Radiographic demonstration of a liquid surface bounded by a wet solid surface.

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At the line of contact between a liquid surface and a bounding wet solid wall deformation of the surface is produced by surface tension, and this deformation gives rise to various features in the radiograph. For the interpretation of these image features a detailed analysis was performed by means of model experiments. Tubes and rods of methyl acrylate with different diameters and covered with wet sheets of porous paper were used. The tubes were partly filled with water. In some cases a rod was placed concentrically or eccentrically inside the tube. The shape of the image of the liquid surface in vertical and inclined models was examined by conventional radiographic technique and computed tomography. At the walls the surface tension resulted in formation of meniscoids. When the distance between solid walls was short enough adjacent meniscoids joined to form a discoid. The shape of the meniscoid and discoid varied with the shape and inclination of the walls. Distinct boundaries representative of the shape and position of the surface were produced only from those places where the beam was tangential to the surface. When the surface was concave towards the gas in the direction of the beam an internal boundary with a light Mach line was produced. When the surface was convex towards the gas in the direction of the beam an external boundary with a dark Mach line was produced. A boundary was straight when the surface was plane or was part of a cylindric surface. The seemingly simple form of the liquid surface gave rise to surprisingly complex boundary formations, which are analyzed in detail. The findings reported may have a variety of implications for the interpretation of clinical radiographs and may act as a key for the reconstruction of the structures reproduced.