Analytical solution to the transient phase of steady‐state free precession sequences

The transient phase of short–TR steady‐state free precession (SSFP) sequences exhibits an often striking complexity and is not only important for nonequilibrium applications (e.g., rapid T₁–measurements), but can also cause severe artifacts in conventional imaging. In both cases, balanced SSFP sequences are practically (with regard to preparation efficiency) and conceptually (concerning the theoretical understanding of the decay) easier to handle their unbalanced counterparts, for which currently no theory is available. Based on a decomposition of coherence pathways into irreducible subpaths, an exact mathematical solution to the transient phase of unbalanced SSFP sequences is presented in this article, which also includes the known results for balanced SSFP and the steady state of arbitrary SSFP sequences as special cases. As an application, it is shown that the familiar Look–Locker expression for the accelerated magnetization recovery in RF‐spoiled sequences is only valid for T₂ → 0. In addition to oscillatory perturbations, systematic deviations from the monoexponential decay are observed for T₂ 0 as a consequence of memory effects. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Wideband SSFP: alternating repetition time balanced steady state free precession with increased band spacing.

Balanced steady-state free precession (SSFP) imaging is limited by off-resonance banding artifacts, which occur with periodicity 1/TR in the frequency spectrum. A novel balanced SSFP technique for widening the band spacing in the frequency response is described. This method, called wideband SSFP, utilizes two alternating repetition times with alternating RF phase, and maintains high SNR and T(2)/T(1) contrast. For a fixed band spacing, this method can enable improvements in spatial resolution compared to conventional SSFP. Alternatively, for a fixed readout duration this method can widen the band spacing, and potentially avoid the banding artifacts in conventional SSFP. The method is analyzed using simulations and phantom experiments, and is applied to the reduction of banding artifacts in cine cardiac imaging and high-resolution knee imaging at 3T.     

Denolin and Metens. On the calculation and interpretation of signal intensity in echo‐shifted sequences,Magn Reson Med 2004; 51:123‐134

The original article to which this Erratum refers was published in Magnetic Resonance in Medicine (2004) 51(1) 123–134.