RF signals provide additional information on embolic events recorded during TCD monitoring

Introduction of an embolus detection system based on analysis of the transcranial Doppler audio-signal

“…The ZCI is not the only algorithm used for emboli detection based on the raw Doppler shift. Other examples include the temporal and spatial resolution method [16,17], wavelet transform [18,19], and analysis of the TCD signal by nonlinear dynamics [20]. Nonlinear analysis was initially implemented in the system to detect periodicity of MES but the ZCI proved to be more robust in MES signals of short duration.…”

Coded Excitation in TCD Ultrasound Systems to Improve Axial Resolution

“…This is the principle behind current multigate systems used to automatically discriminate between emboli and artefacts, i.e., that a change in depth with time will be apparent from an embolic signal but no such change is present with a signal from an artefact. It may be that, using the system described in this paper, i.e., extracting a number of small, nonoverlapping gates from the pulse-compressed signal, multigate systems could be made more reliable; it would reduce the likelihood of an embolus appearing in two gates simultaneously (Cowe et al 2005), it would allow a shorter distance to be monitored with more gates (i.e., increasing the possibility of multiple gates insonating the Where used, the window was a Dolph-Chebyshev window with 60-dB sidelobe magnitude.…”

“…Research in our centre has focused on developing new signal processing techniques to discriminate more reliably between the two. In particular, we processed the raw radiofrequency (RF) signal instead of the conventional subject of processing, the demodulated Doppler signal (Cowe et al 2005). This technique allowed us to track the motion of an embolus, but it was seriously limited by the narrow bandwidth of the transmitted pulse which led to very poor axial resolution.…”

Transcranial Doppler Embolus Detection: A Primer

“…Currently, a two second recording of the RF signal is computationally expensive to store and analyse in real time, so RF data analysis is usually reserved for research studies. 32,33 Conclusions In understanding embolic stroke, the detection and characterization of emboli is an important and rapidly developing field of research. Although the extension of embolus detection techniques to routine clinical use remains in its infancy, I hope that this article has demonstrated a wide range of interesting problems, and promising applications in the detection and characterization of cerebral emboli using transcranial Doppler ultrasound.…”