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1. WO2020192872 - METHOD OF ESTIMATING A POSITION OF A MEDICAL INSTRUMENT TIP

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[ EN ]

CLAIMS

1 . A computer implemented medical method of estimating a position of a medical instrument tip (1 1 ), the method comprising the steps:

providing (S10) a virtual model of a shape of a medical instrument (10) comprising the instrument tip (1 1 );

providing (S20) a virtual model of a shape of a calibration device (20) comprising an indentation (21 ) onto which the instrument tip (1 1 ) is introduced for calibration; and

matching (S30) the model of the shape of the instrument tip (1 1 ) onto the model of the shape of the calibration device (20) thereby estimating a position of the instrument tip (1 1 ).

2. The method according to claim 1 , comprising the step:

using the estimated position of the instrument tip (1 1 ) as an updated reference point (Pi) in a surgical navigation system.

3. The method according to any of the preceding claims, further comprising the step:

tracking the instrument (10) by a tracking device (30) and a, preferably passive, tracker arranged on the instrument (10).

4. The method according to any of the preceding claims, comprising the steps:

determining an actual spatial orientation of the instrument (10), preferably along an axis of the instrument (10); and

using said determined actual spatial orientation during matching (S30) the model of the instrument tip (1 1 ) onto the model of the calibration device (20).

5. The method according to any of the claims 3 or 4, wherein

the actual spatial orientation is determined based on a result of tracking the instrument (10).

6. The method according to any of claims 3 to 5, comprising the step:

determining the actual spatial orientation based on an estimation of the axis of the instrument (10) and/or based on learning from a rotation movement of the instrument tip (11 ) in the indentation (21 ), which is recorded by a tracking device (30).

7. The method according to any of the preceding claims, comprising the step:

measuring, calibrating, validating and/or verifying the medical instrument

(10) using the estimated position of the instrument tip (11 ) as an updated reference point (Pi).

8. The method according to any of the preceding claims, comprising the steps:

generating a plurality of frames of different positions of the instrument tip

(11 ) in the indentation (21 ) by using a surgical navigation device;

matching the model of the shape of the instrument tip (11 ) onto the model of the shape of the calibration device (20) for each frame and estimating a position of the instrument tip (11 ) for each frame; and

calculating an average position of the instrument tip (11 ) based on the estimated positions of the instrument tip (11 ) of every frame.

9. The method according to claim 8, comprising the step:

using the calculated average position of the instrument tip (11 ) as an updated reference point (Pi) in a surgical navigation system.

10. The method according to any of the preceding claims, wherein the matching (S30) of the models comprises the step of:

calculating, based on the model of the instrument tip (1 1 ) and the model of the calibration device (20), at least one collision point (C1 ) between the model of the instrument tip (1 1 ) and the model of the calibration device (20).

1 1 . The method according to any of the preceding claims, comprising the steps:

placing the model of the instrument tip (1 1 ) onto a reference point (P) of the model of the calibration device (20);

executing an elevation step, thereby elevating the model of the instrument tip (1 1 ) onto model of the indentation (21 ) along a base axis (Z) perpendicular to a surface of the model of the calibration device (20), thereby determining a first collision point (C1 ); and

executing at least one first descending step, thereby shifting the model of the instrument tip (1 1 ) onto the model of the indentation (21 ) along a known gradient of the indentation (21 ) from the first collision point (C1 ) towards the reference point (P) of the calibration device (20), thereby determining a second collision point (C2) and a shifted first collision point (CT).

12. The method according to any of claim 1 1 , comprising the step:

determining a third collision point (C3) by virtually shifting the model of the instrument tip (1 1 ) onto the model of the indentation (21 ) along a horizontal shifting vector (V3), which is a projection of a gradient of the indentation (21 ) from a centre point (M12) between the shifted first collision point (CT) and the second collision point (C2) towards the reference point (P) of the calibration device (20) in a horizontal plane through the centre point (M12);

repositioning the model of the instrument tip (1 1 ) to an average position between the shifted first collision point (CT), the second collision point (C2) and the third collision point (C3) in the horizontal plane; and

descending the model of the instrument tip (1 1 ) onto the model of the indentation (21 ) along the base axis (Z), thereby determining a final collision point (CT', C2\ C3’).

13. The method according to any of claims 1 1 or 12, wherein

the model of the instrument tip (1 1 ) comprises a mesh of surface points; wherein the elevation of the instrument tip (1 1 ) onto the indentation (21 ) is determined by an elevation vector (V1 ), being the longest vector between the respective surface points of the instrument tip (1 1 ) and the indentation (21 ) along the base axis (Z).

14. The method according to any of claims 1 1 to 13, wherein

the gradient of the indentation (21 ) of the calibration device (20) determines a common shifting direction vector towards the reference point (P) of the calibration device (20);

wherein a shifting amount is determined by a shifting vector (V2), being the shortest vector between the respective surface points of the instrument tip (1 1 ) and the indentation (21 ) along the common shifting direction vector.

15. The method according to any of claims 1 1 to 14, comprising the steps:

determining a force vector (Vf) correlating to an estimated force applied onto the instrument (10) by a user based on the shape of the indentation (21 ); executing a force shifting step, shifting the instrument tip (10) onto the indentation (21 ) along the determined force vector (Vf).

16. The method according to any of the preceding claims, wherein

the surface of the model of the instrument (10) comprises a mesh of surface points, wherein the method comprises the step:

optimizing the surface of the model of the instrument (10) by reducing the surface of the instrument (10) to a relevant surface, by mesh optimization and/or by transforming the surface of the model of the instrument (10) into a local coordinate system of the indentation (21 ).

17. The method according to any of the preceding claims, wherein

the shape of the indentation is a cone or a pyramid.

18. Use of the estimated position of the instrument tip estimated by a method of any of the claims 1 to 17 in a surgical navigation system.

19. An instrument calibration system (100) comprising a medical instrument (10) with a tracker and a tracking device (30), configured for tracking the tracker arranged on the medical instrument (10), the instrument calibration system (100) being configured for executing the method of any of the claims 1 to 17.

20. A surgical navigation system for computer assisted surgery, the system comprising an instrument calibration system (100) according to claim 19.

21. A computer program which, when running on a computer or when loaded onto a computer, causes the computer to perform the method steps of the method according to any of the preceding claims;

and/or a program storage medium on which the program is stored; and/or a computer comprising at least one processor and a memory and/or the program storage medium, wherein the program is running on the computer or loaded into the memory of the computer;

and/or a signal wave or a digital signal wave, carrying information which represents the program;

and/or a data stream which is representative of the program.