An integrative model for neuronal activity-induced signal changes for gradient and spin echo functional imaging

Uludağ, Kâmil; Müller‐Bierl, Bernd; Uğurbil, Kâmil

doi:10.1016/j.neuroimage.2009.05.051

Cited by 402 publications

(499 citation statements)

References 96 publications

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“…Consistent with the spatial scales described above, the point spread function (PSF) of the CBF response to visual stimulation has been measured to be~0.5 mm in the cat primary visual cortex by arterial spin labeling fMRI at 9.4 T, whereas a larger value (~1.6 mm) has been obtained by BOLD fMRI using a conventional GE-EPI sequence . In fact, it is recognized that GE-EPI is sensitive to local susceptibility gradients (Ogawa et al, 1992) which originate predominantly near veins (Uludağ et al, 2009). Note that, as underlined by many authors (Harrison et al, 2002;Harel et al, 2006;Weber et al, 2008), the vascular PSF is closely linked to the minimum spatial scale for the vascular control of blood flow changes.…”

Section: Hemodynamic Variations Induced By Local Vasodilationsmentioning

confidence: 95%

“…Due to the indirect nature of the BOLD signal as a surrogate for neural activity, the spatial resolution of BOLD fMRI is a complex interplay between technical constraints (e.g., field strength, see Harel et al, 2006) that determine voxel size, physics (e.g., signal production as a function of sequence type and sensitivity to various vessel types and sizes, see Uludağ et al, 2009) and vascular point spread function (Menon and Goodyear, 1999;Sheth et al, 2004b;Harel et al, 2006;Shmuel et al, 2007;Yacoub et al, 2008;Kim and Fukuda, 2008). Thus, as pointed out by Harrison et al, 2002, further detailed mapping studies of blood pathways and associated control points are needed to estimate the ultimate spatial resolution of hemodynamic-based functional imaging methods such as fMRI.…”

Section: Hemodynamic Variations Induced By Local Vasodilationsmentioning

confidence: 99%

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Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

Lorthois¹,

Cassot²,

Lauwers³

2011

NeuroImage

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. In a companion paper (Lorthois et al., Neuroimage, in press), we perform the first simulations of blood flow in an anatomically accurate large human intra-cortical vascular network (~10000 segments), using a 1D non-linear model taking into account the complex rheological properties of blood flow in microcirculation. This model predicts blood pressure, blood flow and hematocrit distributions, volumes of functional vascular territories, regional flow at voxel and network scales, etc. Using the same approach, we study flow reorganizations induced by global arteriolar vasodilations (an isometabolic global increase in cerebral blood flow). For small to moderate global vasodilations, the relationship between changes in volume and changes in flow is in close agreement with Grubb's law, providing a quantitative tool for studying the variations of its exponent with underlying vascular architecture. A significant correlation between blood flow and vascular structure at the voxel scale, practically unchanged with respect to baseline, is demonstrated. Furthermore, the effects of localized arteriolar vasodilations, representative of a local increase in metabolic demand, are analyzed. In particular, localized vasodilations induce flow changes, including vascular steal, in the neighboring arteriolar trunks at small distances (b 300 μm), while their influence in the neighboring veins is much larger (about 1 mm), which provides an estimate of the vascular point spread function. More generally, for the first time, the hemodynamic component of various functional neuroimaging techniques has been isolated from metabolic and neuronal components, and a direct relationship with several known characteristics of the BOLD signal has been demonstrated. IntroductionThere is increasing recognition that, by its structural implication in neuro-vascular coupling, underlying vascular architecture is a key player in hemodynamically based functional imaging techniques (including fMRI and PET) (Harrison et al., 2002;d'Esposito et al., 2003;Logothetis and Wandell, 2004;Lauwers et al., 2008;Weber et al., 2008). In particular, the spatial resolution and specificity of such techniques are bound to the density of blood capillary vasculature and blood flow regulating structures (Harel et al., 2006). This is especially important in the context of high field fMRI Harel et al., 2006), because, despite a dramatic increase in the theoretical spatial resolution obtained by using higher magnetic fields, associated with other hardware advancements, "the spatial extent of the hemodynamic response ultimately will impose a fundamental limitation on the spatial resolution of fMRI modalities" ).However, little is known about the fundamentals of the relationship between vascular structure and hemodynamic changes induced by brain activation. A growing body of evidence indicates that neurons, glia, and cerebral blood vessels, actin...

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Section: Hemodynamic Variations Induced By Local Vasodilationsmentioning

confidence: 95%

Section: Hemodynamic Variations Induced By Local Vasodilationsmentioning

confidence: 99%

Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

Lorthois¹,

Cassot²,

Lauwers³

2011

NeuroImage

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“…The opposite scenario is also theoretically possible in which an artifactually diminished arterial compartment could result if vasodilatation exceeds the CBF increase, leading to decreased blood velocity. As an estimate of the potential error, if the arteriolar fraction of the microvasculature is B20% (van Zijl et al, 1998;Uludag et al, 2009) and if the whole microvascular volume is B2% to 2.5% of a voxel (Uludag et al, 2009), then the arteriolar volume is B0.4% to 0.5% of a voxel. This would be the rough maximum amount of artifactual aBV enlargement, if we were to assume the extreme case of the entire arteriolar contribution being shunted from the microvascular compartment to the arteriolar compartment.…”

