (.sup.INN1T.sub.WOR) between the coordinate (WOR) of the measuring unit (10) and the coordinate system (INN.sub.1) of the internal structure (I.sub.1) with a coordinate transformation (.sup.INN2T.sub.INN1) between the coordinate system (INN.sub.1) of the internal structure (I.sub.1) and a coordinate system (INN.sub.2) of the further internal structure (I.sub.2).

19. The medical system according to claim 17 or 18, wherein the medical system (100) is configured to track said outer surface (2) using one of: e. the surface fiducial markers (F.sub.i), wherein particularly the medical system (100) is configured to track the position or the pose of each individual surface fiducial marker (F.sub.i), particularly using one of the following: an optical measurement principle, a video-optical measurement principle, an electromagnetic measurement principle, a time-of-flight measurement principle; f. tracking of the outer surface (2) by using one of: laser scanning of the outer surface (2), scanning the outer surface (2) with structured light.

20. The medical system according to one of the preceding claims, wherein the medical system (100) comprises different measurement modalities within one coordinate system to allow tracking of surface fiducial markers (F.sub.i) and the at least one adapter (A.sub.1) simultaneously using the different measurement modalities.

21. The medical system according to one of the preceding claims, wherein the medical system (100) comprises a pose-trackable surgical robotic device (8) configured to generate an access to the internal structure (I.sub.1) of the physical object (1) and to deliver the at least one adapter (A.sub.1) to the internal structure (3) and position the at least one adapter (A.sub.1) on the internal structure (3).

22. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to track several internal structures (10 within the physical object (1) independently and to establish and track several coordinate transformations between those internal structures (I.sub.i) and the outer surface (2), wherein at least one adapter (A.sub.1) has been delivered to each of the several internal structures (I.sub.i) by the pose-trackable surgical robotic device (8).

23. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to track several internal structures (I.sub.i) relative to one another and absolutely against the outer surface (2) simultaneously.

24. The medical system according to one of the preceding claims, wherein the at least one adapter (A.sub.1) comprises a connecting portion (5b) that is configured to be releasably connected to a structure fiducial marker (S.sub.1), and an anchoring portion (5c) that is configured to be attached to the internal structure (I.sub.1) so that an initially registered pose of the structure fiducial marker (S.sub.1) relative to the internal structure (I.sub.1) is reproduced upon re-connection of the structure fiducial marker (S.sub.1) to the adapter (A.sub.1).

25. The medical system according to claim 24, wherein the anchoring portion (5c) comprises a thread (51) on an outside of the anchoring portion (5c) for anchoring the at least one adapter (A.sub.1) to the internal structure (I.sub.1) by screwing the anchoring portion (5c) into a bore hole of the internal structure (I.sub.1).

26. The medical system according to claim 24 or 25, wherein the connecting portion (5b) is configured to protrude from an outside of the internal structure (I.sub.1) when the anchoring portion (5c) is anchored to the internal structure (I.sub.1), wherein the connecting portion (5b) comprises a plurality of image localization features (52) that are integrated into the connecting portion (5b), wherein particularly the respective image localization feature (52) is a radiopaque marker.

27. The medical system according to claim 26, wherein the medical system (100) is configured to intraoperatively acquire at least one image (IM) of the internal structure (I.sub.1) and the image localization features (52) of the adapter (A.sub.1) and to locate the internal structure (I.sub.1) and the image localization features (52) in the at least one intraoperatively acquired image (IM) and to compute a coordinate transformation (.sup.INN′T.sub.WOR) between the coordinate system (WOR) of the measuring unit (10) and a coordinate system (INN′) of the internal structure (I.sub.1).

28. The medical system according to claim 26 or 27, wherein the respective image localization feature (52) is formed by a cylindrical rod, wherein particularly the rods (52) are arranged obliquely with respect to one another.

