Self-Diffusion Imaging by Spin Echo in Earth's Magnetic Field |
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| Institution: | 1. Department of Astronomy, Wellesley College, Wellesley, MA 02481, USA;2. Department of Astronomy, Cornell University, Ithaca, NY 14853, USA;3. Department of Physics, University of Idaho, Moscow, ID 83844, USA;1. Department of Astronomy, Wellesley College, Wellesley, MA 02481, USA;2. formerly Department of Astronomy, Wellesley College, Wellesley MA 02481, USA;3. Museum of Science, Boston, MA 02114, USA;4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA;5. Department of Astronomy, Cornell University, Ithaca NY 14853, USA;6. Department of Physics, University of Idaho, Moscow, ID 83844, USA;7. Department of Electrical Engineering, San Jose State University, San Jose CA 95192, USA;8. Department of Physics, University of Central Florida, Orlando FL 32816, USA |
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| Abstract: | The NMR of the Earth's magnetic field is used for diffusion-weighted imaging of phantoms. Due to a weak Larmor field, care needs to be taken regarding the use of the usual high field assumption in calculating the effect of the applied inhomogeneous magnetic field. The usual definition of the magnetic field gradient must be replaced by a generalized formula valid when the strength of a nonuniform magnetic field and a Larmor field are comparable (J. Stepišnik,Z. Phys. Chem.190, 51–62 (1995)). It turns out that the expression for spin echo attenuation is identical to the well-known Torrey formula only when the applied nonuniform field has a proper symmetry. This kind of problem may occur in a strong Larmor field as well as when the slow diffusion rate of particles needs an extremely strong gradient to be applied. The measurements of the geomagnetic field NMR demonstrate the usefulness of the method for diffusion and flow-weighted imaging. |
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