A maximum a posteriori algorithm for the reconstruction of dynamic SPECT data

A 4D ordered-subsets maximum a posteriori (OSMAP) algorithm for dynamic SPECT is described. It uses a temporal prior that constrains each voxel´s behavior in time to obey a compartmental model. No a priori limitations on kinetic parameters are applied; rather, the parameter estimates evolve as the algorithm iterates to a solution. The estimated parameters are also used to model changes in the activity distribution as the camera rotates, avoiding artifacts due to data inconsistencies between angles. This allows for fewer, longer duration scans to be used. Initial evaluations of the algorithm are presented for dynamic cardiac SPECT imaging with teboroxime using a two compartment model. Canine study results demonstrated qualitative improvements for OSMAP compared to OSEM. In a simulation 100 noise realizations were reconstructed using both OSEM and OSMAP. Population means and standard deviations of regional kinetic parameters were compared: True values: k₂₁=0.8, k₁₂=0.4 min^-1; OSEM: k₂₁ =77±06, k₁₂=41±06; OSMAP: L₂₁=.76±.04, k₁₂=.41±.05. The OSMAP algorithm provided parameter estimates with significantly lower standard deviations than did OSEM at similar levels of bias. This algorithm may where potentially improve dynamic SPECT imaging through its implications for noise control, ability to accurately model and reconstruct data in which the activity distribution is changing, and the potential for accurate reconstruction and data analysis using fewer, longer duration scans