Myocardial Fiber Shortening in Humans: Initial Results of MR Imaging

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Abstract
To use diffusion-sensitive magnetic resonance (MR) imaging to obtain images of fiber orientation in vivo and to map fiber shortening in humans by means of integrating such data with strain images. Images of fiber shortening for midventricular short-axis sections were acquired in eight healthy subjects. Fiber orientation maps obtained by means of diffusion-sensitive MR imaging were coregistered with systolic strain maps obtained by means of velocity-sensitive MR imaging. Fiber shortening was quantified by use of the component of systolic strain in the fiber direction. The results were reproducible among subjects and were consistent with published values. MR imaging of myocardial fibers showed axisymmetric progression of fiber angles from -90 degrees epicardially to +90 degrees endocardially, with maxima near 0 degrees. Fiber shortening (mean, 0.12 +/- 0.01 [SD]) was more uniform than radial, circumferential, longitudinal, or cross-fiber strain or any principal strain. Fiber orientation coincided with the direction of maximum contraction epicardially, with that of minimum contraction endocardially, and varied between these extremes linearly with wall depth (r = 0.6). Registered diffusion and strain MR imaging can be used quantitatively to map fiber orientation and its relations to myocardial deformation in humans.