Quantitative Susceptibility Mapping of Brain Function During Auditory Stimulation

Functional quantitative susceptibility mapping (fQSM) is a recently established method that, based on the same acquisition technique as conventional functional magnetic resonance imaging, has two very appealing features: 1) it is quantitative and 2) it is considerably less affected by nonlocal effects than the blood oxygenation level-dependent (BOLD) signal. Here, the response of the auditory cortex to the presentation of short acoustic stimuli has been studied with fQSM. fQSM responses to stimuli were obtained by using a data-driven approach based on signal deconvolution to avoid assumptions regarding the response shape. fQSM and BOLD responses showed similar shapes, however, while the majority (82%) of fQSM responses described transient decreases in magnetic susceptibility (explainable by the same mechanisms behind the typical, positive BOLD responses), some voxels exhibited transient increments in magnetic susceptibility, which might reflect the interplay among changes in fractional oxygen saturation, cerebral blood flow, and volume. Statistically significant fQSM responses were observed not only in veins (which constitute the largest sources of magnetic susceptibility contrast) but also in gray matter tissue, suggesting that this technique is sensitive to subtle, stimulus-dependent changes also in the parenchyma, and therefore it might be useful to localize and interpret the sources of activation.