An investigation of segmentation methods and texture analysis applied to tomographic images of human vertebral cancellous bone

The goal of this study is to determine architectural and textural parameters on computed tomographic (CT) images, allowing us to explain the mechanical compressive properties of bone. Although the resolution (150 μm) is of the same order of magnitude as the trabecular thickness, this method enables the possibility of perfecting an in vivo peripheral CT system with an acceptable radiation dose for the patient. This study was performed on L2 vertebrae cancellous bone specimens taken after necropsy in 22 subjects aged 47–95 years (mean: 79 years). The segmentation process is a crucial point in the determination of accurate architectural parameters. In this paper the use of two different segmentation methods is investigated, based on an edge enhancement and a region growing approach. The images are compared and the architectural parameters extracted from the images segmented by both methods lead to a quantitative evaluation. The parameters are found to be globally robust towards the segmentation process, although some of them are much more sensitive to the approach used. Highly significant correlations ( P  < 0.0005) have been obtained between the two segmentation methods for all the parameters, with ρ ranging from 0.70 to 0.93. In order to improve the assessment of bone architecture, texture analysis (run length method) was investigated. New features are obtained from an image reduced to 16 grey-levels. Textural parameters in addition to architectural parameters in a multivariate regression model increase significantly ( P  = 0.01) the prediction of the maximum compressive strength (variation of r ² from 0.75 up to 0.89).     

Complementarity of a photon-counting system and radioscopy for inspection of cast aluminium components

This study aims at establishing X-ray methods for inspection of cast aluminium components by combining two approaches, a radioscopic inspection, and a photon-counting system.Indeed, radioscopy is widely used in castings inspection for automatic defect detection and is an efficient method for characterising rather small thicknesses, typically less than 40 mm. However, cast components often show a high range of thicknesses and imaging the whole range is difficult. We propose to use photon-counting measurements to complement the radioscopic image for high thicknesses. Photon-counting is not an imaging tool, but the thickness sensitivity obtained from photon-counting measurements (number of X-ray photons transmitted through the object) is much better than what can be obtained by classical radioscopy for up to 60 mm of aluminium. For high thicknesses of aluminium, within small volumes where defects are believed to be critical, the photon-counting system allows getting information additional to that obtained from classical radioscopy images.     

Mechanical properties of ewe vertebral cancellous bone compared with histomorphometry and high-resolution computed tomography parameters

This paper is the result of discussions between scientists working in widely separated areas, united by an interest in the hippocampus. The discussions focused on the possible role of GABA in the development and maturation of the hippocampus and in neurodegeneration in Alzheimer's disease (AD). GABA neurons are among the first to differentiate in the hippocampus and the properties of GABA neurotransmission in the developing hippocampus are distinct from those in the adult. GABAergic transmission may play a role in the clustering and maturation of GABA receptors, as well as of receptors for other neurotransmitters. The development and maturation of synaptic connections involves changes in the organization of the cytoskeleton, and mechanical force generation is probably required to establish appropriate points of contact. This generation of force may require coupling of specific receptors to the cytoskeleton through specialized proteins. In AD, much of the developmental process is progressively unraveled in the hippocampus, as afferent fibers, most notably from entorhinal excitatory neurons and from basal forebrain cholinergic cells, degenerate. This denervation undoubtedly has consequences for receptor systems, dendritic morphology and the underlying cytoskeleton. GABA neurons remain in the AD hippocampus, and may actually contribute to abnormal firing and degeneration of remaining pyramidal neurons. This attempt to bring together data from different areas of research has allowed the development of a scheme which identifies significant specific gaps in our knowledge, which could be readily filled by focused experimental work.