Fully three-dimensional OSEM-based image reconstruction for Compton imaging using optimized ordering schemes.
Although the ordered subset expectation maximization (OSEM) algorithm does not converge to a true maximum likelihood solution, it is known to provide a good solution if the projections that constitute each subset are reasonably balanced. The Compton scattered data can be allocated to subsets using scattering angles (SA) or detected positions (DP) or a combination of the two (AP (angles and positions)). To construct balanced subsets, the data were first arranged using three ordering schemes: the random ordering scheme (ROS), the multilevel ordering scheme (MLS) and the weighted-distance ordering scheme (WDS). The arranged data were then split into J subsets. To compare the three ordering schemes, we calculated the coefficients of variation (CVs) of angular and positional differences between the arranged data and the percentage errors between mathematical phantoms and reconstructed images. All ordering schemes showed an order-of-magnitude acceleration over the standard EM, and their computation times were similar. The SA-based MLS and the DP-based WDS led to the best-balanced subsets (they provided the largest angular and positional differences for SA- and DP-based arrangements, respectively). The WDS exhibited minimum CVs for both the SA- and DP-based arrangements (the deviation in mean angular and positional differences between the ordered subsets was smallest). The combination of AP and WDS yielded the best results with the lowest percentage errors by providing larger and more uniform angular and positional differences for the SA and DP arrangements, and thus, is probably optimal Compton camera reconstruction using OSEM.
Kim
Soo Mee
SM
Department of Nuclear Medicine and Interdisciplinary Programs in Radiation Applied Life Science Major, College of Medicine, Seoul National University, Seoul, Korea.
Lee
Jae Sung
JS
Lee
Chun Sik
CS
Kim
Chan Hyeong
CH
Lee
Myung Chul
MC
Lee
Dong Soo
DS
Lee
Soo-Jin
SJ
D000465:Algorithms; D016477:Artifacts; D015902:Gamma Cameras; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000295:instrumentation* / Q000379:methods; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity