Fig. 5.

Motion Search Direction Accuracy. Here we compare the accuracy of the motion search direction (∇ in Eqn. 8, which is the difference between the motion estimates at each step of the search, i.e. θ⁽ⁱ⁺¹⁾ = θ⁽ⁱ⁾ + ∇⁽ⁱ⁾), when updating a subset of target voxels, versus assuming the image is constant (no voxels updates). A. The motion search direction error is plotted as a function of the alternating step (i.e. how many times the image volume has been reconstructed). B. The motion search direction is plotted for the no voxel updates and target voxel updates method. The first row shows the search direction at step 2 of the motion optimization, and the second row shows the search direction at step 11 of the motion optimization. Each method (solid) is compared to the full model search direction (dotted), and the average % difference is shown in the top right of each plot.