HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lee, V. S. Articles by Carroll, B. A. Search for Related Content PubMed PubMed Citation Articles by Lee, V. S. Articles by Carroll, B. A.

Assessment of Stenosis: Implications of Variability of Doppler Measurements in Normal-appearing Carotid Arteries¹

¹ From the Department of Radiology, Duke University Medical Center, PO Box 3808, Durham, NC. Received August 13, 1998; revision requested September 25; revision received October 21; accepted January 11, 1999. Address reprint requests to V.S.L., Department of Radiology-MRI, New York University Medical Center, 530 First Ave, HCC Basement, New York, NY 10016.

	Abstract

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To examine the variability of Doppler measurements along the extracranial courses of the nondiseased common carotid artery (CCA) and internal carotid artery (ICA) and determine the effect of this variability on assessment of carotid arterial stenosis.

MATERIALS AND METHODS: During the study period, 580 patients were referred for carotid arterial ultrasonography (US), including Doppler measurements of flow velocities in the proximal, middle, and distal portions of the CCA, in the bulb, and in the proximal and distal portions of the ICA. Eighty-five patients (average age, 59 years) with normal ICAs and CCAs formed the cohort for this study.

RESULTS: The range of peak systolic velocity (PSV) measurements (maximum minus minimum) averaged 20 cm/sec ± 13 in the CCA and 15 cm/sec ± 13 in the ICA. ICA/CCA velocity ratios varied, depending on the CCA measurement location. In five arteries, PSV ratios exceeded a threshold of 1.8 (suggesting 60% stenosis); in 23 arteries, end diastolic velocity ratios exceeded a threshold of 2.4 (also suggesting 60% stenosis). Right-to-left CCA PSV ratios were abnormal in up to 26 patients (suggesting >50% ICA stenosis), depending on where CCA measurements were obtained. When the CCA ratios were obtained at the same level, 16 were in the abnormal range.

CONCLUSION: Variability of Doppler measurements in the CCA and ICA in patients without visible disease is substantial and could lead to inaccuracies in carotid arterial stenosis assessment.

Index terms: Carotid arteries, flow dynamics, 172.12984 • Carotid arteries, stenosis or obstruction, 172.721 • Carotid arteries, US, 172.12983, 172.12984

	Introduction

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Duplex ultrasonography (US) has become a widely used means of detecting and characterizing carotid arterial atherosclerotic disease. For quantitative assessment of the degree of stenosis, the most frequently used Doppler parameters include peak systolic velocity (PSV) and end diastolic velocity (EDV) in the internal carotid artery (ICA), as well as ICA-to-common carotid artery (CCA) PSV and EDV ratios. Despite the common use of these quantitative parameters, there has been no consensus between laboratories on the interpretation of clinical measurements: No universal table of measurement standards that reliably estimates the degree of stenosis found with contrast material–enhanced angiography has been established (1–10). The differences in measurement standards between laboratories may reflect methodologic differences in protocol or imaging technique (11,12), physiologic differences between patient populations (eg, prevalence of cardiac dysfunction or hypertension), or the random variation in measurement. Velocity ratios may provide more robust estimates than do absolute velocity measurements by reducing the effects of differences in technique or equipment and compensating, at least in part, for physiologic differences (2).

We suspected that variability in velocity measurements along the courses of the ICA and CCA might influence the interpretation of ratio parameters. Therefore, we performed a prospective study to measure the variability of velocity measurements in patients without visible evidence of disease and determine the likelihood that this variability would produce spuriously elevated velocity ratios in this setting.

	MATERIALS AND METHODS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Between September 1996 and March 1997, 580 patients were referred for carotid arterial US. All patients who had prior carotid endarterectomy, cardiac arrhythmia, or any visible disease of either the CCA or ICA at gray-scale or color Doppler US imaging were excluded. Eighty-five patients (47 women, 38 men; average age ± SD, 59 years ± 12) formed the cohort for this study. Indications for study in these patients were as follows: stroke or transient ischemic attack (n = 49), dizziness or syncope (n = 12), asymptomatic carotid bruit (n = 9), mental status changes (n = 1), headache (n = 1), retinal arterial occlusion (n = 1), and preoperative evaluation for heart surgery (n = 1). Indications were either unknown or not recorded in 11 patients.

