title: Functional MRI impulse response for BOLD and CBV contrast in rat somatosensory cortex.
abstract: The contrast mechanism in functional MRI (fMRI) results from several vascular processes with different time scales, thus establishing a finite temporal resolution to fMRI experiments. In this work we measured the blood oxygen level-dependent (BOLD) and iron-oxide-derived cerebral blood volume (CBV) impulse response (IR) in a rat model of somatosensory brain activation at 11.7T. A binary m-sequence probe method was used to obtain high-sensitivity single-pixel estimates of the IR, from which two parameters-the full width at half maximum (FWHM) and the time to peak (TTP)-were determined as indices of the temporal resolution of the hemodynamic response (HDR). The results (N = 11) show that the CBV IR (N = 5, subset) is significantly narrower (FWHM = 1.37 +/- 0.11 s), and peaks earlier (TTP = 1.65 +/- 0.15 s) than the BOLD IR (N = 11, FWHM = 1.92 +/- 0.22 s and TTP = 2.18 +/- 0.14 s, respectively). These findings indicate that neurovascular control mechanisms have a temporal resolution better than 1.5 s FWHM, and point to a substantial contribution to BOLD of the dispersive transit of oxygenated hemoglobin across the rat vasculature, bringing important implications for the ultimately attainable temporal resolution of fMRI.
authors.affiliation: Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-1065, USA. silvaa@ninds.nih.gov
authors.forename: Afonso C
authors.initials: AC
authors.lastname: Silva
authors.forename: Alan P
authors.initials: AP
authors.lastname: Koretsky
authors.forename: Jeff H
authors.initials: JH
authors.lastname: Duyn
mesh_terms: D000465:Algorithms; D000818:Animals; D001931:Brain Mapping / Q000379:methods*; D004558:Electric Stimulation; D005552:Forelimb; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000033:anatomy & histology* / Q000502:physiology*