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Iterative shim method for base field magnet of nuclear spin tomography appts. - repeatedly varying shim current to increase correlation coefficients of echo signals resulting from bipolar gradient pulse sequence following HF stimulation
Iterative shim method for base field magnet of nuclear spin tomography appts. - repeatedly varying shim current to increase correlation coefficients of echo signals resulting from bipolar gradient pulse sequence following HF stimulation
The appts. includes shim coils carrying an adjustable shim current and gradient coils. A spin system in the investigation vol. is stimulated by a HF stimulation pulse (RF). Several echo signals (S) are generated by a bipolar gradient coil sequence (RO). Each is detected and its detected signals written into a row of a measurement data matrix. Correlation coefficients for at least one row are formed w.r.t. a reference row. The shim current through at least one shim coil is varied to increase the correlation coefficients and the process is repeated. The entire procedure is repeated until sufficient homogeneity of the base field in the investigation vol. is achieved. ADVANTAGE - Base field homogeneity is achieved using a rapid iterative shim technique.
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