Navigation System for and Method of Tracking the Position of a Work Target

• US 20150327948A1
• Filed: 05/13/2015
• Published: 11/19/2015
• Est. Priority Date: 05/14/2014
• Status: Active Grant

• Current Assignee: Stryker European Operations Holdings, LLC (Stryker Corporation)
• Original Assignee: Stryker European Holdings I, LLC (Stryker Corporation)
• Inventors: Schoepp, Hans, Breisacher, Jochen, Kaltenbrunn, Juergen
• Granted Patent: US 10,575,756 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2017/00946 malleable
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2034/2055 Optical tracking systems
• CPC Class Codes: A61B 2034/2072 Reference field transducer attached to an instrument or patient
• CPC Class Codes: A61B 2090/364 Correlation of different images or relation of image positions in respect to the body
• CPC Class Codes: A61B 2090/3983 Reference marker arrangements for use with image guided surgery
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 5/061 Determining position of a probe within the body employing means separate from the probe, e.g. sensing internal probe position employing impedance electrodes on the surface of the body A61B1/00158 takes precedence

Abstract

A navigation system for and method of tracking the position of the work target is provided. The navigation system can detect distortions of a trackable device during the navigation procedure and compensate for such deformation in a way that reduces or eliminates navigational error and/or avoids or reduces the need to re-set the navigation system during a navigation procedure.

Claims

1. A navigation system for tracking the position of a work target located inside a body, wherein the body is compressible and has a distortable outer surface, the navigation system comprising:

a trackable device comprising a plurality of tracking points configured to be secured to the distortable outer surface of the body, wherein the plurality of tracking points are configured to be moveable relative to each other when the trackable device is secured to the distortable outer surface of the body; and

a computer-implemented tracking system that is adapted to remotely track the positions of each of the plurality of tracking points relative to a coordinate system, the computer-implemented tracking system including a computer processor arrangement adapted to implement a navigation routine that includes the following steps;

accessing an initial model of the trackable device, the initial model having an initial shape based on initial locations of a set of the tracking points;

registering the initial model of the trackable device with an initial position of the work target in an image of the work target;

sensing a deformation of the trackable device with the computer-implemented tracking system after the step of registering the initial model of the trackable device;

creating a refined model of the trackable device that compensates for the deformation of the trackable device; and

calculating a current position of the work target from the refined model of the trackable device.

2. The navigation system of claim 1, wherein the step of creating the refined model of the trackable device includes removing at least one of the tracking points of the set of tracking points that is deformed more than a deviation threshold from the initial shape of the initial model.

3. The navigation system of claim 1, wherein the step of sensing the deformation of the trackable device comprises:

tracking subsequent locations of the tracking points of the set of tracking points after the initial model of the trackable device is registered, the subsequent locations of the tracking points of the set defining a deformed shape; and

identifying the deformation of the trackable device based on a difference between the deformed shape of the trackable device and the initial shape of the trackable device.

4. The navigation system of claim 3, wherein the step of identifying the deformation of the trackable device comprises:

matching the initial shape of the trackable device to the deformed shape of the trackable device; and

calculating a spatial deviation of at least one tracking point of the set of tracking points.

5. The navigation system of claim 4, wherein the step of creating a refined model of the trackable device comprises:

removing the at least one tracking point from the set of tracking points to form a reduced set of tracking points when the spatial deviation for the at least one tracking point exceeds a deviation threshold and has the largest spatial deviation of all of the tracking points in the set, with the refined model of the trackable device created based on the reduced set of tracking points without the subsequent location of the at least one removed tracking point.

6. The navigation system of claim 5, wherein prior to the step of calculating the current position of the work target, the steps of matching the initial shape of the trackable device to the deformed shape of the trackable device, calculating the spatial deviation, and removing the at least one tracking point are iteratively repeated until at least one of:

no further tracking points are removed from the set of tracking points; and

the set of tracking points or the reduced set of tracking points includes fewer than a pre-defined minimum number of tracking points.

7. The navigation system of claim 9, wherein the step of creating the refined model comprises:

adjusting the sensed initial location of at least one tracking point relative to the set of tracking points to the sensed initial locations of the other tracking points in the set of tracking points as a function of relative positions of the tracking points to each other and spatial deviations of these relative positions.

8. The navigation system of claim 1, wherein the navigation routine further includes the steps of:

estimating an expected error of the current position of the work target calculated from the initial model and the deformation of the trackable device; and

providing an indication to a user when the expected error exceeds a pre-defined maximum error threshold for the current position of the work target, wherein the indication optionally includes at least one of a warning message and ending the navigation routine.

9. The navigation system of claim 1, wherein the navigation routine includes the steps of:

sensing the initial locations of the tracking points of the set of tracking points with a navigation sensor configured to measure a position of the set of tracking points relative to the navigation sensor; and

creating the initial model of the trackable device from the sensed initial locations of the set of tracking points.

