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Abstract #2830

Fast RF Flip Angle Calibration by Bloch-Siegert Shift

Laura Sacolick1, Ling Sun2, Mika W. Vogel1, Ileana Hancu3

1GE Global Research, Garching b. Munchen, Germany; 2GE Healthcare, Waukesha, WI, United States; 3GE Global Research, Niskayuna, NY, United States

Here we present a novel method for automated RF flip angle calibration based on the Bloch-Siegert shift. The Bloch-Siegert shift is an effect where spin resonance frequency shifts when an off-resonance RF field is applied. Two off-resonance RF pulses were added to a slice-selective spin echo sequence. The off-resonance pulses induce a phase shift in the acquired signal that is proportional to B12. The signal is spatially localized in two dimensions- by slice selection and readout filter, and the signal weighted average B1 over the slice is calculated. This calibration from a starting system transmit gain to measured average flip angle is used to calculate the transmit gain setting needed to produce the desired flip angle. This is shown here at 3 Tesla in the brain, shoulder, abdomen, breast, and wrist with a total scan time for a robust implementation of 1.6 seconds.