A projector, backprojector pair which accounts for the two-dimensional depth and distance dependent blurring in SPECT

The speed and accuracy of iterative reconstruction routines for single-photon-emission computed tomography (SPECT) are highly dependent on the projection and backprojection algorithms used. A projector-backprojector pair which accounts for the two-dimensional, spatially dependent blurring encountered in SPECT and which reduces the computational load has been developed. These algorithms assume that the attenuator is a uniform elliptical cylinder that is invariant in the axial direction. They further assume that the blur can be modeled using the sum of several separable functions, e.g. separate Gaussian functions for the geometric and scatter components. When implemented on an array processor of moderate computational power, a projection or backprojection of a SPECT study, with 64 64-pixel×64-pixel projection images and a 64×64×64 reconstruction space, can be completed in less than 2.4 h, or 2.3 min per transverse slice