Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1996-08-19
1999-06-22
Barlow, John
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324309, 324319, G01R 3300
Patent
active
059145994
ABSTRACT:
This invention relates to a technique for compensating for the inhomogeneity of the field generated by the RF coil (B1) in a nuclear magnetic resonance experiment. Current techniques for achieving accurate flip angles with non-uniform B1 transmit fields, are based upon modulation of the RF waveform. Inherent disadvantages of any RF-based compensation is an increased pulse length and/or increased RF power. Moreover, for some important applications, e.g. multi-slice excitation, no suitable pulses are known. We present an alternative strategy involving a Bz field whose spatial variation is correlated with that of the B1 field. This spatial correlation between the fields allows Bz-based compensation for the effects of B1 inhomogeneity. Successful operation over a wide bandwidth and range of B1 intensities may be achieved without any modification of the RF pulses. An alternative approach for compensating for B1 inhomogeneity is to apply a rapid oscillatory phase-modulation to an existing RF pulse waveform. This approach does not require an additional Bz field, but does not have the minimum RF power advantage of the first approach.
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Review Article--Composite Pulses (62 pages).
Review Article--Insensitive Adiabatic RF Pulses (39 pages).
Research Article--Magnetic Field Mapping (6 pages).
Research Article -BIRP, An Improved Implementation of Low-Angle Adiabatic (BIR-4) Excitation Pulses (3 pages).
Barlow John
Battison Adrian D.
Bui Bryan
National Research Council of Canada
Thrift Murray E.
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