Spectral-Spatial Pulse Design with Spectral Decomposition

Cungeng Yang¹, Victor Andrew Stenger¹

Signal loss caused by susceptibility induced intravoxel dephasing is a major limitation in high field MRI applications such as BOLD fMRI. Spectral-spatial (SPSP) pulses have been shown to be very effective at reducing through-plane signal loss in axial slices using a single excitation. SPSP pulse design assumes a linear relationship between off-resonance frequency and through-plane susceptibility gradient Gs(f)=αf. Previous studies show empirically α=-2.0 μT/m/Hz works well for many brain regions at 3T, however, no detailed measurement of α was investigated. We propose spectral decomposition technique using a spiral spectroscopic imaging sequence to directly measure α at all locations in the brain. Resultant SPSP pulses were demonstrated in T2*-weighted brain images showing reduced signal loss at 3T. Inferior slices were found to require α values of opposite sign and smaller magnitude. This indicates that using more than one pulse may improve the efficacy of the SPSP technique.