29. The medical system according to one of the preceding claims, wherein the medical system (100) is configured to compute the coordinate system (SUR) of the surface fiducial markers (F.sub.i) by using a position of a first surface fiducial marker (F.sub.1) as a center of the coordinate system (SUR) of the surface fiducial markers (F.sub.i), wherein the medical system is further configured to use as a first coordinate axis (x) of the coordinate system (SUR) of the surface fiducial markers (F.sub.i) a normalized vector extending from the first surface fiducial marker (F.sub.1) to a second surface fiducial marker (F.sub.2) and as a second coordinate axis (y) a normalized vector extending from the first surface fiducial marker (F.sub.1) to a third surface fiducial marker (F.sub.3) and as a third coordinate axis (z) the cross product between the first and the second coordinate axis (x, y).

30. A method for determining a coordinate transformation between a coordinate system (INN.sub.1) of an internal structure (I.sub.1) inside a physical object (1) and an image coordinate system (IMA) of a 3D image of the internal structure (I.sub.1), wherein the method comprises the steps of: (a) computing a first coordinate transformation (.sup.SURT.sub.IMA) between a coordinate system (SUR) of surface fiducial markers (F.sub.i) attached to an outer side (2) of the physical object (1) and the image coordinate system (IMA) of the 3D image; (b) computing a second coordinate transformation (.sup.INN1T.sub.SUR) between the coordinate system (SUR) of the surface fiducial markers (F.sub.i) attached to the physical object's outer side (2) and a coordinate system (INN.sub.1) of an internal structure (I.sub.1) inside the physical object (1); (c) automatically extending the coordinate transformation (.sup.SURT.sub.IMA) computed in step (a) by the coordinate transformation (.sup.INN1T.sub.SUR) computed in step (b) to create a coordinate transformation (.sup.INN1T.sub.IMA) between the image coordinate system (IMA) of the 3D image and the coordinate system (INN.sub.1) of the internal structure (I.sub.1).

31. The method according to claim 30, wherein the outer surface (2) is tracked by one of: a. individually tracking the pose or position of the surface fiducial markers (F.sub.i), particularly by means of one of optical tracking, video-optical tracking, electromagnetic tracking, time-of-flight tracking; b. tracking of the outer surface (2) by means of laser scanning or scanning with structured light.

32. The method according to claim 30, wherein additionally at least one adapter (A.sub.1) is attached to the internal structure (I.sub.i) by a pose-trackable surgical robotic device (8) and wherein the at least one adapter (A.sub.1) can be tracked relative to the surface fiducial markers (F.sub.i) by the processing unit (7) computing the coordinate transformations (.sup.SURT.sub.IMA and .sup.INN1T.sub.SUR and .sup.INN1T.sub.IMA).

Description

[0114] In the following embodiments as well as further features and advantages of the present invention are described with reference to the Figures, wherein

[0115] FIG. 1 shows a schematic illustration of a medical system according to the present invention;

[0116] FIG. 2 shows a detailed illustration of the adapters for holding the structure fiducial markers of the system according to FIG. 1 when attached to the internal structure (e.g. vertebrae) of the patient,

[0117] FIG. 3A shows an illustration of an embodiment of a surface fiducial marker;

[0118] FIG. 3B shows an illustration of a further embodiment of a surface fiducial marker;

[0119] FIG. 4 shows an embodiment of an adapter of the medical system that is configured to be attached to an internal structure (e.g. vertebra) and allows for a releasable but reproducible connection of a structure fiducial marker to the adapter;

[0120] FIG. 5 shows an embodiment of a structure fiducial marker that can be connected to the adapter shown in FIG. 4; and

[0121] FIG. 6 shows refining of a coordinate transformation between a coordinate system of an internal structure and the coordinate system of the measuring unit using an intraoperatively obtained image.

