fMRI at ultra-high field: From acquisition to interpretation

Human ultra-high-field (UHF, ≥7 Tesla) scanners provide increased spatial resolution, advancing functional magnetic resonance imaging (fMRI) research toward the submillimeter scale and enabling fMRI of cortical layers, columns, and other small structures. This offers the potential to non-invasively investigate intracortical circuits and processing mechanisms in the human brain. In this primer, we review applications of 7T, data acquisition and processing challenges, and current open questions. We highlight how the rich information in UHF fMRI challenges traditional analysis tools and the interpretation of high-resolution fMRI data. Because fMRI responses are hemodynamic signals and indirect measures of neural activity, careful consideration of neurovascular coupling is essential when interpreting fMRI data, particularly at high resolution. We discuss the implications of increased resolution for fMRI data acquisition, data processing, and interpretation, with an emphasis on cortical layers.