Refocused steady-state free precession (SSFP) is limited by its high sensitivity to local field variation, particularly at high field strengths or the long repetition times (TRs) necessary for high resolution. Several methods have been proposed to reduce SSFP banding artifact by combining multiple phase-cycled SSFP acquisitions, each differing in how individual signal magnitudes and phases are combined. These include maximum-intensity SSFP (MI-SSFP) and complex-sum SSFP (CS-SSFP). The reduction in SSFP banding is accompanied by a loss in signal-to-noise ratio (SNR) efficiency. In this work a general framework for analyzing banding artifact reduction, contrast, and SNR of any multiple-acquisition SSFP combination method is presented. A new sum-of-squares method is proposed, and a comparison is performed between each of the combination schemes. The sum-of-squares SSFP technique (SOS-SSFP) delivers both robust banding artifact reduction and higher SNR efficiency than other multiple-acquisition techniques, while preserving SSFP contrast.
Copyright 2004 Wiley-Liss, Inc.