The fine structure of pancreatic stones as shown by scanning electron microscopy and x-ray probe microanalyser
SummaryTo delineate the process of pancreatic stone formation, stones from four patients were studied with a scanning electron microscope and X-ray probe microanalyser.The stones consisted of a central core and surrounding shell. Two kinds of stones were demonstrated:one had a core composed of a calcium-rich amorphous substance and interlacing fibrils; the other had a core consisting of multiple cavities with smooth walls composed of a calcium-deficient amorphous substance.The shells showed a common structure: zones of layers or bands of a calcium-rich amorphous substance, network fibrils filled with a calcium-rich amorphous substance, and laminated parallelogrammic or polygonal plates of calcite parallel to the surface in one layer and oblique or perpendicular in the next layer. Calcium was in the crypto-crystalline state as well as crystalline state of calcite. Crystalline calcite showed spiral and epitaxial growth along with findings of dissolution, resembling cholesterol crystals of gall stones. Pancreatic stones are probably formed through central core formation and layered growth of a shell. Comparison of stones and protein plugs suggests that protein plugs can grow to stones with calcite deposition accompanied by precipitation of network fibrils and an amorphous substance.
Investigation at the micrometer scale of pancreatic calcifications in chronic pancreatitis by μFTIR spectroscopy and field emission scanning electron microscopy
A set of pancreatic stones and surgical specimens with chronic pancreatitis from various etiologies has been investigated by Fourier Transform Infra-Red spectroscopy and field emission scanning electron microscopy in order to gather information regarding their chemical composition and their structural characteristics at the mesoscopic scale. These physicochemical data were compared to the medical data of the patients. Regarding the pancreatic stones, the complete set of data underlines the presence of the three calcium carbonate polymorphs as well as a great diversity on their spatial distribution (core versus surface), a wide range of protein content and the presence of other phases in a limited number of samples. These results suggest that very different mechanisms are involved in stone formation. Major results have been also obtained on pancreas tissues. Chemical diversity exists also for ectopic calcifications. The presence of CA and its amorphous precursor (ACCP) constitutes a real challenge for clinicians, such chemical compounds being associated to biological parameters far from those related to calcium carbonate.
Graphs of polyhedra; polyhedra as graphs
Relations between graph theory and polyhedra are presented in two contexts. In the first, the symbiotic dependence between 3-connected planar graphs and convex polyhedra is described in detail. In the second, a theory of nonconvex polyhedra is based on a graph-theoretic foundation. This approach eliminates the vagueness and inconsistency that pervade much of the literature dealing with polyhedra more general than the convex ones.