FIGURE 1.  Different stages involved in realigning emission data with Polaris-based methods. MTfbf is a 1-stage process, where reconstructed frames (F1 and F2) are moved to position of the transmission scan (TR), using the average frame position derived from Polaris data. MT is a 1-stage process in which lines of response (LORs) are moved to the transmission scan position based on Polaris data. LMCfbf is a 2-stage process: First, LORs within a frame are realigned to average position in the frame using Polaris data; then reconstructed frames are moved to transmission scan position using the average frame position derived from Polaris data. For all methods, only 1 Polaris coordinate is shown for simplicity. Full details of the different methods are given in the text.