DEFORMABLE TEMPLATES USING LARGE-DEFORMATION KINEMATICS

A general automatic approach is presented for accommodating local shap e variation when mapping a two-dimensional (2-D) or three-dimensional (3-D) template image into alignment with a topologically similar targe t image, Local shape variability is accommodated by applying a vector- field transformation to the underlying material coordinate system of t he template while constraining the transformation to be smooth (global ly positive definite Jacobian), Smoothness is guaranteed without speci fically penalizing large-magnitude deformations of small subvolumes by constraining the transformation on the basis of a Stokesian limit of the fluid-dynamical Navier-Stokes equations, This differs fundamentall y from quadratic penalty methods, such as those based on linearized el asticity or thin-plate splines, in that stress restraining the motion relaxes over time allowing large-magnitude deformations, Kinematic non linearities are inherently necessary to maintain continuity of structu res during large-magnitude deformations, and are included in all resul ts, After initial global registration, final mappings are obtained by numerically solving a set of nonlinear partial differential equations associated with the constrained optimization problem, Automatic regrid ding is performed by propagating templates as the nonlinear transforma tions evaluated on a finite lattice become singular, Application of th e method to intersubject registration of neuroanatomical structures il lustrates the ability to account for local anatomical variability.