University of California

Ching Yao

Leon Kaufman

Lawrence E Crooks

James D Hale

At least one extra NMR measurement cycle is performed without any imposed magnetic gradients during readout and recordation of the NMR RF response. Calibration data derived from this extra measurement cycle or cycles can be used for resetting the RF transmitter frequency and/or for phase shifting other conventionally acquired NMR RF response data to compensate for spurious changes in magnetic fields experienced during the NMR data measuring processes. Some such spurious fields may be due to drifting of the nominally static magnetic field. Another source of spurious fields are due to remnant eddy currents induced in surrounding conductive structures by magnetic gradient pulses employed prior to the occurrence of the NMR RF response signal. Special procedures can be employed to permit the compensation data itself to be substantially unaffected by relatively static inhomogeneities in the magnetic field and/or by differences in NMR spectra of fat and water types of nuclei in imaged volumes containing both.

MRI compensated for spurious NMR frequency/phase shifts caused by

Reduced T2 decay is achieved through use of at least one asymmetrically truncated RF nutation pulse and an asymmetrically sampled NMR RF response with missing asymmetric data being supplied by complex conjugate synthesis.

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Belmont, CA, United States of America

Ching Yao