Passband balanced steady state free precession (b-SSFP) fMRI employs the flat portion of the SSFP off-resonance response to obtain microscopic susceptibility changes elicited by changes in blood oxygenation following enhancement in neuronal activity. This technique can reduce geometric distortion and signal dropout while maintaining rapid acquisition and high signal-to-noise ratio (SNR) compared with traditional fMRI techniques. In the study, we developed a novel multi-phase passband b-SSFP fMRI technique that can achieve a spatial resolution of a few mm3 and a high temporal sampling rate of 50 ms per slice at 7 Tesla. This technique was further applied for an event-related (ER) fMRI paradigm. As a comparison, gradient-echo echo-planar imaging (GE-EPI) with similar spatial resolution and temporal sampling rate was carried out for the same ER-fMRI experiment. Experiments with visual cortex stimulation were carried out at 7 Tesla to demonstrate whether the multi-phase b-SSFP technique and GE-EPI are able to differentiate temporal delays in hemodynamic response function (HRF) separated by 100 ms in stimulus onset. Consistent with ERP results, the upslope of the HRF of both techniques can differentiate 100 ms delay in stimulus onset, with the former showing a lower level of intersubject variability. The present study demonstrated that the multi-phase passband b-SSFP fMRI technique can be applied for resolving neuronal events on the order of 100 ms at ultrahigh magnetic fields.
Bibliographical noteFunding Information:
We would thank Dr. Rui Wang, Dr. Ziwei Cheng, Mr. Jing Luo and Ms. Kun Hu for their technical contributions and assistance to the study. The work was supported in part by the Ministry of Science and Technology of China (MOST) grants ( 2012CB825500 and 2015CB351701 ), National Natural Science Foundation of China grants ( 91132302 and 81271567 ), Chinese Academy of Sciences Strategic Priority Research Program B grants ( XDB02010001 and XDB02050001 ), and US NIH grants ( R01-EB014922 and R01-NS081077 ).
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- 50 ms sampling rate
- 7 Tesla
- Balanced SSFP (b-SSFP)
- Event-related functional MRI (ER-fMRI)
- Event-related potential (ERP)