Selected high-intensity transient signals detected by transcranial Doppler ultrasonography have been shown to correspond to microemboli made of air, platelet, fibrinogen, or atheromatous material in laboratory models.1 2 They have also been detected in various clinical settings.3 4 5 6 7 8 Recent studies of their occurrence in comparable patient populations have revealed variable findings among centers. Reasons for this discrepancy include differences in signal identification criteria by various investigators and in the display on various instrument screens, as signal characteristics depend on equipment settings at the time of recording and use different ultrasonic carrier frequencies. To address this problem, the Consensus Committee recommends that an individual Doppler microembolic signal must always have the following basic features.
1. A Doppler microembolic signal is transient, usually lasting less than 300 milliseconds. Its duration depends on its time of passage through the Doppler sample volume.
2. The amplitude of a Doppler microembolic signal is usually at least 3 dB higher than that of the background blood flow signal and depends on the characteristics of the individual microembolus.
3. Within the appropriate dynamic range of bidirectional Doppler equipment, a signal is unidirectional within the Doppler velocity spectrum.
4. Depending on the equipment used and its own velocity, a microembolic signal is accompanied by a “snap,” “chirp,” or “moan” on the audible output.
The preceding criteria are not meant to be definitive or complete. They are proposed as minimal features that should constitute a useful reference for investigators and physicians. Investigators who select different criteria for their studies are urged to specify equipment ultrasonic frequency, dynamic range and gain settings, and the selected identification criteria in their publications.
The members of the Consensus Committee of the Ninth International Cerebral Hemodynamics Symposium, as selected by the president, Merrill P. Spencer, MD, are Robert G.A. Ackerstaff, MD, PhD; Viken L. Babikian, MD; Dimitrios Georgiadis, MD; David Russell, MD, PhD; Mario Siebler, MD; Merrill P. Spencer, MD; and David Stump, PhD.
- Copyright © 1995 by American Heart Association
1. Russell D, Madden KP, Clark WM, Sandset PM, Zivin JA. Detection of arterial emboli using Doppler ultrasound in rabbits. Stroke. 1991;22:253-258.
Markus HS, Brown MM. Differentiation between different pathological cerebral embolic materials using transcranial Doppler in an in vivo model. Stroke. 1993;24:1-5.
Babikian VL, Hyde C, Pochay V, Winter MR. Clinical correlates of high-intensity transient signals detected on transcranial Doppler sonography in patients with cerebrovascular disease. Stroke. 1994;25:1570-1573.
Georgiadis D, Grosset DG, Kelman A, Faichney A, Lees KR. Prevalence and characteristics of intracranial microemboli signals in patients with different types of prosthetic cardiac valves. Stroke. 1994;25:587-592.
Jansen C, Ramos LMP, van Heesewijk JPM, Moll FL, van Gijn J, Ackerstaff RGA. Impact of microembolism and hemodynamic changes in the brain during carotid endarterectomy. Stroke. 1994;25:992-997.
Siebler M, Kleinschmidt A, Sitzer M, Steinmetz H, Freund HJ. Cerebral microembolism in symptomatic and asymptomatic high-grade internal carotid artery stenosis. Neurology. 1994;44:615-618.
Spencer MP, Thomas GI, Nicholls SC, Sauvage LR. Detection of middle cerebral artery emboli during carotid endarterectomy using transcranial Doppler ultrasonography. Stroke. 1990;21:415-423.