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

Laminar-specific functional magnetic resonance imaging (fMRI) has been widelyused to study circuit-specific neuronal activity by mapping spatiotemporal fMRIresponse patterns across cortical layers. Hemodynamic responses reflect indirectneuronal activity given the limitation of spatial and temporal resolution.Previously, a gradient-echo-based line-scanning fMRI (GELINE) method wasproposed with high temporal (50 ms) and spatial (50 µm) resolution tobetter characterize the fMRI onset time across cortical layers by employing twosaturation RF pulses. However, the imperfect RF saturation performance led topoor boundary definition of the reduced region of interest (ROI) and aliasingproblems outside of the ROI. Here, we propose an α (alpha)-180spin-echo-based line-scanning fMRI (SELINE) method in animals to resolve thisissue by employing a refocusing 180˚ RF pulse perpendicular to theexcitation slice (without any saturation RF pulse) and also achieve highspatiotemporal resolution. In contrast to GELINE signals which peaked at thesuperficial layer, we detected varied peaks of laminar-specific BOLD signalsacross deeper cortical layers using the SELINE method, indicating thewell-defined exclusion of the large draining-vein effect using the spin-echosequence. Furthermore, we applied the SELINE method with a 200 ms repetitiontime (TR) to sample the fast hemodynamic changes across cortical layers with aless draining vein effect. In summary, this SELINE method provides a novelacquisition scheme to identify microvascular-sensitive laminar-specific BOLDresponses across cortical depth.