"Tail sign" associated with microembolic signals.

BACKGROUND AND PURPOSE Transcranial Doppler ultrasound (TCD) can detect circulating microembolic signals (MES). We focused our attention on tail signs (TS), a signal associated with MES that appeared as a small reversal signal after MES on the high time resolution spectral display. We examined MES and artifacts in an animal study to determine whether TS were specific changes associated with MES and investigated the characteristics of TS in both animal and clinical studies. METHODS In an animal study, adult pigs with venoarterial extracorporeal membrane oxygenation and minimal anticoagulation therapy were used as a model for cerebral embolism. After performing TCD monitoring with a multigated approach, we did an offline analysis to investigate several parameters concerning MES and TS. We also examined TS in patients in a clinical study. RESULTS From a total of 362 MES investigated in the animal study, 72.9% were followed by TS. We could not find any TS associated with artifacts. The time delay between TS and MES was negatively correlated with the velocity of MES. MES almost always appeared first in the proximal channel, whereas TS conversely appeared first in the distal channel. In the clinical study, we were also able to observe TS associated with MES. CONCLUSIONS TS may represent emboli passing down a branch vessel or twisted downstream vessel. TS are specific for MES and can be used as another criterion for MES identification.