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


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.


CONCLUSIONS
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.
Deoni
Sean C L
SC
Centre for Neuroimaging Research, Institute of Psychiatry, King's College London, London, UK. sdeoni@mac.com
D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging