Biomedical Engineering Reference
In-Depth Information
3.4 Summary
Analytical (Fourier rebinning) type backprojection methods provide fast
and reliable reconstruction for the standard X{ray PET model without scat-
ter. Parameters can be chosen in an optimal way. Images can be guaranteed
to deliver a certain precision, which depends on scanner geometry and mea-
surement accuracy. Deviations from the model need to be handled in pre{ or
postprocessing and cannot be included in the image reconstruction algorithm.
Also, a priori knowledge about activity distribution functions (like positivity)
cannot be handled by the algorithms internally.
Iterative (EM, OSEM) type methods provide much more flexibility with
respect to changes of the physical and the noise model. Typically, since they
can handle the correct noise model, deal with the pure data without rebinnning
(list mode) and take a priori assumptions into account, they deliver improved
image quality. However, that comes with a price tag: fully 3D list mode it-
erative EM algorithms are typically slow, optimal stopping criteria are not
available, and the derivation of exact error bounds is not possible.
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