Multiple-Quantum Vector Imaging
Abstract of talk 420 from ISMRM 2005 Meeting (need password for access)
L-S. Bouchard, W. S. Warren
A novel methodology based on measurements of the distant dipolar field, or intermolecular multiple-quantum coherences, is presented for tracking the vector orientation of parallel fiber bundles or other anisotropic structures in materials or biological tissues. The method uses a CRAZED sequence (Warren et al., Science 262:2005-9, 1993) with correlation gradient applied along the X, Y and Z axes. A subtraction |Gx|+|Gy|-|Gz| gives a signal when structural anisotropy is present and zero when the material is isotropic. For a material consisting of oriented fibers, the strength of the subtraction is related to the polar angle of the directional vector of the fibers. A comparison of X and Y gradients is related to the azimuthal angle. Experimental results in the petiole of celery show that anisotropy can be readily detected by this method. Tilting the sample with respect to the applied field, and rotating the sample in the transverse plane allow gave subtraction results that are consistent with theoretical calculations and demonstrate its applicability. The method can clearly detect structural anisotropy even for very weak gradient pulses well outside any diffusion-weighted regime. The structure sizes that can be detected are on the order of the length of the correlation distance. Thus, material heterogeneities can be detected on the tens of microns to millimeters scales and the method nicely complements currently existing techniques such as diffusion tensor imaging or high resolution MRI. This method finds potential applications in the materials and biomedical sciences. It could perhaps be of use in detecting tumor vascularity or for mapping trabecular bone anisotropy.
L-S. Bouchard, W. S. Warren
A novel methodology based on measurements of the distant dipolar field, or intermolecular multiple-quantum coherences, is presented for tracking the vector orientation of parallel fiber bundles or other anisotropic structures in materials or biological tissues. The method uses a CRAZED sequence (Warren et al., Science 262:2005-9, 1993) with correlation gradient applied along the X, Y and Z axes. A subtraction |Gx|+|Gy|-|Gz| gives a signal when structural anisotropy is present and zero when the material is isotropic. For a material consisting of oriented fibers, the strength of the subtraction is related to the polar angle of the directional vector of the fibers. A comparison of X and Y gradients is related to the azimuthal angle. Experimental results in the petiole of celery show that anisotropy can be readily detected by this method. Tilting the sample with respect to the applied field, and rotating the sample in the transverse plane allow gave subtraction results that are consistent with theoretical calculations and demonstrate its applicability. The method can clearly detect structural anisotropy even for very weak gradient pulses well outside any diffusion-weighted regime. The structure sizes that can be detected are on the order of the length of the correlation distance. Thus, material heterogeneities can be detected on the tens of microns to millimeters scales and the method nicely complements currently existing techniques such as diffusion tensor imaging or high resolution MRI. This method finds potential applications in the materials and biomedical sciences. It could perhaps be of use in detecting tumor vascularity or for mapping trabecular bone anisotropy.
posted by Curt at 11:55 AM
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