Recovering TSNR and BOLD Sensitivity by Combining Hyperbolic Secant RF Excitation Pulses and Compensatory Gradients

Stephen James Wastling¹, David J. Lythgoe¹, Gareth John Barker¹

Functional MRI data acquired using gradient-echo echo-planar imaging (GE-EPI) suffers from signal-dropout in the orbitofrontal cortex (OFC) and temporal lobes (TL) caused by susceptibility gradients in the slice-selection, Gz,s, phase-encoding, Gy,s, and readout, Gx,s ,directions. For the first time we combine the use of full-passage scaled-down Hyperbolic Secant (HS) excitation pulses and gradient compensation in the readout direction to recover BOLD signal in regions with signal dropout caused by Gz,s and Gx,s. We demonstrate improvements in temporal signal-to-noise ratio and BOLD sensitivity in the OFC and TL of six healthy male volunteers compared to conventional GE-EPI.