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One of the application areas of three-dimensional rotational X-ray imaging (3D-RX) techniques is focused on the 3D visualization of coronary vessel structures (3D rotational coronary angiography, 3DRCA). Since the heart is a moving object, only projections can be used, which correspond to the same acquisition time (e.g. end diastole) in the cardiac cycle. This significantly limits the number of projections available for reconstruction causing streaking artefacts in the reconstructed image due to the angular undersampling. The involvement of additional projections in the reconstruction procedure from different viewing angles would increase the quality of the volume data. However, each successive acquired projection is slightly different compared with the previous one due to two reasons: First, a nonlinear movement owing to the heart beat and, second, a linear movement owing to a different viewing angle. In order to use additional projections, the movement due to the different heart phase has to be transformed in the desired prior heart phase and the transformation (motion compensation) must take into account the geometrical rotation of the gantry. Therefore, considering two successive acquired projections and calculating the transformation matrix that transforms one projection into another must include both components. The purpose of this work is to determine and to separate the two mentioned movements and to involve additional projections (acquired at different acquisition geometry and in different motion state) in the reconstruction procedure. Motion-compensated reconstructed volume data will be presented for coronary arteries in an animal (pig) model. |
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