Preliminary study of contrast-enhanced harmonic endosonography with second-generation contrast agents

Purpose. We developed a novel echoencloscope that enables contrast harmonic imaging using ultrasound contrast agents and performed contrast-enhanced harmonic endosonography (EUS) both in vitro and in vivo. Methods. An experimental convex-array echoendoscope equipped with a wideband transducer and a specific mode for contrast harmonic imaging was used. A Doppler phantom model was employed in in vitro experiments to determine the optimal mechanical indices for contrast harmonic imaging by the echoendoscope. In the in vivo experiments, the echoendoscope was inserted into the stomachs of dogs. The digestive organs were observed after intravenous infusion of a contrast agent, Definity, using contrast-enhanced harmonic EUS. Two patients, one with pancreatic carcinoma and one with a gastrointestinal stromal tumor (GIST), underwent contrast-enhanced harmonic EUS. Results. In vitro experiments revealed that the optimal mechanical indices were 0.35-0.40 for intermittent imaging and 0.30 or less for real-time imaging. In the in vivo experiments, branching vessels and subsequent homogeneous distribution of the signal in the pancreatic tissue were observed. During clinical application, typical vascular patterns were observed in pancreatic carcinoma and a GIST. Conclusion. Contrast-enhanced harmonic EUS visualized parenchymal perfusion and the fine vascular structure in digestive organs and should be a useful and powerful method for clinical investigations.