Estimation of contact force by a medical device

• US 20070021742A1
• Filed: 07/11/2006
• Published: 01/25/2007
• Est. Priority Date: 07/18/2005
• Status: Active Grant

• Current Assignee: Stereotaxis, Inc.
• Original Assignee: Stereotaxis, Inc.
• Inventors: Viswanathan, Raju R.
• Granted Patent: US 8,192,374 B2
• Time in Patent Office: Days
• US Class Current: 606/27
• CPC Class Codes: A61B 18/04 by heating by applying electromagnetic radiation A61B18/18; hyperthermia using electric or magnetic fields, radiation or ultrasound A61N
• CPC Class Codes: A61B 2034/102 Modelling of surgical devices, implants or prosthesis
• CPC Class Codes: A61B 2034/2051 Electromagnetic tracking systems
• CPC Class Codes: A61B 2090/064 for measuring force, pressure or mechanical tension
• CPC Class Codes: A61B 2090/065 for measuring contact or contact pressure
• 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 34/73 Manipulators for magnetic surgery

Abstract

A method is provided for establishing contact of a medical device against a tissue surface within a subject body, the method comprising determination of the geometrical configuration of the distal portion of the medical device, and using this together with known control variable information to determine and control the contact force of the distal tip of the medical device against the tissue surface.

Claims

1. A method for establishing controlled contact of a medical device against a tissue surface within a subject body, the method comprising:

input of discrete data indicative of the geometry of the distal portion of the medical device;

computationally constructing a curve representative of the distal portion of the medical device from a pivot point to the tip of the medical device;

estimating from this curve the local rotation rate of the flexible portion of the distal portion of the medical device; and

estimating the contact force based on the rotation rate, a known bending stiffness and the estimated torque applied to the distal portion of the medical device.

2. The method of claim 1, where additionally local surface geometry information in a neighborhood of the target location is used to estimate the contact force.

3. The method of claim 1, where the estimated contact force is displayed to a user.

4. The method of claim 2, where the estimated contact force is displayed to a user.

5. The method of claim 1, further comprising determining an external magnetic field to be applied to the subject body and distal end of the medical device for providing a desired estimated contact force against the tissue surface within the subject body.

6. The method of claim 5, where the desired estimated contact force against the tissue surface provides for enhanced ablation of the tissue surface.

7. The method of claim 6, where the contact of the distal end of the medical device against the tissue surface is driven by an externally applied magnetic field that applies a magnetic torque to the medical device to provide enhanced contact against the tissue surface.

8. The method of claim 1 further comprising establishing contact by incrementally moving a minimum distance towards the tissue surface, and applying a control variable suitable for establishing a torque that will provide a pre-determined contact force against the tissue surface.

9. The method of claim 2 further comprising establishing contact by incrementally moving a minimum distance towards the tissue surface, and applying a control variable suitable for establishing a torque that will provide a pre-determined contact force against the tissue surface.

10. The method of claim 8, where the control variable is an externally applied magnetic field.

11. The method of claim 8, where the control variable is a mechanical control variable.

12. The method of claim 2 wherein the surface geometry is derived from a pre-operative image that is suitably registered with the subject body.

13. The method of claim 2 wherein the surface geometry is obtained from an anatomical map derived from a localization system that maps the local surface geometry.

14. The method of claim 5 wherein the medical device is a magnetically navigable device.

15. The method of claim 13 wherein the medical device is a localized device sending tip position and orientation data to a remote navigation system used for device actuation and control.

16. A method of predicatively controlling contact force of a medical device against a tissue surface with a remote navigation system, where the method employs a model of the surface geometry, a computational virtual device model, and the estimated contact force of the medical device is predicted within the model prior to moving the medical device against the tissue surface to provide enhanced wall contact.

17. A method for establishing controlled contact of a medical device against a three-dimensional tissue surface within a subject body, the method comprising obtaining three dimensional geometry information for the distal portion of the medical device, constructing a curve representative of the distal portion of the medical device from the pivot point to the tip of the medical device, estimating the local rotation rate of the flexible portion of the distal portion of the medical device, estimating the current contact force based on the rotation rate, the bending stiffness and the total torque applied to the flexible portion of the medical device, and determining a control variable to be applied to the medical device for providing a desired estimated contact force against the tissue surface within the subject body.

18. The method of claim 17, where the control variable is an externally applied magnetic field.

19. The method of claim 17, where the control variable is a mechanical control variable.

20. The method of claim 17, where the estimated contact force against the tissue surface provides for enhanced ablation of the tissue surface.

21. The method of claim 17 wherein surface geometry information is additionally employed to determine the contact force.

22. The method of claim 21, where the surface geometry information is derived from a pre-operative image that is suitably registered with the subject body.

23. The method of claim 21 wherein the surface geometry information is obtained from an anatomical map derived from a localization system that maps the local surface geometry.

24. The method of claim 21 wherein the medical device is a magnetically navigable device.

25. The method of claim 21 wherein the method further comprises comparing the angular lag between the magnetic field vector and the actual orientation of the tip of the medical device to verify the establishment of a sufficient degree of contact against the tissue surface.