Partially Rigid Bone Registration in CT Angiography

Maximum intensity projection (MIP) studies of CT angiography (CTA) images are a widely used tool for artery and vein visualization especially in the brain. Due to their high CT intensity bone structures lead to visualization artifacts in MIP studies, therefore they have to be removed to get an undistorted view of the vessel structures. Often this removal is possible by a rigid registration step of an additional native scan to the contrast-enhanced CTA scan followed by a bone mask subtraction. This technique is also referred to as ”Matched Mask Bone Elimination” [14]. However, sometimes several unrelated patient movements occur during and between contrast-enhanced and native scans. These intraand inter-scan motion artifacts cannot be removed by a single rigid registration step. To address these problems in an efficient and general way we have developed a refinement of the ”Matched Mask Bone Elimination” technique that incorporates a joint segmentation and registration method in an iterative fashion. We describe our experiments and show our qualitative and quantitative results in terms of decreasing numbers of misregistration voxels and sum of squared intensity differences on several large volume data sets of the head, where independent rigid movements have been successfully removed.