[0122] FIG. 1 shows an embodiment of a medical system 100 according to the present invention that allows for determination of a geometric transformation between an internal structure 11 such as a spinal vertebra inside a physical object 1, i.e., the body 1 of the patient, and a 3D image of the object/body 1. To this end, the medical system 100 comprises a measuring unit 10, a processing unit 7, a medical imaging unit 6 (e.g. a CT scanner or an MRI device) and preferably also a surgical robotic device 8. It is well understood that the optical tracking system may be used to track the pose of surgical instruments, the surgical robotic device 8 and adapter devices. The processing unit 7 can comprise any suitable computer. The processing unit 7 can be a stand-alone unit, but may also be an integral part of another component of the system 100. The processing unit 7 preferably comprises interfaces to connect to the medical imaging unit 6 (e.g. to receive a 3D image of the patient) and particularly to the surgical robotic device 8, e.g. for controlling the latter. Furthermore, the processing unit 7 can comprise an interface for connecting to the measuring unit 10.

[0123] Furthermore, the medical system 100 comprises a plurality of surface fiducial markers F.sub.i (wherein i is a natural number that labels the surface fiducial markers) that can each be configured as shown in FIG. 3A below. The surface fiducial markers F.sub.i are each designed to be attached to an outer surface 2 of a physical object 1 (e.g. skin 2 of a body 1 of a patient) in arbitrary spatial configurations with respect to each other.

[0124] Further, the medical system 100 comprises at least one adapter A.sub.1 for providing reproducible connection of an associated structure fiducial marker S.sub.1 to the adapter A.sub.1 (several such adapters A.sub.i/structure fiducial marker S.sub.i are used in case several internal structures I.sub.i shall be tracked, wherein i is again a natural number that labels the adapters, surface fiducial markers, and internal structures, respectively), wherein the adapter A.sub.1 is configured to be attached to an internal structure I.sub.1 of the physical object 1. An embodiment of a preferred adapter A.sub.1 will be described in conjunction with FIG. 4 in detail further below.

[0125] Particularly, the medical imaging unit 6 is configured to generate a 3D image of said physical object 1 and the surface fiducial markers F.sub.i attached to said outer surface 2 of the object 1 with respect to an image coordinate system IMA.

[0126] With help of the processing unit 7 (for example a computer on which a suitable software is executed) each surface fiducial marker's pose is measured within the 3D image and relative to the image coordinate system IMA. This may be carried out automatically or guided by a user/physician. Further, the processing unit 7 is configured to compute a coordinate system SUR of the surface fiducial markers F.sub.i from the positions of the surface fiducial markers as well as a first coordinate transformation .sup.SURT.sub.IMA between the image coordinate system IMA and the coordinate system SUR of the surface fiducial markers F.sub.i.

[0127] Further, the measuring unit 10 (for example a stereotactic camera) is configured to acquire the poses of the surface fiducial markers F.sub.i with respect to a coordinate system WOR of the measuring unit 10 when the respective surface fiducial marker F.sub.i is attached to said outer surface 2 of the object 1 as shown in FIG. 1.

[0128] Regarding this measurement unit 10, the processing unit 7 is further configured to compute a second coordinate system transformation .sup.IMAT.sub.WOR between the coordinate system WOR of the measuring unit 10 and the image coordinate system IMA via the coordinate system SUR of the surface fiducial markers F.sub.i, thereby allowing for reference between points on said outer surface 2 of the object 1 to points within the 3D image or model generated with help of the medical imaging unit 6.

[0129] The system 1 is now configured to measure the pose of the at least one adapter A.sub.1 attached to the internal structure Ii relative to the surface fiducial markers F.sub.i. Particularly a surgical robotic device 8 can measure the pose of the adapter A.sub.1 upon attaching the adapter A.sub.1 to the internal structure I.sub.1 by means of the robotic device 8 of the system 100. The skilled person will understand that the pose of the robotic device 8 may also be measured through a tracking camera in conjunction with tracking markers positioned on the robotic device 8 (e.g., on the joints of the robotic device 8) or may be deduced through the medical imaging unit 6 providing data on the position of surgical instruments attached to the robotic device 8. In this regard, the coordinate system of the tracking camera may measure both the position of an end effector of the robotic device 8 in space as well as the position of the surface fiducial markers on the patient, thus allowing the deduction of the position of the end effector with respect to the patient coordinate system. Further, the processing unit 7 is configured to compute a third coordinate transformation .sup.INN1T.sub.SUR between the coordinate system SUR of the surface fiducial markers F.sub.i and a coordinate system INN.sub.1 of the internal structure I.sub.1.

