From the Departments of Neurology (F.R., C.P., C.B., M.M.) and Cardiology
(K.T., H.B.), University of Bonn (Germany).
Correspondence to Fernand Ries, MD, Department of Neurology, Sigmund-Freud Str 25, D-53105 Bonn, Germany.
Background and
Purpose—High-intensity transient signals (HITS) detected by
transcranial Doppler ultrasonography correspond to
microemboli in intracranial arteries. The purpose of this study was to
develop new diagnostic criteria for the differentiation of
these microembolic signals from artifact, based on a
high-resolution analysis of Doppler power spectra in an in
vitro model.
Methods—Two hundred seventy-six formed emboli, consisting of
different biological and nonbiological materials and as air bubbles,
were injected into a flow phantom with artificial blood vessels and
perfused in a steady or a pulsatile way. Embolic passage was assessed
with a modified 2.5-MHz pulsed Duplex machine and a commercial 2-MHz
Doppler system. Embolic HITS were analyzed using
internationally accepted criteria for the audiovisual characteristics
of HITS. Doppler spectra changes associated with HITS were
evaluated by means of a specially developed high-resolution
analysis of Doppler raw data.
Results—Seventy-seven percent of all embolic events could be
identified using conventional audiovisual criteria for embolic HITS.
Analysis of Doppler spectra showed that all injected emboli
generated high-amplitude signals with a minimum of at least 3 dB above
background level. In addition, using high-resolution processing,
specific changes in Doppler spectral patterns could be identified
after all embolic HITS caused by solid particles. These postembolic
spectral patterns were always characterized by a Doppler frequency
shift decreasing in time and resembling the letter lambda (
Conclusions—In this study, highly specific changes in Doppler
spectral patterns associated with microembolic HITS
could be characterized, resulting in further criteria for the
differentiation between microembolic signals and
artifact in Doppler emboli detection. The sensitivity of the
detection of these signals can be increased by high-resolution
analysis of raw Doppler data.
© 1998 American Heart Association, Inc.
Original Contributions
High-Resolution Emboli Detection and Differentiation by Characteristic Postembolic Spectral Patterns
).
Duration and appearance of the postembolic spectral patterns were
mainly influenced by the size and velocity of the embolus. Similar
phenomena could not be found in case of embolism by either small air
bubbles or in case of provoked artifact registration. Using a
commercial Doppler system specific, we documented postembolic
spectral patterns in 47% of injected emboli.
Key Words: diagnostic imaging • embolism • spectrum analysis • ultrasonography, Doppler
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