US Examination
Prior to the US examination, the heart rate and blood pressure were recorded with the patient in the supine position. Bilateral carotid arterial US was performed with HDI 3000 (Advanced Technology Laboratories, Bothell, Wash) and model 128 (Acuson, Mountain View, Calif) units by using a variety of broadband linear-array transducers with frequencies ranging from 4 to 7 MHz. Each examination was performed by an experienced sonographer with a radiologist in attendance. The ICA and CCA were examined initially by using gray-scale and color Doppler US imaging. Spectral Doppler waveform measurements were obtained at multiple locations: three locations in the CCA (as close to the aortic arch as possible, in the middle portion, and before the widening of the bulb), one location in the bulb, and two locations in the ICA (just beyond the bulb widening and in the most distal part visible). A single measurement was recorded at each location. In all cases, the measured angle of insonation was kept below 60°.

The PSV and EDV were determined from velocity waveforms at all locations by using electronic calipers during the examination. The following velocity ratios were calculated for each possible combination of locations: ICA/CCA PSV ratio, ICA/CCA EDV ratio, and right-to-left CCA ratio. The following published thresholds were used to predict 60% or greater ICA stenosis: ICA PSV greater than 130 cm/sec, ICA EDV greater than 40 cm/sec, ICA/CCA PSV ratio greater than 1.8, and ICA/CCA EDV greater than 2.4 (3). The right-to-left CCA PSV ratios also were computed, and a threshold of less than 0.7 or greater than 1.3 was used to predict stenosis greater than 50% (13).

For each side of each patient, the maximum ICA/minimum CCA and minimum ICA/maximum CCA ratios were computed for the PSV and EDV to determine the effects of sampling location on ICA/CCA ratios. We then determined the number of patients whose values (maximum ICA/minimum CCA) would have exceeded the published thresholds.

For example, consider a patient whose PSV measurements on the right side were as follows: proximal CCA, 95 cm/sec; middle CCA, 63 cm/sec; distal CCA, 64 cm/sec; bulb, 43 cm/sec; proximal ICA, 56 cm/sec; and distal ICA, 33 cm/sec. The two limits for ICA/CCA PSV ratios on the right can be computed as follows: maximum ICA/minimum CCA = 56 cm/sec ÷ 63 cm/sec = 0.89 and minimum ICA/maximum CCA = 33 cm/sec ÷ 95 cm/sec = 0.35. For this particular patient, both values would fall within the range of normal (<1.8) on the basis of published criteria (3). The difference in velocity ratio values in this patient is calculated to be 0.54 (0.89 - 0.35). This analysis was performed for all carotid arteries studied (n = 170). A similar analysis was performed to determine right-to-left CCA PSV ratios.

Statistical Analyses
The statistical significance of differences in velocity measurements along the course of the ICA was assessed by using the two-tailed Student t test, and that of differences along the course of the CCA was assessed by using analysis of variance. The correlation between left and right measurements was evaluated by using Pearson correlation coefficients. To assess the effects of patient age, blood pressure, and heart rate on Doppler parameters, patients were stratified into the following pairs of groups: age 60 years or older or age older than 60 years, hypertensive (systolic blood pressure 160 mm Hg or diastolic blood pressure 95 mm Hg) or normotensive, and heart rate 75 beats per minute or higher or less than 75 beats per minute. The two-tailed Student t test was used to compare velocity measurements in each pair of groups. For all statistical tests, which were performed with Excel software (Microsoft, Redmond, Wash), a P value of less than .05 was used to assign statistical significance.

	RESULTS

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 
Eighty-five of the patients who were referred for evaluation for possible carotid arterial disease were found to have no visible evidence of extracranial carotid disease at gray-scale and color Doppler US imaging. In this ostensibly disease-free population, the systolic and diastolic velocities demonstrated wide variability along the course of each individual CCA and ICA, as summarized in Tables 1 and 2.

A variability of measurements in the ICA also was observed (Table 2). The mean range of PSV measurements (greater minus lesser PSV value) in each individual ICA was 15.4 cm/sec ± 13.2 (range, 0–83 cm/sec). Unlike in the CCA, in the ICA, the more distal PSV measurements (65.1 cm/sec ± 18.0) exceeded the proximal measurements (59.0 cm/sec ± 19.6) (P = .003). In five (3%) vessels, the difference in PSV between the proximal and distal portions of the ICA differed by 50 cm/sec or more; in 48 (28%) vessels, the difference was 20 cm/sec or more. No correlation was observed between the range of PSV measurements obtained in the right ICA compared with those obtained in the left ICA (r = 0.15).

