Quantitative validation of a new coregistration algorithm

The Neuro900 Image Coregistration Software (Strichman Medical Equipment) for SPECT was evaluated for translational and rotational registration accuracy. A Tc-99m HM-PAO split-dose study (0.53 mCi low dose, L, and 1.01 mCi high dose, H) was simulated with a Hoffman Brain Phantom with five fiducial markers. Translation error was determined by a shift in image centroid, and rotation error was determined by a simplified two-axis approach. Changes in registration accuracy were measured with respect to: 1) slice spacing, using the four different combinations LL, LH, HL, HH, 2) translational misalignment before coregistration, 3) changes in the step size of the iterative parameters. In all the cases the algorithm converged with only small difference in translation offset, θ and φ. At 6 mm slice spacing, translational errors ranged from 0.9 to 2.8 mm (system resolution at 100 mm, 6.8 mm). The converged parameters showed little sensitivity to count density. In addition the correlation coefficient increased with decreasing iterative step size, as expected. Based on the authors´ results, they found that this algorithm based on the maximization of the correlation coefficient between studies was an effective and efficient way to coregister SPECT data