[0130] The processing unit 7 then combines the second coordinate transformation .sup.IMAT.sub.WOR with the first coordinate transformation .sup.SURT.sub.IMA and with the third coordinate transformation .sup.INNA1T.sub.SUR, for example by multiplying the associated matrices:

.sup.INN1T.sub.SUR.sup.SURT.sub.IMA.sup.IMAT.sub.WOR=.sup.INN1T.sub.WOR.

[0131] to create a final coordinate transformation represented by the matrix .sup.INN1T.sub.WOR, thereby allowing to measure the pose of the adapter A.sub.1 (or of a structure fiducial marker S.sub.1 connected to the adapter A.sub.1) in the coordinate system WOR.

[0132] In order to be able to attach the structure fiducial marker S.sub.1 in an efficient and reproducible manner to the respective internal structure I.sub.i, the medical system 100 preferably comprises the at least one adapter A.sub.1 as shown in FIG. 4. The system 100 can comprise several adapters A.sub.i and associated structure fiducial markers S.sub.i).

[0133] The at least one adapter A.sub.1 comprises a connecting portion 5b that is configured to be releasably connected to the at least one structure fiducial marker S.sub.1 (cf. e.g. FIG. 5). For this, the adapter A.sub.1 may comprise a connector 53 e.g. formed by an opening 53 arranged in a face side 5a of the connecting portion 5b of the adapter 5. The fiducial marker Si can be configured to engage with the connector/opening 53 to generate a releasable mechanical connection between the marker S.sub.1 and the adapter A.sub.1 (the structure fiducial marker S.sub.1 is not indicated in FIG. 2 but shown in FIG. 5). Furthermore, the adapter A.sub.1 comprises an anchoring portion 5c that is configured to be attached to the internal structure I.sub.1. In case the system 100 comprises several adapters A.sub.1 and structure fiducial markers S.sub.i, these adapters and structure fiducial markers can be designed as the adapter A.sub.1 and marker S1, respectively.

[0134] Due to the specific design of the at least one adapter A.sub.1, an initially registered pose of the structure fiducial marker S.sub.1 (when connected to the adapter A.sub.1) relative to the internal structure I.sub.1 is reproduced upon re-connection of the released structure fiducial marker 20 to the adapter A.sub.1.

[0135] For anchoring the anchoring portion 5c in the internal structure (e.g. bone, particularly vertebra) I.sub.1 the adapter A.sub.1 comprises a thread 51 formed on an outside of the anchoring portion 5c. Thus, the anchoring portion 5c can be screwed into a bore hole provide in the internal structure I.sub.1 (e.g. by way of the pose-trackable surgical robotic device 8). Particularly, the anchoring portion 5c is tapered to form a pointed end of the anchoring portion 5c which improves insertion into the bore hole.

[0136] Particularly, the connecting portion 5b is configured to extend along an outside of the internal structure I.sub.1 when the anchoring portion 5c is anchored to the internal structure I.sub.1 as described above, wherein the connecting portion 5c comprises a plurality of image localization features 52 that are integrated into the connecting portion 5b, wherein particularly the respective image localization feature 52 is a radiopaque marker. In an embodiment, the respective image localization features 52 is formed by a cylindrical rod, wherein the rods are arranged obliquely with respect to one another as indicated in FIG. 4.

