Method of calibrating a medical instrument using virtual models

Patent metadata

Field	Value
Publication number	US-12096992-B2
Application number	US-202017049634-A
Country	US
Kind code	B2
Filing date	Mar 16, 2020
Priority date	Mar 22, 2019
Publication date	Sep 24, 2024
Grant date	Sep 24, 2024

Abstract

A computer implemented medical method of calibrating a medical instrument is provided. The method calculates a position of the instrument tip model within the indentation model, associated with an estimated position of the instrument tip within the indentation and calibrates the medical instrument, thereby using the determined position of the instrument tip model. The position of any arbitrary medical instrument tip, such as an indentation of a calibration device, can be estimated. This is an improvement of accuracy in view of the generic approach of using the same reference point of the indentation of the calibration device for any arbitrary medical instrument tip. A virtual model of a shape of a medical instrument, such as the instrument tip, is matched onto a virtual model of a shape of a calibration device, such as an indentation of the calibration device.

First claim

The invention claimed is:

1. A computer implemented method of calibrating a medical instrument, the method comprising:
providing an instrument model comprising an instrument tip model, wherein the instrument tip model is a virtual model of a shape of the medical instrument comprising an instrument tip;
providing a calibration device model comprising an indentation model, wherein the indentation model is a virtual model of a shape of a calibration device comprising an indentation onto which the instrument tip is introduced for calibration;
matching the instrument tip model onto the indentation model, thereby determining a position of the instrument tip model within the indentation model; and
calibrating the medical instrument, thereby using the determined position of the instrument tip model.

2. The method according to claim 1 , further comprising:
tracking the medical instrument by a tracking device, wherein the tracking device comprises a passive tracker arranged on the medical instrument.

3. The method of claim 1 , wherein matching the instrument tip model onto the indentation model comprises:
determining an instrument model coordinate system; and
calibrating the medical instrument, thereby using the determined instrument model coordinate system.

4. The method of claim 3 , wherein calibrating the medical instrument comprises:
determining an instrument-marker-to-instrument-tip-coordinate-transformation, which describes a transformation between an instrument marker coordinate system and an instrument tip coordinate system, thereby using the determined instrument model coordinate system.

5. The method of claim 4 , wherein calibrating the medical instrument comprises:
providing a calibration-device-to-instrument-tip-coordinate-transformation, which describes a transformation between a calibration device coordinate system and the instrument tip coordinate system; and
determining the instrument-marker-to-instrument-tip-coordinate-transformation, thereby using the calibration-device-to-instrument-tip-coordinate-transformation.

6. The method according to claim 1 , comprising:
determining an actual spatial orientation of the medical instrument along an axis of the medical instrument; and
using the determined actual spatial orientation during matching the instrument tip model onto the indentation model.

7. The method according to claim 6 , wherein determining the actual spatial orientation comprises determining the actual spatial orientation based on a result of tracking the medical instrument.

8. The method according to claim 6 , comprising:
determining the actual spatial orientation based on estimating the axis of the medical instrument and/or based on learning from a rotation movement of the instrument tip in the indentation, which is recorded by a tracking device.

9. The method according to claim 1 , comprising:
generating a plurality of frames of different positions of the instrument tip in the indentation by using a surgical navigation device;
matching the instrument tip model onto the indentation model for each frame of the plurality of frames and determining a position of the instrument tip model within the indentation model for each frame of the plurality of frames; and
calculating an average position of the instrument tip model based on the determined positions of the instrument tip models of the plurality of frames.

10. The method according to claim 1 , wherein matching the instrument tip model onto the indentation model comprises:
calculating, based on the instrument tip model and the indentation model, at least one collision point (between the instrument tip model and the indentation model; and
determining the position of the instrument tip model within the indentation model, thereby using the at least one collision point.

11. The method according to claim 1 , comprising:
placing the instrument tip model onto a reference point of the calibration device model;
executing an elevation step, the elevation step comprising elevating the instrument tip model onto the indentation model along a base axis perpendicular to a surface of the calibration device model, thereby determining a first collision point; and
executing at least one first descending step, the at least one first descending step comprising shifting the instrument tip model onto the indentation model along a known gradient of the indentation model from the first collision point towards the reference point of the calibration device model, thereby determining a second collision point and a shifted first collision point.

12. The method according to claim 11 , comprising:
determining a third collision point by virtually shifting the instrument tip model onto the indentation model along a horizontal shifting vector, which is a projection of a gradient of the indentation model from a centre point between the shifted first collision point and the second collision point towards the reference point of the calibration device model in a horizontal plane through the centre point;
repositioning the instrument tip model to an average position between the shifted first collision point, the second collision point and the third collision point in the horizontal plane; and
descending the instrument tip model onto the indentation model along the base axis, thereby determining a final collision point.

13. The method according to claim 11 , wherein the instrument tip model comprises a mesh of surface points; and comprising:
determining, by an elevation vector, the elevation of the instrument tip model onto the indentation model, wherein the elevation vector is the longest vector between the respective surface points of the instrument tip model and the indentation model along the base axis.

14. The method according to claim 11 , wherein the gradient of the indentation model of the calibration device model determines a common shifting direction vector towards the reference point of the calibration device model; and comprising:
determining, by a shifting vector, a shifting amount, wherein the shifting vector is the shortest vector between respective surface points of the instrument tip model and the indentation model along the common shifting direction vector.

15. The method according to claim 11 , comprising:
determining a force vector correlating to an estimated force applied onto the medical instrument by a user based on the shape of the indentation; and
executing a force shifting step, the force shifting step comprising shifting the instrument tip model onto the indentation model along the determined force vector.

16. The method according to claim 1 , wherein a surface of the instrument model comprises a mesh of surface points, wherein the method comprises:
optimizing the surface of the instrument model by one or more of the following:
reducing the surface of the instrument model to a relevant surface;
mesh optimization; and/or
transforming the surface of the instrument model into a local coordinate system of the indentation model.

17. The method according to claim 1 , wherein the shape of the indentation is a cone or a pyramid.

18. An instrument calibration system comprising:
a medical instrument with a tracker; and
a tracking device configured for tracking the tracker arranged on the medical instrument,
wherein the instrument calibration system is configured to:
provide an instrument model comprising an instrument tip model, wherein the instrument tip model is a virtual model of a shape of the medical instrument comprising an instrument tip;
provide a cali

Assignees

• Brainlab Ag

Inventors

• Drexl Thomas
• Wegner Melanie

Classifications

• A61B2090/3945

  Active visible markers, e.g. light emitting diodes · CPC title

• A61B2090/3966

  Radiopaque markers visible in an X-ray image · CPC title

• A61B2034/102

  Modelling of surgical devices, implants or prosthesis · CPC title

• A61B2017/00725

  Calibration or performance testing · CPC title

• A61B2034/207

  Divots for calibration · CPC title