Detailed knowledge of myocardial dynamics is central to understanding normal cardiac physiology and motion abnormalities are closely correlated with many cardiac pathologies. Much of what has been learned concerning myocardial dynamics has been though the use of invasive techniques which can track individual myocardial segments. Current noninvasive techniques have not been able to exactly reproduce these data, in part because they do not follow individual segments and may confuse bulk motion with wall thickening. While other MRI methods offer promise to partially address these limitations through the use of magnetic myocardial tagging, they have limited spatial and temporal resolution, are unable to examine the entire cardiac cycle, and require long examination times. We propose to overcome these limitations through the development, evaluation and validation of acquisition and analysis methods based on phase contrast MRI maps of myocardial velocity. This novel approach allows arbitrarily positioned regions, as small as a few cubic mm, to be selected retrospectively anywhere in the heart and followed in d-D throughout the entire cardiac cycle. Further, instantaneous regional strain, shear, torsion and twist can be measured directly without requiring sophisticated pattern recognition algorithms. The method will be thoroughly evaluated through the use of phantoms and by comparison with fluoroscopic measurements in animals and patients who have had radiopaque markers implanted at the time of surgery. Myocardial dynamics after surgery will be studied in patients and animals, and the myocardial mechanics of the normal and transplanted human heart will be evaluated. Once validated, this technique should allow the noninvasive study of myocardial motion with unprecedented resolution and scope, and can be made available to MRI centers throughout the world. The proposed phase contrast MRI techniques could have a significant impact in the understanding of normal myocardial function, in the evaluation of cardiac pathologies in patients, and in the choice, impact and timing of therapy.
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