Published Online
on December 18, 2008

A more recent version of this article appeared on February 1, 2009

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Submitted on February 20, 2008
Revised on March 17, 2008
Accepted on March 20, 2008

A Spectrum of Knock-Type Doppler Signals in the Intracranial Vessels

Georgios Tsivgoulis MD^*; Bing L. Man MD; Annabelle Y. Lao MD; Vijay K. Sharma MD; Vassilios Kotsis MD; Konstantinos Vadikolias MD; and Andrei V. Alexandrov MD^*

From Comprehensive Stroke Center (G.T., A.V.A.), Department of Neurology, University of Alabama at Birmingham, Birmingham, Ala; Barrow Neurological Institute (G.T., B.L.M., A.Y.L., V.K.S., A.V.A.), St. Joseph's Hospital and Medical Center, Phoenix, Ariz; Division of Neurology (B.L.M.), Department of Medicine and Therapeutics, the Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, China; Division of Neurology (V.K.S.), National University Hospital, Singapore; 3rd Department of Medicine (V.K.), Aristotle University of Thessaloniki, Thessaloniki, Greece; Department of Neurology (K.V.), Democritus University of Thrace, University Hospital of Alexandroupolis, Alexandroupolis, Greece.

^* To whom correspondence should be addressed. E-mail: tsivgoulisgiorg{at}yahoo.gr or avalexandrov{at}att.net.

Background and Purpose—Knock-type Doppler signals (KTDS) are detectable by transcranial Doppler, and it has been hypothesized that they are related to an occlusion of a small perforating artery and microvascular ischemia. However, the nature of KTDS has not been prospectively defined. We aimed at describing the spectral and power motion Doppler characteristics of KTDS and ultrasound exposure conditions that lead to their appearance.

Methods—Consecutive patients referred with symptoms of stroke or transient ischemic attacks to our cerebrovascular ultrasound laboratory were screened for the presence of KTDS. The presence of microvascular ischemia was assessed using brain MRI.

Results—Among 327 patients with cerebrovascular symptoms, 46 (14%) had KTDS. KTDS were found more frequently in posterior circulation vessels (55% vertebral artery, 21.5% basilar artery, and 6% posterior cerebral artery). There was no association between ultrasound identification of KTDS and the presence of brain ischemia in the distribution of any vessel (OR, 0.37; 95% CI, 0.09–1.53; P=0.171) on univariate logistic regression analyses. KTDS was not related to the presence of microvascular ischemia on brain MRI (OR, 1.12; 95% CI, 0.55–2.29; P=0.761). We described the range of spectral and power motion Doppler appearances of KTDS and experimentally demonstrated the most likely underlying mechanism being a large vessel wall movement artifact.

Conclusions—Although KTDS can be distinguished from other spectral flow signals, they can be found in normal vessels, they do not seem to be associated with the vessel affected by ischemia, and they should not be overinterpreted.

Key words: knock-type Doppler signals • small vessel knock • transcranial Doppler

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