Alpha-180 spin-echo based line-scanning method for high resolution laminar-specific fMRI

Abstract

Laminar-specific functional magnetic resonance imaging (fMRI) has been widely used to study circuit-specific neuronal activity by mapping spatiotemporal fMRI response patterns across cortical layers. Hemodynamic responses reflect indirect neuronal activity given limit of spatial and temporal resolution. Previous gradient-echo based line-scanning fMRI (GELINE) method was proposed with high temporal (50 ms) and spatial (50 μm) resolution to better characterize the fMRI onset time across cortical layers by employing 2 saturation RF pulses. However, the imperfect RF saturation performance led to poor boundary definition of the reduced region of interest (ROI) and aliasing problems outside of the ROI. Here, we propose α (alpha)-180 spin-echo-based line-scanning fMRI (SELINE) method to resolve this issue by employing a refocusing 180° RF pulse perpendicular to the excitation slice. In contrast to GELINE signals peaked at the superficial layer, we detected varied peaks of laminar-specific BOLD signals across deeper cortical layers with the SELINE method, indicating the well-defined exclusion of the large drain-vein effect with the spin-echo sequence. Furthermore, we applied the SELINE method with 200 ms TR to sample the fast hemodynamic changes across cortical layers with a less draining vein effect. In summary, this SELINE method provides a novel acquisition scheme to identify microvascular-sensitive laminar-specific BOLD responses across cortical depth.

Neuroimaging at ultra-high spatiotemporal resolutions: line-scanning fMRI

“…Future line-scanning efforts could also benefit from sharper saturation profiles or spin-echo based line-scanning (i.e. beam excitation using orthogonal 90°and 180°selective RF pulses [278] to improve the sharpness of the line profile. At present, however, we argue that the strong correlations of tstats between dimension-adjusted planar (2D-EPI) obtained through CASE1-LSD and CASE2-NOM (R=0.81±0.12) indicate that line-scanning can be used for fMRI with very limited within slice, out-of-line BOLD signal contributions.…”