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 ||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.
Bouchard
Louis-S
LS
Department of Chemistry, Princeton University, NJ 08544, USA. LSBouchard@waugh.cchem.berkeley.edu
Warren
Warren S
WS
D000818:Animals; D016880:Anisotropy; D000077102:Apium; D001931:Brain Mapping / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051381:Rats