Transcranial Doppler Characteristics of Different Embolic Materials During In Vivo Testing

PURPOSE: The authors investigated whether ultrasonic characteristics of embolic signals could be used to differentiate embolic composition. MATERIALS AND METHODS: The authors analyzed high-intensity transient signals (HITS) from 3 patients with patent foramen ovale during the bubble contrast test and during total joint replacement surgery. In 3 anesthetized dogs, latex microspheres, fat particles, and air bubbles were injected into the internal carotid artery and HITS were identified in the cerebral circulation. The area under the receiver operating characteristic curve quantified the usefulness of each measure to distinguish embolic composition. RESULTS: In humans, HITS intensity (area: 0.80) and frequency (area: 0.73) but not duration (area: 0.32) were useful to distinguish air bubbles from presumed solid emboli. In animals, intensity distinguished microspheres from air (area: 0.94) and microspheres from fat (area: 0.94) but was less useful for fat and air (area: 0.64). The duration (area: 0.54-0.76) and frequency (area: 0.54-0.63) were poor discriminators. CONCLUSION: The HITS intensity best distinguished embolic composition. Particle size should be taken into account in future research.