A5079442137- Advanced MRI Techniques and Applications
- Atomic and Subatomic Physics Research
- Functional Brain Connectivity Studies
- Advanced Neuroimaging Techniques and Applications
- Medical Imaging Techniques and Applications
- NMR spectroscopy and applications
- MRI in cancer diagnosis
- Advanced NMR Techniques and Applications
- Cardiac Imaging and Diagnostics
- Neural dynamics and brain function
- Optical Imaging and Spectroscopy Techniques
- Traumatic Brain Injury and Neurovascular Disturbances
- Neuroscience and Neuropharmacology Research
- Heart Rate Variability and Autonomic Control
- Lanthanide and Transition Metal Complexes
- Neuroscience of respiration and sleep
- Cardiovascular Function and Risk Factors
- High Altitude and Hypoxia
- Classical Antiquity Studies
- Neural and Behavioral Psychology Studies
- Ultrasound and Hyperthermia Applications
- Photoacoustic and Ultrasonic Imaging
- Acute Ischemic Stroke Management
- Memory and Neural Mechanisms
- Cerebrovascular and Carotid Artery Diseases
University of California, San Diego
2014-2024
University of Bern
2014
John Carroll University
2010
University of California San Diego Medical Center
1991-2002
University of California, Irvine Medical Center
2002
Resonance Research (United States)
1991-2000
VA San Diego Healthcare System
1999
Harvard University
1985-1997
Beth Israel Deaconess Medical Center
1997
University of California, Irvine
1990-1992
The cerebellum traditionally has been viewed as a neural device dedicated to motor control. Although recent evidence shows that it is involved in nonmotor operations well, an important question whether this involvement independent of control and guidance. Functional magnetic resonance imaging was used demonstrate attention performance independently activate distinct cerebellar regions. These findings support broader concept function, which the diverse cognitive noncognitive neurobehavioral...
Abstract Using a one‐dimensional rapid imaging technique, we have found that injection of lanthanide chelates such as Gd(DTPA) 2− leads to significant decrease (50%) in rat brain signal intensity at 1.45 T using 2 ‐weighted pulse sequences; however, no effect comparable size is observed with 1 sequences. The transient and its kinetics were followed temporal resolution between 8 s. Experiments different show the correlates magnetic moment each agent but not their longitudinal relaxivity....
We describe here experimental considerations in the implementation of quantitative perfusion imaging techniques for functional MRI using pulsed arterial spin labeling. Three tagging techniques: EPISTAR, PICORE, and FAIR are found to give very similar results despite large differences static tissue contrast. Two major sources systematic error measurement identified: transit delay from region slice; inclusion intravascular tagged signal. A modified technique called QUIPSS II is described that...
Abstract We calculate the effects of subvoxel variations in magnetic susceptibility on MR image intensity for spin‐echo (SE) and gradient‐echo (GE) experiments a range microscopic physical parameters. The model used neglects overlap gradients from one inclusion to next, so is valid low volume fractions weak perturbations field. Transverse relaxation predicted deviate significantly linear exponential decay both SE GE at particle radius 2.5 μm. Calculated changes transverse rates increase...
Changes in neuronal activity are accompanied by the release of vasoactive mediators that cause microscopic dilation and constriction cerebral microvasculature manifested macroscopic blood oxygenation level-dependent (BOLD) functional MRI (fMRI) signals. We used two-photon microscopy to measure diameters single arterioles capillaries at different depths within rat primary somatosensory cortex. These measurements were compared with cortical depth-resolved fMRI signal changes. Our results...
The blood oxygenation level-dependent (BOLD) contrast is widely used in functional magnetic resonance imaging (fMRI) studies aimed at investigating neuronal activity. However, the BOLD signal reflects changes volume and rather than activity per se. Therefore, understanding transformation of microscopic vascular behavior into macroscopic signals foundation physiologically informed noninvasive neuroimaging. Here, we use oxygen-sensitive two-photon microscopy to measure BOLD-relevant...
Identification of the cellular players and molecular messengers that communicate neuronal activity to vasculature driving cerebral hemodynamics is important for (1) basic understanding cerebrovascular regulation (2) interpretation functional Magnetic Resonance Imaging (fMRI) signals. Using a combination optogenetic stimulation 2-photon imaging in mice, we demonstrate selective activation cortical excitation inhibition elicits distinct vascular responses identify vasoconstrictive mechanism as...
Abstract Under ideal conditions, continuous arterial spin labeling (ASL) techniques are higher in SNR than pulsed ASL by a factor of e. Presented here is direct theoretical and experimental comparison ASL, using versions both that amenable to multislice imaging insensitive variations transit times (continuous with delay before imaging, QUIPSS II (Quantitative Imaging Perfusion Using Single Subtraction–second version)). image quality for comparable time was nearly identical single‐slice...
Abstract We present, here, a simple method for measurement and correction of off‐resonance related geometric distortion in echo‐planar imaging (EP1). This uses high signal‐to‐noise ratio (SNR) EPI‐based field maps, rapidly acquired using series gradient recalled images collected across range TE values. map is distorted the same manner as EPI to be unwarped, providing direct look‐up table correct location each pixel data. adds very little scan time robust easy implement.
In vivo radioactive tracer and microsphere studies have differing conclusions as to the magnitude of gravitational effect on distribution pulmonary blood flow. We hypothesized that some apparent vertical perfusion gradient in is due compression dependent lung increasing local density therefore perfusion/volume. To test this, six normal subjects underwent functional magnetic resonance imaging with arterial spin labeling during breath holding at residual capacity, quantified nonoverlapping 15...
FUNCTIONAL magnetic resonance imaging (fMRI) was used to explore the brain substrate associated with global and local processing of visuospatial patterns. Systematic differences in activation, consistent observed reaction time data collected under conditions visual hemifield presentation, were found occipitotemporal regions right left hemispheres. Within hemisphere, area activation fractional signal changes greater than conditions. In input high comparable.
In vivo imaging of cerebral tissue oxygenation is important in defining healthy physiology and pathological departures associated with disease. We used a recently developed two-photon microscopy method, based on novel phosphorescent nanoprobe, to image the rat primary sensory cortex response stimulation. Our measurements showed that stimulus-evoked increase pO 2 depended baseline level. particular, during sustained stimulation, steady-state at low-baseline locations remained baseline,...
Quantification of hepatic fat content by application MR phase-contrast imaging (Dixon method) at 1.5 T was compared with results biopsy in 16 patients a variety liver abnormalities. Motion artifact suppressed employing six or eight averages short TR in-phase (echo offset, 0 msec), out-of-phase 1.1 and 2.2 msec) spin-echo pulse sequences. The 360 degree sequence used to assess the impact T2* decay on this method estimating fraction. A standard two-echo long also obtained all patients....
The gravitational gradient of intrapleural pressure is suggested to be less in prone posture than supine. Thus the distribution ventilation expected more uniform prone, potentially affecting regional ventilation-perfusion (V̇a/Q̇) ratio. Using a novel functional lung magnetic resonance imaging technique measure V̇a/Q̇ ratio, gradients proton density, ventilation, perfusion, and ratio were measured supine posture. Data acquired seven healthy subjects single sagittal slice right at residual...