Browse Prior Art Database

NMR Auto Shimming

IP.com Disclosure Number: IPCOM000087605D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

Double, GP: AUTHOR [+4]

Abstract

In the field of NMR (nuclear magnetic resonance) spectrometry, it has been customary to use shim coils to compensate for inhomogeneities in the magnetic field used to excite a sample. Described herein is a system providing for a computer controlled automated shimming or auto-shimming. As shown in Fig. 1, a computer 1 is connected over an I/O bus 2 to an adapter 3 which controls the operation of an FFT (fast Fourier transform) NMR spectrometer 4. The computer or computing system includes the programs necessary to carry out the various control and analytical functions.

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NMR Auto Shimming

In the field of NMR (nuclear magnetic resonance) spectrometry, it has been customary to use shim coils to compensate for inhomogeneities in the magnetic field used to excite a sample. Described herein is a system providing for a computer controlled automated shimming or auto-shimming. As shown in Fig. 1, a computer 1 is connected over an I/O bus 2 to an adapter 3 which controls the operation of an FFT (fast Fourier transform) NMR spectrometer 4. The computer or computing system includes the programs necessary to carry out the various control and analytical functions.

As shown in Fig. 2, spectrometer 4 includes a permanent magnet having poles 5N and 5S that provide a unidirectional high strength magnetic field in which a test sample contained in a test tube 6 is positionable. A pulse-modulated RF exciting signal from transmitter 7 is applied to an excitation coil 8 and resonates various nuclei within the sample. The resonating signal is picked up by a coil 9, the signal being fed to receiver 10 for subsequent processing to produce a free induction decay (FID) signal as shown at 11. Shim coils 12N and 12S are placed in front of the pole faces 5N and 5S, respectively, and are connected to shim coil drivers 13 that are settable under the control of computer 1 to cause various levels of current to flow within the respective shim coils. Preferably, the shim coil drivers provide a linear output that is proportional to a program- controlled voltage applied to the drivers.

In accordance with the auto-shimming process, a sample 6 is placed in the magnetic field and a series of measurements are made by spectrophotometer 4 to provide a series of FID signals. Information is extracted from the FID signals and analyzed, and changes are made in the degree to which different shim coils and combinations thereof are energized. The quantity or functional that is being optimized or minimized is the magnetic field contribution to the spectral line width. Preferably, the optimizing bits of information derived from the FID are the second moment of the line shape and the absolute area of the FID normalized. The second moment is available directly fro...