Rapid T₂ estimation with phase-cycled variable nutation steady-state free precession

Variable nutation SSFP (DESPOT2) permits rapid, high-resolution determination of the transverse (T₂) relaxation constant. A limitation of DESPOT2, however, is the presence of T₂ voids due to off-resonance banding artifacts associated with SSFP images. These artifacts typically occur in images acquired with long repetition times (TR) in the presence of B₀ inhomogeneities, or near areas of magnetic susceptibility difference, such that the transverse magnetization experiences a net phase shift during the TR interval. This places constraints on the maximum spatial resolution that can be achieved without artifact. Here, a novel implementation of DESPOT2 is presented incorporating RF phase-cycling which acts to shift the spatial location of the bands, allowing reconstruction of a single, reduced artifact-image. The method is demonstrated in vivo with the acquisition of a 0.34 mm³ isotropic resolution T₂ map of the brain with high precision and accuracy and significantly reduced artifact. Magn Reson Med 52:435–439, 2004. © 2004 Wiley-Liss, Inc.