1. A method for reconstructing an image of a three-dimensional subject comprising the steps of: acquiring a plurality of projections of a three-dimensional subject, each projection comprising a dataset of spatially contiguous data values; supplying said projections to a computer; replacing a first part of the data values of the projections with new data values, with a second part of the data values of the projections remaining unchanged, and thereby generating changed projections; and reconstructing an image of the subject in the computer using the changed projections.