The EDVs in the ICA also varied substantially. The average distal value (23.4 cm/sec ± 8.6) was significantly higher than the average proximal value (18.9 cm/sec ± 7.8; P < .001).

The effects of age, blood pressure, and heart rate on differences in velocity measurements also were considered. The range of PSV measurements along the ICA and CCA did not differ significantly in patients older than 60 years (n = 35, 41%) compared with those 60 years or younger (n = 50, 59%) (P > .05). Eighteen (21%) patients were considered to be hypertensive (systolic blood pressure 160 mm Hg or diastolic blood pressure 95 mm Hg), and no statistically significant difference in variability of velocities was observed when patients were stratified by blood pressure. The absolute PSV values were also not significantly different among patients stratified by age or blood pressure. However, although we did observe that patients with heart rates of 75 beats per minute or greater (n = 43, 51%) had higher velocity measurements in the carotid arteries than did patients with lower rates (n = 42, 49%), there was no significant difference in the range or variability of velocities in the ICA or CCA (Table 3).

To evaluate whether variability in velocity measurements along a vessel can affect stenosis estimates based on ICA/CCA ratios, we determined the number of patients whose calculated ratios would have exceeded published thresholds. Figures 1 and 2 demonstrate the effects of sampling location on ICA/CCA ratios. By using an ICA/CCA PSV ratio threshold of greater than 1.8 to indicate 60% or greater ICA stenosis, five (3%) vessels in a total of three (4%) patients had maximum ICA/minimum CCA values that were abnormal without other visible US evidence of disease (Fig 1). By using an ICA/CCA EDV ratio threshold of greater than 2.4, 23 (14%) vessels in 19 (22%) patients had ICA/CCA EDV values that exceeded the threshold, which suggested 60% or greater ICA stenosis (Fig 2). The mean difference in velocity ratio (ICA/CCA) values, depending on the location of the CCA measurements, was 0.2 ± 0.1 for the PSV ratio and 0.4 ± 0.4 for the EDV ratio.

View larger version (52K): [in this window] [in a new window]   Figure 1. Histogram of the highest (maximum/minimum) and lowest (minimum/maximum) ICA/CCA PSV ratios based on measurements of velocities in different locations along each ipsilateral vessel. The published ICA/CCA PSV threshold of greater than 1.8 was used to indicate 60% or greater stenosis (3). max/min = maximum ICA velocity divided by minimum ipsilateral CCA velocity, min/max = minimum ICA velocity divided by maximum ipsilateral CCA velocity, striped bars = all values exceeding the threshold (>1.8).

View larger version (51K): [in this window] [in a new window]   Figure 2. Histogram of the highest (maximum/minimum) and lowest (minimum/maximum) ICA/CCA EDV ratios based on measurements of velocities in different locations along each ipsilateral vessel. Values of greater than 2.4, the threshold, were considered to indicate 60% or greater stenosis (3). max/min = maximum ICA velocity divided by minimum ipsilateral CCA velocity, min/max = minimum ICA velocity divided by maximum ipsilateral CCA velocity, striped bars = all values exceeding the threshold (>2.4).

Right-to-left CCA PSV ratios demonstrated wide variability that was based on the location in the CCA that the measurements were obtained (Fig 3). By using maximum CCA (right) PSV/minimum CCA (left) PSV ratios, 26 (31%) patients had abnormal values (<0.7 or >1.3), which suggested stenosis of greater than 50% (13). When velocity ratio measurements were taken from matching locations, from side to side (ie, proximal CCA/proximal CCA, middle CCA/middle CCA, and distal CCA/distal CCA), the ratios fell in the abnormal range in 16 (19%) patients.

View larger version (49K): [in this window] [in a new window]   Figure 3. Histogram of the maximum and minimum and matched values for right CCA/left CCA PSV ratios. Values less than 0.7 or greater than 1.3, the thresholds, were considered to indicate ICA stenosis of greater than 50% (13). max/min = maximum right CCA PSV divided by minimum left CCA PSV or maximum left CCA PSV divided by minimum right CCA PSV, matched = all values in which the velocity ratios were matched at the same level (right proximal CCA/left proximal CCA, right middle CCA/left middle CCA, and right distal CCA/left distal CCA), striped bars = all values less than the 0.7 threshold or greater than the 1.3 threshold.

