Cone beam CT reconstructions are an accurate and efficient intra-procedural method for assessing the positioning of biopsy or ablation needles inside the human body. Commonly encountered issues are metal artefacts produced by the needle that is crossing the border of the field of view (FOV). We combine two approaches for metal artefact reduction (MAR) by exchanging information between the two methods. The first method performs a second pass reconstruction after segmenting the metal inside the FOV volume and subtracting the metal shadow from the sinogram. The second method focuses on the sinogram data to suppress objects outside the reconstruction FOV. Superior performance of this combined method is demonstrated on simulated and clinical data.
Cardiac C-arm computed tomography (CT) imaging using interventional C-arm systems can be
applied in various areas of interventional cardiology ranging from structural heart disease and
electrophysiology interventions to valve procedures in hybrid operating rooms. In contrast to
conventional CT systems, the reconstruction field of view (FOV) of C-arm systems is limited to
a region of interest in cone-beam (along the patient axis) and fan-beam (in the transaxial plane)
direction. Hence, highly X-ray opaque objects (e.g. cables from the interventional setup) outside
the reconstruction field of view, yield streak artifacts in the reconstruction volume. To decrease
the impact of these streaks a cable tracking approach on the 2D projection sequences with subsequent
interpolation is applied. The proposed approach uses the fact that the projected position
of objects outside the reconstruction volume depends strongly on the projection perspective.
By tracking candidate points over multiple projections only objects outside the reconstruction
volume are segmented in the projections. The method is quantitatively evaluated based on 30
simulated CT data sets. The 3D root mean square deviation to a reference image could be
reduced for all cases by an average of 50 % (min 16 %, max 76 %). Image quality improvement
is shown for clinical whole heart data sets acquired on an interventional C-arm system.