METHOD FOR REGISTERING ARTICULATED ANATOMICAL STRUCTURES

Abstract

The present invention relates to a method for registering a first anatomical structure (1) which is articulately coupled to a second anatomical structure (2), the method being constituted to be executed by a computer and comprising the steps of: acquiring second structure correlation data describing the spatial position of at least one correlation feature (3) relative to the second anatomical structure (2); acquiring coupling data describing a positional fixation (6) of the first anatomical structure (1) relative to the second anatomical structure (2), which is set by the articulated coupling (4) between the first anatomical structure (1) and the second anatomical structure (2); determining, based on the second structure correlation data and the coupling data, first structure correlation data describing the spatial position of the at least one correlation feature (3) relative to the first anatomical structure (1).

The present invention further relates to a corresponding computer program and system.

Claims

1.-15. (canceled)

16. A computer implemented method for providing surgical guidance information, the method comprising: assigning a first coordinate system to a pelvis of a patient, the pelvis being joined to a femur of the patient by a hip joint having a center of rotation; registering the femur in a second coordinate system, wherein a mechanical axis of the femur is defined at a first spatial position in the second coordinate system; defining, based on an image of the patient, (i) a second spatial position of a midsagittal plane relative to the pelvis, and (ii) a spatial relationship between a reference feature and the center of rotation; calculating, based on the second spatial position, a third spatial position of the midsagittal plane in the second coordinate system; aligning the second coordinate system with the first coordinate system based on the spatial relationship, thereby defining a fourth spatial position of the midsagittal plane within the first coordinate system; and outputting surgical guidance information based on the third spatial position to a computer-readable storage device.

17. The method of claim 16, wherein aligning the second coordinate system with the first coordinate system comprises virtually rotating the femur together with the second coordinate system around the center of rotation.

18. The method of claim 16, wherein a y-axis of the second coordinate system is parallel to the mechanical axis an x-axis of the second coordinate system is parallel to a medial-lateral-direction with respect to the femur.

19. The method of claim 16, wherein the image of the patient comprises a two-dimensional x-ray image of the pelvis and the femur from an anterior-posterior view.

20. The method of claim 16, wherein the reference feature comprises an anterior superior iliac spine of the pelvis.

21. The method of claim 16, wherein defining the spatial relationship comprises measuring a distance between the reference point and the center of rotation relative to the midsagittal plane.

22. The method of claim 16, wherein defining the spatial relationship comprises determining an angle within a plane of the image defined between the midsagittal plane and a line including the reference point and the center of rotation.

23. The method of claim 16, wherein the midsagittal plane is defined as parallel to the mechanical axis.

24. The method of claim 16, wherein calculating the third spatial position is based further on a distance between the center of rotation and the midsagittal plane in the image.

25. The method of claim 16, wherein the second spatial position and the spatial relationship are defined based further on user input.

26. A system for providing surgical guidance information, the system comprising: one or more processors; and a non-transitory computer-readable medium storing instructions that, when executed, cause the one or more processors to: assign a first coordinate system to a pelvis of a patient, the pelvis being joined to a femur of the patient by a hip joint having a center of rotation; register the femur in a second coordinate system, wherein a mechanical axis of the femur is defined at a first spatial position in the second coordinate system; define, based on an image of the patient, (i) a second spatial position of a midsagittal plane relative to the pelvis, and (ii) a spatial relationship between a reference feature and the center of rotation; calculate, based on the second spatial position, a third spatial position of the midsagittal plane in the second coordinate system; align the second coordinate system with the first coordinate system based on the spatial relationship, thereby defining a fourth spatial position of the midsagittal plane within the first coordinate system; and output surgical guidance information based on the third spatial position to a computer-readable storage device.

27. The system of claim 26, wherein the instructions that cause the one or more processors to align the second coordinate system with the first coordinate system comprise instructions that, when executed, cause the one or more processors to virtually rotate the femur together with the second coordinate system around the center of rotation.

28. The system of claim 26, wherein a y-axis of the second coordinate system is parallel to the mechanical axis an x-axis of the second coordinate system is parallel to a medial-lateral-direction with respect to the femur.

29. The system of claim 26, wherein the image of the patient comprises a two-dimensional x-ray image of the pelvis and the femur from an anterior-posterior view.

30. The system of claim 26, wherein the reference feature comprises an anterior superior iliac spine of the pelvis.

31. The system of claim 26, wherein the instructions that cause the one or more processors to define the spatial relationship comprise instructions that, when executed, cause the one or more processors to measure a distance between the reference point and the center of rotation relative to the midsagittal plane.

32. The system of claim 26, wherein the instructions that cause the one or more processors to define the spatial relationship comprise instructions that, when executed, cause the one or more processors to determine an angle within a plane of the image defined between the midsagittal plane and a line including the reference point and the center of rotation.

