Screening for carotid junction disease by spectral analysis of Doppler signals

Frequency-Domain Characteristics Response to Passive Exercise in Patients With Coronary Artery Disease

Purpose: The enhanced external counterpulsation (EECP), a kind of passive exercise, is a novel non-invasive therapy used to improve peripheral perfusion in patients with coronary artery disease (CAD). However, whether frequency-domain characteristics of peripheral hemodynamics may benefit from passive exercise needs to be verified.

Methods: We recruited 21 patients with CAD and 21 healthy controls in this study. Ultrasonic blood flow velocity spectrum in left carotid (LC) and right carotid (RC) common arteries, and right brachial (RB) and right femoral (RF) arteries was monitored using an ultrasonic Doppler. Frequency-domain characteristics before, during, and after passive exercise were extracted from ultrasonic spectrum images. The first and second peak amplitudes/frequencies (y1, y2, x1, x2) and power spectral energy ratio (PSER) in the 0–2.05 Hz/0.87 Hz (p5, p6) were calculated by fast Fourier transform and power spectrum density analysis.

Results: For the amplitude and frequency characteristics of the spectrum, y1 in the LC of patients with CAD was significantly decreased during exercise (p = 0.036), whereas, y2 was significantly decreased immediately after passive exercise (p = 0.038). Besides those, y1 only in the RC and RB of controls was significantly decreased during exercise. Immediately after exercise, y2 in the LC of control was significantly lower than at the baseline (p = 0.014). For the energy ratio characteristics of the spectrum, there was an opposite response in the two groups that p6 was significantly reduced and elevated in the LC of controls and in the RB of patients with CAD during exercise (both p < 0.05).

Conclusions: Passive exercise reduces amplitude and frequency characteristics of carotid arteries, while there was an opposite response of energy ratio characteristics in the LC and RB arteries to passive exercise between CAD patients and controls. Additionally, energy ratio characteristics of spectrum in the brachial artery were markedly elevated in CAD patients during passive exercise. Moreover, passive exercise only reduces amplitude characteristics of LC artery in the control group.

Detection of Disease at the Carotid Bifurcation Using Ultrasound – Including an Imaging System1

A two-stage approach is described for the detection of occlusive arterial disease at the carotid bifurcation using continuous wave Doppler-shift ultrasound with spectral analysis of backscattered signals from erythrocytes. The first stage involves analysis of Doppler-shift signals from the supraorbital and common carotid arteries. Abnormal signals from these arteries are frequently caused by the presence of atheroma at the carotid bifurcation and are used to indicate the necessity for imaging the bifurcation. This latter technique produces a physiological image of the arteries, as it depends on detecting erythrocyte velocities beneath a transducer which is guided over the surface of the neck. The investigation has advantages over arteriography in that it is noninvasive, has no attendant risk and may be repeated as often as required.

In order to evaluate the accuracy of these methods the results have been compared with x-ray findings in patients undergoing carotid arteriography. In 20 comparisons there were no false positives and one false negative in which the arteriogram showed a small lesion. These results indicate that the two noninvasive methods may be used in sequence to demonstrate operable disease around the carotid junction.

Fluid Resuscitation in Septic Patients Improves Systolic but not Diastolic Middle Cerebral Artery Flow Velocity

To investigate the effects of fluid resuscitation on cerebral hemodynamics in sepsis, the following set of transcranial Doppler (TCD) parameters was used: maximal change in flow velocity (FV) during stroke onset (acc), maximal FV during first (sys1) or second (sys2) phase of systole and mean diastolic FV (dias@560). We aim to evaluate changes in cerebral hemodynamics that result from (i) sepsis and (ii) adequate fluid resuscitation in critically ill septic patients. In the majority of 16 septic patients sys2 was initially absent but reappeared during the period of fluid resuscitation; whereas sys2 absence was never seen in healthy controls. Second, adequate fluid resuscitation resulted in a significant increase of the systolic FV components (acc, sys1, sys2 and systolic blood pressure); whereas the diastolic components (dias@560 and diastolic blood pressure) remained unchanged. Sys2 absence and reappearance in sepsis suggests that TCD could become a non-invasive alternative for hemodynamic monitoring.

