A Signal Processing Method for Artefact Rejection in Transcranial Doppler Signals used for Micro-embolus detection

Atefacts are classified as High Intensity Transient Signals appearing in the Doppler signal, during TCD recording. Artefacts could be caused by probe tapping or displacement, movement of the patient as well as various external factors. In Holter TCD, the number of artefacts are further increased due to the servo-controlled probe positioning and long recording time. Current artefact rejection methods must be adapted to the new holter devices. Therefore, in this paper we present a complete procedure for eliminating two types of artefacts that occur during Holter TCD. The latter two types are bidirectional areftact, occurring in the energy of both positive and negative frequencies, and unidirectional artefacts occuring only in the energy of the negative frequencies. From a dataset of 25 signals, 218 artefact signatures were identified; 95% of which are bidirectional and 5% unidirectional. As a final result, 98% of the artefacts where successfully removed.