Noise and signal decoupling in maximum likelihood reconstructions and Metz filters for PET images
IEEE Nuclear Science Symposium and Medical Imaging Conference
EM algorithm have much lower noise in some structures compared to those reconstructed with Filtered Backprojection (FBP). The use of a statistically correct noise model in the ML algorithm has probably provided this noise improvement, but whether this correct model confers a general advantage for ML, over FBP with no noise model but any filter is unknown. We have chosen some Metz filters for FBP reconstructions based on m a t c h the mean signal amplitude spectra of FBP images with those of ML reconstructions. Our results demonstrate that for the mean signal behavior, FBP with Me& filter of various orders can achieve similar performance to ML over a range of image resolution. However, for images with resolution beyond the intrinsic detector resolution, the variance as shown by the noise power spectrum increased significantly for FBP compared to ML. This suggested that the noise was decoupled from the signal in the process of signal recovery for ML due to its noise model and nonlinearity. Such decoupling is not possible with FBP. However, ML has very limited advantages over FBP for most images with resolution equivalent to or lower than the intrinsic resolution, or if mean signals are obtained from a large number of noisy ensembles.
Liow J.-.S. & Strother S.C.
Conference record of the 1992