Wireless blood velocity spectra measurement system for healthcare evaluation: reference data

The aim of the present study was to determine the blood velocity and its indices in common carotid artery (CCA) as reference value for clinical and healthcare application using the constructed portable wireless Doppler blood flow velocimeter system. Evaluation of CCA blood velocity waveforms was performed in 202 healthy volunteers in the age range of 20 to 69 years. Multivariate analysis was used to determine the relationship between the fixed factor and the outcome hemodynamic variables after adjustment for the related covariates. Results show a general age-related decrease in flow velocities and change in the velocity waveform. There is also a gender difference in velocity indices, except for peak systolic blood velocity. Gender difference is also found in systolic and pulse blood pressures. The findings suggest that waveform indices provide a more reliable evaluation of effects of aging and gender on CCA flow. In conclusion, normal CCA blood velocity parameters are determined in a total of 202 healthy volunteers between the third and seventh age decade after adjustment for gender and exercise effects. Findings may contribute to improved means of healthcare monitoring and clinical evaluation.

Effects of aging and exercise training on the common carotid blood velocities in healthy men

An age-related alteration in the cardiovascular response to exercise training are evident. The purpose of the study was to investigate the effects of exercise and age on blood velocities in common carotid artery in 82 healthy men between the age ranges of 21 to 67 years old. Blood velocities are characterized to five components of velocity waveforms as peak systolic (S1), second systolic (S2), incisura between systole and diastole (I), peak diastolic (D) and end-diastolic velocity wave (d). Decrease of blood velocities in peak systolic (r= -0.711, P<0.0001) and in peak diastolic velocities (r= -0.521, P<0.0001) with aging are improved and partially restore in particularly older men. The velocity ratio of S2/S2-1 as a reflection index increase with age (r= 0.797, P<0.0001), however is smaller in exercise-trained older compared with sedentary peers. The ratio of 1-I/D as a vascular elastic recoil index decrease with aging (r= -0.640, P<.0001), but is relatively higher in exercise-trained men. Exercise training improves the age-related deterioration in blood velocities and its indices in healthy men. In the further investigations, the assessment of aerobic fitness and vascular aging has potential by using the criteria of peak systolic and peak diastolic, and its indices.

Nonsubtractive spiral phase contrast velocity imaging

Phase contrast velocity imaging is a standard method for accurate in vivo flow measurement. One drawback, however, is that it lengthens the scan time (or reduces the achievable temporal resolution) because one has to acquire two or more images with different flow sensitivities and subtract their phases to produce the final velocity image. Without this step, non-flow-related phase variations will give rise to an erroneous, spatially varying background velocity. In this paper, we introduce a novel phase contrast velocity imaging technique that requires the acquisition of only a single image. The idea is to estimate the background phase variation from the flow-encoded image itself and then have it removed, leaving only the flow-related phase to generate a corrected flow image. This technique is sensitive to flow in one direction and requires 50% less scan time than conventional phase contrast velocity imaging. Phantom and in vivo results were obtained and compared with those of the conventional method, demonstrating the new method's effectiveness in measuring flow in various vessels of the body. Magn Reson Med 42:704-713, 1999.

Measurement of arterial blood flow by Doppler ultrasound

A review is given of quantitative techniques and clinical applications of arterial Doppler ultrasound. The currently available Doppler equipment of stand-alone continuous wave and pulsed wave units, duplex systems and colour flow systems is briefly described. Doppler ultrasound can be divided into procedures concerned with waveform analysis, volume flow measurement and more recently colour flow imaging. Arterial Doppler waveform analysis is considered for a number of areas including carotid, lower limb, renal and renal transplant, obstetrics, adult cerebral, neonatal cerebral, and tumour studies. Using a duplex scanner volume flow in arteries can be measured from estimates of vessel cross sectional area, mean Doppler frequency and beam-vessel angle. The errors associated with each of these measurements is discussed, and reports of experimentally determined in vivo accuracy of volume flow measurements made using this technique are considered. Other volume flow measurement techniques including the promising attenuation compensation method are also explored.

A simple quantitative screening test for the detection of extracranial carotid artery disease

A simple screening test, using continuous wave Doppler ultrasound, for the detection of all grades of extracranial carotid artery disease has been described. The test is composed of two parts: (1) the determination of the direction of flow at the orbit and (2) on-line principal component factor analysis of the maximum frequency envelope of the Doppler shifted signal obtained from the common carotid artery. A total of 154 vessel segments have been investigated; 69 normal, 41 with a stenosis of 10-49%, 32 with a stenosis of 50-99% and 12 occlusions. Of these, 70 vessel segments were assessed prospectively and they formed the data base from which the principal components and the classification factor were calculated. The remaining 84 vessel segments were analysed prospectively on-line. The combined results gave an overall sensitivity to the detection of disease of 90% and a specificity of 77%. It has been shown that although classification of Doppler waveforms by principal component analysis is a fairly sophisticated technique it is possible, by careful design of the algorithms, to design a near real-time on-line analysis system for derived waveforms such as the maximum frequency envelope.

