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Systematic investigation of balanced steady‐state free precession for functional MRI in the human visual cortex at 3 Tesla
Author(s) -
Zhong Kai,
Leupold Jochen,
Hennig Juergen,
Speck Oliver
Publication year - 2007
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21103
Subject(s) - dephasing , signal (programming language) , nuclear magnetic resonance , steady state free precession imaging , functional magnetic resonance imaging , physics , contrast (vision) , magnetic resonance imaging , computer science , neuroscience , optics , medicine , quantum mechanics , biology , radiology , programming language
Previous studies have applied balanced steady‐state free precession (bSSFP) to functional brain imaging. Methods that exploit the strong frequency dependence of the MR signal in the bSSFP transition band are strongly affected by field inhomogeneity and frequency drifts. Recent bSSFP studies using “on‐resonance” (in the bSSFP passband) acquisition claimed that higher sensitivity was achieved compared to traditional fMRI methods. However, the contrast mechanism that generates activation‐related signal changes in bSSFP imaging is not yet fully understood. We performed a systematic study of on‐resonance bSSFP signal behavior using a multiecho balanced SSFP sequence with different TRs at 3 Tesla. We conclude that intravoxel dephasing, or the off‐resonance averaged steady state, dominates the bSSFP signal decay and determines the bSSFP fMRI contrast. Experimental findings were confirmed by simulations based on existing theories for signal formation around blood vessels in inhomogeneous tissues. The activation‐induced signal change in on‐resonance bSSFP increases with TE, and the TE dependence of the contrast‐to‐noise ratio (CNR) in bSSFP is similar to that in gradient echo‐planar imaging (GE‐EPI). However, GE‐EPI has a significantly higher CNR efficiency. Magn Reson Med 57:67–73, 2007. © 2006 Wiley‐Liss, Inc.