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The ability to detect brain anatomy and pathophysiology with MRI is limited by the contrast-to-noise ratio (CNR), which depends on the contrast mechanism used and the spatial resolution. In this work, we show that in MRI of the human brain, large improvements in contrast to noise in high-resolution images are possible by exploiting the MRI signal phase at(More)
Heart rate fluctuations occur in the low-frequency range (<0.1 Hz) probed in functional magnetic resonance imaging (fMRI) studies of resting-state functional connectivity and most fMRI block paradigms and may be related to low-frequency blood-oxygenation-level-dependent (BOLD) signal fluctuations. To investigate this hypothesis, temporal correlations(More)
Recent blood oxygenation level dependent functional MRI (BOLD fMRI) studies of the human brain have shown that in the absence of external stimuli, activity persists in the form of distinct patterns of temporally correlated signal fluctuations. In this work, we investigated the spontaneous BOLD signal fluctuations during states of reduced consciousness such(More)
Recent advances in high-field MRI have dramatically improved the visualization of human brain anatomy in vivo. Most notably, in cortical gray matter, strong contrast variations have been observed that appear to reflect the local laminar architecture. This contrast has been attributed to subtle variations in the magnetic properties of brain tissue, possibly(More)
Phase images in susceptibility-weighted MRI of brain provide excellent contrast. However, the phase is affected by tissue geometry and orientation relative to the main magnetic field (B(0)), and phase changes extend beyond areas of altered susceptibility. Magnetic susceptibility, on the other hand, is an intrinsic tissue property, closely reflecting tissue(More)
Signal fluctuations in functional magnetic resonance imaging (fMRI) can result from a number of sources that may have a neuronal, physiologic or instrumental origin. To determine the relative contribution of these sources, we recorded physiological (respiration and cardiac) signals simultaneously with fMRI in human volunteers at rest with their eyes closed.(More)
Recent advances in high-field (>or=7 T) MRI have made it possible to study the fine structure of the human brain at the level of fiber bundles and cortical layers. In particular, techniques aimed at detecting MRI resonance frequency shifts originating from local variation in magnetic susceptibility and other sources have greatly improved the visualization(More)
Magnetic resonance (MR) tracking of magnetically labeled stem and progenitor cells is an emerging technology, leading to an urgent need for magnetic probes that can make cells highly magnetic during their normal expansion in culture. We have developed magnetodendrimers as a versatile class of magnetic tags that can efficiently label mammalian cells,(More)
Functional magnetic resonance imaging (fMRI) is a tool for mapping brain function that utilizes neuronal activity-induced changes in blood oxygenation. An efficient three-dimensional fMRI method is presented for imaging brain activity on conventional, widely available, 1.5-T scanners, without additional hardware. This approach uses large magnetic(More)
A number of recent studies of human brain activity using blood-oxygen-level-dependent (BOLD) fMRI and EEG have reported the presence of spatiotemporal patterns of correlated activity in the absence of external stimuli. Although these patterns have been hypothesized to contain important information about brain architecture, little is known about their origin(More)