	DISCUSSION

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

The results of our study demonstrated a progressive decline in PSV from the proximal to distal CCA. This result is in agreement with that reported by Meyer et al (14), who examined 20 healthy volunteers and found an average decrease in PSV of 9 cm/sec for each centimeter increment in distance from the proximal CCA to the distal CCA (approaching the bifurcation). Because the age of their volunteers ranged from 25 to 43 years, the authors provided the caveat that the applicability of their results to an older or symptomatic population is uncertain. Our study results substantiate the presence of a similar velocity change in patient populations that are more representative of those who are referred for carotid arterial US.

The results of our study further demonstrate that the effect of this variability on velocity measurements such as ICA/CCA PSV and EDV ratios and right-to-left CCA ratios is substantial and could lead to diagnostic error. Interestingly, none of the 85 patients had ICA PSV measurements that exceeded 130 cm/sec, a commonly used threshold for the indication of 60% or greater stenosis (3); this supports claims that the PSV may be the most reliable Doppler measurement for estimating stenosis (15–17). Nevertheless, the absolute PSV is potentially influenced by differences in equipment and technique (11,12) and by physiologic factors such as cardiac output and contralateral restriction of blood flow (10,18). Velocity ratios have been promoted as a means of providing an internal standard that can account for some of these systematic (nonrandom) effects. As such, these ratios provide valuable complementary information, assuming that the variability of CCA velocities is considered in the interpretation.

When we evaluated whether ICA/CCA ratios would be less likely to be misleading if we obtained CCA measurements from each of the three locations, we found no substantial difference in ratios. Although some authors (3,8,17) have advocated the routine practice of obtaining CCA measurements just below the bifurcation (which corresponds to the distal CCA in our study) for ICA/CCA velocity ratios, our results do not clearly substantiate this preference. However, our results may be limited because of the small sample size.

The variability of velocities along the course of the CCA may be a result of several factors. Laminar (nonturbulent) flow within a rigid tube is governed by the law of conservation of momentum: A1 x V1 = A2 x V2, where A1 and A2 are cross-sectional areas at two points in the tube, and V1 and V2, the corresponding mean velocities in the two areas. Thus, velocity changes along the course of a vessel may, in part, correspond to changes in cross-sectional area. In the CCA and ICA, however, blood flow is not laminar where the vessel is tortuous, or where it bifurcates (18). Furthermore, the normal compliance of the vessel wall may serve to dampen velocities and thereby contribute to the progressive decline in velocity along the course of the CCA (14).

Our study results did not reveal statistically significant effects based on age or hypertension. Although Hansen et al (19) observed decreased vessel compliance with age, we did not observe an age-related pattern in ICA or CCA velocities. Similarly, we did not observe a substantial difference in velocity measurements when patients were stratified by blood pressure; our findings in the CCA are essentially in agreement with those reported by Ferrara et al (20), although in our study, we did not reproduce their finding of slightly increased mean velocities in the ICA in hypertensive patients. It is possible that differences exist but could not be detected with our sample size. Nonetheless, the magnitude of the effect is likely to be small and possibly not of clinical importance. We did find that patients with higher heart rates had higher velocities at all locations. However, there was no difference in the variability of velocities in the CCA or in the ICA/CCA PSV ratios between the two groups.

The criteria for hemodynamically significant carotid arterial stenosis vary among laboratories (8,10,11,16,17). These different criteria may stem from differences in equipment and measurement techniques, as well as differences in the test characteristics (sensitivity vs specificity) of particular patient populations and practice patterns. Although the use of slightly different thresholds could have shifted the percentage of cases that were regarded as abnormal in our study, it is unlikely that the use of different criteria would alter the basic conclusions of this study.

One limitation of this study is the assumption that patients who did not have visible disease on gray-scale and color Doppler US images were truly disease-free. Although it is possible that a minority of patients had imperceptible carotid plaque, this is unlikely to have been a common occurrence, given the high correlation between color Doppler US and angiographic findings in patients without visible carotid arterial disease (9,21). Still, vessel compliance can be focally or segmentally altered in the early stages of atherosclerosis.

