Biomechanical model assisted image guided surgery system and method

1. A method of performing image-guided surgery, comprising:

obtaining intraoperative location data for a patient comprising intraoperative fiducial location data for a non-rigid structure of interest in the patient and intraoperative rigid structure location data for at least one rigid structure in the patient associated with the non-rigid structure;

estimating a gravity deformation for the non-rigid structure of interest based on a first rigid registration for preoperative fiducial location data in a preoperative computer model of the patient with respect to the intraoperative fiducial location data and a second rigid registration for the preoperative rigid structure location data for at least one rigid structure in the computer model with respect to the intraoperative rigid structure location data;

modifying the preoperative fiducial location data using first rigid registration and the gravity deformation to yield modified fiducial location data;

determining a third rigid registration comprising a rigid registration for the modified fiducial location data with respect to the intraoperative fiducial location data;

calculating a non-rigid transformation for the computer model based on the volumetric gravity field deformation and first boundary conditions derived from errors in the third rigid registration;

displaying deformed image data comprising preoperative image data corresponding to the computer modified to undergo the non-rigid transformation.

2. The method of claim 1 , wherein the estimating comprises:

determining a gravity vector rotation based on a comparison of the first rigid registration and the second rigid registration; and

computing the volumetric gravity field deformation using the gravity vector location and a three-dimensional elastic model.

3. The method of claim 2 , wherein the computing comprises a finite element analysis.

4. The method of claim 1 , wherein the modifying comprises:

applying a transformation based on the first rigid registration to at least a portion of the computer model corresponding to the non-rigid structure to yield a modified computer model;

performing a finite element analysis for the modified computer model based on the gravity deformation and second boundary conditions to yield the modified fiducial data,

wherein the second boundary conditions specify that nodes of the modified computer model associated with the portion and adjacent to the at least one rigid structure are fixed and other nodes of the portion are stress-free.

5. The method of claim 1 , wherein the calculating comprises:

performing a principal components analysis (PCA) on the errors in a transformation corresponding the third rigid registration to extract a PCA error vector describing principal components of the errors in the third rigid registration; and

computing the boundary conditions based on the PCA error vector.

6. The method of claim 1 , wherein the calculating comprises performing a finite element registration for the computer model with respect to the intraoperative location data subject to the volumetric gravity field deformation and the boundary conditions to yield the non-rigid transformation.

7. The method of claim 1 , prior to the displaying repeating, using the computer model modified to undergo the non-rigid transformation, the obtaining, estimating, modifying, determining, and calculating.

8. The method of claim 1 , wherein the intraoperative location data comprises intraoperative shape data for the non-rigid structure, wherein the computer model comprises preoperative shape data for the non-rigid structure, and wherein at least one of the first rigid registration, the second rigid registration, and the third rigid registration further involve a registration of the preoperative shape data with respect to the intraoperative shape data.

9. The method of claim 1 , further comprising performing, prior to the displaying, the steps of:

assessing an alignment error of the non-rigid transformation for the computer model with respect to the intraoperative fiducial location data;

detecting that the alignment error is outside a pre-defined error tolerance; and

in response to detecting that the alignment error is outside the pre-defined error tolerance, updating the first boundary conditions; and

repeating the calculating, assessing, detecting and updating until the alignment error is within the pre-defied error tolerance or another termination condition has been met.

10. A non-transitory computer-readable medium, having stored thereon a computer program executable by a computing device, the computer program comprising a plurality of code sections for performing the method comprising:

obtaining intraoperative location data for a patient comprising intraoperative fiducial location data for a non-rigid structure of interest in the patient and intraoperative rigid structure location data for at least one rigid structure in the patient associated with the non-rigid structure;

estimating a gravity deformation for the non-rigid structure of interest based on a first rigid registration for preoperative fiducial location data in a preoperative computer model of the patient with respect to the intraoperative fiducial location data and a second rigid registration for the preoperative rigid structure location data for at least one rigid structure in the computer model with respect to the intraoperative rigid structure location data;

modifying the preoperative fiducial location data using first rigid registration and the gravity deformation to yield modified fiducial location data;

determining a third rigid registration comprising a rigid registration for the modified fiducial location data with respect to the intraoperative fiducial location data;

calculating a non-rigid transformation for the computer model based on the volumetric gravity field deformation and first boundary conditions derived from errors in the third rigid registration;

displaying deformed image data comprising preoperative image data corresponding to the computer modified to undergo the non-rigid transformation.

