Image reconstruction from truncated cone-beam projections

In cone-beam CT, an image of an object is reconstructed from a series of cone-beam projections acquired while the source moves along some trajectory around the object. An accurate reconstruction is possible, provided the source trajectory satisfies a certain completeness condition and none of the cone-beam projections is truncated. Complete source trajectories may be realized by a suitable measuring system, but in medical cone-beam CT, some truncation of the projections is inevitable. An image reconstructed from truncated projections by a standard cone-beam reconstruction algorithm may suffer from severe artifacts. In principle, these artifacts can be reduced by extrapolating the truncated projections prior to the reconstruction. In this paper, a favorable extrapolation method is described in more detail, and the effectiveness of the method is demonstrated using simulated data.