Transverse relaxation time (T2) mapping in the brain with off-resonance correction using phase-cycled steady-state free precession imaging.

摘要

PURPOSE: To investigate a new approach for more completely accounting for off-resonance affects in the DESPOT2 (driven equilibrium single pulse observation of T(2)) mapping technique. MATERIALS AND METHODS: The DESPOT2 method derives T(2) information from fully balanced steady-state free precession (bSSFP) images acquired over multiple flip angles. Off-resonance affects, which present as bands of altered signal intensity throughout the bSSFP images, results in erroneous T(2) values in the corresponding calculated maps. Radiofrequency (RF) phase-cycling, in which the phase of the RF pulse is incremented along the pulse train, offers a potential method for eliminating these artifacts. In this work we present a general method, referred to as DESPOT2, with full modeling (DESPOT2-FM), for deriving T(2), as well as off-resonance frequency, from dual flip angle bSSFP data acquired with two RF phase increments. RESULTS: The method is demonstrated in vivo through the acquisition of whole-brain, 1 mm(3) isotropic T(2) maps at 3T and shown to provide near artifact-free maps, even in areas with steep susceptibility-induced gradients. CONCLUSION: DESPOT2-FM offers an efficient method for acquiring high spatial resolution, whole-brain T(2) maps at 3T with high precision and free of artifact.