Comparison of diffusion-weighted high-resolution CBF and spin-echo BOLD fMRI at 9.4 T (original) (raw)
Related papers
Journal of Cerebral Blood Flow & Metabolism, 2010
Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is the most widely used method for mapping neural activity in the brain. The interpretation of altered BOLD signals is problematic when cerebral blood flow (CBF) or cerebral blood volume change because of aging and/or neurodegenerative diseases. In this study, a recently developed quantitative arterial spin labeling (ASL) approach, bolus-tracking ASL (btASL), was applied to an fMRI experiment in the rat brain. The mean transit time (MTT), capillary transit time (CTT), relative cerebral blood volume of labeled water (rCBV lw ), relative cerebral blood flow (rCBF), and perfusion coefficient in the forelimb region of the somatosensory cortex were quantified during neuronal activation and in the resting state. The average MTT and CTT were 1.939 ± 0.175 and 1.606 ± 0.106 secs, respectively, in the resting state. Both times decreased significantly to 1.616±0.207 and 1.305±0.201 secs, respectively, during activation. The rCBV lw , rCBF, and perfusion coefficient increased on average by a factor of 1.123±0.006, 1.353±0.078, and 1.479±0.148, respectively, during activation. In contrast to BOLD techniques, btASL yields physiologically relevant indices of the functional hyperemia that accompanies neuronal activation.
Diffusion‐weighted spin‐echo fMRI at 9.4 T: Microvascular/tissue contribution to BOLD signal changes
Magnetic Resonance in Medicine, 1999
The nature of vascular contribution to blood oxygenation level dependent (BOLD) contrast used in functional MRI (fMRI) is poorly understood. To investigate vascular contributions at an ultrahigh magnetic field of 9.4 T, diffusion-weighted fMRI techniques were used in a rat forepaw stimulation model. Tissue and blood T 2 values were measured to optimize the echo time for fMRI. The T 2 of arterial blood was 40.8 ؎ 3.4 msec (mean ؎ SD; n ؍ 5), similar to the tissue T 2 of 38.6 ؎ 2.1 msec (n ϭ 16). In comparison, the T 2 of venous blood at an oxygenation level of 79.6 ؎ 6.1% was 9.2 ؎ 2.3 msec (n ؍ 11). The optimal spin-echo time of 40 msec was confirmed from echo-time dependency fMRI studies. The intravascular contribution was examined using a graded diffusion-weighted spin-echo echo-planar imaging technique with diffusion weighting factor (b) values of up to 1200 sec/mm 2 . Relative BOLD signal changes induced by forepaw stimulation showed no dependence on the strength or direction of the diffusion-sensitizing gradients, suggesting that the large vessel contribution to the BOLD signal is negligible at 9.4 T. However, gradient-echo fMRI performed with bipolar diffusion sensitizing gradients, which suppress intravascular components from large vessels, showed higher percent signal changes in the surface of the brain. This effect was attributed to the extravascular contribution from large vessels. These findings demonstrate that caution should be exercised when interpreting that higher percent changes obtained with gradientecho BOLD fMRI are related to stronger neural activation. Magn Reson Med 42:919-928, 1999. 1999 Wiley-Liss, Inc.
Comparison of spatial and temporal pattern for fMRI obtained with BOLD and arterial spin labeling
Journal of Neural Transmission, 2006
Summary. Functional magnetic resonance imaging (fMRI) is presently either performed using blood oxygenation level-dependent (BOLD) contrast or using cerebral blood flow (CBF), measured with arterial spin labeling (ASL) technique. The present fMRI study aimed to provide practical hints to favour one method over the other. It involved three different acquisition methods during visual checkerboard stimulation on nine healthy subjects: 1) CBF
Dynamic magnetic resonance imaging of cerebral blood flow using arterial spin labeling
Methods Mol Biol, 2009
Modern functional neuroimaging techniques, including functional MRI, positron emission tomography and optical imaging of intrinsic signals, rely on a tight coupling between neural activity and cerebral blood flow (CBF) to visualize brain activity using CBF as a surrogate marker. Because the spatial and temporal resolution of neuroimaging modalities is ultimately determined by the spatial and temporal specificity of the underlying hemodynamic signals, characterization of the spatial and temporal profiles of the hemodynamic response to focal brain stimulation is of paramount importance for the correct interpretation and quantification of functional data. The ability to properly measure and quantify CBF with MRI is a major determinant of progress into our understanding of brain function. This chapter reviews the dynamic arterial spin labeling (DASL) method to measure CBF and the CBF functional response with high temporal resolution.
NeuroImage, 2015
Calibrated BOLD imaging, in which traditional measurements of the BOLD signal are combined with measurements of cerebral blood flow (CBF) within a BOLD biophysical model to estimate changes in oxygen metabolism (CMRO2), has been a valuable tool for untangling the physiological processes associated with neural stimulus-induced BOLD activation. However, to date this technique has largely been applied to the study of essentially steady-state physiological changes (baseline to activation) associated with block-design stimuli, and it is unclear whether this approach may be directly extended to the study of more dynamic, naturalistic experimental designs. In this study we tested an assumption underlying this technique whose validity is critical to the application of calibrated BOLD to the study of more dynamic stimuli, that information about fluctuations in venous cerebral blood volume (CBVv) can be captured indirectly by measuring fluctuations in CBF, making the independent measurement o...
