A modified strategy for 3D image reconstruction from axially adjacent bed positions [positron emission tomography]

Elimination of the forward projection step is an important goal in the progress toward clinically useful 3D image reconstruction. For imaging applications involving the torso or whole body, projection data are normally acquired at several adjacent bed positions, each of which is reconstructed individually, including recalculation of missing oblique projections. With appropriate overlap, missing projections in one bed position are available in the next bed position. For an axially long object such as the torso, this can amount to substantial computational savings. Reprojection of missing data is still necessary at the axial extremes of the imaged volume, but is limited to a fixed number of axial lines of response. For the case of the ECAT 921, ring difference of ±11, 170 of the 576 axial LORs (30%) must be synthesized for each bed position. If 4 adjacent bed positions are combined with appropriate overlap, only 170 of 1435 axial LORs (12%) must be synthesized. As the forward projection step typically requires 40% of the time necessary for 3D image reconstruction, this amounts to roughly a 25% savings in computational effort