Dephased FLAPS for improved visualization of susceptibility-shifted passive devices for real-time interventional MRI

Recently, balanced steady-state free precession (SSFP) magnetic resonance imaging at small flip angles (i.e. FLAPS imaging) has been shown to preferentially enhance the visibility of spins residing near susceptibility-shifted media by exploiting the unique spectral response of SSFP signals. Nevertheless, the use of FLAPS imaging to visualize passive, susceptibility-shifted devices within thick slices is complicated by partial volume effects that reduce the conspicuity of the devices. In this work, dephased FLAPS (dFLAPS), a variation of the FLAPS method with dephasing gradients applied in the slice direction, is presented as a method for improving the contrast of susceptibility-shifted interventional devices in thick-slice magnetic resonance images by suppressing signal from on-resonant spins. In comparison to FLAPS imaging, results demonstrate that dFLAPS imaging of thick, projection-like slices improves the contrast of susceptibility-shifted devices relative to background signal with no increase in acquisition time.