Radial MILO: A 4D Image Registration Algorithm Based on Filtering Block Match Data via l1-minimization
Master of Arts
Minimal l1 Perturbation to Block Match Data (MILO) is a spatially accurate image registration algorithm developed for thoracic CT inhale/exhale images. The MILO algorithm consists of three components: (1) creating an initial estimate for voxel displacement via a Mutual Minimizing Block Matching Algorithm (MMBM), (2) a filtering step based on l1 minimization and a uniform B-spline parameterization, and (3) recovering a full displacement field based on the filtered estimates. This thesis presents a variation of MILO for 4DCT images. In practice, the use of uniform B-splines has led to rank deficient linear systems due to the spline's inability to conform to non-structured MMBM estimates. In order to adaptively conform to the data an octree is paired with radial functions. The l1 minimization problem had previously been addressed by employing QR factorization, which required substantial storage. As an alternative a block coordinate descent algorithm is employed, relieving the need for QR factorization. Furthermore, by modeling voxel trajectories as quadratic functions in time, the proposed method is able to register multiple images.