Transcranial Doppler ultrasound (TCD) has been used to detect microembolic material. The detection of microembolic signals (MES) by TCD was achieved by placing two probes on the bilateral temporal windows using a closely fitting headband, on the patient's head. The probes detected blood flow velocity of the bilateral middle cerebral arteries (MCA) or posterior cerebral arteries (PCA) continuously through the temporal windows. Blood flow velocity of the MCA or PCA was measured for 30 min. Although the optimum criteria for MES have not been established, our tentative criteria were the following: 1) a single direction; 2) decibel threshold from the general background noise and spontaneous speckle-like intensity fluctuations of the physiological Doppler flow signal of 6 dB; 3) a short duration (under 300 ms) ; 4) an accompanying chirp or snap sound; and 5) a time difference between signals of dual gate. Because the systems available for the auto-detection of MES may pick up artifacts, close observation of the signals during examination is essential. Detection of MES by TCD is a useful method to evaluate the pathophysiology of stroke and efficacy of antithrombotic agents.
