Magnetization-Transfer 2D Echo Planar Imaging for 7T Laminar fMRI

Motivation: Ultrahigh-field fMRI has achieved sub-millimeter nominal resolution, but macrovascular contributions significantly reduce the spatial specificity of activation, limiting the laminar fMRI applications. Goal(s): We aim to develop a time-efficient magnetization-transfer (MT) preparation method that is less sensitive to the macrovascular signal changes. Approach: We designed an MT-preparation module using on-resonance binomial pulses, followed by 2D EPI acquisition. This MT module introduces CBV contrast during activation, reducing sensitivity to blurring effects from draining veins and large pial veins. Results: MT-EPI shows more localized activation in gray matter compared to BOLD-EPI. The laminar profiles in human V1 and M1 demonstrate higher spatial specificity with MT-EPI. Impact: The MT-EPI method enhances the spatial specificity in laminar fMRI. It is time-efficient and allows flexible adjustment of MT parameters to optimize the sequence under SAR constraints.