Peter George Vandehaar PhD, Presenter: Employee, Koninklijke Philips Electronics NV

Jan Timmer PhD, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Peter Forthmann, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV, Hamburg, Germany

3D image quality of a C-arm system with XperCT option was improved through application of a two-pass reconstruction method, which suppresses artefacts due to both bone beam hardening and incomplete data associated with a circular orbit and a 2D detector.

Neuro patients were 3D X-ray scanned on a commercial C-arm system (Philips Allura FD20, XperCT option) equipped with a large field of view flat-panel detector of size 40cm x 30 cm with a pixel pitch of 0.15 mm. 600 projections were acquired at 30 frames per second during a semicircular planar 205° rotation of the C-arm. 3D reconstruction was performed in two passes. During the first pass corrections for geometry, gain, offset, X-ray water beam hardening and scatter (caused by both patient and detector assembly) were carried out. Cone-beam volumetric reconstruction was performed using the Feldkamp algorithm and angular weighting. The resulting volume is segmented twice, (1) to generate a bone-only volume and (2) a volume in which bone voxels are unchanged, soft-tissue-like is reset to water and air-like is reset to zero. Forward projection of both volumes is applied to generate line integrals. In case (1), line integrals are corrected for bone beam hardening, applying a model of the X-ray spectrum used. Both sets of projections are reconstructed to (1) generate an error volume for bone beam hardening, (2) to generate a volume for cone beam artefacts; these volumes are used to correct the first-pass volume.

This correction method was found to significantly reduce artefacts due to (1) bone beam hardening and (2) incomplete data. With (1), shading in the inner skull is reduced. With (2), deep shading below the frontal skull and streaks through the cerebellum are reduced.

3D imaging on interventional C-arm systems approaches that of CT. Spatial resolution is higher and contrast resolution is lower compared to that of CT. Acquisition along a circular orbit with large cone angles causes artefacts unknown to CT. The method presented here significantly reduces these artefacts, together with shading due to bone beam hardening.

Soft-tissue imaging (neuro) as part of an interventional procedure, using a C-arm system.

Vandehaar, P, Timmer, J, Forthmann, P, Enhancing C-Arm CT Image Quality through Two-pass Reconstruction.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5010635.html