Signal Drop-Out Reduction in Gradient Echo Imaging with a Hyperbolic Secant Excitation Pulse - An Evaluation Using an Anthropomorphic Head Phantom
Shmueli K, Thomas D, Ordidge R
University College London
The Hyperbolic Secant (HS) excitation pulse produces a through-slice quadratic phase variation, partly cancelling the through-slice susceptibility-induced phase gradient that causes signal drop-out. The HS-90 pulse parameters can be altered to vary the quadratic phase coefficient, thereby allowing selection of a pulse for optimal recovery of signal drop-out in specific regions. Different HS-90 pulses were used to excite GE-EPI images of an anthropomorphic head phantom with realistic susceptibility artifacts. Every HS-90 pulse resulted in recovery of dropped-out signal, at the expense of overall signal intensity. The pulse with a 1.22 rad/mm2 coefficient gave a good compromise between drop-out recovery and signal reduction.