Detection of stenoses in the internal carotid artery by waveform analysis of continuous wave ultrasound signals (I)

In this prospective study, the reliability of the morphologic analysis of the continuous Doppler signal was evaluated. Three parameters were considered: the maximum systolic frequency (max A), a resistance parameter (RP) and the degree of spectral broadening (SB). The apparatus used allowed us to construct a color arterial image. Seventy-four subjects were included in this study: 17 volunteers investigated by ultrasound only, and 57 patients investigated by ultrasound and arteriography. Anatomic correlation was obtained in 31 operated cases. The threshold values, as determined in the volunteers, were as follows: 3.5 kHz for max A, 0.86 for RP and 58% for SB. Sensitivity was 94% when max A, SB and cartography were combined to detect tight stenoses. The sensitivity for each of the parameters alone was much weaker (61% for max A and 33% for RP). For all carotid lesions, the sensitivity of detection when all parameters were combined was 68%. Specificity was 77%. The study of the carotid bifurcation by the continuous Doppler effect allowed us to identify tight stenosis with reliability. On the other hand, it was impossible to distinguish between normal arteries and moderate stenosis, or between tight stenosis and complete occlusion.

Detection of stenoses in the internal carotid artery by waveform analysis of continuous wave ultrasound signals (II)

Analysis of the morphological aspects of continuous-wave Doppler examination is a reliable means of detecting carotid stenosis involving 50% or more of the diameter of the arterial lumen. This study was undertaken to evaluate the indexes likely to increase the diagnostic accuracy of this noninvasive investigation method. The indexes studied were the variations of the maximal frequency and the systolic peak frequencies, measured proximal to and at the level of stenosis, and the ratio of the systolic peak frequency measured in the internal carotid artery and in the common carotid artery. After obtaining data on an experimental model, the study was conducted in healthy volunteers (n = 24) and in patients with carotid atherosclerotic disease (n = 23). The experimental study confirmed that stenosis greater than 50% leads to a reduction of blood flow and that there is a mathematical relationship between the frequency measured proximal to and at the level of the stenosis and the degree of stenosis. Clinical data showed that there was a significant decrease in the frequency of the systolic peak in elderly "healthy" subjects as compared with younger subjects. However there was no difference between patients with and without stenosis. The index was 0.8 in young subjects, 1.3 in healthy elderly subjects, and greater than 1.3 in subjects who had a stenosis. There was no statistically significant difference between these two last groups. At the threshold value of 2.3, the sensitivity of the FI index was 22% and the specificity was 94% in the detection of carotid artery stenosis. In the assessment of the tight stenosis, sensitivity was 44%.

Computer based pattern recognition of carotid artery Doppler signals for disease classification: prospective validation

A computer based pattern recognition method has been developed to classify the percent diameter reduction in nonoccluded internal carotid arteries. Using a combined B-mode/pulsed Doppler unit, the system utilizes spectral waveforms obtained from the low common and proximal internal carotid artery locations. The ECG-R wave is used as a time reference to synchronize the averaging of Doppler spectra from 20 heart cycles. An averaged waveform is generated and represents the spectral data from which features are extracted for analysis. A stepwise selection algorithm identifies a feature subset for partitioning the entire range of disease into two states, less than and greater than a decision point. Three such partitions are made, leading to the following categories: Normal, 1-20, 21-50 and 51-99% dia. reduction. A classifier was trained, tested prospectively against unknown data and the results compared to angiography. Of the 170 vessels tested, 141 (82%) were classified in the same category by angiography and the computer system. Agreement for each category was 93% (27/29) for the normals, 81.5% (44/54) for the 1-20% lesions, 78% (29/37) for the 21-50% lesions and 82% (41/50) for the 51-99% lesions. The computer method and angiography differed by more than one category in only one of the 170 tests. The level of agreement corrected for chance (Kappa +/- SE(K] was 0.769 +/- 0.039. Future efforts will be directed toward dividing classification of disease further (especially in the 51-99% category), developing a dedicated microprocessor for on-line analysis of the signals and using the system for prospective epidemiological studies of various populations.

