The rotate-plus-shift C-arm trajectory. Part II. Exact reconstruction from less than 180 degrees rotation

摘要

Purpose: CT reconstruction requires an angular coverage of 180 degrees. or more for each point within the field of measurement. Thus, common trajectories use a 180 degrees. plus fan angle rotation. This is sometimes combined with a translation of the rotational isocenter in order to achieve circular trajectories with an isocenter different from the mechanical rotation center or elliptical trajectories. Rays measured redundantly are appropriately weighted. In case of an angular coverage smaller than 180 degrees, the reconstructed images suffer from limited angle artifacts. In mechanical constructions with a rotation range limited to less than 180 degrees. plus fan angle, the angular coverage can be extended by adding one or two shifts to the rotational motion. If the missing angle is less than the fan angle, the shifts can completely compensate for the limited rotational capabilities.