An approach to 2D/3D registration of a vertebra in 2D x-ray fluoroscopies with 3D CT images

In order to use pre-operative images during an operation for navigation, they must be registered to the patient's coordinate system in the operating theater or to an intra-operative image. One problem in this area is the registration of a vertebra in intra-operatively acquired x-ray fluoroscopies with 3D CT images obtained before the intervention. The result can be used to support the placement of pedicle screws in spine surgery or stents in Transfemoral Endovascular Aneurysm Management (TEAM). For this 2D/3D registration task a novel voxel-based method is presented. Using a small part of the CT image covering the vertebra only, pseudo projections are computed and the resulting vertebra template is compared to the x-ray projection. A new similarity measure was introduced for that purpose, because commonly used measures did not work. The method allows for a much faster implementation than other voxel-based 2D/3D registration approaches, because they use the entire CT image to calculate pseudo projections. Unlike contour-based 2D/3D registration approaches, the method does not require segmentation of the vertebra's contours in the x-ray projection. Application and performance of the proposed registration method are demonstrated by application to images of a TEAM procedure.