TY - JOUR
T1 - Signal-to-noise optimization and observed volume localization with circular surface coils
AU - Evelhoch, Jeffrey L.
AU - Crowley, Michael G.
AU - Ackerman, Joseph J.H.
N1 - Funding Information:
We acknowledge stimulating and helpful discussions with Professor W. T. Dixon, Professor R. Yaris, and Dr. D. R. Perchak on the art of three-dimensional numerical integration. Support for this work was provided by Washington University Intramural Funds, the Washington University Computer Facility, NSF Instrument Grant CHE 8 1002 11, and NIH Grant 1 RO 1 GM3033 1-O1 . In addition, this project was also supported in part by BRSG SO7 RR07054 awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health. J.L.E. is an NIH Postdoctoral Fellow.
PY - 1984/1
Y1 - 1984/1
N2 - Sensitivity optimization in surface coil NMR is complicated by the inhomogeneity (or shape) of the B1 field produced by the surface coil antenna. The sensitivity and the size and location of the observed volume are dependent upon experimental conditions. Therefore, we have derived three-dimensional signal intensity maps for a single-turn, flat, circular coil operating on resonance in the single-coil mode to determine the effect of experimental conditions on the sensitivity and spatial characteristics of the observed volume. The results indicate that rapid repetition rates (T ≪ T1) provide optimum sensitivity and contribute significant signal intensity from regions not immediately adjacent to the coil. Intermediate repetition rates (T ∼ T1) provide a significant sensitivity increase over slow repetition rates (T ≥ 5T1) while localizing the volume observed primarily to regions adjacent to the coil. For homogeneous samples further separated from the coil (0.2-0.4 radii), longer pulse widths provide signal from a large region of the sample with a minimum loss in sensitivity. This analysis is verified by agreement of calculated and experimental total intensities as a function of flip angle (pulse width), relaxation time (T1), and repetition rate. Furthermore, the results from 2H (30 MHz) and 19F (188 MHz) NMR experiments with ionic and nonionic solutions indicate that rf attenuation problems associated with conductive samples are not likely to be significant in surface coil NMR experiments that utilize small diameter coils at high fields.
AB - Sensitivity optimization in surface coil NMR is complicated by the inhomogeneity (or shape) of the B1 field produced by the surface coil antenna. The sensitivity and the size and location of the observed volume are dependent upon experimental conditions. Therefore, we have derived three-dimensional signal intensity maps for a single-turn, flat, circular coil operating on resonance in the single-coil mode to determine the effect of experimental conditions on the sensitivity and spatial characteristics of the observed volume. The results indicate that rapid repetition rates (T ≪ T1) provide optimum sensitivity and contribute significant signal intensity from regions not immediately adjacent to the coil. Intermediate repetition rates (T ∼ T1) provide a significant sensitivity increase over slow repetition rates (T ≥ 5T1) while localizing the volume observed primarily to regions adjacent to the coil. For homogeneous samples further separated from the coil (0.2-0.4 radii), longer pulse widths provide signal from a large region of the sample with a minimum loss in sensitivity. This analysis is verified by agreement of calculated and experimental total intensities as a function of flip angle (pulse width), relaxation time (T1), and repetition rate. Furthermore, the results from 2H (30 MHz) and 19F (188 MHz) NMR experiments with ionic and nonionic solutions indicate that rf attenuation problems associated with conductive samples are not likely to be significant in surface coil NMR experiments that utilize small diameter coils at high fields.
UR - http://www.scopus.com/inward/record.url?scp=0000969126&partnerID=8YFLogxK
U2 - 10.1016/0022-2364(84)90195-1
DO - 10.1016/0022-2364(84)90195-1
M3 - Article
AN - SCOPUS:0000969126
SN - 0022-2364
VL - 56
SP - 110
EP - 124
JO - Journal of Magnetic Resonance (1969)
JF - Journal of Magnetic Resonance (1969)
IS - 1
ER -