[0137] An embodiment of a structure fiducial marker S.sub.1 that can e.g. be used for tracking during surgery and is not necessary for the registering process according to the present invention is shown in FIG. 5. According thereto, the marker S.sub.1 comprises a base portion 21 that is configured to engage with the connector 53 of the adapter A.sub.1 so as to releasably connect the marker S.sub.1 to the adapter A.sub.1. Furthermore, the marker S.sub.1 can comprise several (e.g. three) individivally trackable fiducial elements 23, particularly in the form of spheres, that can be connected to the base 21 portion via arms 22.

[0138] Furthermore, FIG. 3A shows an embodiment of a surface fiducial marker F.sub.1 that comprises a flat cylindrical body 40 into which a visually trackable fiducial element 41 cab be embedded.

[0139] FIG. 3B shows an alternative embodiment of a surface fiducial marker F.sub.1, wherein here the fiducial element 41 is formed by a retroreflective sphere, wherein the tracking element 41 can be connected to a circular base 40 and can further be covered by a transparent cover 42 connected to the base 40.

[0140] Furthermore, FIG. 6 shows that the transformation .sup.INN1T.sub.WOR can be further refined or replaced via an intraoperative imaging method, wherein the previously existing coordinate system transformation .sup.INN1T.sub.WOR is refined by algorithmically locating the internal structure I.sub.1 and the image localization features 52 of the adapter A.sub.1 in the resulting imagery and by computing a subsequent incremental registration transformation .sup.INN′T.sub.WOR. Particularly, the medical system 100 can be configured to compute a coordinate transformation .sup.IMAT.sub.INN′ from a coordinate system INN′ of the internal structure Ii in an intraoperatively obtained image IM to an image coordinate system IMA of the intraoperatively obtained image IM as indicated in FIG. 6, and by combining this transformation .sup.IMAT.sub.INN′ with the already computed coordinate transformation .sup.IMAT.sub.WOR

.sup.INN′T.sub.WOR=(.sup.IMAT.sub.INN′).sup.−1,IMAT.sub.WOR.

[0141] to determine the refined coordinate transformation .sup.INN′T.sub.WOR from the coordinate system WOR of the measuring unit 10 to the coordinate system INN′ of the internal structure.

[0142] The medical system 100 according to the present invention as described herein is particularly suited to perform the methods according to the present invention.

[0143] The non-surgical methods allow for determination of a coordinate transformation between a coordinate system INN.sub.1 of an internal structure I.sub.1 as shown in FIG. 1 inside a physical object 1 and a coordinate system of a 3D image thereof (e.g. obtained with the medical imaging unit 6), wherein generating this transformation is achieved stepwise by: [0144] (a) computing an initial coordinate transformation .sup.SURT.sub.IMA between a coordinate system SUR of surface fiducial markers F.sub.i (i=1, 2, . . . ) attached to the outer side 2 of the physical object 1 and the 3D image (i.e. registration); [0145] (b) computing a coordinate transformation .sup.INN1T.sub.SUR between the coordinate system SUR of the surface fiducial markers F.sub.i (i=1, 2, . . . ) attached to the physical object's outer side 2 and a coordinate system INN.sub.1 of an internal structure I.sub.1 to which at least one adapter A.sub.1 is already attached inside the physical object 1. Particularly, the adapter A.sub.1 serves for connecting a structure fiducial marker S.sub.1 (cf. FIG. 5) to the adapter A.sub.1 in a reproducible fashion that can later be tracked (e.g. during surgery); and [0146] (c) extending the coordinate transformation computed in step (a) by the coordinate transformation computed in step (b) to create a coordinate transformation between the image coordinate system IMA of the 3D image and the coordinate system INN.sub.1 associated with the internal structure I.sub.1.

[0147] Particularly, in an embodiment, this method may be employed with respect to internal structures of a patient formed by spinal vertebrae I.sub.i (i=1, 2, . . . ), wherein the physical object 1 is an upper body of the patient. However, the present invention can also be applied to any other internal structure that allows placement of the adapters or structural fiducial markers.

