Artery wall motion and strain play important roles in vascular remodeling and may be important in the pathogenesis of vascular disease. In vivo observations of circumferentially nonuniform wall motion in the human aorta suggest that nonuniform strain may contribute to the localization of vascular pathology. A velocity-based method to investigate circumferential strain variations was previously developed and validated in vitro; the current study was undertaken to determine whether accurate displacement and strain fields can be calculated from velocity data acquired in vivo. Wall velocities in the porcine thoracic aorta were quantified with PC-MRI and an implanted coil and were then time-integrated to compute wall displacement trajectories and cyclic strain. Displacement trajectories were consistent with observed aortic wall motion and with the displacements of markers in the aortic wall. The mean difference between velocity-based and marker-based trajectory points was 0.1 mm, relative to an average pixel size of 0.4 mm. Propagation of error analyses based on the precision of the computed displacements were used to demonstrate that 10% strain results in a standard deviation of 3.6%. This study demonstrates that it is feasible to accurately quantify strain from low wall velocities in vivo and that the porcine thoracic aorta does not deform uniformly.