Improved retroperitoneal and gastrointestinal sonography using oral contrast agents in a porcine model

Abdominal sonography can be compromised by the presence of air within the scanning field. Gas-displacing oral contrast agents have the potential to improve the diagnostic yield of routine abdominal sonography. The purpose of this study was to investigate two oral contrast agents and water and to compare their ability to improve abdominal sonography with an unenhanced baseline study and each other in a porcine model.

The acoustic properties of agent 1 (Oralex; Molecular Biosystems, San Diego, CA), a suspension of polydextrose in purified water; agent 2, a homemade agent (named BMW), a suspension of polysaccharide particles in water; and water were assessed in finger phantoms under laboratory conditions. Each solution was subsequently evaluated in 10 pigs, for a total of 30 animals. The bolus character, gas artifact, abdominal viscera, vessels, and gut wall were graded from 1 (nondiagnostic) to 5 (excellent) in the unenhanced and postcontrast states. Postcontrast grades were compared with unenhanced baseline grades using the Wilcoxon signed-rank correlation. Agents were compared with each other using the Mann-Whitney U test (Wilcoxon rank sum test).

All three solutions were hypoechoic, were homogeneous, and showed minimal attenuation and backscatter. Both oral contrast agents had excellent bolus characteristics (agent 1, grade 5.0 +/- 0; agent 2, grade 4.6 +/- 0.5), displaced gas from the scanning field, and significantly improved visibility in all categories, particularly the gut. No difference in performance was found between agents 1 and agent 2. Water had poor bolus characteristics (grade 1.3 +/- 0.48) and did not improve visibility over baseline.

The acoustic in vitro properties of agent 1 and agent 2 approach that of an ideal sonographic contrast agent. Both agents are superior to water in their improvement of direct visualization of the retroperitoneum and the gut in abdominal sonography in a porcine model.