Validation Method for Non-rigid Registration

We have presented a novel validation method for non-rigid image registration in [6,7]. It is based on applying the registration to misaligned images, generated from plausible deformations simulated by biomechanical models using finite element methods. For this, pre- and post-contrast image sets, which showed no motion, were selected from a large patient data base (Figure 1a,b).
Then a finite element model of the breast was generated by segmenting the breast into fatty and glandular tissue and enhancing lesion via ANALYZE, extracting the breast surface via vtk and meshing the breast into 10-noded tetrahedral elements via the ANSYS FEM package. Material properties from literature were then assigned to the element in accordance to the image segmentation, surface displacements applied and a solution obtained with the ANSYS FEM package. Figure 1(d,e) show an animation of the simulated deformation for a regional displacement of 10mm on the breast surface.
Images of these deformed breasts were then generated by quadratic shape interpolation of the 10-noded tetrahedral elements (Figure 1f). Finally, the pre-contrast images were registered to the FEM deformed post-contrast images (Figure 1h) and the registration accuracy was determined at each voxel position within the breast.
Note that the same method can be applied to other organs as long as a plausible finite element model can be generated.

(a) (b) (c)
(d) (e)
(f) (g) (h)
Figure 4: Illustration of validation strategy: 2D example slice of (a) original pre-contrast image, (b) original post-contrast image (c) difference image (b-a); (d,e) simulated deformation (regional displacement) showing in colour magnitude of displacement at (d) surface and (e) cut through finite element model; (f) deformed post-contrast image within model (g) difference image after deformation (f-a), (h) difference image after non-rigid registration of (a) to (f)

References:

[7] J. A. Schnabel, C. Tanner, A. D. Castellano-Smith, A. Degenhard, M. O. Leach, D. R. Hose, D. L. G. Hill, D. J. Hawkes. Validation of non-rigid image registration using finite element methods: Application to breast MR images. IEEE Transactions on Medical Imaging, vol. 22(1), 2003. In press.

[6] J. A. Schnabel, C. Tanner, A. Castellano-Smith, M. O. Leach, C. Hayes, A. Degenhard, R Hose, D. L. G. Hill, D. J. Hawkes. Validation of non-rigid registration using finite element methods. In Proc. Information Processing in Medical Imaging (IPMI'01), University of California at Davis, 2001, 18-22 June 2001, vol. 2082 of Lecture Notes in Computer Science, pp. 344-357, Springer Verlag, 2001.