In vivo quantification of vessel wall motion and cyclic strain using cine phase contrast magnetic resonance imaging

Vessel wall motion, stress, and strain are important in adaptation and disease processes, and are thought to contribute to the localization of vascular disease. During the course of this research, a general method was developed for quantifying Green-Lagrange cyclic wall strain from velocity data acquired with phase contrast MR imaging. This method produces circumferentially-varying strain fields, throughout the cardiac cycle. Algorithms for segmenting and tracking the vessel wall were also developed. The feasibility and precision of this method were evaluated using both in vitro and in vivo validation studies.; An experimental flow rig, including compliant strain phantoms, was designed and built for the in vitro validation study. Markers embedded in the wall of the phantoms were used to evaluate the accuracy of the velocity tracking; mean differences between marker trajectories and integrated-velocity trajectories were 0.21 ± 0.16 mm, relative to a pixel size of 0.39 mm. An implantable coil was designed and built for imaging the porcine descending thoracic aorta. As in the in vitro study, excellent results were obtained, with the average trajectory difference being 0.12 mm, relative to an average pixel size of 0.44 mm.; Propagation of error analyses were performed to extrapolate error in velocity tracking to error in strain. Retrospective propagation of error analyses indicated that strain could be quantified to within 3–5%. A prospective propagation of error analysis was developed to evaluate the quality of the computed strain data based on image SNR, amount of strain, and known imaging parameters.; Preliminary studies were conducted to evaluate the current feasibility of quantifying strain in the human aorta. Porcine aortic wall strain patterns were compared to wall architecture; results indicate that areas of higher strain directly correlate to areas of increased medial thickness.; This method for quantifying time-varying, circumferentially-varying Green-Lagrange cyclic strain in vessel walls has numerous applications and will provide the framework for addressing clinically relevant problems in occlusive and aneurysmal disease. As “normal” strain patterns are defined, it will then be feasible to describe “abnormal” patterns, thus laying a new foundation for diagnosis and treatment of vascular disease based on wall mechanics.