Doppler power frequency spectrum analysis in the diagnosis of carotid artery disease

Power Frequency Spectral Analysis (PFSA) which evaluates the power of the frequency components at a selected interval, was applied in this preliminary study using a 5MHz Doppler continuous wave flow velocity meter and a modified Edwards Spectraview 500 analyzer. PFSA was used to study the common, internal and external carotid arteries of ten young adult control subjects and 31 patients with angiographically documented carotid bifurcation lesions. Two useful indices are described: (1) the frequency band width at 50% of maximum power (f50%) and (2) the highest frequency recorded (fmax). An f50% wider than 1900 Hz (corresponding to spectrum broadening) identified stenoses as low as a 15% diameter reduction. An fmax higher than 6500 Hz practically always indicated a 50% or greater diameter reduction. Eighty two percent of stenoses with 11-25% diameter reduction were detected, as were 95% of stenoses from 36-50%. All stenoses from 51-99% were identified.

25 + 1 channel pulsed ultrasound Doppler velocity meter for quantitative flow measurements and turbulence analysis

A multichannel pulsed ultrasound Doppler instrument designed to measure velocity and volume flow rate quantitatively has been applied for turbulence detection. A 7-MHz transmitting frequency and a phase locked loop technique for the frequency to velocity conversion have been used to obtain high temporal resolution in the single channel mode. To provide for reliable positioning of the single gate within the arterial lumen the device could first be operated in the multichannel mode measuring the velocity profiles with zero crossing detection methods. Measurements of the velocity in the center of the lumen of the common and internal carotid arteries have been recorded on a beat to beat basis. An ensemble average of 16 consecutive pulses was determined. Thereafter, the root mean square of the differences between ensemble average and individual velocity pulses was computed, and a disturbance index was defined by dividing the disturbance velocity by the mean velocity. First clinical results show that the method presented is a valuable complement to the analysis of flow pulse patterns in the transcutaneous examination of carotid arteries.

Ultrasound screening for internal carotid disease-II. Sensitivity and specificity of a single site periorbital artery test

Supraorbital artery blood flow was examined non-invasively with continuous wave Doppler-shifted ultrasound and spectral analysis. The results were used to assess the ipsilateral internal carotid artery in 155 patients undergoing carotid angiography. The ultrasound parameters used were the temporal artery occlusion test and A/B ratios of both resting and augmented supraorbital sonagrams. A retrospective study showed this combination to have a sensitivity of 65% for internal carotid disease which did not encroach on the lumen and for all other angiographically demonstrated lesions an average sensitivity of 94% and specificity of 92%. Augmented supraorbital pulses were more sensitive for detection of carotid artery disease than resting supraorbital pulses. Of the 61 lesions in which both resting and augmented supraorbital A/B ratios were obtained, the augmented supraorbital pulse detected 48 (79%) whilst the resting supraorbital pulse detected 29 (48%). Localised carotid bruits were poor indicators of carotid artery disease, having a sensitivity of only 27%.

Doppler ultrasound assessment of the internal carotid artery following carotid endarterectomy

Doppler-shifted ultrasound with spectral analysis was used to assess the internal carotid arteries of 48 patients who had undergone carotid endarterectomy (58 carotid endarterectomies). Three patients died in the immediate post-operative period, therefore 45 patients, who represented 54 endarterectomies, were assessed for up to six years following surgery (mean--thirty-four months). Ultrasound tests demonstrated total occlusion of the internal carotid artery in 7 patients within the first post-operative week. Sonograms from the supraorbital and common carotid arteries exhibit two peaks during cardiac systole (A and B). The post-operative A/B ratios were abnormal in 24 instances and these were associated with symptoms in seven. Of these 24, 7 developed severe disease in the internal carotid artery during the six year follow-up period; five were associated with symptoms. Post-operative A/B ratios were normal in 23 instances, 19 of which remained normal at follow-up. None of these nineteen developed symptoms. Only patients with abnormal post-operative A/B ratios subsequently developed severe occlusive disease in the internal carotid artery during the follow-up assessment. Thirty-eight patients underwent unilateral carotid endarterectomy, eight of whom had severe internal carotid artery disease at the contralateral bifurcation at the time of carotid endarterectomy. A further four patients developed severe occlusive disease in the contralateral internal carotid artery during the follow-up period, one of whom was symptomatic.

