EVIDENCE AGAINST MOLECULAR AGGREGATES IN CONCENTRATED-SOLUTIONS OF X-RAY CONTRAST-MEDIA

In order to evaluate the possible existence of large molecular aggrega tes in concentrated solutions of X-ray contrast media used for medical imaging, a comprehensive study of the effect of the contrast medium c oncentration on the osmolarity, light scattering and molecular diffusi on has been performed for the two X-ray contrast media, Omnipaque (ioh exol) and Visipaque (iodixanol). The measured change in osmolarity and light scattering with increasing concentration of contrast medium was well explained by solvent-solute and solute-solute interactions. Mini ma were observed for both the concentration-normalized osmolarity and the inverse of the concentration-nonnalized Rayleigh ratio, observatio ns which are incompatible with the hypothesis of aggregation at higher concentrations. From the observed minima, dynamic clusters containing at maximum two to three molecules were demonstrated. The apparent mol ecular diameter measured with dynamic light scattering, was found to b e well predicted from the thermodynamic expression of the concentratio n dependency of the mutual diffusion coefficient. The observed scatter ing intensity was incompatible with an actual increase in the geometri c size of the scatterers (i.e. aggregation) with increasing concentrat ion. Contrary to the conclusions made by other investigators, the resu lts presented clearly demonstrate the absence of large colloidal-like structures or molecular aggregates' in the X-ray contrast media invest igated. (C) 1998 Elsevier Science B.V. All rights reserved.