Section: Cbf Abv(lv) Abv(gm)mentioning

confidence: 99%

Similarities and Differences in Arterial Responses to Hypercapnia and Visual Stimulation

Petersen

Zimine³

et al. 2010

J Cereb Blood Flow Metab

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Despite the different origins of cerebrovascular activity induced by neurogenic and nonneurogenic conditions, a standard assumption in functional studies is that the consequence on the vascular system will be mechanically similar. Using a recently developed arterial spin labeling method, we examined arterial blood volume, arterial-microvascular transit time, and cerebral blood flow (CBF) in the gray matter and in areas with large arterial vessels under hypercapnia, visual stimulation, and a combination of the two. Spatial heterogeneity in arterial reactivity was observed between conditions. During hypercapnia, large arterial volume changes contributed to CBF increase and further downstream, there were reductions in the gray matter transit time. These changes were not significant during visual stimulation, and during the combined condition they were moderated. These findings suggest distinct vascular mechanisms for large and small arterial segments that may be condition specific. However, the power relationships between gray matter arterial blood volume and CBF in hypercapnia (a = 0.69 ± 0.24) and visual stimulation (a = 0.68 ± 0.20) were similar. Assuming consistent capillary and venous volume responses across these conditions, these results offer support for a consistent total CBV-flow relationship typically assumed in blood oxygen-level dependent calibration techniques.

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“…The spin-echo BOLD signals at a higher magnetic field originate largely from the capillaries in the activated cortex (Yacoub et al, 2003) because the spin-echo refocuses the dephasing of the spin around the pial draining vein, and the intravascular effect is negligible due to extremely short transverse relaxation time (T 2 ) of the blood (Uludağ et al, 2009). Therefore, the level of blood oxygenation in capillaries could be monitored by the spin-echo BOLD signals at a higher magnetic field.…”

Section: Discussionmentioning

confidence: 99%

Comprehensive correlation between neuronal activity and spin-echo blood oxygenation level-dependent signals in the rat somatosensory cortex evoked by short electrical stimulations at various frequencies and currents

Kida

Yamamoto

2010

Brain Research

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It is essential to elucidate the relationship between blood oxygenation level-dependent (BOLD) signals and neuronal activity for the interpretation of the functional magnetic resonance imaging (fMRI) signals; this relationship has been quantitatively investigated by animal studies measuring evoked potentials as indices of neuronal activity. Although most human fMRI studies employ the event-related task design, in which the stimulus duration is short, few studies have investigated the relationship between BOLD signals and evoked potentials at short stimulus durations. The present study investigated this relationship in the somatosensory cortex of anesthetized rats by using electrical forepaw stimulation at a short duration of 4 s and comprehensively analyzed it at different frequencies (1-10 Hz) and currents (0.5-2.0 mA). Somatosensory evoked potential (SEP) responses were measured at the scalp using silver ball electrodes. The sum of the peak-to-peak amplitude (ΣSEP) and average SEP (avg. SEP) responses were calculated. BOLD signals were obtained using a spin-echo echo-planar imaging sequence at 7 T. The relationship between the avg.SEP and BOLD signals varied with frequency, whereas that between ΣSEP and BOLD signals showed a significant correlation at varying frequencies and currents. In particular, the relationship between ΣSEP and ΣBOLD, which is the sum of the BOLD signals obtained at each time point reflecting the area under the BOLD response curves, mostly converged, irrespective of the frequency. Our results suggest that ΣBOLD obtained using a spin-echo sequence reflects the neural activity as quantified by ΣSEP, which was determined at different frequencies and currents. Section: Regulatory SystemsKeywords: BOLD; fMRI; Forepaw; Neurovascular coupling; SEP Abbreviations: BOLD, blood oxygenation level-dependent; CBF, cerebral blood flow; CMRO 2 , cerebral metabolic rate of oxygen consumption; EPI, echo planar imagining; TE, echo time; fMRI, functional magnetic resonance imaging; LDF, laser Doppler flowmetry; SEP, somatosensory evoked potential; T 2 , transverse relaxation time -2 - IntroductionFunctional magnetic resonance imaging (fMRI) based on blood oxygenation level-dependent (BOLD) effect has been widely used in neuroscience and psychology to study brain function. fMRI reflects cerebral hemodynamic changes, and its signals have been interpreted by assuming a neuronal hemodynamic response (Friston et al., 1995) based on the 19 th century hypothesis of Roy and Sherrington that neuronal activity induces an increase in the regional cerebral blood flow (CBF) (Roy and Sherrington, 1890). Thus, fMRI is an indirect method for assessing neuronal activity. Therefore, it is essential to elucidate the relationship between BOLD signals and neuronal activity for interpreting the fMRI signals; this relationship has been investigated mainly by animal studies measuring evoked potentials as indices of the neuronal activity in the somatosensory cortex (Brinker et al., 1999;Van Camp et al., 2006;Goloshevsk...

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An integrative model for neuronal activity-induced signal changes for gradient and spin echo functional imaging

Cited by 402 publications

References 96 publications

Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

Simulation study of brain blood flow regulation by intra-cortical arterioles in an anatomically accurate large human vascular network. Part II: Flow variations induced by global or localized modifications of arteriolar diameters

Similarities and Differences in Arterial Responses to Hypercapnia and Visual Stimulation

Comprehensive correlation between neuronal activity and spin-echo blood oxygenation level-dependent signals in the rat somatosensory cortex evoked by short electrical stimulations at various frequencies and currents

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