11. The non-transitory computer-readable medium of claim 10 , wherein the estimating comprises:

determining a gravity vector rotation based on a comparison of the first rigid registration and the second rigid registration; and

computing the volumetric gravity field deformation using the gravity vector location and a three-dimensional elastic model.

12. The non-transitory computer-readable medium of claim 11 , wherein the computing comprises a finite element analysis.

13. The non-transitory computer-readable medium of claim 10 , wherein the modifying comprises:

applying a transformation based on the first rigid registration to at least a portion of the computer model corresponding to the non-rigid structure to yield a modified computer model;

performing a finite element analysis for the modified computer model based on the gravity deformation and second boundary conditions to yield the modified fiducial data,

wherein the second boundary conditions specify that nodes of the modified computer model associated with the portion and adjacent to the at least one rigid structure are fixed and other nodes of the portion are stress-free.

14. The non-transitory computer-readable medium of claim 10 , wherein the calculating comprises:

performing a principal components analysis (PCA) on the errors in a transformation corresponding the third rigid registration to extract a PCA error vector describing principal components of the errors in the third rigid registration; and

computing the boundary conditions based on the PCA error vector.

15. The non-transitory computer-readable medium of claim 10 , wherein the calculating comprises performing a finite element registration for the computer model with respect to the intraoperative location data subject to the volumetric gravity field deformation and the boundary conditions to yield the non-rigid transformation.

16. A system for performing image-guided surgery, comprising:

a sensing system configured to measure physical space and configured to obtain intraoperative location data for a patient comprising intraoperative fiducial location data for a non-rigid structure of interest in the patient and intraoperative rigid structure location data for at least one rigid structure in the patient associated with the non-rigid structure;

a display device;

a storage medium for storing preoperative computer model of the patient, a computer model of a non-rigid structure of interest in a patient corresponding to the preoperative image, and the surface data, the computer model comprising a plurality of nodes; and

a processing element communicatively coupled to the sensing system, the display device, and the storage medium, wherein the processing element is configured for:

estimating a gravity deformation for the non-rigid structure of interest based on a first rigid registration for preoperative fiducial location data in the preoperative computer model with respect to the intraoperative fiducial location data and a second rigid registration for the preoperative rigid structure location data for at least one rigid

structure in the computer model with respect to the intraoperative rigid structure location data;

modifying the preoperative fiducial location data using first rigid registration and the gravity deformation to yield modified fiducial location data;

determining a third rigid registration comprising a rigid registration for the modified fiducial location data with respect to the intraoperative fiducial location data;

calculating a non-rigid transformation for the computer model based on the volumetric gravity field deformation and first boundary conditions derived from errors in the third rigid registration;

displaying deformed image data comprising preoperative image data corresponding to the computer modified to undergo the non-rigid transformation.

17. The system of claim 16 , wherein the estimating comprises:

determining a gravity vector rotation based on a comparison of the first rigid registration and the second rigid registration; and

computing the volumetric gravity field deformation using the gravity vector location and a three-dimensional elastic model.

18. The system of claim 16 , wherein the modifying comprises:

applying a transformation based on the first rigid registration to at least a portion of the computer model corresponding to the non-rigid structure to yield a modified computer model;

performing a finite element analysis for the modified computer model based on the gravity deformation and second boundary conditions to yield the modified fiducial data,

wherein the second boundary conditions specify that nodes of the modified computer model associated with the portion and adjacent to the at least one rigid structure are fixed and other nodes of the portion are stress-free.

19. The system of claim 16 , wherein the calculating comprises:

performing a principal components analysis (PCA) on the errors in a transformation corresponding the third rigid registration to extract a PCA error vector describing principal components of the errors in the third rigid registration; and

computing the boundary conditions based on the PCA error vector.

20. The system of claim 16 , wherein the calculating comprises performing a finite element registration for the computer model with respect to the intraoperative location data subject to the volumetric gravity field deformation and the boundary conditions to yield the non-rigid transformation.