Purpose
The authors recently developed a preconditioned alternating
projection algorithm (PAPA) for solving the penalized-likelihood SPECT
reconstruction problem. The proposed algorithm can solve a wide variety of
non-differentiable optimization models. This work is dedicated to comparing
the performance of PAPA with total variation (TV) regularization (TV-PAPA)
and a novel forward-backward algorithm with nested expectation maximization
(EM)-TV iteration scheme (FB-EM-TV).
Methods
Monte Carlo technique was used to simulate multiple noise
realizations of the fan-beam collimated SPECT data for a piecewise constant
phantom with warm background, and hot and cold spheres with uniform
activities at two noise levels. They were reconstructed using the
aforementioned algorithms with attenuation, scatter, distance-dependent
collimator blurring and sensitivity corrections. Noise suppressing
performance, lesion detectability, lesion contrast, contrast recovery
coefficient, convergence speed and selection of optimal parameters were
evaluated. The conventional EM algorithms with TV post-filter (TVPF-EM) and
Gaussian post-filter (GPF-EM) were used as benchmarks.
Results
The TV-PAPA and FB-EM-TV demonstrated similar performance in all
investigated categories. Both algorithms outperformed TVPF-EM in terms of
image noise suppression, lesion detectability, lesion contrast and
convergence speed. We established that the optimal parameters versus
information density approximately followed power laws, which offers a
guidance in parameter selection for reconstruction methods.
Conclusions
For the simulated SPECT data, TV-PAPA and FB-EM-TV produced
qualitatively and quantitatively similar images. They performed better than
the benchmark TVPF-EM and GPF-EM, with only limited loss of lesion
contrast.