Image Registration for CT and intra-operative ultrasound data of the liver

The paper is concerned with image registration algorithms for the alignment of computer tomography (CT) and 3D-ultrasound (US) images of the liver. The necessity of registration arises from the surgeon's request to benefit from the planning data during surgery. The goal is to align the planning data, derived from pre-operative CT-images, with the current US-images of the liver acquired during the surgery. The registration task is complicated by the fact, that the images are of a different modality, that the US-images are severely corrupted by noise, and that the surgeon is looking for a fast and robust scheme. To guide and support the registration, additional pairs of corresponding landmarks are prepared. We will present two different approaches for registration. The first one is based on the pure alignment of the landmarks using thin plate splines. It has been successfully applied in various applications and is now transmitted to liver surgery. In the second approach, we mix a volumetric distance measure with the landmark interpolation constraints. In particular, we investigate the promising normalized gradient field distance measure. We use data from actual liver surgery to illustrate the applicability and the characteristics of both approaches. It turns out that both approaches are suitable for the registration of multi-modal images of the liver.