Detection of microscopic diffusion anisotropy on a whole‐body MR system with double wave vector imaging

Double‐wave‐vector diffusion‐weighting experiments can detect diffusion anisotropy on a microscopic level which, e.g., could distinguish lower fiber densities from reduced fiber coherence. The underlying signal difference between parallel and orthogonal wave vector orientations has been observed on vertical‐bore MR systems (≥500 mT m−1); however, numerical simulations reveal that it is expected to be considerably reduced for typical whole‐body MR gradient pulse durations. Here, pig spinal cord tissue and a reference fluid phantom were investigated on a 3 T clinical MR system (40 mT m−1). By averaging over different absolute wave vector orientations, signal variations caused by experimental imperfections like background gradient fields and eddy currents were minimized and a rotationally invariant anisotropy measure could be assessed. A significant microscopic anisotropy was observed in gray and white matter tissue even in the plane perpendicular to the cord which is consistent with previous vertical‐bore experiments. Thus, it is demonstrated that double‐wave‐vector experiments can investigate the microscopic anisotropy on whole‐body MR systems. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

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