An algorithm to extract three-dimensional motion by marker tracking in the kV projections from an on-board imager: four-dimensional cone-beam CT and XXXX tracking implications.

@entity1 @entity5 @entity2167
The purpose of this work is to extract three-dimensional (3D) motion trajectories of internal implanted and external skin-attached markers from kV cone-beam projections and reduce image artifact from @entity1 motion in cone-beam computed tomography (CBCT) from on-board imager. Cone beam radiographic projections were acquired for a mobile phantom and liver @entity1 with internal implanted and external skin-attached markers. An algorithm was developed to automatically find the positions of the markers in the projections. It uses normalized cross-correlation between a template image of a metal seed marker and the projections to find the marker position. From these positions and time-tagged angular views, the marker 3D motion trajectory was obtained over a time interval of nearly one minute, which is the time required for scanning. This marker trajectory was used to remap the pixels of the projections to eliminate motion. Then, the motion-corrected projections were used to reconstruct CBCT. An algorithm was developed to extract 3D motion trajectories of internal and external markers from cone-beam projections using a kV monoscopic on-board imager. This algorithm was tested and validated using a mobile phantom and @entity1 with liver masses that had radio-markers implanted in the @entity5 and attached to the skin. The extracted motion trajectories were used to investigate motion correlation between internal and external markers in liver @entity1 . Image artifacts from respiratory motion were reduced in CBCT reconstructed from cone-beam projections that were preprocessed to remove motion shifts obtained from marker tracking. With this method, motion-related image artifacts such as blurring and @entity2167 were reduced, and contrast and position resolutions were improved significantly in CBCT reconstructed from motion-corrected projections. Furthermore, correlated internal and external marker 3D-motion tracks obtained from the kV projections might be useful for 4DCBCT, beam gating and @entity5 motion monitoring or tracking.