It is also possible that some patients may have had disease beyond the areas visualized. In the Joint Study of Extracranial Arterial Occlusion (22), more than 4,000 patients were evaluated with conventional angiography, and stenosis was observed in the brachiocephalic artery in 4.2%, in the proximal left CCA in 4.8%, and in the intracranial portion of the ICA, on the left and right sides, in 6.6% and 6.7%, respectively. However, these data would likely be an overestimation of the prevalence of stenosis in our population, given the complete absence of discernible disease over the examined length of the extracranial carotid system in our study patients.

In conclusion, we have demonstrated a statistically significant variability in PSV and EDV along the course of the CCA in patients without visible US evidence of disease. This result is important because it was found in a patient population representative of those who are referred for carotid arterial US and because the observed variability of velocity measurements along the CCA was shown to affect Doppler velocity ratios and result in misleadingly abnormal values. If such variation is present in an ostensibly healthy group of patients, one is left to wonder how much more variation might exist in patients with demonstrable disease. Our findings may explain, in part, the inconsistent results reported between different laboratories when fixed thresholds for Doppler parameters are used. For improved consistency and comparability, a consensus in the community may need to be reached with regard to the optimal location of CCA measurements; further evaluation of Doppler criteria based on carefully defined and reproducible CCA measurements may then be justified.

	Footnotes

 
Abbreviations: CCA = common carotid artery EDV = end diastolic velocity ICA = internal carotid artery PSV = peak systolic velocity

Author contributions: Guarantor of integrity of entire study, V.S.L.; study concepts and design, all authors; definition of intellectual content, all authors; literature research, V.S.L., B.A.C.; clinical studies, all authors; data acquisition, all authors; data and statistical analyses, V.S.L.; manuscript preparation, V.S.L.; manuscript editing and review, all authors.

	References

TOP Abstract Introduction MATERIALS AND METHODS RESULTS DISCUSSION References

 