10. The navigation system of claim 1, wherein the trackable device comprises:

a flexible substrate configured to be secured to the distortable outer surface of the body, wherein the plurality of the tracking points is carried by the flexible substrate.

11. The navigation system of claim 10, wherein the flexible substrate is in the shape of a frame defining a window in a central portion of the trackable device.

12. The navigation system of claim 1, wherein the trackable device comprises:

a plurality of separate substrates, each of the plurality of separate substrates configured to be secured to the distortable outer surface of the body in a location spaced apart from the other substrates of the plurality of separate substrates, wherein each substrate of the plurality of separate substances carries at least one of the plurality of tracking points.

13. The navigation system of claim 1, wherein each of the plurality of tracking points includes at least one of an LED, a reflective surface, a reflective pattern, a magnetic coil, and an optically identifiable geometric shape that uniquely defines position and orientation.

14. The navigation system of claim 1, further comprising:

a work piece adapted to be tracked by the computer-implemented tracking system, wherein the computer-implemented tracking system is adapted to track the position of the work piece relative to the coordinate system, and

wherein the navigation routine further comprises the step of;

calculating the position of the work piece relative to the position of the work target based on a tracked position of the work piece and the calculated current position of the work target.

15. The navigation system of claim 1, wherein the navigation system is a surgical navigation system adapted for use in a surgical operating room, and the trackable device is adapted to be attached to the skin of a surgical patient and to extend around a surgical area on the surgical patient without covering the surgical area.

16. A method of tracking the position of a work target located inside a body with a navigation system, wherein the body is compressible and has a distortable outer surface, the navigation system comprising a trackable device and a computer-implemented tracking system, the trackable device comprising a plurality of tracking points configured to be secured to the distortable outer surface of the body, wherein the plurality of tracking points are configured to be moveable relative to each other when the trackable device is secured to the distortable outer surface of the body, and the computer-implemented tracking system is configured to remotely track the positions of the plurality of tracking points relative to a coordinate system, the method comprising the steps:

accessing an initial model of the trackable device, the initial model having an initial shape based on initial locations of a set of the tracking points;

registering the initial model of the trackable device with an initial position of the work target in an image of the work target;

sensing a deformation of the trackable device with the computer-implemented tracking system after registering the initial model of the trackable device;

creating a refined model of the trackable device that compensates for the deformation of the trackable device; and

calculating the current position of the work target from the refined model of the trackable device.

17. The method of claim 16, wherein the step of creating a refined model includes removing at least one of the tracking points of the set of tracking points that is deformed more than a deviation threshold from the initial shape of the initial model.

18. The method of claim 16, wherein the step of sensing the deformation comprises:

tracking subsequent locations of the tracking points of the set of tracking points after the initial model of the trackable device is registered, the subsequent sequent locations of the trackable points of the set of tracking points defining a deformed shape; and

identifying the deformation of the trackable device based on a difference between the deformed shape of the trackable device and the initial shape of the trackable device.

19. The method of claim 18, wherein the step of identifying the deformation comprises:

matching the initial shape of the trackable device to the deformed shape of the trackable device; and

calculating a spatial deviation of at least one tracking point of the set of tracking points.

20. The method of claim 19, wherein the step of creating a refined model of the trackable device comprises:

removing the at least one tracking point from the set of tracking points to form a reduced set of tracking points when the spatial deviation for the at least one tracking point exceeds a deviation threshold and has the largest spatial deviation of all the tracking points in the set of tracking points, with the refined model of the trackable device created based on the reduced set of tracking points without the subsequent location of the at least one removed tracking point.

21. The method of claim 20, wherein prior to the step of calculating the position of the work target, the steps of matching the initial shape of the trackable device to the deformed shape of the trackable device, calculating the spatial deviation, and removing the at least one tracking point are iteratively repeated until at least one of:

no further tracking points are removed from the set of tracking points; and

the set of tracking points or the reduced set of tracking points include fewer than a pre-defined minimum number of tracking points.

22. The method of claim 16, further comprising the steps of:

sensing the initial locations of the tracking points of the set of the tracking points with a navigation sensor configured to measure a position of the set of tracking points relative to the navigation sensor; and

creating the initial model of the trackable device from the sensed initial locations of the set of the plurality of tracking points,

wherein the step of creating a refined model comprises;

adjusting the sensed initial location of at least one tracking point of the set of tracking points relative to sensed initial locations of the other tracking points in the set of tracking points as a function of relative positions of the tracking points to each other and spatial deviations of these relative positions.

23. The method of claim 16, further comprising the steps:

estimating an expected error of the current position of the work target calculated from the initial model and the deformation of the trackable device; and

providing an indication to a user when the expected error exceeds a pre-defined maximum error threshold for the current position of the work target, wherein the indication optionally includes at least one of a warning message and ending the navigation routine.