Characterization of the BOLD Hemodynamic Response Function at 7T: towards separation of vasculature and parenchyma

Introduction A limitation of T2weighted BOLD fMRI is the confounding contribution of signal from the larger vasculature. An improved BOLD specificity to parenchyma can be achieved at high field strengths such as 7T due to increased contrast-to-noise ratio, and reduced contribution of intravascular signal as compared to lower field strengths. Moreover, at 7T high spatial and temporal resolution of the BOLD signal can be achieved [1], making it possible to investigate the BOLD response in much finer detail. Previous human work at 3T has shown that the temporal characteristics of the BOLD response in the visual cortex are related to the organization of the local vasculature [2]. A correlation of the time-to-peak (TTP) and width (FWHM) of the BOLD response function was shown. Based on this previous work we expect to obtain a better separation between parenchyma and the macrovasculature at a high resolution. We characterized the spatio-temporal properties of the BOLD response in the visual cortex at 7T using an event-related fMRI paradigm with very short visual stimuli, higher sampling rate, and for different spatial resolutions.