Figure 4.

(a) Reference motion field between the MRI frames #5 (end inspiration) and #1 (end expiration, reference frame) in the coronal view. (b) Motion fields estimated with R-HARP using the tagged-MRI simulations with 5% and 25% noise levels with and without regularization. As explained in Sec. 2B, our motion tracking procedure was masked in the lungs where little MRI signal was detected. Motion fields are shown in the coronal view and deformation vectors are in pixel units divided by five in this figure.