Embolus Detection and Differentiation Using Multifrequency Transcranial Doppler
To the Editor:
In our articles in Stroke in August 2002,1,2 we presented our findings using the first multifrequency transcranial Doppler (TCD) to detect and differentiate cerebral emboli. Since this time, we have had considerable experience using multifrequency TCD in medical patients during invasive cardiovascular investigations and perioperatively during heart surgery. We found that results are most reliable for embolus differentiation when the Doppler signal enhancement, ie embolus-blood-ratio (EBR), is >28 dB/ms (ie, a Doppler power increase >7 dB, which lasts >4 ms) simultaneously in 2.0-MHz and 2.5-MHz channels. The lower dEBR limit for the classification of solid microemboli2 should also not be horizontal but have a slight slope of y=−0.1x−0.12 dB, where y=dEBR and x=2.0 MHz EBR.
Embolus detection and differentiation is also very difficult when there are bursts of gaseous or solid emboli, when several emboli may enter the sample volume at the same time. Ultrasound contrast bubbles may make detection and differentiation difficult because of changes in the background signal or resonance effects of single contrast bubbles.
Brucher R, Russell D. Automatic online embolus detection and artifact rejection with the first multifrequency transcranial Doppler. Stroke. 2002; 33: 1969–1974.
Russell D, Brucher R. Online automatic discrimination between solid and gaseous cerebral microemboli with the first multifrequency transcranial Doppler. Stroke. 2002; 33: 1975–1980.