33. The system of claim 26, wherein the midsagittal plane is defined as parallel to the mechanical axis.

34. The system of claim 26, wherein the instructions that cause the one or more processors to calculate the third spatial position comprise instructions that, when executed, cause the one or more processors to calculate the third spatial position based on the second spatial position and a distance between the center of rotation and the midsagittal plane in the image.

35. The system of claim 26, wherein the instructions that cause the one or more processors to define the second spatial position and the spatial relationship comprise instructions that, when executed, cause the one or more processors to define the second spatial position and the spatial relationship based further on user input.

Description

[0050] In the following, the invention is described with reference to the enclosed figures which represent preferred embodiments of the invention. The scope of the invention is however not limited to the specific features disclosed in the figures, which show:

[0051] FIG. 1 schematically shows the geometrical consideration underlying the present invention for a pelvis-femur-registration.

[0052] FIG. 2 shows a two-dimensional X-ray-image partially depicting a human pelvis and a human femur

[0053] FIG. 1 shows a human pelvis 1 to which a human femur 2 (shown in broken lines) is coupled via a hip joint 4 having a centre of rotation 6.

[0054] In case the pelvis 1 cannot be sufficiently registered, for example when the patient is lying in a lateral position, the inventive idea is to use data obtained by the registration of the femur 2, for the registration of the pelvis 1. For this purpose, the inventive method considers the fact that the position of the centre of rotations 6 of the hip joint 4 is invariant with respect to both, the pelvis 1 and the femur 2, even though the spatial position of the femur 2 can be altered relative to the pelvis 1 within the limits defined by the hip joint 4.

[0055] According to the present invention, the spatial position of the midsagittal plane 3 with respect to the pelvis 1 can be obtained as follows: First of all, coordinate systems 1a and 2a are assigned to the pelvis 1 and to the femur 2, respectively. For example, the coordinate system 2a may be defined to have an y-axis being parallel to the mechanical axis 7 of the femur, wherein the x-axis of the coordinate system 2a may be defined as a direction being perpendicular to the y-axis and parallel to the medial-lateral-direction with respect to the femur 2. Both, the x-axis and the y-axis of the femur-coordinate system 2a can be obtained by a (full) registration of the femur 2, which is widely known in the prior art.

[0056] Further, a two-dimensional x-ray-image is taken in an anterior-posterior direction from the pelvis 1 and the femur 2, which allows to define within the image the spatial position of the midsegittal plane 3 relative to the pelvis 1, as this is shown in FIG. 2. Moreover, the spatial positions of the centre of rotation 6 and of the anterior superior iliac spine 5 serving as a reference point are determined within the image, wherein the spatial relationship between the reference point 5 and the centre of rotation 6 is also determined. This can be done by either measuring, for example in a medial-lateral direction, the distance of the points 5 and 6 relative to the midsagittal plane 3, or by determining the angle α drawn within the image plane by the midsagittal plane 1 and the straight including points 5 and 6.

[0057] The (full) registration of the femur 2 further provides the spatial position of the mechanical axis of the femur 2, which runs through the centre of rotation 6.

[0058] Since the spatial alignment of the midsagittal plane 3 within the coordinate system 2a of the femur 2 is by definition parallel to the mechanical axis 7 of the femur 2, and the distance between the mechanical axis 7 and the midsagittal plane 3 in a medial direction is known to be equal to the distance between the centre of rotation 6 and the midsagittal plane 3 measured in the x-ray-image, the spatial position (spatial location and spatial alignment) of the midsagittal plane 3 within the coordinate system 2a can be calculated.

[0059] In order to determine the midsegittal plane 3 within the coordinate system 1a assigned to the femur 1, the coordinate system 2a has to be aligned with coordinate system 1a.

[0060] For this purpose, the relative position between the anterior superior iliac spine 5 and the centre of rotation 6 within the coordinate system 2a is adjusted to the corresponding and invariant spatial relationship within coordinate system 1 by virtually rotating the femur 2 together with coordinate system 2a around the centre of rotation 6. In the case shown in FIG. 1, the same spatial relationship between the anterior superior iliac spine 5 and the centre of rotation 6 will be reached by rotating the femur 2 around the centre of rotation 6 in a clockwise direction by an angle α. As a result, the angle α drawn between the midsagittal plane 3 and the straight including the anterior superior iliac spine 5 and the centre of rotation 6 within the coordinate system 1a is equal to the angle β drawn between the midsagittal plane 3 or the mechanical axis 7 and the straight including the anterior iliac spine 5 and the centre of rotation 6 within coordinate system 2a.

[0061] As a result, the spatial position of the midsagittal plane 3 within the coordinate system 1a of the pelvis 1 can be calculated from the registration of the femur 2 and the spatial position of the anterior superior iliac spine 5 of the pelvis 1. It also becomes apparent from FIG. 1 that the information obtained as to the spatial position of the midsagittal plane 3 with respect to the pelvis 1 can be used later on for a patient registration in situ. For such registration it is not necessary to approach reference points on both sides of the pelvis 1, which is especially beneficial with a patient lying in a lateral position.