1. Garth KE, Carroll BA, Sommer FG, Oppenheimer DA. Duplex ultrasound scanning of the carotid arteries with velocity spectrum analysis. Radiology 1983; 147:823-827.[Abstract/Free Full Text]
2. Zweibel WJ. Spectrum analysis in carotid sonography. Ultrasound Med Biol 1987; 13:625-636.[Medline]
3. Bluth EI, Stavros AT, Marich KW, Wetzner SM, Aufrichtig D, Baker JD. Carotid duplex sonography: a multicenter recommendation for standardized imaging and Doppler criteria. RadioGraphics 1988; 8:487-506.[Abstract]
4. Robinson ML, Sacks D, Perlmutter GS, Marinelli DL. Diagnostic criteria for carotid duplex sonography. AJR 1988; 151:1045-1049.[Abstract/Free Full Text]
5. Friedman SG, Hainline B, Feinberg AW, Lesser ML, Napolitano BA. Use of diastolic velocity ratios to predict significant carotid artery stenosis. Stroke 1988; 19:910-912.[Abstract/Free Full Text]
6. Withers CE, Gosink BB, Keightley AM, et al. Duplex carotid sonography: peak systolic velocity in quantifying internal carotid artery stenosis. J Ultrasound Med 1990; 9:345-349.[Abstract]
7. Hunink MGM, Polak JF, Barlan MM, O'Leary DH. Detection and quantification of carotid artery stenosis: efficacy of various Doppler velocity parameters. AJR 1993; 160:619-625.[Abstract/Free Full Text]
8. Carpenter JP, Lexa FJ, Davis JT. Determination of sixty percent or greater carotid artery stenosis by duplex Doppler ultrasonography. J Vasc Surg 1995; 22:697-705.[Medline]
9. Srinivasan J, Mayberg MR, Weiss DG, Eskridge J. Duplex accuracy compared with angiography in the Veterans Affairs Cooperative Studies Trial for Symptomatic Carotid Stenosis. Neurosurgery 1995; 36:648-655.[Medline]
10. Zwiebel WJ. New Doppler parameters for carotid stenosis. Semin Ultrasound CT MR 1997; 18:66-71.[Medline]
11. Howard G, Baker WH, Chambless LE, Howard VJ, Jones AM, Toole JF. An approach for the use of Doppler ultrasound as a screening tool for hemodynamically significant stenosis (despite heterogeneity of Doppler performance): a multicenter experience. Stroke 1996; 27:1951-1957.[Abstract/Free Full Text]
12. Wolstenhulme S, Evans JA, Weston MJ. The agreement between colour Doppler systems in measuring internal carotid artery peak systolic velocities. Br J Radiol 1997; 70:1043-1052.[Abstract]
13. Vaisman U, Wojciechowski M. Carotid artery disease: new criteria for evaluation by sonographic duplex scanning. Radiology 1986; 158:253-255.[Abstract/Free Full Text]
14. Meyer JI, Khalil RM, Obuchowski NA, Baus LK. Common carotid artery: variability of Doppler US velocity measurements. Radiology 1997; 204:339-341.[Abstract/Free Full Text]
15. Schwartz SW, Chambless LE, Baker WH, Broderick JP, Howard G. Consistency of Doppler parameters in predicting arteriographically confirmed carotid stenosis. Stroke 1997; 28:343-347.[Abstract/Free Full Text]
16. Faught WE, Mattos MA, van Bemmelen PS, et al. Color-flow duplex scanning of carotid arteries: new velocity criteria based on receiver operator characteristic analysis for threshold stenoses used in the symptomatic and asymptomatic carotid trials. J Vasc Surg 1994; 19:818-828.[Medline]
17. Moneta GL, Edwards JM, Papanicolaou G, et al. Screening for asymptomatic internal carotid artery stenosis: Duplex criteria for discriminating 60% to 99% stenosis. J Vasc Surg 1995; 21:989-994.[Medline]
18. Steinke W, Kloetzsch C, Hennerici M. Variability of flow patterns in the normal carotid bifurcation. Atherosclerosis 1990; 84:121-127.[Medline]
19. Hansen F, Mangell P, Sonesson B, Länne T. Diameter and compliance in the human common carotid artery: variations with age and sex. Ultrasound Med Biol 1995; 21:1-9.[Medline]
20. Ferrara LA, Mancini M, Iannuzzi R, et al. Carotid diameter and blood flow velocities in cerebral circulation in hypertensive patients. Stroke 1995; 26:418-421.[Abstract/Free Full Text]
21. Zierler RE, Kohler TR, Strandness DE, Jr. Duplex scanning of normal or minimally diseased carotid arteries: correlation with arteriography and clinical outcome. J Vasc Surg 1990; 12:447-455.[Medline]
22. Hass WK, Fields WS, North RR, Kricheff II, Chase NE, Bauer RB. Joint study of extracranial arterial occlusion. II. Arteriography, techniques, sites, and complications. JAMA 1968; 203:961-968.[Medline]

This article has been cited by other articles:

				F. Kantarci, I. Mihmanli, M. S. Albayram, H. Barutca, F. Gulsen, N. Kocer, and C. Islak Follow-up of extracranial vertebral artery stents with Doppler sonography. Am. J. Roentgenol., September 1, 2006; 187(3): 779 - 787. [Abstract] [Full Text] [PDF]

				R. Sheiman, V. S. Lee, B. S. Hertzberg, M. A. Kliewer, and B. A. Carroll Arterial Doppler US: Disturbing Conservation of Erroneous Terms Dr Lee and colleagues respond: Radiology, December 1, 2000; 217(3): 919 - 920. [Full Text]

				V. S. Lee, B. S. Hertzberg, M. J. Workman, T. P. Smith, M. A. Kliewer, D. M. DeLong, and B. A. Carroll Variability of Doppler US Measurements along the Common Carotid Artery: Effects on Estimates of Internal Carotid Arterial Stenosis in Patients with Angiographically Proved Disease Radiology, February 1, 2000; 214(2): 387 - 392. [Abstract] [Full Text]

				S. Napel, H. Xu, D. S. Paik, B. A. Ross, T. S. Sumanaweera, J. A. Hossack, and R. B. Jeffrey Jr Carotid Disease: Automated Analysis with Cardiac-gated Three-dimensional US—Technique and Preliminary Results Radiology, February 1, 2002; 222(2): 560 - 563. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lee, V. S. Articles by Carroll, B. A. Search for Related Content PubMed PubMed Citation Articles by Lee, V. S. Articles by Carroll, B. A.