Myocardial fiber shortening in humans: Initial results of MR imaging

PURPOSE: To use diffusion-sensitive magnetic resonance (MR) imaging to obta in images of fiber orientation in vivo and to map fiber shortening in human s by means of integrating such data with strain images. MATERIALS AND METHODS: Images of fiber shortening for midventricular short- axis sections were acquired in eight healthy subjects. Fiber orientation ma ps obtained by means of diffusion-sensitive MR imaging were coregistered wi th 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. RESULTS: The results were reproducible among subjects and were consistent w ith published values. MR imaging of myocardial fibers showed axisymmetric p rogression of fiber angles from -90 degrees epicardially to +90 degrees end ocardia[ly, with maxima near 0 degrees. Fiber shortening (mean, 0.12 +/- 0. 01 CSD]) was more uniform than radial, circumferential, longitudinal, or cr oss-fiber strain or any principal strain. Fiber orientation coincided with the direction of maximum contraction epicardially, with that of minimum con traction endocardially, and varied between these extremes linearly with wal l depth (r = 0.6). CONCLUSION: Registered diffusion and strain MR imaging can be used quantita tively to map fiber orientation and its relations to myocardial deformation in humans.