T.S. Padayachee

Carotid Plaque Characterization by Duplex Scanning Observer Error May Undermine Current Clinical Trials

BACKGROUND AND PURPOSE Clinical studies currently in progress are using subjective methods to characterize plaque morphology from ultrasound images. However, there are few studies on the intraobserver and interobserver variability of these classifications. This study was designed to assess these variables. METHODS Grading of plaque morphology from ultrasound images, stored both digitally and to hard copy, was performed by 2 classification schemes. Interobserver agreement was determined by 4 observers. Within-observer agreement was performed at intervals for up to 6 months. Accuracy of the 2 methods was determined by comparison with histology. RESULTS Within- and between-observer agreement was moderate to good for full-color digital image analyses, with pooled kappa values of kappap=0.49+/-0.10 and kappap=0.62+/-0.07 for the 2-category method and kappap=0.53+/-0.06 and kappap=0.52+/-0.05 for the 4-category method, respectively. Hard copy data analyses gave lower kappa values. The more experienced observers produced higher within-observer agreements and higher correlation with histology. CONCLUSIONS Reproducible grading of ultrasound images is not consistently achievable among experienced observers, and within-observer agreement may vary with time. The current subjective ultrasound characterization of carotid plaque morphology used in clinical trials may be associated with unacceptable levels of reproducibility in some centers. Variability between observers may be reduced by using the simpler 2-category grading of plaque morphology to interrogate full-color digitally stored images. Observer agreement should be audited regularly.

The measurement of internal carotid artery stenosis: Comparison of duplex with digital subtraction angiography

OBJECTIVES To compare the subjective (eyeballed) method for measuring internal carotid artery (ICA) stenosis by non-selective intra-arterial digital subtraction angiography (IA-DSA) with objective and duplex methods. DESIGN Retrospective study. MATERIALS AND METHODS Fifty-three consecutive patients underwent IA-DSA prior to carotid endarterectomy providing 103 carotid angiograms. Objective assessment of ICA stenosis was by the North American Symptomatic Carotid Endarteectomy Trial (NASCET) criterion and the Carotid Stenosis Index (CSI). Duplex estimation of stenosis was derived from peak systolic and diastolic velocities in the ICA and common carotid artery (CCA). RESULTS The coefficient of repeatability was poorest for NASCET stenosis estimates (40%), whilst the improved values for CSI (20%) were consistent with the lower variability recorded for measuring the CCA diameter. Correlation and agreement levels between subjective (r = 0.80, -41% to +33%) or objective assessments and duplex (NASCET: r = 0.76; -52 to +28%; CSI: r = 0.72; -27 to +39%) showed similar values. CONCLUSIONS We conclude that the inter-observer variability for assessing angiograms obtained by arch injection is considerable and precludes high agreement when IA-DSA is compared with other methods. As the agreement of duplex ultrasound with IA-DSA is similar to the agreement between DSA methods, duplex can be offered as the first stage assessment of ICA stenosis, with the proviso that the duplex assessment is performed consistently by an experienced operator.

Intraoperative high resolution duplex imaging during carotid endarterectomy: which abnormalities require surgical correction?

OBJECTIVES This study evaluates high resolution, duplex ultrasound imaging for quality control of carotid endarterectomy in order to determine which technical factors were linked to residual stenosis and to define duplex criteria for re-exploration. DESIGN, MATERIAL AND METHODS A consecutive series of 100 patients undergoing carotid endarterectomy were evaluated. Duplex imaging was performed prior to wound closure and repeated at 6-8 weeks postoperatively. Stenoses were classified as non-significant, moderate or severe based on duplex criteria. Intimal flaps, shelves, kinks, clamp damage and fronds were identified by ultrasound imaging. RESULTS Five moderate stenoses were noted in the proximal endarterectomy site (PES), and at follow-up three had resolved. Adherent fronds were detected in 83% of vessels and resolved in all but three cases. At the distal endarterectomy site there were 10 severe and 12 moderate stenoses. Intimal flaps were associated with an increased incidence of residual stenosis (p = 0.010). CONCLUSIONS We conclude that severe stenoses with an intimal flap should be corrected immediately. Further data is required to establish the significance of kinks. Residual intimal flaps in the PES appear to remodel. The role of completion duplex may lie in the modification of surgical technique to eradicate anatomical and haemodynamic imperfections.

