Estimation of blood-flow quality by statistical analysis or an ultrasonic Doppler signal: application to the study of perturbations caused by a vascular stenosis.

Abstract

The noninvasive detection of pathological stenoses by Doppler ultrasound velocimetry is based on the appearance of modifications in velocity waveform or of a local increase in velocity. Nevertheless, these methods suffer from a lack of sensitivity. An extension of ultrasonic velocimetry including a statistical treatment of the Doppler signals affords a quantitative approach to the flow quality and seems to be able to improve the diagnosis of vascular obliterans. Accordingly a perturbation index can be computed on a microprocessor as the relative standard deviation of the zero-crossings histogram of the Doppler signal. A theoretical and experimental approach has been attempted to validate this method. Moreover, this index has been tested in vitro on calibrated flows. The in vivo experiments, performed on the abdominal aorta of the dog with artificial stenoses (0 to 50% in diameter) show a significant increase in the index value downstream from the stenosis. The relative increase of the index is greater than that of velocities for the same degree of obstruction. At the moment, it is possible to detect stenoses of 20% and above. It should be noted that changes in the perturbation index can be observed on a large part of the arterial segment, in relation with the severity of teh stenosis. Taking into account the increase in the index value and the length of the disturbed zone downstream of the stenosis, an estimation of the severity itself can be attempted. Clinical applications are in progress pointing out the diagnostic and prognostic abilities of the index method. The index perturbation method adds to velocity measurement the possibility of blood flow stability estimation. It appears useful for the localisation of stenoses, offers the possibility of quantifying their severity and could help the prognosis of their development.