The use of common carotid waveform analysis in the diagnosis of carotid occlusive disease

Duplex scanning with spectral analysis of the pulsed Doppler signal are currently used to detect and classify disease at the carotid bifurcation. Although the sensitivity of the test exceeds 90%, the method has a lower specificity which ranges between 8 and 50%. The poor specificity is due to the difficulty in distinguishing flow disturbances normally present at the carotid bifurcation from those produced by minimal amount of disease. In order to improve the ability of the method to predict normalcy, new features measured from the low common carotid waveform are evaluated on 150 sides. The difference of frequency from the systolic peak (a) to the point of first zero slope after peak systole (b) was used to define the ratio (a-b)/a. A ratio greater than 0.5 was associated with 76% of the normal sides and only 7% of the diseased sides. A ratio below 0.5 was associated with 83% of the diseased sides. This ratio, when used alone, can improve the specificity of the method to 76%.

111-Indium platelet imaging, Doppler spectral analysis and angiography compared in patients with transient cerebral ischaemia

We have evaluated carotid gamma imaging using 111Indium-labelled platelets in the diagnosis of carotid artery disease and measured the accumulation of labelled platelets on endarterectomy specimens. Autologous 111In labelled platelets were injected in 25 patients with TIA. Gamma images were then taken daily and independently interpreted by two observers. Carotid endarterectomy was performed in 11 patients allowing measurement of the radioactivity on the operative specimen. These results were compared to the findings on angiography and Doppler spectral analysis. All endarterectomy specimens accumulated platelets with the most active equivalent to platelets from 1.8 ml blood. Atheromatous ulcers were more active than stenoses with mean (+/- SEM) activities of 1.12 +/- 0.37 and 0.38 +/- 0.10 respectively. These radioactivity levels were at the threshold of gamma camera resolution in a theoretical model. Both observers agreed that 22 of the 50 carotid bifurcations showed platelet accumulation on gamma imaging. Of the 12 atheromatous ulcers demonstrated by angiography 11 were visualized, but only five of ten stenoses greater than 80% were detected. As Doppler identified all stenoses only one angiographically diseased carotid was not detected by combining ultrasound with platelet scanning. Atherosclerotic arteries accumulate 111In platelets and the more thrombogenic ulcerated plaques are identified more frequently than stenoses. Long-term follow-up is required to establish the clinical relevance of platelet deposition.

Continuous wave Doppler ultrasound in evaluation of cerebral blood flow in neonates

The cerebral circulation of 25 normal term infants was investigated using continuous wave Doppler ultrasound. Serial blood flow velocity signals were obtained from the common carotid and anterior cerebral arteries during the first week of life. The records were processed using a frequency spectrum analyser to provide cerebral blood velocity waveforms. The pulsatility index (PI), A/B ratio, and rise and fall slope of the waveforms were calculated. The results indicated that cerebrovascular resistance was raised appreciably on day 1 of life compared with later in the first week. In 18 of 25 infants (72%) there was no continuous carotid blood flow in the first hours of life. We suggest that the human cerebral circulation adapts to the process of birth in a similar fashion to that of animal models.

Noninvasive versus invasive evaluation of the extracranial circulation in patients with suspected cerebral vascular disease

This is the second in an ongoing series of evaluations in an attempt to find a combined system of noninvasive cerebral vascular evaluation of the extracranial circulation reliable enough so that decisions can be made, utilizing this system regarding further diagnostic studies and management. The current study evaluates a system of combined doppler arterial scanning of the extracranial circulation with Real Time B-Mode imaging of the territory of the carotid bifurcations and show that such a system, in skilled hands, is capable of very high levels of accuracy both quantitatively and qualitatively regarding the status of the carotid bifurcations as well as giving much indirect information about the cerebral vascular and subclavian circulations. The paper ends with a strong statement supporting the routine utilization of noninvasive screening of patients with suspected cerebral vascular disease. This conclusion is reached after comparing 59 patients representing 118 carotid bifurcations studied; first by physical examination and noninvasive evaluation and subsequently by angiography.

