Comparison of robustness of the sGTMo to sGTM and GTMo methods in terms of registration errors. Normalized RCs are plotted as a function of registration error. The misregistration was applied in the lateral directions to (a) the simulated sphere phantom, (b) the simulated brain phantom, and (c) the physical sphere phantom. The error bars are standard deviations. The ideal values for RC are shown as green lines. RC: recovery coefficient, GTM: geometric transfer matrix, sGTM: symmetric GTM, GTMo: GTM implemented in sinogram-space, sGTMo: sGTM implemented in sinogram-space, VOI: volume of interest, puta: putamen, caud: caudate nucleus, gry: grey matter, and wht: white matter.