Non-stationary diffeomorphic registration: Application to endo-vascular treatment monitoring

This paper proposes a new pairwise registration algorithm called Large Diffeomorphic Free-Form Deformation (LDFFD). In the LDFFD algorithm, the diffeomorphic mapping is represented as a composition of Free-Form Deformation (FFD) transformations at each time step, all time steps being jointly optimized. The fact that the transformation at one time step influences all subsequent time steps, naturally enforces temporal consistency in the transformation compared to other existing diffeomorphic registration algorithms and does not restrict the space of solutions to stationary displacement fields over all time steps. A multiresolution strategy is presented to find the optimal number of time steps and solve efficiently the joint optimization of all transformations in the registration chain. Accuracy of the algorithm in the presence of large deformations is illustrated and compared to other standard or diffeomorphic registration algorithms. Our algorithm is applied here in the context of monitoring disease progression by image-based quantification of aneurysmal growth post endovascular treatment. In this context, aneurysm volume changes occurring after embolization are quantified by integrating the Jacobian of the diffeomorphic transformation between 3D rotational angiography images acquired at subsequent followups.