Critical evaluation of continuous-wave Doppler probes for carotid studies

A new pulsatile flow visualization method using a photochromic dye with application to Doppler ultrasound

A nonintrusive method for the visualization of pulsatile flow velocity profiles is described. The method is based on the use of a photochromic dye that is added to the fluid being studied and a nitrogen laser which excites the dye producing a marker "line" whose movement can be photographed. A microcomputer is used as a system controller, to coordinate the system timing and to manage the data transfer. The method used for analysis of the photographs to determine the velocity profiles is described. Examples are presented of instantaneous velocity profiles obtained from velocity waveforms that are similar to those of the femoral artery. In addition, application of the system for studying the relationship between Doppler ultrasound spectral recordings and flow velocity profiles is discussed.

Ultrasonic Doppler probe assessment by scanned hydrophone

A method is described for using a scanned hydrophone to assess the transmit-receive response of ultrasonic Doppler transducers. The method was used on batches of six probes at each of the nominal resonant frequencies of 2, 4 and 8 MHz. The method has the advantage of showing unwanted field characteristics and identifying the element that may be causing them. The resonant frequencies and the overall sensitivities of the elements and probes are determined, the latter varying by as much as a factor of two.

Limitations in the accuracy of peak frequency measurements in the diagnosis of carotid disease

Peak Doppler frequency is an index of the severity of carotid stenosis. Variability in this measurement is examined through in vitro and clinical studies. In vitro studies, using a carotid flow model, show that observers locate a stenosis and interpret the peak frequency differently, and each observer uses a different probe-vessel angle. Clinical studies support these findings. Comparison of 304 carotid Doppler studies with arteriograms demonstrates 90% overall clinical accuracy. Each observer has a consistent range of peak frequency measurements, yet the description of a discrete percent stenosis is limited by observer variability.

Spectral analysis of Doppler flow velocity signals: assessment of objectives, methods, and interpretation

The objective of this paper is to review the theoretical basis and clinical application of electrical impedance plethysmography in the noninvasive evaluation of peripheral arterial and venous disease. Theoretical, experimental and clinical studies have not demonstrated a direct relationship between electrical impedance changes and limb volume changes. Potential sources of error have also been identified. This has led to the development of clinical tests based on impedance plethysmography for the detection of peripheral arterial disease, venous insufficiency and venous outflow obstruction. Impedance plethysmography, using the method of venous occlusion, is presently the most commonly employed noninvasive method for the detection of deep venous thrombosis.

An in vitro model and its application for the study of carotid Doppler spectral broadening

A new in vitro model has been developed for studying the changes in the ultrasound Doppler spectrum that occur in the region of a stenosis. Pulsatile flow in rigid acrylic tubes was produced by means of a modified hemodialysis pump. The Doppler spectral waveforms were measured using a continuous wave Doppler system, a probe of a known field pattern, a real-time high resolution frequency analyzer, and a video display and recording system. The flow velocity waveforms were found to be nearly identical to those seen in the human carotid. Measurements were made to determine the critical stenosis and the results are similar to those reported from in vivo studies. In a preliminary study, the extent of spectral broadening was found to be dependent on the recording site in relation to the stenosis, the severity of the stenosis, and the flow rate. Using qualitative methods it was not possible to determine either the influence of the shape of the stenosis or the phase of the cardiac cycle on spectral broadening.