Yves Langlois

Noninvasive mapping of lower limb arterial lesions.

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.

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.

Flow velocity patterns in the carotid bifurcations of young, presumed normal subjects

Spectral analysis of pulsed Doppler velocity waveforms has been found useful as a diagnostic technique in the assessment of carotid artery disease. While spectral broadening of the velocity waveform obtained at center stream sites is usually associated with arterial disease, the present study describes spectral patterns resulting from disturbed blood flow in the proximal branches of the carotid bifurcation in young, presumed normal human subjects. In those studied, spectral patterns in the bifurcation region exhibit characteristics similar to those occurring in zones of flow separation in model studies under conditions of steady flow. It is important to distinguish the spectral patterns due to arterial disease from those occurring in the normal bifurcation. This paper describes the types of flow disturbances noted in presumed normal arteries and points out the need to understand the flow velocity patterns that may be found at specific anatomical sites across the carotid bifurcation.

Limitations of ultrasonic duplex scanning for diagnosing lower limb arterial stenoses in the presence of adjacent segment disease

PURPOSEnThe purpose of this study was to provide a quantitative evaluation of the effect of adjacent segment lesions on disease classification in lower limb arteries by ultrasonic duplex scanning.nnnMETHODSnLower limb arterial duplex scanning from the distal aorta to the popliteal artery was performed in 55 patients. Arterial lesions evaluated by visual interpretation of Doppler spectra were compared blindly with those measured by angiography.nnnRESULTSnTo recognize severe stenoses (50% to 100% diameter reduction) in any arterial segment, duplex scanning had sensitivity and specificity rates of 74% and 96%, respectively. However, sensitivity and specificity rates increased to 80% and 98%, respectively, when there was no 50% to 100% diameter-reducing lesion in adjacent segments, whereas they decreased to 66% and 94%, respectively, when there was at least one 50% to 100% diameter-reducing lesion in adjacent segments. Moreover, among the 48 duplex misclassifications underestimating or overestimating the degree of arterial stenoses, 30 (62.5%) involved a segment with at least one 50% to 100% lesion in adjacent segments. The segments mostly affected by proximal and distal arterial lesions were the popliteal arteries and the common and deep femoral arteries, where it was found that 86% (24/28) of the misclassifications involved the presence of either proximal or distal severe stenoses.nnnCONCLUSIONnThe results demonstrated that the presence of multiple stenoses was an important limitation of duplex scanning for the detection and quantification of lower limb arterial disease.

Natural history of carotid artery disease on the side contralateral to endarterectomy

The natural history of the nonoperated carotid artery opposite an endarterectomy was examined in 134 patients by means of ultrasonic duplex scanning over a period extending to 48 months. None of the nine deaths that occurred during follow-up was stroke related. A total of 22 arteries showed progression of disease over this period. By life-table analysis the mean annual rate of progression for all categories of disease was 12.6% and 7.4% for progression to a diameter reduction greater than 50%. Disease progression was more rapid in patients under 65 years of age. Symptoms occurred in 13 patients for an overall incidence of 10% and a mean annual rate estimated at 5%. All symptoms indicated transient ischemic attacks; there were no strokes. There was a strong relationship between the development of symptoms and stenoses greater than 80% either at the initial examination or secondary to progression. No correlation was found between the presence of bruits or their change over time and the progression or appearance of symptoms. Conservative management of nonoperated vessels opposite an endarterectomy appears appropriate until symptoms develop or a lesion greater than 80% is detected.

Sources of variability in carotid duplex examination: A prospective study

Interobserver and intraobserver variability of ultrasonic, duplex carotid artery examinations was studied in a prospective, randomized, and blinded clinical trial. Forty-eight patients were examined by two technologists, yielding 96 carotid artery examinations. The kappa statistic was calculated to determine the degree of agreement corrected for chance. The kappa value between examinations by different technologists was 0.476. Variability occurred at both steps in the examination procedure: (1) obtaining the velocity waveforms (kappa = 0.536); and (2) using these waveforms to classify the extent of carotid disease (kappa = 0.609 for interobserver variability in reading waveforms). Minimal to moderate disease categories accounted for most of the variability. There was little disagreement in categorizing lesions as greater than or less than 50% diameter reduction. Intraobserver variability in rereading spectral waveforms was minimal (kappa = 0.842 and 0.894). Recognition of disturbed flow patterns in normal carotid bulbs may reduce variability.