Non-Invasive Assessment of the Circle of Willis Using Transcranial Pulsed Doppler Ultrasound With Angiographic Correlation

The ability of transcranial pulsed Doppler ultrasound (TCD) to provide a dynamic assessment of the functional capability of the Circle of Willis was assessed using conventional cerebral angiography for anatomic correlation. Eleven patients had normal four-vessel cerebral angiography prior to being investigated with ultrasound. Angiography and ultrasound both demonstrated a functional anterior communicating artery in nine of the eleven patients, giving complete agreement between the two techniques. Posterior communicating arteries were visualized angiographically in all eleven patients. Ultrasound identified bilateral functional vessels in nine, the other two patients having non-functional vessels. In these latter two patients, angiography demonstrated three of the four posterior communicating arteries to be hypoplastic and it was uncertain whether these vessels carried significant blood flow. The fourth posterior communicating artery was shown to have an absent proximal segment of the ipsilateral posterior cerebral artery, with a persistent fetal posterior communicating artery. This anatomical variation is a potential limitation of ultrasound for assessing functional posterior communicating arteries. These preliminary results indicate that a combination of the anatomical (angiographic) and dynamic (ultrasonic) data may prove to be complementary for assessing the Circle of Willis.

The results of routine primary closure in carotid endarterectomy.

PURPOSE OF STUDY The aims of this study were to determine the incidence of restenosis following carotid endarterectomy with primary closure of the arteriotomy and to observe the natural history of disease progression in the 1st postoperative year. METHODS The study group consisted of a consecutive series of 126 patients undergoing carotid endarterectomy. Duplex imaging was performed preoperatively and at 8 weeks, 6 months and 1 year postoperatively. RESULTS Five patients (4%) had a residual stenosis. At 12 months, the overall restenosis rate was 15%: 8.5% for males and 28.9% for females. None of these restenoses were symptomatic. There was no significant difference in the diameter of the internal carotid artery between male and female patients (U = 896, P = 0.60) and no significant difference in the diameter of the arteries that had restenosed at 12 months and those that had remained patent (U = 391, P = 0.33). CONCLUSIONS Carotid endarterectomy with primary closure is associated with a low incidence of restenosis in men, but not in women. Criteria for selective patching should consider both gender and vessel calibre.

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%.

Ultrasound screening for internal carotid disease-I. The temporal artery occlusion test--which periorbital artery?

Using continuous wave Doppler-shifted ultrasound and spectral analysis the response to the temporal artery occlusion test was compared when insonating the supraorbital and supratrochlear arteries of 203 internal carotid pathways. The test involved monitoring the periorbital artery whilst simultaneously compressing a single branch of the external carotid artery, the ipsilateral superficial temporal artery. In 41 instances carotid angiography demonstrated severe disease of the internal carotid artery, that is lesions of 75% or more reduction in lumen diameter. A positive response to the temporal artery occlusion test, when performed on the supraorbital artery, indicated severe disease with a sensitivity of 90% and a specificity of 89%. When this test was performed on the supratrochlear artery a low sensitivity of 36% was obtained, although specificity was high at 96%.

An online technique for estimating cerebral carbon dioxide reactivity

A technique for measuring cerebral reactivity using transcranial pulsed Doppler ultrasound is described; the system includes a spectrum analyser and capnometer. Data acquisition and manipulation is under software control. Main stem middle cerebral artery blood velocity is monitored continuously using the transcranial Doppler technique, whilst the operator initiates data collection and controls the inspired gas composition. The calculation of cerebral CO2 reactivity is based upon linear regression analysis of normalized, time-averaged middle cerebral velocity on end-tidal pCO2 and is displayed graphically. Measurement of middle cerebral CO2 reactivities can be completed within 15 min. Results from two subjects, a healthy volunteer and a patient with occlusive disease, are shown to illustrate the technique.

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.

Chromaticity-coded doppler blood velocity sonagrams: Preliminary observations

This paper describes the application of chromaticity to spectrally analysed Doppler blood velocity signals. Chromaticity enables a particular colour to be assigned to the power/frequency distribution within each instantaneous spectral sweep of a sonagram. Successive spectral sweeps of a sonagram can then be colour-coded in this fashion to produce a chromaticity-coded sonagram. Two chromaticity-coded sonagrams are presented to illustrate various blood flow features. Standard sonagram display formats are also presented for comparison purposes. It appears that the chromaticity-coded sonagram offers the ability to digitally encode the instantaneous power spectral distribution with a single chromaticity vector.