Ries F, Tiemann K, Pohl C, Bauer C, Mundo M, Becher H
Department of Neurology, University of Bonn, Germany.
Stroke. 1998 Mar;29(3):668-72. doi: 10.1161/01.str.29.3.668.
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.
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.
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 (lambda). 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.
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.
经颅多普勒超声检测到的高强度瞬态信号（HITS）与颅内动脉中的微栓子相对应。本研究的目的是基于体外模型中多普勒功率谱的高分辨率分析，制定新的诊断标准，以区分这些微栓子信号与伪像。
将276个由不同生物和非生物材料组成的已形成栓子以及气泡注入带有人工血管的血流模拟装置中，并以稳定或搏动方式灌注。使用改良的2.5兆赫脉冲双功超声仪和商用2兆赫多普勒系统评估栓子通过情况。使用国际上公认的HITS视听特征标准分析栓子HITS。通过专门开发的对多普勒原始数据的高分辨率分析来评估与HITS相关的多普勒频谱变化。
使用传统的栓子HITS视听标准可以识别77%的所有栓子事件。多普勒频谱分析表明，所有注入的栓子都会产生高于背景水平至少3分贝的高振幅信号。此外，使用高分辨率处理，在由固体颗粒引起的所有栓子HITS之后，可以识别多普勒频谱模式的特定变化。这些栓子后的频谱模式总是以多普勒频移随时间减小且类似希腊字母λ（λ）为特征。栓子后的频谱模式的持续时间和外观主要受栓子的大小和速度影响。在小气泡栓塞或诱发伪像记录的情况下未发现类似现象。使用特定的商用多普勒系统，我们在47%的注入栓子中记录到了栓子后的频谱模式。
在本研究中，可以表征与微栓子HITS相关的多普勒频谱模式的高度特异性变化，从而为多普勒栓子检测中微栓子信号与伪像的区分提供进一步的标准。通过对原始多普勒数据的高分辨率分析可以提高这些信号检测的灵敏度。
