Abstract
ObjectiveResting-state functional MRI (rsfMRI) has been increasingly used for understanding brain functional architecture. To date, most rsfMRI studies have exploited blood oxygenation level-dependent (BOLD) contrast using gradient-echo (GE) echo planar imaging (EPI), which can suffer from image distortion and signal dropout due to magnetic susceptibility and inherent long echo time. In this study, the feasibility of passband balanced steady-state free precession (bSSFP) imaging for distortion-free and high-resolution rsfMRI was investigated.MethodsrsfMRI was performed in humans at 3 T and in rats at 7 T using bSSFP with short repetition time (TR = 4/2.5 ms respectively) in comparison with conventional GE-EPI. Resting-state networks (RSNs) were detected using independent component analysis.Results and SignificanceRSNs derived from bSSFP images were shown to be spatially and spectrally comparable to those derived from GE-EPI images with considerable intra- and inter-subject reproducibility. High-resolution bSSFP images corresponded well to the anatomical images, with RSNs exquisitely co-localized to the gray matter. Furthermore, RSNs at areas of severe susceptibility such as human anterior prefrontal cortex and rat piriform cortex were proved accessible. These findings demonstrated for the first time that passband bSSFP approach can be a promising alternative to GE-EPI for rsfMRI. It offers distortion-free and high-resolution RSNs and is potentially suited for high field studies.
Highlights
Resting-state functional MRI examines the temporal correlations in blood oxygenation level-dependent (BOLD) signal in the absence of stimulus or task
The main difference from SE is that balanced steady-state free precession (bSSFP) sequence allows for stimulated echo pathways that can give rise to increase in signal and BOLD contrast. bSSFP signal may include an intravascular component of macrovasculature, mainly due to water molecules diffusion in and out of the red blood cells [25]. bSSFP with lengthened TR for high spatial resolution exhibits T2* dephasing and the sequence behaves essentially like a poorly-spoiled GE [58]
This study shows that passband bSSFP is feasible for rsfMRI studies free of severe image distortion and signal dropout
Summary
Resting-state functional MRI (rsfMRI) examines the temporal correlations in blood oxygenation level-dependent (BOLD) signal in the absence of stimulus or task. High field improves the signal to noise ratio (SNR) and sensitivity of rsfMRI [15], but it increases the field inhomogeneites and susceptibility effects that cause image distortion and signal dropout. To overcome these limitations, a variety of methods have been proposed, including parallel imaging [16], spiral-in/out acquisition [17], 3D z-shimming [18] and so on. The other limiting factor in EPI approach is the significant T2*-
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