MEASUREMENT AND CORRECTION OF GRADIENT-INDUCED CROSS-TERM MAGNETIC FIELDS IN EPI SEQUENCE

摘要

PPROBLEM TO BE SOLVED: To measure and correct a gradient-induced cross-term magnetic field in an echo planar imaging (EPI) sequence, relating to magnetic resonance imaging (MRI), especially to a high speed EPI technique. PSOLUTION: The method for determining the gradient-induced cross-term magnetic field in a magnetic resonance imaging (MRI) system, includes processes of: positioning an examined body (object) in a static magnetic field; applying a radio frequency (RF) excitation pulse for spatially selecting a slice of the object; applying an incremented phase encode gradient magnetic field along a phase encoding gradient magnetic field direction parallel to the slice phase; applying a selective RF refocusing pulse to select a line (linear portion) in the slice; applying a switched readout magnetic field gradient, which causes the cross-term magnetic field; generating a data array of a phase-encoding gradient and a corresponding sample data point along the selected line; and determining a center frequency distribution (CF) for the selected line, which indicates the gradient induced cross-term magnetic field. PCOPYRIGHT: (C)2007,JPO&INPIT