Evaluating carotid artery disease. The concordance between pulsed Doppler/spectrum analysis and angiography

The results of ultrasonic pulsed Doppler duplex scanning with spectral analysis and computer pattern recognition are compared with the results of contrast arteriography in patients screened for extracranial carotid artery disease. The intraangiographer variability (one radiologist reading the same films twice) and the interangiographer variability (two radiologists reading the same film independently) were also studied. To calculate degrees of agreement corrected for chance, the Kappa statistic was computed for all the evaluation methods employed. At the present time, the concordance between spectral analysis and cerebral contrast angiography reaches a Kappa value of 0.682 +/- 0.064. This level of agreement compares favorably with the interangiographer agreement level (K = 0.568 +/- 0.058) and the intraangiographer agreement (K = 0.711 +/- 0.054). The computer pattern recognition program predicted the degree of stenosis by angiography with an agreement of K = 0.721 +/- 0.059. This concordance compares favorably to that observed when the radiologists are compared with themselves and is greater than that reached by two different radiologists. The continuous improvement in precision and accuracy of duplex scanning offers the promise of its usefulness in clinical and epidemiological studies.

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.

Detection of carotid bifurcation disease: comparison of ultrasound tests with angiography

Doppler-shift ultrasound with spectral analysis permits the measurement of the relative heights of systolic peaks (the A/B ratio) in blood velocity sonograms from supra-orbital and common carotid arteries, the temporal artery occlusion test, the common carotid resistance index and transit times of flow-velocity waves in the internal carotid pathway. The results are compared with 201 carotid angiograms and expressed in terms of sensitivity (true positive) and specificity (true negative). Supra-orbital and common carotid A/B ratios, in combination with the temporal artery occlusion test, detected all grades of carotid artery disease with a sensitivity of 72 per cent and a specificity of 93 per cent. The corrected transit time gave a sensitivity of 57 per cent and a specificity of 89 per cent, whilst the Resistance Index gave a sensitivity of 60 per cent and a specificity of 80 per cent. The values of ultrasound parameters associated with severe disease, defined as reductions in lumen diameter of 75 per cent or more, of the internal carotid artery are examined. The temporal artery occlusion test gave a sensitivity of 91 per cent and a specificity of 94 per cent. These results were more accurate than those obtained for the corrected transit time (sensitivity 83 per cent, specificity 92 per cent) and for the Resistance Index (sensitivity 75 per cent and specificity 92 per cent). The results show that of the tests described the supra-orbital and common carotid artery A/B ratios, together with the temporal artery occlusion test, gave the best sensitivity and specificity for detection of both severe and minor carotid bifurcation disease.

Carotid artery occlusion following endarterectomy: evaluation by spectral analysis of Doppler ultrasound signals

The clinical results of carotid endarterectomy are well documented, but there is little objective information on the incidence of postoperative occlusion. We have studied the postoperative patency of the internal and external carotid arteries using continuous wave Doppler ultrasound with spectral analysis (Spectrascribe BOC--Medishield). Seventy-nine patients who had had 89 endarterectomies during the past 5 years entered the study. The mean follow-up was 21 months. Fourteen patients had an occluded internal carotid artery of whom 4 had suffered an immediate postoperative stroke and 1 a delayed stroke: transient ischaemic attacks occurred in another 4 patients. Of the 60 patients with a patent internal carotid artery one suffered an immediate postoperative stroke and 2 a delayed stroke; 6 patients had recurrent transient ischaemic attacks. None of the 5 patients who had an external carotid endarterectomy developed postoperative symptoms, although there was occlusion in 2. The carotid artery was occluded in 4 of 43 completely asymptomatic patients. Thus, 18 per cent of all carotid endarterectomies and 9 per cent of asymptomatic patients in this series had postoperative occlusion of the carotid artery.

Turbulence measurements with pulsed Doppler ultrasound employing a frequency tracking method

A phase lock loop method of tracking doppler ultrasound frequencies is applied to the measurement of turbulent velocities. A pulsed Doppler ultrasound system capable of detecting two velocity components was employed to resolve axial and radial velocity components at the centerline of turbulent pipe flows and distal to stenoses in pulsatile flow. Measurements with the ultrasound system are compared with laser Doppler and hot film anemometer data. The results demonstrate that the phase lock loop method of tracking accurately follows turbulent velocity fluctuations for turbulence intensities up to approx. 20%, after which signal dropout becomes a significant factor. An important application of the method is that of detecting flow disturbances created by mild to moderate degrees of stenosis in arterial disease.