NeuroImage, 2006
Spatial specificity of functional magnetic resonance imaging (fMRI) signals to sub-millimeter functional architecture remains controversial. To investigate this issue, high-resolution fMRI in response to visual stimulus was obtained in isoflurane-anesthetized cats at 9.4 T using conventional gradient-echo (GE) and spin-echo (SE) techniques; blood oxygenation-level dependent (BOLD) and cerebral blood volume (CBV)-weighted data were acquired without and with injection of 10 mg Fe/kg monocrystalline iron oxide nanoparticles (MION), respectively. Studies after MION injection at two SE times show that the T 2 V contribution to SE fMRI is minimal. GE and SE BOLD changes were spread across the cortical layers. GE and SE CBV-weighted fMRI responses peaked at the middle cortical layer, which has the highest experimentally-determined microvascular volume; full-width at halfmaximum was <1.0 mm. Parenchymal sensitivity of GE CBV-weighted fMRI was¨3 times higher than that of SE CBV-weighted fMRI and 1.5 times higher than that of BOLD fMRI. It is well known that GE CBV-weighted fMRI detects a volume change in vessels of all sizes, while SE CBV-weighted fMRI is heavily weighted toward microvascular changes. Peak CBV change of 10% at the middle of the cortex in GE measurements was 1.8 times higher than that in SE measurements, indicating that CBV changes occur predominantly for vasculature connecting the intracortical vessels and capillaries. Our data supports the notion of laminar-dependent CBV regulation at a sub-millimeter scale. D
Real-time functional MRI using pseudo-continuous arterial spin labeling
Magnetic Resonance in Medicine, 2011
The first implementation of real-time acquisition and analysis of arterial spin labeling-based functional magnetic resonance imaging time series is presented in this article. The implementation uses a pseudo-continuous labeling scheme followed by a spiral k-space acquisition trajectory. Real-time reconstruction of the images, preprocessing, and regression analysis of the functional magnetic resonance imaging data were implemented on a laptop computer interfaced with the MRI scanner. The method allows the user to track the current raw data, subtraction images, and the cumulative t-statistic map overlaid on a cumulative subtraction image. The user is also able to track the time course of individual time courses and interactively selects a region of interest as a nuisance covariate. The pulse sequence allows the user to adjust acquisition and labeling parameters while observing their effect on the image within two successive pulse repetition times. This method is demonstrated by two functional imaging experiments: a simultaneous finger-tapping and visual stimulation paradigm, and a bimanual finger-tapping task. Magn Reson Med 65:1570-1577, Conventional functional magnetic resonance imaging (fMRI) collects blood oxygen level-dependent (BOLD)contrast MR images of a subject's brain while performing a cognitive task, whereas subsequent image reconstruction and analysis are performed offline (i.e., on a separate computer after the experiment is completed). Real-time fMRI is an exciting extension to conventional fMRI techniques that enables the user to analyze fMRI data as it is being collected. Thus, in real-time fMRI, the results are immediately available as the subject is being scanned, and the results can be used to reveal and guide the subject's cognitive processes. It can also facilitate the experimenter's parameter selections or a clinician's interventions (1).
Magnetic Resonance in Medicine, 2003
The BOLD signal consists of an intravascular (IV) and an extravascular (EV) component from both small and large vessels. Their relative contributions are dependent on field strength, imaging technique, and echo time. The IV and EV contributions were investigated in the human visual cortex at 4 and 7 T using spin-echo and gradient-echo BOLD fMRI with and without suppression of blood effects. Spin-echo acquisition suppresses EV BOLD from large veins and reflects predominantly blood T 2 changes and EV BOLD signal from small blood vessels. At a short echo time (32 ms), diffusion gradient-based suppression of blood signals resulted in a 75% and 20% decrease in spin-echo BOLD changes at 4 T and 7 T, respectively. However, at echo times (55-65 ms) approximating tissue T 2 typically used for optimal BOLD contrast, these gradients had much smaller effects at both fields, consistent with the decreasing blood T 2 with increasing field strength. Gradient-echo BOLD percent changes, with relatively long echo times at both fields, were virtually unaffected by gradients that attenuated the blood contribution because the EV BOLD surrounding both large and small vessels dominated. These results suggest that spin-echo BOLD fMRI at 4 and 7 T, with TE approximating tissue T 2 , significantly reduces nonspecific mapping signals from large vessels and significantly accentuates microvasculature contributions.
Journal of Cerebral Blood Flow & Metabolism, 2021
Methods for imaging of cerebral blood flow do not typically resolve the cortex and thus underestimate flow. However, recent work with high-resolution MRI has emphasized the regional and depth-dependent structural, functional and relaxation times variations within the cortex. Using high-resolution Arterial Spin Labeling (ASL) and T1 mapping acquisitions, we sought to probe the effects of spatial resolution and tissue heterogeneity on cortical cerebral blood flow (CBF) measurements with ASL. We acquired high-resolution (1.6mm) 3 whole brain ASL data in a cohort of 10 volunteers at 3T, along with T1 and transit-time (ATT) mapping, followed by group cortical surface-based analysis using FreeSurfer of the different measured parameters. Fully resolved regional analysis showed higher than average mid-thickness CBF in primary motor areas (+15%,p<0.002), frontal regions (+17%,p<0.01) and auditory cortex, while occipital regions had lower average CBF (-20%,p<10−5). ASL signal was hig...