Quantification of ultrasound emboli signals in patients with cardiac and carotid disease.

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Abstract
The use of Doppler ultrasound to detect arterial emboli has major implications for the classification and treatment of stroke. Experimental studies indicate that embolic materials produce different ultrasound signals, depending on their acoustic properties. To examine the possibility of characterizing emboli of different sources in the clinical setting, we compared the emboli signals of patients with cardiac embolic sources with those of patients with signals of carotid embolic sources. Transcranial Doppler monitoring (30 minutes per patient) of the middle cerebral arteries was performed in 80 patients with prosthetic cardiac valves and 20 patients with internal carotid artery stenosis. The signal power of emboli was calculated in relation to the background Doppler signal. In patients who were embolizing from prosthetic heart valves, the frequency of embolus signals was greater than in patients with carotid stenosis who were embolizing (mean +/- SEM: 58.2 +/- 11 versus 8.2 +/- 3 signals per hour; P < .0001, two-sample t test), and total signal power and duration also were higher (power, 2231 +/- 63 versus 455 +/- 109 power units; duration, 55.9 +/- 0.8 versus 29.9 +/- 1.4 milliseconds; both P < .001). The majority of emboli signals were seen during cardiac systole, especially in patients with carotid stenosis (89% in the first half of the cardiac cycle versus 72% in prosthetic valve patients). In 19 patients with prosthetic valves, embolus signals were also recorded from the anterior cerebral artery; the signal count was not significantly different from the middle cerebral artery (43.2 +/- 12.5 versus 64.3 +/- 16 per hour), but anterior cerebral artery signals were of higher power (3306 +/- 148 versus 2441 +/- 109 power units, P < .001). There is promise of being able to distinguish emboli on the basis of power measurements. Emboli of different sources (eg, carotid and cardiac) appear to have different ultrasonic characteristics, which are likely to be based on composition and size.