“Tail Sign” Associated With Microembolic Signals

Abstract

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. C erebral microembolic signals (MES) were first described during carotid surgeries. 1 Transcranial Doppler ultrasound (TCD) has been reported 2,3 to be capable of detecting circulating cerebral MES in patients with ischemic stroke. Most common identification criteria for MES are based on the basic audiovisual characteristics of high-intensity transient signals. 4 Applying this technique to clinical practice, it is not always easy to differentiate true embolic signals from artifact. Spontaneous speckling in the background signal makes differentiation even more difficult. Automated detection software including neural network 5 or multigate approach 6 systems have been developed recently. Although the differentiation between MES and artifact is, in principle, possible with these methods, they are all dependent on different methodological limitations. The optimal recording time of TCD monitoring remains undetermined. 7 If the prevalence of MES is too low and the intensity of MES is too small throughout the entire recording time, the differentiation of MES from artifact is extremely difficult. Therefore, another useful criterion is needed. We noticed and focused on tail signs (TS), a postembolic signal associated with MES which appeared as a small reversal signal after MES on the high time-resolution spectral display ( Figure 1A). We attempted to determine whether TS were characteristic of the change associated with MES in both animal and clinical studies. Conclusions-TS See Editorial Comment, page 866 Subjects and MethodsThe same TCD machine (Multi-Dop X4, DWL) was used with a multigate 2-MHz probe in both animal and clinical studies.In an animal study, 2 adult pigs weighing 24 to 26 kg, treated with venoarterial extracorporeal membrane oxygenation (VA ECMO) and minima...

The Depth of Microembolic Signal Direction Change Corresponds with Vessel Anatomy

“…The coincidence of the CFD values from TCCD and MES analyses confirms the suspected relationship between vascular anatomy and MES signature [4, 7]. Furui et al [4, 5] discussed the relationship between the MES and the ‘tail sign’ in the time domain data, when two serially placed sample volumes were used.…”

“…The incidence of the ‘tail sign’ was on the same order as in the work of Furui et al [4], who also considered patients with artificial heart valves. Uhlmann et al [8] never encountered artefacts with a tail sign.…”

“…Furui et al [4, 5] discussed the relationship between the MES and the ‘tail sign’ in the time domain data, when two serially placed sample volumes were used. These authors reported that characteristically the time delay between the MES and the ‘tail sign’ was shorter in the more superficially placed sample volume.…”

“…Not only the clinical impact of MES in several patient groups is questionable [3], but also the MES itself still poses questions. One of these questions was the meaning of the so-called ‘tail-sign’, first described by Furui et al [4] in a subgroup of MES. These MES in the fast Fourier transform (FFT) typically are followed by a small signal with a reversed direction.…”

Neurosonology of emboli detection and monitoring

“…Sometimes, a mirror appearance with lower intensity at the other side of the zero line can accompany with real MES. This shadowing is called as lambda or tail sign, and is quite specific for MES (14)(15).…”