颅内动脉狭窄栓子起源部位微栓子信号的特性研究

目的经颅多普勒超声(TCD)可以在脑动脉血流中监测到微栓子信号(MES),通过分析MES在频谱和声窗中的参数,比较来源于颅内动脉狭窄部位(栓子起源部位)和来源于颈动脉狭窄或机械性心瓣膜置换术患者(远距离栓子源)MES特点,描述在颅内动脉狭窄处微栓子起源部位MES的特点,分析产生这些特点的可能机制。方法研究了2000年1月～2005年10月,经TCD监测到的微栓子信号,研究组325个MES来自10例颅内动脉狭窄患者,其中大脑中动脉狭窄者8例,大脑后动脉狭窄者2例,在该狭窄动脉分布区均发现多发急性梗死灶。对照组56个MES来自8例颈内动脉或心脏。全部MES均脱机分析频谱和声窗信号。根据MES在频谱中频率的部位和分布将其分成3种类型:局限性频率信号(FFS):局限在某一频率范围;多频率信号(MFS):占据多个频率范围;基底频率信号(BFS):频率很低与基线几乎相连。结果研究组的325个MES中MFS 305个(占93．8%),FFS有11个(占3．4%),BFS有9个(占2．8%);对照组的56个MES中最多的是FFS 52个(占92．8%),BFS有2个(占3．6%), MFS有2个(占3．6%),两组间差异有显著性意义(P=0．001)。在颅内动脉狭窄中最常见的MFS在频谱中不仅占据多个频率范围,而且其低频部分往往是双向的,在声窗中也由多个不同频率组成,频率最高部分类似一个扭曲了的振幅-调节正弦波,低频部分的振幅在近端深度随时间的推移而降低,在远端深度则随时间的推移而增大,由于MFS在声窗中的起点和振幅最高点不明显,因此很难测量双深度间的时间差。对照组中最常见类型FFS在声窗内的信号表现为一个规整的振幅-调节正弦波(纺锤波),并且在双深度之间有明显的时间差。结论TCD在脑动脉中监测到的来自于远距离栓子源的MES具有局限性频率特点,但从颅内动脉狭窄栓子起源处监测到的MES具有多频且低频部分呈双向的特点,描述了一个振动的微栓子旋转滚动着从脱落的血管壁移动到血管中央的轨迹。

Characteristics of Microembolic Signals Detected near its Origin from the Intracranial Artery Stenosis

Objective Usually microembolic signal(MES)are monitored distal to source.The aim of this study is to describe characteristics of MES as they originated from the intracranial artery,stenosis.Methods We studied the MES detected with TCD duing 2000 to 2005.In study group,a total of 325 MES recorded from ten patients with acute ischemic stroke within intracranial artery stenosis territories.In control group,a total of 56 MES recorded from eight patients with central sources of in- ternal carotid artery(ICA)severe stenosis or prothetic valvula heart disease,we performed an offline analysis of the recorded MES from a 2 MHz bi-gate transducer both in spectrum and sound track.MES were classified into three types :focused-fre- quency signal(FFS),bottom-frequency signal(BFS)and multi-frequency signal(MFS)according to the frequency of sig- nal displayed on spectrum.Results Among these 325 MES recorded from intraeranial artery stenosis,305(93.8%)were MFS,11(3.4%)were FFS and 9(2.8%)were BFS.On spectrum,MFS occupied multiple frequencies along the vertical axis and the low frequency part usually was bi-directional.On sound track,the signals were also composed of multiple frequen- cies.The highest frequency part presented a distorted amplitude-modulated sine wave.The amplitude of the low frequency part diminished with time in proximal channel but enlarged with time in distal channel in a short period.In control group,among 56 MES,52(92.8%)were FFS,2(3.6%)were BFS and2(3.6%)were MFS on spectrum.There is significant difference in the MES type between intracranial artery stenosis and other embolic sources(P =0.001).On sound track,the signal usually had an amplitude-modulated sine wave with marked time delay between two channels.Conclusion The MES recorded from the site of intracranial artery stenosis have special characteristics of multiple frequencies both on spectrum and sound track.Our find- ings may represent a rotating or vibrating embolus as they are just dislodged from the thrombus and are moving from the vessel wall to the centre-stream.