Three-dimensional reconstruction of tracked freehand ultrasound using non-rigid registration

Freehand three-dimensional ultrasound produces a set of irregularly spaced and orientated B-scans. These are usually reconstructed on a regularly spaced three-dimensional grid using an appropriate interpolation technique. This paper presents a novel method to interpolate intensity values between a set of non-intersecting B-scans. The method uses an intensity based non-rigid registration algorithm based on B-splines to establish spatial correspondence between neighbouring B-scans. Linear interpolation of the image intensities is carried out along the directions calculated by the registration algorithm. The method is compared to voxel nearest neighbour interpolation in 4 datasets. Results show our method to have on average a 16% improved performance over voxel nearest neighbour interpolation using mean square difference as an error measure.