APPROXIMATE 3D ITERATIVE RECONSTRUCTION FOR SPECT

Compared with slice-by-slice approaches for SPECT reconstruction, thre e-dimensional iterative methods provide a more accurate physical model and an improved SPECT image. Clinical application of these methods, h owever, is limited primarily by their computational demands. This pape r investigates methods for approximate 3D iterative reconstruction tha t greatly reduce this demand by excluding from the reconstruction the smaller magnitude elements of the system matrix. A new method is descr ibed which is designed to control the resulting bias in the SPECT imag e for a given reduction in computation. The approximate methods were c ompared to fully 3D iterative reconstruction in terns of SPECT image b ias and visual quality. All methods were incorporated into the ML-EM a lgorithm and applied to data from 3D mathematical and experimental bra in phantoms. The SPECT images reconstructed by the approximate methods exhibited a positive bias throughout the image that was in general sm aller with the new method (in the range of 2%-6%). The bias was smalle st in locally hot regions and largest in locally cold regions. The hig h quality brain phantom images demonstrated the capability of the new method in realistic imaging contexts. The time per iteration for an en tire 3D brain phantom on a modern workstation using the approximate 3D method was 7.9 s. (C) 1997 American Association of Physicists in Medi cine.