Improved Non-rigid Registration of Prostate MRI

This paper introduces a fast non-rigid registration method for aligning pre-operative 1.5 T MR images to intra-operative 0.5 T MR images for guidance in prostate biopsy. After the acquisition of both pre-operative 1.5 T and intra-operative 0.5 T, an intensity correction method is applied to the pre-operative images to reduce the significant artifacts in the signal intensities due to the presence of an endo-rectal coil. A fast manual segmentation of prostate in both modalities is carried out to enable conformal mapping of the surface of the pre-operative data to the intra-operative data. A displacement field is estimated with a linear elastic inhomogeneous material model using the surface displacements established by the conformal mapping. We then use this as an initialization for a mutual information based non-rigid registration algorithm to match the internal structures of the prostate. This non-rigid registration is based on a finite element method discretization using the mutual information metric with a linear elastic regularization constraint. The registration is accelerated while preserving accuracy by using an adaptive mesh based on the body-centered cubic lattice and a significantly improved registration is achieved.