Simultaneous recording of task-induced changes in blood oxygenation, volume, and flow using diffuse optical imaging and arterial spin-labeling MRI (original) (raw)
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PloS one, 2013
Simultaneous implementation of magnetic resonance imaging methods for Arterial Spin Labeling (ASL) and Blood Oxygenation Level Dependent (BOLD) imaging makes it possible to quantitatively measure the changes in cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO(2)) that occur in response to neural stimuli. To date, however, the range of neural stimuli amenable to quantitative analysis is limited to those that may be presented in a simple block or event related design such that measurements may be repeated and averaged to improve precision. Here we examined the feasibility of using the relationship between cerebral blood flow and the BOLD signal to improve dynamic estimates of blood flow fluctuations as well as to estimate metabolic-hemodynamic coupling under conditions where a stimulus pattern is unknown. We found that by combining the information contained in simultaneously acquired BOLD and ASL signals through a method we term BOLD Constrained Perfusion (BCP) estimatio...
Journal of Cerebral Blood Flow & Metabolism, 1996
Changes in cerebral blood oxygenation due to functional activation of the primary sensorimotor cortex during a unilateral finger opposition task were simultaneously mapped by deoxyhemoglobin-sensitive magnetic resonance imaging (MRI) and monitored by near-infrared spectroscopy (NIRS). Activation foci along the contralateral central sulcus displayed task-associated increases in MRI signal intensity, indicating a concomitant decrease of the focal concentration of deoxyhemoglobin. This interpretation was confirmed by simultaneous reductions in deoxyhemoglobin measured optically. Since observation of the latter effect required exact spatial matching of the MRI-detected activation foci and position of the fiber optic bundles ("optodes") used for transmitting and receiving light, it may be concluded that optical recordings of changes in deoxyhemoglobin during functional challenge probe only a restricted brain tissue region. While deoxyhemoglobin responses seen by NIRS were smaller for ipsithan for contralateral finger movements, task-related increases in oxyhemoglobin were rather similar between both conditions and, thus, seem to be less specific. Furthermore, no consistent changes were obtained for total hemoglobin during task performance, possibly due to the short timing of the repetitive protocol. In general, results underline, in humans, the hitherto assumed signal physiology for functional brain mapping by oxygenationsensitive MRI and allow assessment of both constraints and practicability of functional studies by NIRS.
Neuroimage, 2001
Functional magnetic resonance imaging (fMRI) is based on the coupling between neural activity and changes in the concentration of the endogenous paramagnetic contrast agent deoxygenated hemoglobin. Changes in the blood oxygen level-dependent (BOLD) signal result from a complex interplay of blood volume, flow, and oxygen consumption. Optical imaging spectroscopy (OIS) has been used to measure changes in blood volume and saturation in response to increased neural activity, while laser Doppler Flowmetry (LDF) can be used to measure flow changes and is now commonplace in neurovascular research. Here, we use concurrent OIS and LDF to examine the hemodynamic response in rodent barrel cortex using electrical stimulation of the whisker pad at varying intensities. Spectroscopic analysis showed that stimulation produced a biphasic early increase in deoxygenated hemoglobin (Hbr), followed by a decrease below baseline, reaching minima at ϳ3.7 s. There was no evidence for a corresponding early decrease in oxygenated hemoglobin (HbO 2 ), which simply increased after stimulation, reaching maximum at ϳ3.2 s. The time courses of changes in blood volume (CBV) and blood flow (CBF) were similar. Both increased within a second of stimulation onset and peaked at ϳ2.7 s, after which CBV returned to baseline at a slower rate than CBF. The changes in Hbr, Hbt, and CBF were used to estimate changes in oxygen consumption (CMRO 2 ), which increased within a second of stimulation and peaked ϳ2.2 s after stimulus onset. Analysis of the relative magnitudes of CBV and CBF indicates that the fractional changes of CBV could be simply scaled to match those of CBF. We found the relationship to be well approximated by CBV ؍ CBF 0.29 . A similar relationship was found using the response to elevated fraction of inspired carbon dioxide (FICO 2 ).
Magnetic Resonance in Medicine, 1996
Changes in cerebral blood oxygenation and flow during prolonged activation of human visual cortex (6-min video projection) were monitored using high-resolution T2*and T,-weighted gradient-echo MRI in identical sessions. Oxygenation-sensitive recordings displayed an initial signal increase (oxygenation "overshoot"), a subsequent signal decrease extending over 4-5 min (relative deoxygenation), and a signal drop after the end of stimulation that mirrored the initial response (oxygenation "undershoot"). Flow-sensitive MRI demonstrated that the inflow effect remained elevated during the entire period of Stimulation. The observation of gradually decreasing cerebral blood oxygenation, despite persisting elevation of blood flow, may be understood to be an accumulation of deoxyhemoglobin due to the progressive up-regulation of oxidative phosphorylation. The present findings support a concept in which transitions between functional states lead to an uncoupling of perfusion (oxygen delivery) from oxidative metabolism (oxygen consumption) whereas steady-state activity achieves their recoupling.
