A 3D model of non-uniform attenuation and detector response for efficient iterative reconstruction in SPECT.

A 3D physical model for iterative reconstruction in SPECT has been developed and applied to experimental data. The model incorporates non-uniform attenuation using reconstructed transmission CT data and distance-dependent detector response based on response function measurements over a range of distances from the detector. The 3D model has been implemented in a computationally efficient manner with practical memory requirements. The features of the model that provide efficiency are described including a new region-dependent reconstruction (RDR) technique. With RDR, filtered backprojection is used to reconstruct areas of the image of minimal clinical importance, and the result is used to supplement the iterative reconstruction of the clinically important areas of the image. The 3D model was incorporated into the maximum likelihood-expectation maximization (ML-EM) reconstruction algorithm and tested in three phantom studies--a point source, a uniform cylinder, and an anthropomorphic thorax--and a patient 9Tc(m) sestamibi study. Reconstructed images with the 3D method exhibited excellent noise and resolution characteristics. With the sestamibi data, the RDR technique produced essentially the conventional ML-EM estimate in the cardiac region with substantial time savings.