Abstract
An integrated system for acquisition and processing of intracranial and extracranial Doppler signals and automatic embolic signal detection has been developed. The hardware basis of the system is a purpose-built acquisition/processing board that includes a multigate Doppler unit controlled through a computer. The signal-processing engine of the system contains a fast Fourier transform (FFT)-based, spectral-analysis unit and an embolic signal-detection unit using expert system reasoning theory. The system is designed so that up to four receive gates from a single transducer can be used to provide useful reasoning information to the embolic signal-detection unit. Alternatively, two transducers can be used simultaneously, either for bilateral transcranial Doppler (TCD) investigations or for simultaneous intra- and extracranial investigation of different arteries. The structure of the software will allow the future implementation of embolus detection algorithms that use the information from all four channels when a single transducer is used, or of independent embolus detection in two sets of two channels when two transducers are used. The user-friendly system has been tested in-vitro, and it has demonstrated a 93.6% sensitivity for micro-embolic signal (MES) identification. Preliminary in-vivo results also are encouraging.
Highlights
Doppler ultrasound is a valuable technique for the detection of circulating emboli, whether they are solid or gaseous in nature [1]–[4]
The basis of the detection technique is that, if the acoustic properties of the embolus are sufficiently different from those of the surrounding blood, when it enters the Doppler sample volume there will be a transient increase in the power of the Doppler signal at a frequency corresponding to the velocity of the embolus through the sample volume [5]
This is not, the only mechanism that can cause a transient rise in Doppler signal power; careful analysis of the signal is necessary to distinguish between signals arising from embolic events and those arising from other mechanisms such as probe movement or electrical interference
Summary
Doppler ultrasound is a valuable technique for the detection of circulating emboli, whether they are solid or gaseous in nature [1]–[4]. The basis of the detection technique is that, if the acoustic properties of the embolus are sufficiently different from those of the surrounding blood, when it enters the Doppler sample volume there will be a transient increase in the power of the Doppler signal at a frequency corresponding to the velocity of the embolus through the sample volume [5]. There is considerable evidence that, for many embolic signals, observer reproducibility is poor Because of these difficulties, various systems have been developed in order to automate the detection task [6]–[18]. When an embolic event is detected, the data archival structure of the system automatically stores a pair of one-second long raw audio Doppler signals (forward and reverse flow directions) for each gate.
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