Multiple-quantum vector field imaging by magnetic resonance

We introduce a method for non-invasively mapping fiber orientation in materials and biological tissues using intermolecular multiple-quantum coherences. The nuclear magnetic dipole field of water molecules is configured by a CRAZED sequence to encode spatial distributions of material heterogeneities. At any given point r in space, we obtain the spherical coordinates of fiber orientation (theta,phi) with respect to the external field by comparing three signals parallel to G(X)parallel to parallel to G(Y)parallel to, and parallel to G(Z)parallel to (modulus), acquired with linear gradients applied along the X, Y, and Z axes, respectively. For homogeneous isotropic materials, a subtraction parallel to G(Z)parallel to - parallel to G(X)parallel to - parallel to G(Y)parallel to gives zero. With anisotropic materials, we find an empirical relationship relating parallel to G(Z)parallel to - parallel to G(X)parallel to - parallel to G(Y)parallel to/(parallel to G(X)parallel to + parallel to G(Y)parallel to + parallel to G(Z)parallel to) to the polar angle theta, while parallel to G(X)parallel to - parallel to G(Y)parallel to/(parallel to G(X)parallel to + parallel to G(Y)parallel to + parallel to G(Z)parallel to) is related to the azimuthal angle phi. Experiments in structured media confirm the structural sensitivity. This technique can probe length scales not accessible by conventional MRI and diffusion tensor imaging. (c) 2005 Elsevier Inc. All rights reserved.