Manus J. Donahue

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Coordination between glutamatergic excitatory neurons and gamma-aminobutyric acid (GABA)-ergic inhibitory interneurons is fundamental to the regulation of neuronal firing rates and is believed to have relevance to functional magnetic resonance imaging (fMRI) contrast. While much is known regarding the molecular behavior of excitatory and inhibitory(More)
Vascular space occupancy (VASO)-dependent functional MRI (fMRI) is a blood-nulling technique capable of generating microvascular cerebral blood volume (CBV)-weighted images. It is shown that at high magnetic field (3.0T) and high spatial resolution (1.89 x 1.89 x 3 mm(3)), the VASO signal changes are too large (6-7%) to originate from CBV effects alone.(More)
There is controversy concerning the discrepancy between absolute cerebral blood flow (CBF) values measured using positron emission tomography (PET) and magnetic resonance imaging (MRI). To gain insight into this problem, the increased signal-to-noise ratio (SNR) and extended T(1) relaxation times of blood and tissue at 3.0 T were exploited to perform pulsed(More)
The characterisation of the extravascular (EV) contribution to the blood oxygenation level-dependent (BOLD) effect is important for understanding the spatial specificity of BOLD contrast and for modelling approaches that aim to extract quantitative metabolic parameters from the BOLD signal. Using bipolar crusher gradients, total (b = 0 s/mm(2) ) and(More)
PURPOSE To evaluate the correlation between angiographic measures of Moyamoya disease and tissue-level impairment from measurements of tissue perfusion and cerebrovascular reactivity (CVR). MATERIALS AND METHODS The relationship between perfusion-weighted arterial spin labeling (ASL) and hypercarbic blood oxygenation-level dependent (BOLD) CVR and(More)
PURPOSE To compare diffusion tensor imaging (DTI) measurements at ultra high field strength (7 Tesla [T]) in human volunteers with DTI measurements performed at 1.5 and 3 Tesla. MATERIALS AND METHODS The signal to noise ratio (SNR) and the uncertainty in fitted DTI parameters fractional anisotropy and primary eigenvector are assessed with tractography(More)
Arterial spin labeling (ASL) provides a noninvasive method to measure brain perfusion and is becoming an increasingly viable alternative to more invasive MR methods due to improvements in acquisition, such as the use of a three-dimensional GRASE readout. A potential source of error in ASL measurements is signal arising from intravascular blood that is(More)
Functional neuroimaging is most commonly performed using the blood-oxygenation-level-dependent (BOLD) approach, which is sensitive to changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and the cerebral metabolic rate of oxygen (CMRO(2)). However, the precise mechanism by which neuronal activity elicits a hemodynamic response remains(More)
Cerebrovascular reactivity to vasodilatory hypercapnic and vasoconstrictive hypocapnic challenges is known to be altered in several hemodynamic disorders, which is often attributable to changes in smooth muscle-mediated vascular compliance. Recently, attenuated reactivity to hypercapnia but enhanced reactivity to hypocapnia was observed in patients with(More)
PURPOSE Owing to variability in vascular dynamics across cerebral cortex, blood-oxygenation-level-dependent (BOLD) spatial and temporal characteristics should vary as a function of cortical-depth. Here, the positive response, initial dip (ID), and post-stimulus undershoot (PSU) of the BOLD response in human visual cortex are investigated as a function of(More)