A 3-D Filtered-Backprojection Reconstruction Algorithm for Combined Parallel- and Cone-Beam SPECT Data

Cone-beam (cb) collimation for single-photon emission computed tomography (spect) provides higher sensitivity than parallel-hole collimation, however it produces truncated projection data that can lead to undesirable image artifacts. In response, it has been suggested (Jaszczak 1992) that parallel-beam and cone-beam data be combined to obtain increased sensitivity while maintaining completeness of the data for accurate reconstruction. Herein, a 3-d filtered-backprojection (fbp) approach for reconstructing such data sets is proposed. The algorithm begins with a rebinning of the parallel- and cone-beam (p&cb) data to a common planeintegral projection space: the projection space of the 3-d Radon transform. A normalization step is then implemented to correct for the sampling pattern of the system, thus assuring that the rebinned data are proportional to the plane integrals of the source distribution of the object. Finally, a fully 3-D fbp reconstruction based on the inversion formula of the 3-Radon transform is performed using the rebinned plane integrals. The advantage of this algorithm is that, by making the necessary corrections prior to reconstruction, it avoids residual artifacts that can remain after other methods are employed. In addition, the computation time required by the proposed method is substantially shorter than that reported for maximum-likelihood reconstructions by the expectation-maximization (em) algorithm (Jaszczak 1992).