Title :
Variance reduction on randoms from coincidence histograms for the HRRT
Author :
Byars, Larry G. ; Sibomana, Merence ; Burbar, Ziad ; Jones, Judson ; Panin, Vladimir ; Barker, W. Craig ; Liow, Jeih-San ; Carson, Richard E. ; Michel, Christian
Author_Institution :
Byars Consulting, Oak Ridge, TN
Abstract :
A new algorithm for variance reduction on random coincidences (VRR) has been validated for the HRRT. VRR is crucial to achieve quantitation for low statistics dynamic studies reconstructed with iterative methods based on ordinary Poisson model. On HRRT, VRR cannot be performed in projection space since individual LOR´s are mixed after histogramming in parallel projection space using nearest neighbor approximation and axial compression. The proposed algorithm uses the classical random rate equation on the 4.5 109LOR´s. However, crystal singles are registered at block level and have lower deadtime than coincidences. Variations in layer identification with countrate were reported biasing random estimation from block singles. Our method overcomes these problems by estimating the singles per crystal from delayed coincidences. A singles map is created histogramming every delayed event into 2 singles. Each element represents the number of coincidences between that crystal and the ones in the 5 opposite coincident heads. The algorithm finds iteratively the crystal singles rates compatible with the delayed coincidence events. The method has been validated on decaying phantoms. We compared estimated and measured block singles to identify deadtime difference between singles and coincidences
Keywords :
image reconstruction; image registration; iterative methods; medical image processing; phantoms; positron emission tomography; stochastic processes; HRRT; axial compression; block singles; coincidence histogram; crystal singles rates; decaying phantoms; delayed coincidence events; image reconstruction; image registration; iterative methods; low statistics dynamic studies; nearest neighbor approximation; ordinary Poisson model; parallel projection space; random coincidences; singles map; variance reduction; Crystals; Delay; Histograms; Imaging phantoms; Integral equations; Nuclear and plasma sciences; Organizing; Sorting; Statistics; Throughput;
Conference_Titel :
Nuclear Science Symposium Conference Record, 2005 IEEE
Conference_Location :
Fajardo
Print_ISBN :
0-7803-9221-3
DOI :
10.1109/NSSMIC.2005.1596876