On methods for preprocessing direction Doppler signals to allow display of directional blood-velocity waveforms by spectrum analysers

Simulation of the generation and processing of Doppler ultrasound fetal heart signals to obtain directional motion information

In fetal heart monitoring using Doppler ultrasound signals the cardiac information is commonly extracted from non-directional signals. As a consequence often some of the cardiac events cannot be observed clearly which may lead to the incorrect detection of the valve and wall motions. Here, directional signals were simulated to investigate their enhancement of cardiac events, and hence provide clearer information regarding the cardiac activities. First, fetal Doppler ultrasound signals were simulated with signals encoding forward and reverse motion then obtained using a pilot frequency. The simulation results demonstrate that the model has the ability to produce realistic Doppler ultrasound signals and a pilot frequency can be used in the mixing process to produce directional signals that allow the simulated cardiac events to be distinguished clearly and correctly.

Pulsed Doppler ultrasound system for the measurement of velocity distributions and flow disturbances in arterial prostheses

For the investigation of flow through prosthetic arteries a pulsed Doppler ultrasound system has been characterized. Preliminary in vitro experiments using this system are described; they verify its suitability for making velocity profile and flow disturbance measurements. The output from a frequency tracker is compared with spectral analysis of Doppler signals for both laminar and turbulent flow regimes and the root mean square fluctuations on the tracker output signal are used to identify transition from laminar to turbulent flow. In addition, the turbulent intensity of poststenotic flow is quantified at several axial locations and for different rates of flow. Finally, we present velocity profile measurements which were obtained using a deconvolution technique to account for the finite size of the sample volume.

Doppler echocardiography: theory, instrumentation, technique, and application

A Doppler examination is a valuable adjunct to a complete echocardiographic examination. It has the capability of measuring normal and abnormal velocities of blood flow noninvasively. For the first time, this procedure allows noninvasive quantitation of stenotic gradients, intracardiac pressures, and blood flow as well as semiquantitative assessment of regurgitant lesions. With this procedure, the operator must progress through a learning curve in order to gain a complete understanding of the examination techniques, the limitations of the instruments, and the Doppler physics principles before applications can be made to clinical practice. Evaluation of other aspects of Doppler echocardiography, such as color-flow mapping and assessment of diastolic events, portends great promise for the role of this procedure in the future.

The quantitation of arterial elasticity from Doppler flow measurements

The pattern of phasic pressure and flow in an artery is related to the components of the impedance of that artery and hence to its compliance. Phasic patterns of velocity in peripheral arteries have been recorded by using continuous wave ultrasound Doppler flowmeters coupled to high-speed spectrum analysers; this has enabled display of the stored spectral ensembles as 'sonograms'. Simultaneous recordings at proximal and distal sites in each limb of a variety of subjects were made under standard resting conditions; characteristic patterns of change in the sonogram are recognized where gross abnormalities of arterial anatomy are present. A technique is under development whereby the mean values of velocity for each 7.4 ms time slice are derived, smoothed, and the pulse described by standard Fourier transform analysis. The change of the waveform occurring during passage through the relevant arterial segment is then described by comparing the amplitude/frequency and time-delay/frequency plots at proximal and distal sites. Although results are at present preliminary, changes relating to age and known vascular abnormality are becoming apparent. Further development is in progress to determine the significance of these findings.

Spectral analysis of Doppler ultrasonic flow signals by a personal computer

This paper describes a method of performing spectral analysis on Doppler acoustical signals from peripheral blood vessels with the use of an Apple II plus personal computer. Digitization is accomplished with a commercially available analog-to-digital converter. The data are transformed with a fast Fourier technique, and the resultant information is plotted by an inexpensive X-Y plotter and/or on a television receiver.

Clinical diagnosis by transcutaneous Doppler ultrasound

Transcutaneous Doppler ultrasound represents a convenient, reliable technique for the non-invasive diagnosis and assessment of a rapidly increasing number of diverse circulatory disorders.