title: High b-value diffusion-weighted fMRI in a rat forepaw electrostimulation model at 7 T.
abstract: Spin-echo diffusion-weighted functional MRI (DW-fMRI) was performed on a rat forepaw electrostimulation model at 7 T. This small animal model used electric (rather than visual) stimulation and allowed DW-fMRI experiments to be performed over a broader range of acquisition parameters than previous work on humans and cats. Resting state experiments with injections of ultra-small superparamagnetic iron oxide (USPIO) were also used to investigate the effects of gradient coupling on the signal change. The experiments were performed over five b-values (0, 200, 800, 1400 and 2000s/mm(2)) and three echo-times (30, 60 and 90 ms). Alterations to the stimulation-induced response with respect to TE and b-value were evaluated in two intervals: the positive stimulus-correlated response (5-20s after stimulus onset) and the post-stimulus undershoot (27-40s). There was no strong dependence of the signal change on b-value for any of the intervals or TEs. Similarly, changes to the apparent transverse relaxation rate showed no clear dependence on b-value. In contrast to previous DW-fMRI studies, the simplest explanation for the observed data is a single-compartment signal model with the functional signal changes probably corresponding to extravascular SE-BOLD. Experiments with USPIO suggested that at 7 T and within the range of parameters used, the influence of gradient coupling may be sufficient to explain minor DW-fMRI signal changes.
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan; Department of Neurobiology, A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland.
authors.forename: Joonas A A
authors.initials: JAA
authors.lastname: Autio
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan; School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8503, Japan. Electronic address: len@nirs.go.jp.
authors.forename: Jeff
authors.initials: J
authors.lastname: Kershaw
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Shibata
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Obata
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
authors.affiliation: Molecular Imaging Centre, National Institute of Radiological Sciences, Chiba 263-8555, Japan.
authors.forename: Ichio
authors.initials: I
authors.lastname: Aoki
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D004558:Electric Stimulation; D005552:Forelimb / Q000294:innervation*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000502:physiology*