Shimming method for NMR magnet having large magnetic field inhomogeneities
US5539316A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Aug 25, 1995 |
| Grant date | Jul 23, 1996 |
| Priority date | — |
| Expiry date | Aug 25, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R33/3875
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A method of shimming an NMR magnet uses a plurality of 1D projections through a sample volume to determine the inhomogeneities of the field of the NMR magnet. The frequency distributions obtained are assembled from the phase signals of the various projections. In order to avoid frequency errors due to phase wrapping, the phase of each signal is monitored over time for discontinuities indicative of aliasing. For each phase wrap, the signal is "unwrapped" by adjusting the value of the phase signal by 2.pi.. The same method is used to establish a shim field map for each of the shim coils being used. With one shim coil at a time being driven with a predetermined current, the detection method is repeated to acquire a shim-base frequency map for each shim coil. The base frequency map is then subtracted from the shim-base frequency maps to obtain shim field maps. The proper shim currents are then acquired through matrix operations on the shim field maps and the base frequency map.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.