Resonance Offset as a Design Parameter for Pulse Cascades Producing Uniform Tipping in Inhomogeneous RF Fields
Kaiser L, Young K, Matson G, Schleich T
Department of Veterans Affairs Medical Center, Northern California Institute for Research and Education
At high field (4.0 Tesla and higher), the RF excitation field is inhomogeneous, giving rise to non-uniform tipping of magnetization, which leads to spatially dependent contrast. We previously introduced pulse cascades that provide uniform tipping, and are easy to implement. However, these pulses do produce more SAR than the pulses they replace. Thus, we have developed new, lower SAR rectangular pulse cascades to produce shallow, uniform tips in the presence of non-uniform B1. These new designs make use of excitation at different frequency offsets (resonance offsets) to achieve immunity to both B1 and to spin resonance offset.