Intra-operative ultrasound to MRI fusion with a public multimodal discrete registration tool

We present accurate results for multi-modal fusion of intra-operative 3D ultrasound and magnetic resonance imaging (MRI) using the publicly available and robust discrete registration approach deeds. After pre-processing the scans to have isotropic voxel sizes of 0.5 mm and a common coordinate system, we run both linear and deformable registration using the self-similarity context metric. We use default parameters that have previously been applied for multi-atlas fusion demonstrating the generalisation of the approach. Transformed landmark locations are obtained by either directly applying the nonlinear warp or fitting a rigid transform with six parameters. The two approaches yield average target registration errors of 1.88 mm and 1.67 mm respectively on the 22 training scans of the CuRIOUS challenge. Optimising the regularisation weight can further improve this to 1.62 mm (within 0.5 mm of the theoretical lower bound). Our findings demonstrate that in contrast to classification and segmentation tasks, multimodal registration can be appropriately handled without designing domain-specific algorithms and without any expert supervision.