Hydrogel embolic agents. Theory and practice of adding radio-opacity

Spheres of hydrogel have been developed as embolic material with the ability to incorporate radio-opaque materials. To optimize particle design for radiographic or fluoroscopic visualization, we have examined the theoretical determinants of particle contrast. In addition, loaded hydrogel particles were tested in a rabbit model.

Computer simulations of particle subject contrast were examined regarding particle composition, particle size, patient thickness, and x-ray beam kilovoltage. Embolizations in the rabbit kidney were used to test the practical aspects of the materials.

Tantalum and tungsten offer some theoretical and practical advantages over other materials. With this particular hydrogel preparation, contrast material loading was limited to 20% of the volume as loaded contrast agent. The soft particles passed through catheters as small as 3 French; they were usually injected as a suspension of saline/contrast material. Tantalum/hydrogel particles as large as 2 mm could be forced through the 140 cm/3-Fr catheter with a guide wire.

Radio-opacity of embolic material should add an element of control in embolization procedures that is lacking with the current agents. The heavy metals, tungsten and tantalum, are suitable additives for radiopaque material for hydrogel emboli. The input relationship appears predictable with computer monitoring techniques. Initial results in a study of these radiopaque particles are very encouraging. Further studies are underway to evaluate the long-term effects in renal and hepatic circulations.