Removal of Plaque and Stent Artifacts in Subtraction CT Angiography Using Nonrigid Registration and a Volume Penalty

Computed tomography angiography (CTA) is an established tool for vascular imaging. However, high-intense structures in the contrast image can seriously hamper luminal visualisation. This can be solved by subtraction CTA, where a native image is subtracted from the contrast image. However, patient and organ motion limit the application of this technique. Within this paper, a fully automated intensity-based nonrigid 3D registration algorithm for subtraction CT angiography is presented, using a penalty term to avoid volume change during registration. Visual and automated validation on four clinical datasets clearly show that the algorithm strongly reduces motion artifacts in subtraction CTA. Most artifacts disappear, also artifacts caused by minimal displacement of stents or calcified plaques, allowing a 2D and 3D artifact-free visualisation of the vessel lumen. This enables a quick overview of the whole vascular structure and opens the possibility to the visualisation of smaller vessels.