Separating FID and echo contribution in pass-band bSSFP fMRI with multiple-phase angle cycling

Introduction Pass-band bSSFP is a promising tool for high-resolution fMRI, but its signal sources have been unclear especially at high field. The bSSFP signals are summation of free induction decay (FID) component and echo components from multiple RF pathways. Multiple TR and TE experiments have been used in previous studies to understand contributions of FID and echo components to the signals of bSSFP fMRI (1,2). Although this approach provides useful information, an alternative approach is to acquire datasets using multiple phase cycling angles which enable separation of FID and echo components in the Fourier domain (3). In this study, we performed fMRI experiments at multiple phase cycling angles with the aim to separate the FID and echo components based on Fourier analysis. To help to identify the bSSFP signal sources, we utilized the notion that FID component would have larger draining contribution (i.e., intracortical or surface veins), whereas echo component would be more spatially localized because of stronger T2 contribution. MR venogram was used to confirm the location of the veins on the same animals. This approach of multiple phase cycling angles has the potential to provide new insights into the signal sources of pass-band bSSFP fMRI.