Temporal dynamics of the BOLD fMRI impulse response.
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.
de Zwart
Jacco A
JA
Laboratory of Functional and Molecular Imaging, NINDS, National Institutes of Health, Bethesda, MD 20892-1065, USA. Jacco.deZwart@nih.gov
Silva
Afonso C
AC
van Gelderen
Peter
P
Kellman
Peter
P
Fukunaga
Masaki
M
Chu
Renxin
R
Koretsky
Alan P
AP
Frank
Joseph A
JA
Duyn
Jeff H
JH
D000328:Adult; D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D001923:Brain Chemistry / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D010100:Oxygen / Q000097:blood*; D051381:Rats; D013003:Somatosensory Cortex / Q000033:anatomy & histology / Q000098:blood supply; D013045:Species Specificity; D014793:Visual Cortex / Q000033:anatomy & histology / Q000098:blood supply
D010100:Oxygen