HIGH-RESOLUTION MRI OF MYOCARDIAL DEFORMATION

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The overall objective of this proposal is to develop, implement, and evaluate high-resolution magnetic resonance imaging methods, specifically myocardial tagging, for acquiring a time series of localized strain measurements in the myocardium of the dog. This will allow, for the first time, noninvasive measurements of the transmural dependence of myocardial deformation. The absence of such a noninvasive method has been a major limitation in the field of cardiac mechanics. Because knowledge of local deformation patterns is required to study the relationship between fiber shortening and heart wall thickening in normal and diseased states, investigators have resorted to implanting arrays of radiopaque markers in the myocardium and tracking the motion of these markers with biplane cineradiography. This is now the standard method for performing measurements of strain in the myocardium. With the development of a specialized probe, myocardial tagging pulse sequences and strain calculation algorithms, equivalent, if not superior, measurements of strain may be obtained noninvasively. Thus the specific aims of this proposal are: (1) To refine and validate high-resolution myocardial tagging techniques. This involves the design and construction of a specialized probe, optimization and validation of MRI-derived strain estimates with simulations and experiments in phantoms, and the comparison of selected methods in vivo. (2) To determine the resolution required for sampling myocardial deformation during contraction that permits the calculation of strain in local regions of the heart wall using a linear model. (3) To determine whether myocardial deformation is homogenous or heterogeneous in local and remote regions of the left ventricle. Using the techniques described in this application, we will make strain estimates through the heart wall with an isotropic resolution on the order of 3 mm3. The accomplishment of these aims will have a significant effect on research in cardiac mechanics. Most important, for the first time, investigators will have the ability to measure the local mechanics of myocardial contraction noninvasively.