The Projectionprojection-slice theorem is suitable for CT image reconstruction with parallel beam projections. It can not directly apply to fanbeam or conebeam CT. The theorem was extended to fan-beam and conebeam CT image reconstruction by Shuang-ren Zhao in 1995.<ref name="ZhaoFSliceThoerem">{{cite journal | author=Zhao S.R. and H.Halling | title = A New Fourier Transform Method for fan Beam Tomography | journal=published in 1995 Nuclear Science Symposium and Medical imaging Conference Record | year = 1995 | pages=1287–91 }}</ref>