Concurrent fMRI and optical measures for the investigation of the hemodynamic response function
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, 2005
Functional magnetic resonance imaging (fMRI) signal variations are based on a combination of changes in cerebral blood flow (CBF) and volume (CBV), and blood oxygenation. We investigated the relationship between these hemodynamic parameters in the rodent barrel cortex by performing fMRI concurrently with laser Doppler flowmetry (LDF) or optical imaging spectroscopy (OIS), following whisker stimulation and hypercapnic challenge. A difference between the positions of the maximum blood oxygenation level-dependent (BOLD) and CBV changes was observed in coronal fMRI maps, with the BOLD region being more superficial. A 6.5% baseline blood volume fraction in this superficial region dropped to 4% in deeper cortical layers (corresponding to total hemoglobin baseline volumes Hbt0 = 110 microM and 67 microM, respectively), as inferred from maps of deltaR2*. Baseline volume profiles were used to parameterize the Monte Carlo simulations (MCS) to interpret the 2D OIS. From this it was found that ...
Journal of Cerebral Blood Flow & Metabolism, 2005
The discrepancy between the increases in cerebral blood flow (CBF) and CMRO 2 during neural activation causes an increase in venous blood oxygenation and, therefore, a decrease in paramagnetic deoxyhemoglobin concentration in venous blood. This can be detected by functional magnetic resonance imaging (fMRI) as blood oxygenation level-dependent (BOLD) contrast. In the present study, changes in the cerebral oxygen extraction fraction (OEF) that corresponds to the ratio of CMRO 2 to CBF, and in the BOLD signal during neural activation, were measured by both positron emission tomography (PET) and fMRI in the same human subjects. C 15 O, 15 O 2 , and H 2 15 O PET studies were performed in each subject at rest (baseline) and during performance of a right-hand motor task. Functional magnetic resonance imaging studies were then performed to measure the BOLD signal under the two conditions. During performance of the motor task, a significant increase in CBF and a significant decrease in OEF were observed in the left precentral gyrus, left superior frontal gyrus, right precentral gyrus, right cingulate gyrus, and right cerebellum. A significant positive correlation was observed between changes in the CBF and the BOLD signal, and a significant negative correlation was observed between changes in the OEF and the BOLD signal. This supports the assumption on which BOLD contrast studies during neural activation are based.
NeuroImage, 2000
In this study, the hemodynamic response and changes in oxidative metabolism during functional activation were measured using three functional magnetic resonance imaging (fMRI) techniques: the blood oxygenation level-dependent (BOLD) technique, flowsensitive alternating inversion recovery (FAIR), and bolus tracking (BT) of an MR contrast agent. With these three techniques we independently determined changes in BOLD signal, relative cerebral blood flow (rCBF), and cerebral blood volume (rCBV) associated with brain activation in eight healthy volunteers. In the motor cortex, the BOLD signal increased by 1.8 ؎ 0.5%, rCBF by 36.3 ؎ 8.2% (FAIR), and 35.1 ؎ 8.6% (BT), and rCBV by 19.4 ؎ 4.1% (BT) in response to simultaneous bilateral finger tapping. In the visual cortex, BOLD signal increased by 2.6 ؎ 0.5%, rCBF by 38.5% ؎ 7.6 (FAIR), and 36.9 ؎ 8.8% (BT), and rCBV by 18.8 ؎ 2.8% (BT) during flickering checkerboard stimulation. Comparing the experimentally measured rCBV with the calculated rCBV using Grubb's power-law relation, we conclude that the use of power-law relationship results in systematic underestimate of rCBV.
2010
Cerebral blood flow (CBF) during stepped hypercapnia was measured simultaneously in the rat brain using near-infrared diffuse correlation spectroscopy (DCS) and arterial spin labeling MRI (ASL). DCS and ASL CBF values agree very well, with high correlation (R=0.86, p< 10 −9), even when physiological instability perturbed the vascular response. A partial volume effect was evident in the smaller magnitude of the optical CBF response compared to the MRI values (averaged over the cortical area), primarily due to the inclusion of white matter in the optically sampled volume. The 8.2 and 11.7 mm mid-separation channels of the multi-distance optical probe had the lowest partial volume impact, reflecting ∼75 % of the MR signal change. Using a multiplicative correction factor, the ASL CBF could be predicted with no more than 10% relative error, affording an opportunity for real-time relative cerebral metabolism monitoring in conjunction with MR measurement of cerebral blood volume using super paramagnetic contrast agents.