Differentiation between true microembolic signals and artefacts using an arbitrary sample volume

We evaluated a new discrimination technique between microemboli (MES) and a rtefact signals. Monitoring was performed over the middle cerebral artery ( 55 mm) and the brain parenchyma (29 mm), Intensity changes were expressed a s percent of change compared to the value measured in the proximal depth. T he cut-off value providing the highest sensitivity and specificity in the d ifferentiation was evaluated using 250 MES and 250 artefact signals, and su bsequently analysed in the first part of the study. Intensity values derive d from the distal depth were subsequently evaluated in 10 patients undergoi ng cardiac surgery and 45 patients with potential arterial or cardioembolic source. Intensity changes of 87% (84%-90%) and -58% (-71%--48%) were measu red in the initial 500 signals for MES and artefact signals, respectively, The best intensity cut-off value was calculated at 27%, This value was subs equently applied to a total of 1858 MES and 1958 artefacts, resulting to se nsitivity and specificity of 96% and 98%, respectively, The proposed techni que provided adequate results, warranting further evaluation. (C) 2000 Worl d Federation for Ultrasound in Medicine & Biology.