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.

Post-endarterectomy carotid ultrasonic duplex scanning concordance with contrast angiography.

The results of ultrasonic duplex scanning combined with spectral analysis are compared with the results of contrast angiography in patients after endarterectomy in which recurrence of carotid arterial disease was suspected. Thirty-six patients underwent a duplex scan study within 3 months of their post-operative angiogram, performed at their physicians discretion (44 studies). The overall accuracy of the method was 80%. Our ability to predict a greater than 50% diameter reduction along with total occlusion was 94%. The measure of agreement corrected for chance between arteriography and duplex scanning as expressed by the Kappa statistic was 0.675 +/- SE (K) 0.096. This level of agreement compared favorably to that of inter- and intra-observer variability in reading cerebral angiograms. The accuracy reported justifies the clinical use of ultrasonic duplex scanning in the detection of recurrent stenosis after carotid endarterectomy.

Variability in measurement of specific parameters for carotid duplex examination.

The variability of four carotid artery frequency parameters used for classifying disease with duplex scanning was prospectively studied. Forty-eight patients (94 patent carotid arteries) were each examined by two technologists. Measured parameters were the peak systolic frequency (PSF) and the first zero slope from the common carotid artery, and the PSF and end diastolic frequency (EDF) from the internal carotid artery. Measurements from all the examinations were made twice by each technologist. Interobserver, intraobserver, and interpatient variability in measurement of the first zero slope was so great that we have abandoned its use. Measurement of variability for PSF and EDF was much less (correlation coefficients 0.68 to 0.92). These parameters were measured with sufficient precision to warrant their continued use for important decision steps in classifying carotid artery disease. Interpatient differences in PSF sufficient to cause disagreement regarding the hemodynamic significance of carotid disease occurred in only three instances. In each of these cases the differences were due to examination technique (failure to identify a very distal internal carotid artery stenosis, difficulty distinguishing between a kink and a stenosis, and failure to recognize an improper Doppler angle). We conclude that the variability of PSF and EDF is within clinically acceptable levels and is mainly due to examination technique rather than measurement of waveform parameters or changes in patient hemodynamics.

Computer analysis and pattern recognition of doppler blood flow spectra for disease classification in the lower limb arteries

In the present study, a computer processing method was developed to objectively classify disease in the lower limb arteries evaluated by noninvasive ultrasonic duplex scanning. This method analyzes Doppler blood flow signals, extracts diagnostic features from Doppler spectrograms and classifies the severity of the disease into three categories of diameter reduction (0-19%, 20-49% and 50-99%). The features investigated were based on frequency features obtained at peak systole, spectral broadening indices and normalized amplitudes of the power spectrogram computed in various positive and negative frequency bands. A total of 379 arterial segments studied from the aorta to the popliteal artery were classified using a pattern recognition method based on the Bayes model. Two classification schemes using a two-node decision rule were tested. Both schemes gave similar results, the first one provided an overall accuracy of 83% (Kappa = 0.42) and the second an overall accuracy of 81% (Kappa = 0.35) when compared with conventional biplane contrast arteriography. These performances, especially for the 0 to 19% lesion category, are better than the one obtained by the technologist (accuracy = 76% and Kappa = 0.33), based on visual interpretation of the Doppler spectrograms. To recognize hemodynamically significant stenoses (50-99% lesions), the pattern recognition system has a sensitivity and a specificity of 50% and 99%, respectively, using classification scheme I. With classification scheme II, the sensitivity and the specificity are 50% and 98%, respectively. Visual interpretation of the Doppler spectrograms leads to a sensitivity and a specificity of 50% and 98%, respectively. These results are the first to be obtained by a pattern recognition system in classifying lower limb arterial stenoses.