HIGH-RESOLUTION EMBOLI DETECTION AND DIFFERENTIATION BY CHARACTERISTIC POSTEMBOLIC SPECTRAL PATTERNS

Background ard Purpose-High-intensity transient signals (HITS) detecte d by transcranial Doppler ultrasonography correspond to microemboli in intracranial arteries. The purpose of this study was to develop new d iagnostic criteria for the differentiation of these microembolic signa ls 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 now phantom with artificial blood vessels and perfused in a steady or a pulsatile way, Embolic pas sage was assessed with a modified 2.5-MHz pulsed Duplex machine and a commercial 2-MHz Doppler system. Embolic HITS were analyzed using inte rnationally accepted criteria for the audiovisual characteristics of H ITS, Doppler spectra changes associated with HITS were evaluated by me ans of a specially developed high-resolution analysis of Doppler raw d ata. Results-Seventy-seven percent of all embolic events could be iden tified using conventional audiovisual HITS. Analysis of Doppler spectr a showed that all injected emboli generated high-amplitude signals wit h a minimum of at least 3 dB above background level. In addition, usin g high-resolution processing, specific changes in Doppler spectral pat terns could be identified after all embolic HITS caused by solid parti cles. These postembolic spectral patterns were always characterized by a Doppler frequency shift decreasing in time and resembling the lette r lambda (lambda). Duration and appearance of the postembolic spectral patterns were mainly influenced by the size and velocity of the embol us, Similar phenomena could not be found in case of embolism by either small. air bubbles or in case of provoked artifact registration. Usin g a commercial Doppler system specific, we documented postembolic spec tral patterns in 47% of injected emboli. Conclusions-In this study, hi ghly specific changes in Doppler spectral patterns associated with mic roembolic HITS could be characterized, resulting in further criteria f or the differentiation between microembolic signals and artifact in Do ppler emboli detection. The sensitivity of the detection of these sign als can be increased by high-resolution analysis of raw Doppler data.