Non-rigid Groupwise Registration using B-Spline Deformation Model

In this work, we extend a previously demonstrated entropy based groupwise registration method to include a non-rigid deformation model based on B-splines. We describe an open source implementation of the groupwise registration algorithm using the Insight Toolkit ITK www.itk.org. We provide the source code, parameters, input and output data that we used for validation. We describe an efficient implementation of the algorithm by using a stochastic optimization scheme embedded in a multi-resolution setting. The objective function is optimized using gradient descent algorithm combined with line search for the step size. The derivative of the objective function is evaluated efficiently by computing Jacobian of B-spline deformation field locally. We demonstrate the algorithm in application to different imaging modalities including proton density, FA, T1 and T2 MR images. We validate the algorithm on synthetic datasets varying from 2 to 30 images by recovering randomly applied affine and B-spline transforms.