Middle cerebral artery anatomy and characteristics of embolic signals: A dual gate computer simulation study

In terms of microembolic signal (MES) detection, the anatomy of the middle cerebral artery (MCA) mainstem has only scarcely been considered. The vesse l itself, however, could be at least partly responsible for the enormous va riation when calculating the essential time difference (Delta t) values of MES using the dual-gate technique, Therefore, we studied the time character istics of MES in a computer simulation applying an anatomically realistic v essel and a dual-gate TCD approach. Three different MCA anatomies and two M ES to blood intensities were simulated as well as two different sample volu me settings. The MES length (proximal sample volume t(1); distal sample vol ume t(2)) and Delta t were calculated for different angles of insonation an d sample volume depths. The calculations of the time characteristics of MES showed extreme variation, with only modest changes of the insonation angle (t(1) 4-34 ms; Delta t 9-27 ms) or the sample volume depth (t(1) 7-27 ms; Delta t 6-32 ms). The variation could be considerably reduced with modified TCD settings i.e., a shorter gate separation combined with a shorter recei ver gate time in the distal sample volume (Delta t with changing insonation angles 6-19 ms; Delta t with changing insonation depths 13-17 ms). These r esults not only urge us to a cautious interpretation of the properties of s ingle MES, but also contribute to an understanding of the marked Delta t va riation using the dual-gate technique, (C) 1999 World Federation for Ultras ound in Medicine & Biology.