Gradient‐controlled local L armor adjustment (GC‐LOLA) for simultaneous multislice b SSFP imaging with improved banding behavior

Purpose Simultaneous multislice (SMS) accelerated balanced SSFP (bSSFP) imaging can be impaired by off‐resonance effects, due to slice‐specific alterations in the frequency response. In this work, we introduce gradient‐controlled local Larmor adjustment as a means to restore the frequency response and to stabilize SMS‐accelerated bSSFP imaging with respect to banding artifacts. Methods Providing each simultaneously excited slice with an individual RF phase cycle in SMS‐accelerated bSSFP imaging results in the sequence's frequency response being shifted slice‐specifically along the off‐resonance axis. The net available pass‐band for imaging is effectively reduced, increasing the measurement's susceptibility toward B 0 inhomogeneities. To overcome these issues, gradient‐controlled local Larmor adjustment modifies the Larmor frequency locally and aligns the slice‐specific frequency responses on resonance by (1) unbalancing the slice gradient by a small constant amount and (2) modifying the RF phase cycles homogeneously across all slices. The concept is investigated using simulations and phantom experiments and applied to SMS‐accelerated bSSFP cine cardiovascular MR at 3 T. Results Phantom and in vivo measurements demonstrate the successful removal of banding artifacts and restoration of the bSSFP frequency response using gradient‐controlled local Larmor adjustment. For large slice thicknesses and small slice distances, banding artifacts become slightly widened. Conclusion Gradient‐controlled local Larmor adjustment successfully restores the frequency response in SMS‐accelerated bSSFP imaging without increasing the sequence's susceptibility toward eddy current effects. The concept facilitates combinations of the different SMS encoding concepts and provides a powerful way to actively control off‐resonance effects in slice‐accelerated bSSFP imaging.