PURPOSE: MR diffusion imaging was performed to investigate changes in water diffusion in patients with cerebral infarction.
METHODS: Diffusion maps of the apparent diffusion coefficient (ADC) were created to show local water mobility in the brain tissue in 15 patients. These ADC maps were compared with conventional T2-weighted images.
The potential application of gas microbubbles as a unique intravascular susceptibility contrast agent for MRI has not been fully explored. In this study, the MR susceptibility effect of an ultrasound microbubble contrast agent, Optison, was studied with rat liver imaging at 7 T. Optison suspension in two different doses (0.15 mL/kg and 0.4 mL/kg) was injected into rats, and induced transverse relaxation rate increases (deltaR2*) of 29.1 +/- 1.6 s(-1) (N = 2) and 61.5 +/- 12.9 s(-1) (N = 6), respectively, in liver tissue.
Using functional magnetic resonance imaging (fMRI), we investigated whether the response of auditory and visual cortex was modulated by attending selectively to either heard or seen numbers presented simultaneously. Alternating attention between modalities modulated fMRI signal within the corresponding sensory cortex. This study provides evidence that attention acts locally during early auditory cognitive sensory processing, and that modulation of auditory and visual sensory cortex by attention is modality-dependent.
Neuropsychological, computational, and psycholinguistic data suggest the existence of semantic maps, i.e. localized representations of semantic information in the brain. Using functional magnetic resonance imaging, this hypothesis was directly tested with a picture naming task involving items from four different semantic categories. Small left lateralized fronto-temporal cortical sites of category-specific activation were found when brain activation signals were averaged.
Pulsed field gradient nuclear magnetic resonance methods combined with nuclear magnetic resonance imaging were used to determine the water diffusion anisotropy in perfused rat hearts at 37 degrees C. It was found that the observed diffusion coefficient D(app) (apparent diffusion coefficient) depends on the orientation of the applied gradient g. When g is parallel to the epicardial surface, the observed diffusivity is D(app) parallel = 1.8 +/- 0.4 x 10(-9) m2.s-1, whereas when g is perpendicular to it, diffusivity is D(app) perpendicular = 2.5 +/- 0.5 x 10(-9) m2.s-1.
Functional magnetic resonance imaging (MRI) allows quantitative blood volume imaging in vivo at high tissue resolution. The purpose is to apply this technique for untreated and hyperthermia-treated experimental choroidal melanoma. MS 325 was used as new intravascular albumin-bound gadolinium-based contrast agent. Pigmented choroidal melanomas were established in albino rabbits. MRI was performed in 7 untreated eyes and 7 eyes treated with a Neodymium:Yttrium-Lanthanum-Fluoride-laser at 1047 nm. 3D-spoiled gradient echo pulse sequences were used to acquire T' weighted axial images.
The effects of photic stimulation on the visual cortex of human brain were studied by means of gradient-echo echo-planar imaging (EPI). Whole-body 4 and 1.5 T MRI systems, equipped with a small z axis head gradient coil, were used. Variations of image intensity of up to 28% at 4 T, and up to 7% at 1.5 T, were observed in primary visual cortex, corresponding to an increase of blood oxygenation in regions of increased neural activity. The larger effects at 4 T are due to the increased importance of the susceptibility difference between deoxygenated and oxygenated blood at high fields.
BACKGROUND: We studied the local relation of muscle perfusion and metabolism in patients with severe chronic heart failure. Alterations of skeletal muscle blood flow and oxidative capacity contribute to exercise intolerance in these patients. The interdependence of both parameters has often been questioned.
Topically applied (eyedrop) H2(17)O (10% enrichment) was used in magnetic resonance studies to quantify intraocular water dispersion in vivo. The rate of H2(17)O removed from the aqueous chamber is in the order of 0.1 ml/min/ml of tissue. Similar results are obtained with either proton imaging or 17O spectroscopy. Parallel experiments of direct injection of H2(17)O into the aqueous chamber supported the topical data. Proton MR imaging of H2(17)O dissipation from the aqueous chamber with clinical imagers, coupled with eyedrop application, suggests clinical possibilities.
Water enriched with the stable isotope 17O (H2(17)O) shortens the transverse relaxation time (T2) of protons in water and can therefore be used as the contrast agent for proton magnetic resonance (MR) imaging. This agent can be given topically or intravenously to demonstrate water movement in the eye. Topical H2(17)O (0.05-0.1 ml/eye, 10% enrichment) entered the anterior chamber within 5 min and dissipated from the chamber in a single-exponential fashion (flow-rate constant k = 0.1 min-1), principally due to an exchange with the iridic circulation. No H2(17)O was detected in the vitreous.
