Improving the signal uniformity at 400 MHz: sequential multi-channel excitation with intermediate active shims
Petropoulos L, Taracila V, Eagan T, Brown R
Case Western Reserve University, Hitachi Medical Systems
We present an alternative way to improve signal uniformity of a birdcage by using multi-channel excitations in one combined RF pulse to decrease the scanning time. To build up a uniform transverse magnetization constructively for the entire sample cross-section and at any flip angle, it is necessary to utilize additional small fields, referred to here as active shims (such shims are not driven at the Larmor frequency), interspersed with the RF pulses. Due to topological spin singularities associated with the channels n=2,3, , the uniformity of the signal can only be achieved locally and not over the entire sample cross-section.