Temporal dynamics of the BOLD fMRI impulse response

• Published in: NeuroImage (Orlando, Fla.) Fla.), 2005-02, Vol.24 (3), p.667-677
• Main Authors: de Zwart, Jacco A., Silva, Afonso C., van Gelderen, Peter, Kellman, Peter, Fukunaga, Masaki, Chu, Renxin, Koretsky, Alan P., Frank, Joseph A., Duyn, Jeff H.
• Format: Article
• Language: English
• Subjects: Adult; Animals; Binary m-sequence; Blood; BOLD fMRI; Brain - anatomy & histology; Brain Chemistry - physiology; Capillaries - physiology; Cerebrovascular Circulation - physiology; Computer Simulation; Data Interpretation, Statistical; Female; Flow velocity; Hemodynamic response; Humans; Image Interpretation, Computer-Assisted; Magnetic Resonance Imaging - methods; Male; Medical research; Middle Aged; Monte Carlo Method; Oxygen - blood; Rats; Rodents; Smooth muscle; Somatosensory Cortex - anatomy & histology; Somatosensory Cortex - blood supply; Species Specificity; Vascular dispersion; Visual Cortex - anatomy & histology; Visual Cortex - blood supply
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2004.09.013

Using computer simulations and high-resolution fMRI experiments in humans ( n = 6) and rats ( n = 8), we investigated to what extent BOLD fMRI temporal resolution is limited by dispersion in the venous vasculature. For this purpose, time-to-peak (TTP) and full-width at half-maximum (FWHM) of the BOLD impulse response (IR) function were determined. In fMRI experiments, a binary m-sequence probe method was used to obtain high-sensitivity model-free single-pixel estimates of IR. Simulations of postcapillary flow suggested that flow-related dispersion leads to a TTP and FWHM increase, which can amount to several seconds in larger pial veins. fMRI experiments showed substantial spatial variation in IR timing within human visual cortex, together with a correlation between TTP and FWHM. Averaged across the activated regions and across subjects, TTP and FWHM were 4.51 ± 0.52 and 4.04 ± 0.42 s, respectively. In regions of interest (ROI) weighted toward the larger venous structures, TTP and FWHM increased to 5.07 ± 0.64 and 4.32 ± 0.48 s, respectively. In rat somatosensory cortex, TTP and FWHM were substantially shorter than in humans (2.73 ± 0.60 and 2.28 ± 0.63 s, respectively). These results are consistent with a substantial macrovascular dispersive contribution to BOLD IR in humans, and furthermore suggest that neurovascular coupling is a relatively rapid process, with a resolution below 2.3 s FWHM.