In vitro Doppler detection of axisymmetric stenoses from transverse velocity measurements

Results are presented on Doppler flow measurements distal to models of arterial stenosis under steady and pulsatile flow conditions. The models simulate mild to moderate stenoses. Emphasis is placed on flow structure determination (vortex shedding or coherent eddies) which might be the distinguishing characteristic of a mild stenosis (less than or equal to 50%). A new approach is taken by making the measurements with the ultrasonic beam normal to the axial flow direction. The transverse velocity measurements avoid detecting the superposed axial flow component so that flow structure can be determined, and also provide clinical advantages of the ease of localization. A pulsed RF directional Doppler system is used together with high resolution temporal autoregressive spectral analysis. Vortex shedding and coherent structures are detected under steady and pulsatile flow conditions. The influence of the frequency parameter on the flow pattern is also studied.

Cerebrovascular assessment using a Doppler carotid scanner and real-time frequency analysis

The results of two methods for noninvasively diagnosing carotid disease are described. In the first study, a color-coded continuous-wave Doppler scanner was used. As evaluated by arteriography in 56 sides, the sensitivity and specificity of the Doppler scanner for diagnosing carotid lesions with greater than 50% stenosis was 71% and 82%, respectively. We found that many of our initial problems could be overcome by the concomitant use of a real-time frequency analyzer. Specifically, when the Doppler waveforms were displayed, we found that: 1) signals that had been attenuated by calcification or plaques, or had reduced velocity as a result of a proximal stenosis, could still be detected; 2) when the velocity of flow was increased to compensate for a contralateral carotid stenosis, the waveforms could still be of diagnostic value; 3) distinguishing between the internal and external carotid arteries was easier than relying on the audio signal alone; 4) when the scan showed internal carotid occlusion, morphological evaluation of the external and common carotid waveforms was helpful in verifying the scan result; and 5) artifactual noise on the Doppler waveform could be recognized. In the second study, frequency analysis recordings were evaluated semiquantitatively by measuring peak frequency and the fractional width of the Doppler frequency spectrum at peak systole Our preliminary results show that this approach is of diagnostic value in that it has the potential to detect minor stenoses.

A prospective study of the accuracy of Doppler ultrasound in detecting carotid artery disease

Results are presented from a two year prospective study using a Doppler ultrasound technique for the detection of carotid disease. The patients studied presented with transient cerebral ischaemic attacks or small strokes in the carotid territory. No other form of patient selection was used. Results were compared with those from carotid and arch aortography. 86% of normal vessels and 78% of diseases vessels were correctly classified. It is concluded that this technique offers a safe and accurate screening procedure for the management of patients presenting with transient cerebral ischaemia or small strokes.

Comparison of angiography with continuous wave Doppler ultrasound in the assessment of extracranial arterial disease

Extracranial arterial disease was assessed using non-invasive continuous wave Doppler ultrasound. The results of the Doppler study were compared with those of angiography. There was a positive correlation between the results of angiography and the shape of the Doppler waveform, but the correlation was improved by adding a compression manceuvre to the procedure.

Diagnosis by ultrasound of severe carotid artery disease in patients undergoing cardiopulmonary bypass operations

A non-invasive method using continuous wave Doppler shift ultrasound and spectral analysis was used as a screening test for severe carotid artery disease in patients undergoing cardiopulmonary bypass operations. One hundred and eighty-eight patients were examined before cardiac surgery (91 for ischaemic heart disease, 17 for ischaemic heart disease and valve replacement, 66 for valve replacement alone, and 14 for congenital abnormalities). The mean age of the 108 patients suffering from ischaemic heart disease was 54 years (+/- 8) and that of the 80 patients admitted either for valve replacement alone or for congenital abnormalities was 52 years (+/- 12). Five of the 108 patients suffering from ischaemic heart disease were found to have severe occlusive disease of the internal carotid artery by the ultrasound test, while the test was normal in the other two groups. Patients with severe carotid artery disease proceeded to carotid arteriography and endarterectomy before the planned heart operation.

Pulsed Doppler imaging of the carotid artery

Pulsed Doppler imaging (MAVIS, GEC Medical) of the carotid artery in the neck was compared with selective contrast angiography of 50 arteries. All but one of 23 internal carotid arteries with more than 25% stenosis or complete occlusion on angiography were detected by imaging. One of 17 angiographically normal arteries also had an abnormal image. All 16 arteries thought suitable for endarterectomy had abnormal Doppler images. Imaging of the external carotid artery was less reliable and disease of the common carotid artery was too infrequent to allow imaging to be satisfactorily evaluated. This non-invasive technique may eventually replace selective carotid angiography in some patients.

