Fetal umbilical artery flow velocity waveforms and placental resistance : Clinical significance

During the past 25 years, many attempts have been made to establish effective ultrasound contrast agents for both cardiac and noncardiac applications. The ideal ultrasound contrast agent would be: (a) nontoxic; (b) injectable intravenously; (c) capable of passing through the pulmonary, cardiac and capillary circulations; and (d) stable for recirculation. A variety of potential ultrasound contrast agents have been or are now under development. Present and future ultrasound contrast agents should provide for increased diagnostic capabilities in a variety of normal and abnormal vessels and organs throughout the body. These agents will enhance tumor vascularity, delineate areas of ischemia, as well as improve visualization of vascular stenosis. Future developments with modification of ultrasound equipment should increase the capabilities of these agents to improve imaging as well as Doppler sensitivity.

Ultrasound contrast agents: A review

• A prospective study of carotid endarterectomy specimens showed an acute or recent intraplaque hemorrhage in 49 of 53 plaques (92.5%) from symptomatic patients, compared with seven of 26 plaques (27%) from nonsymptomatic patients. Luminal stenosis of greater than 50% was noted in 46 of 53 symptomatic patients (75%), 43 of whose plaques had evidence of multiple hemorrhages. Intimal disruption (ulceration) occurred over protruding mounds of intraplaque hemorrhage and was associated with retinal cholesterol emboli and prolonged neurologic deficits. Mural recesses with the angiographic appearance of ulceration seldom showed intimal breakdown. Eighteen patients continued to have symptoms while receiving aspirin, 13 of whom had had multiple intraplaque hemorrhages. Angioneogenesis occurred within the plaques in response to hemorrhage, creating vascular lesions vulnerable to mechanical stress and capable of producing further hemorrhage or intimal disruption. ( Arch Surg 1982;117:1479-1488)

Carotid plaque hemorrhage. Its role in production of cerebral ischemia.

Thirty patients with peripheral arterial disease were evaluated using an ultrasonic duplex scanner. A total of 338 arterial segments from the level of the iliac to the popliteal artery were studied and compared with the results of arteriography read independently by two radiologists who were unaware of the results with the scanner. The results demonstrate that this method is not only suitable for clinical use but is as good as arteriography in defining both the location and extent of the arterial involvement.

Noninvasive mapping of lower limb arterial lesions.

We compared ultrasonic duplex scanning and angiography for the localization and classification of arterial stenoses and occlusions in 32 patients. The criteria for the detection of a greater than 50% diameter reducing stenosis was an increase in peak systolic velocity of greater than 100%, loss of reverse flow, and spectral broadening. Duplex studies and angiograms were evaluated in a blinded fashion. The agreement between duplex scanning and angiography for the 383 arterial segments studied was not significantly different than the previously reported agreement between two different radiologists reading the same angiograms (kappa of 0.55 vs 0.63). For detecting stenoses that were greater than 50% diameter reducing by angiography, duplex scanning had a sensitivity of 82%, a specificity of 92%, a positive predictive value of 80%, and a negative predictive value of 93%. These results are as good as previously reported comparisons between two different radiologists' readings of the same angiograms.

Duplex scanning for diagnosis of aortoiliac and femoropopliteal disease: a prospective study.

Tumour detection by ultrasonic Doppler blood-flow signals

A method is presented for describing the shape of the blood-velocity/time waveforms recorded at the posterior tibial artery, using Doppler-shift flowmeters. A third order mathematical model is developed which describes these waveforms in patients with occlusive arterial disease and in normal volunteers. In normals, the model has two complex and one real pole, and in occluded arteries with collateral circulation all the poles are real. The complex poles are shown to be related to the elastic modulus of the artery and also to the lumen size. The third pole is shown to be related to the degree of vasoconstriction of the peripheral circulation.

Physiological interpretation of doppler-shift waveforms—I theoretical considerations

The blood-velocity/time waveforms over the cardiac cycle obtained from the common femoral arteries of 44 limbs, are defined using Fourier transform and curve-fitting techniques. This results in a third order Laplace transform whose coefficients can be related to distal impedance, proximal lumen diameter and stiffness. The sensitivity of this technique has been investigated in the study of aorto-iliac disease, and compared with single plane arteriography and Pulsatility Index. The results show that the Laplace transform method is a sensitive technique for determining the presence of minor stenoses in the aorto-iliac segment, for determining changes in elastic modulus of the proximal vessels, and for studying changes in distal impedance. Pulsatility Index, is sensitive to the presence of proximal disease but it does not seem able to differentiate between stenoses of less than or greater than 50%. PI is sensitive also to changes in distal impedance, but insensitive to changes in arterial elasticity.

Physiological interpretation of Doppler-shift waveforms-III. Clinical results

The blood-velocity/time waveform over the cardiac cycle from the common femoral artery is investigated using Fourier transform and curve-fitting techniques. This results in a third order Laplace transform whose coefficients can be related to distal impedance, proximal lumen diameter and elastic modulus. The validity of the method is investigated by determining the coefficients of the Laplace transform, derived from the common femoral waveform, and from these values, reconstructing the waveform and comparing with the original. The Fourier transform, curve fitting, and reconstruction procedures are shown for each waveform so that all stages of the method can be critically assessed.

Physiological interpretation of Doppler-shift waveforms-II. Validation of the laplace transform method for characterisation of the common femoral blood-velocity/time waveform

Recent developments in ultrasound techniques have made it possible to investigate patients with arterial disease non-invasively by using Doppler blood velocity signal analysis. Since January 1979, 189 patients with pre-stroke syndromes have been investigated by using pulsed Doppler and real-time B-mode ultrasound imaging and waveform analysis. The results were that both imaging systems were highly (more than 92%) sensitive and specific when compared with conventional carotid arteriography. The ultrasound systems detected turbulence and could also be used to measure the distensibility of the arterial wall. The results show that varying grades of carotid stenosis can be demonstrated by two ultrasonic imaging systems, and that lateral scans are particularly helpful.

J.P. Woodcock

Papers

Tumour detection by ultrasonic Doppler blood-flow signals

Physiological interpretation of doppler-shift waveforms—I theoretical considerations

Physiological interpretation of Doppler-shift waveforms-III. Clinical results

Physiological interpretation of Doppler-shift waveforms-II. Validation of the laplace transform method for characterisation of the common femoral blood-velocity/time waveform

Vessel wall and blood flow dynamics in arterial disease