Figure 4.

Three axial slices at three different time points after rigid body registration (col. 1), after nonrigid registration without the constraint (col. 2), and with the constraint (col. 3). In the 4^th row, the zoom-in deformation field without and with the constraint at t₁ (the 1^st and 2^nd panels) and t₂ (the 3^rd and 4^th panels) are shown, respectively.