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Three-dimensional Trajectories (three-dimensional + trajectory)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Three-dimensional trajectories of 60Co-labelled earthworms in artificial cores of soil

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2001
Y. Capowiez
Summary Information on earthworm burrowing behaviour is scarce and therefore the evolution of the macroporosity related to earthworm activities is still poorly known. We have designed a new apparatus, ,Colonne Gamma', to follow the three-dimensional trajectories of radio-labelled earthworms in artificial cores of soil. Earthworms are radio-labelled by injecting into their coelomic cavity a small source of 60Co (volume 0.1 mm3, intensity 13.5 ,Ci). The emission of gamma rays is recorded by three detectors carried by a disc that oscillates vertically around the soil core where the earthworm is introduced. We have also developed a deterministic model to estimate the positions of the 60Co source from the number of gamma rays received by each detector during an oscillation. Numerical experiments showed that the uncertainties of estimates were less than 3 mm for each coordinate. To validate the results, we tracked the trajectory (one position every 4 minutes) of a radio-labelled earthworm for 1 week and compared it with the skeleton of the macroporosity obtained by computer assisted tomography of the same soil core. There was a general qualitative agreement between the trajectory and the skeleton. Moreover, based on the precise study of the successive positions of the earthworm we could distinguish two different kinds of activities in the trajectory: displacement and digging events. The ,Colonne Gamma' apparatus therefore has great potential for studies of the ecology and the behaviour of earthworms. [source]

Influence of changing the chewing region on mandibular movement

AUSTRALIAN DENTAL JOURNAL, Issue 1 2009
K Hashii
Abstract Background:, In the shortened dental arch condition, little is known of how patients adapt their jaw function during mastication to the new oral environment. This study aimed to investigate the changes in mandibular movements when the chewing region was changed from the first molar to the first premolar. Methods:, Thirty clinical residents with natural dentitions were recruited. The subjects were asked to chew a piece of beef jerky using either the first molar or the first premolar on the preferred chewing side. Three-dimensional trajectories of lower incisors and both condyles were analysed using a jaw movement tracking device with six degrees of freedom during the period between the onset and offset of electromyographic bursts from the masseter and anterior temporal muscles. Results:, The closing angle of the lower incisors for first premolar chewing was narrower in comparison with that for first molar chewing (p < 0.05). The lengths of the condylar trajectories and the maximum velocities of the condylar movement for first premolar chewing were smaller and slower, respectively, in comparison with those for first molar chewing (both sides; p < 0.01). Conclusions:, The mandibular movement during mastication might be changed to adapt the premolar chewing because of a loss of posterior occlusal supports. [source]

Three-dimensional trajectories of 60Co-labelled earthworms in artificial cores of soil

Visualization of active devices and automatic slice repositioning ("SnapTo") for MRI-guided interventions

MAGNETIC RESONANCE IN MEDICINE, Issue 4 2010
Ashvin K. George
Abstract The accurate visualization of interventional devices is crucial for the safety and effectiveness of MRI-guided interventional procedures. In this paper, we introduce an improvement to the visualization of active devices. The key component is a fast, robust method ("CurveFind") that reconstructs the three-dimensional trajectory of the device from projection images in a fraction of a second. CurveFind is an iterative prediction-correction algorithm that acts on a product of orthogonal projection images. By varying step size and search direction, it is robust to signal inhomogeneities. At the touch of a key, the imaged slice is repositioned to contain the relevant section of the device ("SnapTo"), the curve of the device is plotted in a three-dimensional display, and the point on a target slice, which the device will intersect, is displayed. These features have been incorporated into a real-time MRI system. Experiments in vitro and in vivo (in a pig) have produced successful results using a variety of single- and multichannel devices designed to produce both spatially continuous and discrete signals. CurveFind is typically able to reconstruct the device curve, with an average error of approximately 2 mm, even in the case of complex geometries. Magn Reson Med 63:1070,1079, 2010. © 2010 Wiley-Liss, Inc. [source]