Abstract
Functional imaging with intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) is demonstrated. Images were acquired at 3 Tesla using a standard Stejskal-Tanner diffusion-weighted echo-planar imaging sequence with multiple b-values. Cerebro-spinal fluid signal, which is highly incoherent, was suppressed with an inversion recovery preparation pulse. IVIM microvascular perfusion parameters were calculated according to a two-compartment (vascular and non-vascular) diffusion model. The results obtained in 8 healthy human volunteers during visual stimulation are presented. The IVIM blood flow related parameter fD* increased 170% during stimulation in the visual cortex, and 70% in the underlying white matter.
Highlights
Focal brain neural activity increases local perfusion through neurovascular coupling [1]
blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is based on the variation of the blood water T2/T2Ã signal, which depends on the paramagnetic deoxyhemoglobin content [7, 8]
We investigated the feasibility of measuring variation of local microvascular brain perfusion parameters f, DÃ, and fDÃ in human volunteers during visual stimulation, as derived from the bi-compartmental intravoxel incoherent motion (IVIM) model, using a diffusion-weighted inversion-recovery sequence to suppress the possibly confounding cerebro-spinal fluid (CSF) movements
Summary
Focal brain neural activity increases local perfusion through neurovascular coupling [1]. BOLD fMRI is based on the variation of the blood water T2/T2Ã signal, which depends on the paramagnetic deoxyhemoglobin content [7, 8]. This method is robust but faces challenges due to the non-trivial signal dependence on several parameters (cerebral blood flow, cerebral blood volume, and blood oxygenation) [9,10,11,12,13,14], while the spatial resolution is limited due to veins draining the sites of activation [15]. Capillary network reactivity to somatosensory stimulation has been investigated in rats [16, 17], and individual capillary increase in red blood cell velocity and flow has been demonstrated with two-photon microscopy during the activation of the olfactory bulb [18] and neocortex
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