Carotid artery velocity patterns in normal and stenotic vessels

Duplex scanning provides real time B-mode images of the carotid bifurcation vessels along with a single gate pulsed Doppler flow velocity detector. By using the B-mode output of the duplex system to measure the Doppler angle and spectrum analysis to measure the frequency content of the Doppler signal, instantaneous flow velocity can be calculated. Mean velocity at peak systole was calculated retrospectively in 68 common (CCA) and internal (ICA) carotid arteries of 39 patients who had undergone prior angiography and prospectively in 30 arteries of 15 healthy young controls. The ratio of mean peak ICA velocity to mean peak CCA velocity at systole (VICA/VCCA) was below 0.8 in all 36 normal arteries and above 1.5 in all 21 high-grade stenoses of 60% or greater diameter reduction. Sixty-one percent of 41 vessels with less than 10 to 55% diameter reduction had a velocity ratio between 0.8 and 1.5. Only 10% of all ICA's with any stenotic lesion were incorrectly classified as normal. VICA/VCCA appears to be an accurate indicator of the degree of ICA stenosis.

Assessment of directional Doppler ultrasound techniques in the diagnosis of carotid artery diseases

Three diagnostic techniques based on the use of directional doppler ultrasound have been evaluated in comparison with direct percutaneous carotid angiography and arch aortography. The results indicate that the non-invasive techniques provide a safe, atraumatic method of assessing patients with symptoms of extracranial occlusive arterial disease.

Assessment of carotid artery stenosis using pulse wave transit time

A prospective study has been undertaken on 24 patients to establish the relationship between the degree of internal carotid artery stenosis, as estimated by arteriography, and the pulse wave transit time in the carotid artery. The technique involves the simultaneous use of two continuous wave Doppler velocimeters, one on the carotid and one on the supraorbital artery, to measure the flow waves and hence deduce the pulse wave transit times. The measured transit times varied from 17 to 124 ms with a beat-to-beat variation of 11 per cent. The absolute transit time in any segment correlated moderately well with the estimated degree of stenosis (r = 0.68, P less than 0.001). However, normalization of the transit times, to correct for the effects of blood pressure and age, produced on improved correlation between the variables (r = 0.8, P less than 0.001). Normalization was achieved by dividing the common carotid to supraorbital transit time by the shortest transit time found between the common carotid and either the superficial temporal or brachial arteries. Significant differences in the normalized transit times were found between arteries that were diametrically stenosed by more than 50 per cent, by between 21 and 50 per cent and by 20 per cent or below. It is concluded that pulse wave transit time measurement can provide a simple and reproducible non-invasive technique for the diagnosis of varying degrees of carotid artery stenosis.

Preliminary report on some ultrasonic methods for detecting carotid artery disease

The use of both Doppler and pulse-echoultrasonic equipment for detecting carotid artery disease is discussed. The need for new non-invasive techniques, capable of detecting small stenoses, is demonstrated and the development of two techniques (analysis of blood velocity waveforms and the measurement of arterial wall movement) is described. The arterial wall movement showed no change with disease, but analysis of the blood velocity waveforms proved capable of detecting even minor stenosis in some cases. Methods for confirming these preliminary results are discussed.

Imaging the carotid bifurcation using continuous-wave Doppler-shift ultrasound and spectral analysis

A non-invasive method is described for visualizing the carotid bifurcation using a continuous-wave Doppler-shift technique simultaneously with spectral analysis of the blood velocities from all parts of the vessel lumen. The system is directional so that arteries can be visualized in the presence of signals from adjacent veins. The technique uses a transducer which is attached to a position-sensing arm so that the position of the ultrasound beam on the neck, when sensing arterial blood flow-velocities, can be translated onto a storage oscilloscope. By repeated passes of the transducer across the vessel lumen a 2 dimensional image of the carotid bifurcation is formed. As each image point is marked, the full spectrum of blood-velocities corresponding to that position is continuously displayed on a second oscilloscope beside the image scope. Ultrasound images are compared with arteriograms and both continuous-wave and pulsed Doppler ultrasound imaging systems are discussed.