Experimental Studies with a New Radiopaque Emulsion

Abstract

A long and generally unsuccessful search has been made for a safe radiopaque colloid or emulsion to be employed in intravenous hepatosplenography. We should like to report our recent experiences in the development and experimental use of such an agent, as well as its apparent benefit in a number of other fields of contrast radiography. The most widely used colloid has been Thorotrast, a 25 per cent colloidal suspension of thorium dioxide. Although it produces a satisfactory opacification of the liver and spleen, it has been almost completely abandoned because it is radioactive and has been shown to produce malignant tumors secondary to its permanent deposition and long half-life, at least 50 such cases having been reported (1, 2, 3). Preparations of nonradioactive, insoluble, heavy-metal salts such as barium sulfate (4), zinc, and tantalum oxide (5) have been prepared and tested. These have been suspensions rather then true colloids and, because of their subsequent instability and large particle size, have proved unsatisfactory. Theoretically, an emulsion of an opaque oil should have many of the advantages of Thorotrast and should also be capable of being metabolized and removed from the body. In 1938 Degkwitz (6) published his experiments with such an emulsion, but no subsequent reports have come from his laboratory. Our current preparation is a 50 per cent emulsion of Ethiodol in 5 per cent glucose. It has been stable for periods of up to six months and can be heat-sterilized. It cannot, however, be autoclaved. Many emulsifying agents have been tested, and at the present time we are using lecithin and pluronic acid. These have produced a satisfactory emulsion, particularly when prepared by a special reversal process. This, in brief, entails the making of an initial water-in-oil emulsion and reversing it by chemical means to an oil-in-water type. Full details of the exact preparation technic will be given in a later publication.2 The principal properties of the final Ethiodol emulsion are as follows: 1. It can be prepared with an oil concentration as high as 60 per cent. 2. The average oil particles are about 0.3 micron in size. 3. It is freely miscible with aqueous media, and, therefore, with all body fluids. 4. It is stable for long periods. 5. The Ethiodol particles, being insoluble, are relatively inert chemically and do not react appreciably with the tissues. 6. It can be heat-sterilized. 7. It can be diluted to a low oil concentration without physical alteration. 8. The emulsion is almost isotonic and will not affect osmotic phenomena. 9. The Ethiodol, after intravenous injection and deposition in the liver and spleen, is eliminated in a relatively short period of time (approximately two to seven days). 10. The emulsion has a viscosity lower than Ethiodol. 11. The emulsion has the property of adhering to raw, irregular, or diseased surfaces.