A NOVEL TECHNIQUE FOR IDENTIFICATION OF DOPPLER MICROEMBOLIC SIGNALS BASED ON THE COINCIDENCE METHOD - IN-VITRO AND IN-VIVO EVALUATION

Background and Purpose The applicability of a novel differentiation te chnique in embolus detection based on the coincidence principle and us ing a multigate probe was evaluated in this study. Methods According t o the coincidence method, high-intensity transients should only be cla ssified as microembolic signals if they appear sequentially in the two sample volumes monitored and within a defined time window calculated from the blood velocity and the spatial distance between the insonatio n depths. Part A: microbubbles were introduced in a continuous flow be nch model of the middle cerebral artery to evaluate the accuracy of th e multigate probe in embolus detection. Part B: in the subjects and pa tients, the minimal and maximum time delays in the appearance of micro embolic signals in the two middle cerebral artery sample volumes were calculated as 0.01 second and set at 0.1 second, respectively. The mul tigate probe was used to monitor (1) 5 normal volunteers in whom 1008 artifact signals were produced, (2) 2 patients undergoing aortic valve replacement surgery, and (3) 12 patients with potential cardiac or ca rotid embolic sources. Results In the bench model, 95.5% of microembol ic signals produced by microbubbles appeared in the two sample volumes with a time delay between 0.02 and 0.05 second, while in the remainin g 4.5% a shorter passage time of 0.01 second was measured. A total of 1968 high-intensity signals were recorded in subjects and patients. Al l but 20 of these (99%) appeared in both monitoring channels within th e above time frame. To summarize, 996 (98.8%) of the 1004 artifact sig nals and 943 (98.1%) of the 961 microembolic signals were correctly cl assified.Conclusions Application of the coincidence theory to distingu ish microembolic signals from artifacts provides a promising new techn ique with high sensitivity and specificity that could decisively impro ve the validity of embolus detection.