[0148] Particularly, using the method according to the present invention, the following procedure relating to the tracking of vertebrae (or other internal structures) I.sub.i can be carried out: [0149] 1) Attaching surface fiducial markers F.sub.i visible in an 3D image created by a medical imaging unit 6 (e.g. CT or MRI) and in a measurement unit (e.g. such as a stereotactic camera) 10 to the outer surface 2 of a body of a subject (i.e. skin) [0150] 2) Producing a 3D image using the medical imaging unit 6 and determination of the surface fiducial marker's position or pose within the image coordinate system IMA. Computation of a (for example perpendicular right-hand) coordinate system SUR from the surface fiducial marker's positions. [0151] 3) Setup of tracking and subsequent tracking of the outer surface 2 via said surface fiducial markers F.sub.i (particularly based on the assumption that no deformation is present as long no surgical intervention (cut, screw placement etc.) is carried out on the body/outer surface of the subject. [0152] 4) Transfer of the 3D image to a software system (e.g. processing unit) 7 and marking of a suitable place to drill and insert an adapter A.sub.1 for a structure fiducial marker S.sub.1 into the internal structure (e.g. vertebra of subject) I.sub.1. This step may be repeated for as often as necessary to prepare the method according to the present invention beforehand, but does not constitute a step of the claimed method. [0153] 5) Use of a suitable surgical device or control of a pose-trackable surgical robotic device 8 to drill a hole into vertebra I.sub.1 at the planned position and orientation (according to step 4). Particularly, minimal to no distortion of the surface fiducial markers F.sub.i is present (also this step does not constitute a step of the claimed method). [0154] 6) Attachment of the adapter A.sub.1 to the internal structure/vertebra I.sub.1 (also this step does not constitute a step of the claimed method). Particularly, the pose of the adapter A.sub.1 is known to the system 100 via the pose-trackable surgical robotic device 8 that can measure the exact pose of the adapter A.sub.1 (and thus of a marker 20 connected to the adapter later on) upon attaching the adapter A.sub.1. [0155] 7) A tracking system (e.g. comprising measurement unit 10) records relative positions or poses of surface fiducial markers F.sub.i and of the adapter A.sub.1 or of a structure fiducial marker S.sub.1 connected to the adapter A.sub.1, and medical system 100 computes relative geometric transformation between the surface and adapter A.sub.1/structure fiducial marker S.sub.1. Registration between tracked internal structure (e.g. vertebra) I.sub.1 and 3D image data set is then made available. [0156] 8) Repeat steps 4-7 for each internal structure (e.g. vertebra) I.sub.i (i>1) and corresponding adapters A.sub.i (i>1).

REFERENCE NUMERALS

[0157] 1 physical object (e.g. body or body portion of patient) [0158] 2 outer surface of physical object [0159] I.sub.i i-th internal structure of the object, not otherwise accessible from the outside [0160] F.sub.i i-th surface fiducial marker attached to the outer surface [0161] A.sub.i i-th adapter attached to the objects internal structure (after creation of access) connectable to structure fiducial marker [0162] 5a face side [0163] 5b connecting portion [0164] 5c anchoring portion [0165] 6 medical imaging device (e.g. CT scanner or MRI device) [0166] 7 processing unit [0167] 8 surgical robot [0168] 10 measurement unit [0169] IMA image coordinate system (of the 3D image/model) [0170] WOR coordinate system of the measurement unit [0171] SUR coordinate system of the surface fiducial markers [0172] INN.sub.1 coordinate system of the objects internal structure [0173] INN′ coordinate system of internal structure [0174] S.sub.i i-th structure fiducial marker for internal structures [0175] 51 thread [0176] 52 image localization feature [0177] 53 opening/connector for connecting structure fiducial marker to adapter [0178] 100 medical system