We carried out an investigation to identify neuromelanin-containing noradrenergic and dopaminergic neurons in the locus ceruleus and substantia nigra pars compacta of healthy volunteers and patients with Parkinson's disease using a newly developed magnetic resonance imaging technique that can demonstrate neuromelanin-related contrast. The high-resolution neuromelanin images obtained by a 3-T scanner revealed high signal areas in the brain stem and these corresponded well with the location of the locus ceruleus and substantia nigra pars compacta in gross specimens. In Parkinson's disease patients, the signal intensity in the locus ceruleus and substantia nigra pars compacta was greatly reduced, suggesting depletion of neuromelanin-containing neurons. We conclude that neuromelanin magnetic resonance imaging can be used for direct visualization of the locus ceruleus and substantia nigra pars compacta, and may help in detecting pathological changes in Parkinson's disease and related disorders.

Abstract. We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data.

Purpose: To investigate age-related changes in the locus ceruleus (LC) in healthy subjects using neuromelanin magnetic resonance (MR) imaging at 3 Tesla.Methods: We examined 64 healthy volunteers (aged 23 to 80 years) using neuromelaninsensitive T 1 -weighted images and measured the contrast of areas of high signal intensity corresponding to the LC.Results: A pair of punctate areas of high signal intensity that represented neuromelanin within the noradrenergic neurons of the LC was easily recognized in all subjects. The contrast ratio of the LC to the adjacent pontine tegmentum increased to the age of 40 to 59 years and gradually and signiˆcantly decreased in elderly subjects. This correlates well with pathologically proven age-related changes in neuromelanin content within the LC.Conclusion: Age-related variance should be considered when determining the existence of abnormalities in the LC.

Abstract.We offer an effective medium model for the elastic moduli of high-porosity ocean-bottom sediments. The elastic constants of the dry-sediment frame depend on porosity, elastic moduli of the solid phase, and effective pressure. The model connects two end points in the elastic-modulusporosity plane: the Hertz-Mindlin modulus of a dense elastic sphere pack at critical porosity; and zero at 100% porosity.The elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. Unlike the suspension model, our model assigns non-zero elastic constants to the dry-sediment frame and can predict the shearwave velocity. Unlike various modifications of the traveltime-average equation, it is first-principle-based and contains only physical parameters. We justify this model by matching sonic data in shallow marine sediments and in an ODP well.

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