Cerebrovascular assessment using a Doppler carotid scanner and real-time frequency analysis.

The results of two methods for noninvasively diagnosing carotid disease are described. In the first study, a color-coded continuous-wave Doppler scanner was used. As evaluated by arteriography in 56 sides, the sensitivity and specificity of the Doppler scanner for diagnosing carotid lesions with greater than 50% stenosis was 71% and 82%, respectively. We found that many of our initial problems could be overcome by the concomitant use of a real-time frequency analyzer. Specifically, when the Doppler waveforms were displayed, we found that: 1) signals that had been attenuated by calcification or plaques, or had reduced velocity as a result of a proximal stenosis, could still be detected; 2) when the velocity of flow was increased to compensate for a contralateral carotid stenosis, the waveforms could still be of diagnostic value; 3) distinguishing between the internal and external carotid arteries was easier than relying on the audio signal alone; 4) when the scan showed internal carotid occlusion, morphological evaluation of the external and common carotid waveforms was helpful in verifying the scan result; and 5) artifactual noise on the Doppler waveform could be recognized. In the second study, frequency analysis recordings were evaluated semiquantitatively by measuring peak frequency and the fractional width of the Doppler frequency spectrum at peak systole Our preliminary results show that this approach is of diagnostic value in that it has the potential to detect minor stenoses.