Kinematics of the heart : strain and strain-rate using time-resolved three-dimensional phase contrast MRI
Abstract: During the cardiac cycle, the myocardium (heart muscle) undergoes large elastic deformations as a consequence of the active muscle contraction along the muscle :fibers and their relaxation, respectively. A four-dimensional (4D) description (three spatial dimensions + time) of the kinematics of the myocardium would bring increased understanding of the mechanical properties of the heart and may be of interest in assessing regional myocardial function.The heart is a complex three-dimensional structure and therefore velocity components in three directions are necessary to accurately describe the velocities in the myocardium. The phase contrast MRI pulse sequence used in this work provides velocity vectors in a 3D spatial grid covering the entire heart throughout the cardiac cycle. The suggested method provides the strain-rate tensor in each measured voxel and time frame of the cardiac cycle, calculated from the velocity field. Coordinates for the measured voxels,obtained from the velocity data, defme the deformation of a finite element mesh. This mesh is used for calculation of myocardial strain.The method presented in this thesis enables automated delineation of the borders of the myocardium, definition of a parametric fmite element mesh and calculation of 4D myocardial strain and strain-rate throughout the cardiac cycle. The suggested visualization method displays the full tensors, including the main direction of deformation or deformation rate without any assumptions of myocardial motion directions in the calculations.
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