title: Multiple-quantum vector field imaging by magnetic resonance.
abstract: 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 ||G(X)||, ||(Y)||, and ||G(Z)|| (modulus), acquired with linear gradients applied along the X, Y, and Z axes, respectively. For homogeneous isotropic materials, a subtraction ||G(Z)|| - ||G(X)|| - ||G(Y)|| gives zero. With anisotropic materials, we find an empirical relationship relating ||G(Z)|| - ||G(X)|| - ||G(Y)||/(||G(X)|| + ||G(Y)|| + ||G(Z)||) to the polar angle theta, while ||G(X|| - ||G(Y)||/(||G(X)|| + ||G(Y)|| + ||G(Z)||) 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.
authors.affiliation: Department of Chemistry, Princeton University, NJ 08544, USA. LSBouchard@waugh.cchem.berkeley.edu
authors.forename: Louis-S
authors.initials: LS
authors.lastname: Bouchard
authors.forename: Warren S
authors.initials: WS
authors.lastname: Warren
mesh_terms: D000818:Animals; D016880:Anisotropy; D000077102:Apium; D001931:Brain Mapping / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats