A study of the physical properties of barium sulphate suspensions for use as radiopaques
The possible use of laboratory methods of (a) testing the efficacy of stabilised and unstabilised barium sulphate suspensions as radiopaques, (b) elucidating the interaction of barium meals with the gastro intestinal tract, and (c) predicting their efficiency as diagnostic tools, was investigated. Two methods involving model systems in which conditions in the gut after administration of a barium meal are closely approximated, were developed. These were established and used to investigate the effect of various physical and chemical parameters, such as concentration of barium sulphate, nature and concentration of stabiliser, pH, state of the mucous membrane of the gut surface upon the thickness and uniformity of the layer of barium sulphate adsorbed upon the gut surface. The efficiency of various charged derivatives of methyl cellulose as stabilisers of barium sulphate suspensions was investigated, and the viscosity, stability, dispersibility of the suspension and the surface properties of particles characterised for suspensions containing various concentrations of different carboxy methyl cellulose grades. The surface properties of particles derived from commercial stabilised suspensions were related to the additives used in their manufacture. The site of adhesion of barium sulphate particles to the gut was shown to be the mucous membrane. The adhesion was not due either to charge/charge interaction of barium sulphate particles with the mucus surface, or to the stabiliser which coated the particle surface. Stabilisers increased the uniformity and reproducibility of the adsorbed layer of barium sulphate upon the gut surface, and particles in this layer become coated with mucus. There was a limiting concentration at which the gut surface was saturated with barium sulphate. The state of the gut surface mucus had a pronounced effect upon the amount of barium sulphate adsorbed on the surface. The physical properties required of an efficient barium meal are discussed with reference to results obtained for the model systems.